ALBERT

Description: Published data on Palaeogene flood basalts of the lower Mull Plateau Group (Scotland) show that the most primitive lavas (MgO 〉 8 wt %) have the greatest extent of crustal assimilation, inconsistent with a simple coupled assimilation–fractional crystallization (AFC) model. We present elemental data on rehomogenized olivine-hosted melt inclusions from four high-MgO flows to investigate the nature of crustal assimilation and melt aggregation processes during the initial stages of flood basalt magmatism on Mull. Whole-rock compositions have been variably modified by hydrothermal alteration associated with the nearby Central Complexes. Nd isotope compositions, which should be insensitive to this alteration, are lower than typical mantle values ( Nd + 2·4 to –5·7), indicating variable modification by crustal assimilation in all four samples. Melt inclusions are protected against alteration effects within their host olivine crystals, and provide more robust estimates of magmatic liquid compositions than whole-rocks, particularly for the alkali elements Na, K and Ba. The whole-rock samples show limited variations in Na 2 O (2·4–2·8 wt %) and K 2 O (0·23–0·29 wt %), despite a wide range in immobile elements (e.g. Zr 62–126 ppm). In contrast, the melt inclusions show far greater variability in Na 2 O (1·8–4·0 wt %) and K 2 O (0·02–0·35 wt %) and positive correlations between K and Na. Melt inclusions from different samples show systematic correlations between alkalis (K + Na) and incompatible element ratios (e.g. Zr/Y), indicating that the inclusions record magmatic values for the fluid-mobile elements. For the two most incompatible-element-enriched samples, the whole-rock analyses are similar to the melt inclusions except for lower Na and higher Ba that are related to alteration. Therefore, the crustal assimilation in these magmas must have taken place prior to growth of the olivines. For the two more depleted samples, the inclusions have less contaminated compositions than the whole-rocks, and show broad trends of increasing K/Ti with decreasing Fo% of the host olivine. For these samples, crustal assimilation must have taken place both during and after growth of the olivines and in an AFC style in which assimilation is linked to magmatic differentiation. Melt inclusions from single samples show limited variability in Zr/Y compared with K/Ti, indicating that aggregation of melts from different parts of the melt column must have occurred at deeper levels prior to growth of the olivines in the samples. Although the whole-rock compositional variations capture the broad details of crustal assimilation and melting histories for the Mull lavas despite the variable effects of hydrothermal alteration, the melt inclusion data more clearly resolve significant details of these magmatic processes. The extent of assimilation and differentiation is linked to the depth of magma stalling: primitive, contaminated magmas in the lower crust vs. evolved, uncontaminated magmas at sub-Moho depths.

Description: The oldest well-preserved komatiites, and the type examples, are found in the Barberton Greenstone Belt in South Africa (3·5–3·3 Ga). All three komatiite types are present, commonly within the same stratigraphic unit. Al-depleted komatiites have low Al/Ti, relatively high concentrations of incompatible elements and depleted heavy rare earth elements (HREE); Al-undepleted komatiites have chondritic Al/Ti and flat HREE patterns; and Al-enriched komatiites have high Al/Ti, low concentrations of incompatible elements, enriched HREE and extremely depleted light rare earth elements. Based on a comprehensive petrological and geochemical study, we propose a new melting model for the formation of these magmas. The basis of the model is the observation, from published experimental studies, that at great depths (~13 GPa) the density of komatiitic liquid is similar to that of solid peridotite. At such depths, melting in a rising mantle plume produces near-neutrally buoyant komatiite melt that does not escape from the residual peridotite. As the source ascends to shallower levels, however, the pressure decreases and the density difference increases, eventually making melt escape possible. Al-depleted komatiites form first at about 13 GPa by equilibrium melting under conditions in which a large proportion of melt (30–40%) was retained in the source and the residue contained a high proportion of garnet (15%). Al-undepleted and Al-enriched komatiites form by fractional melting at intermediate to shallow depths after the escape of a large proportion of melt and after exhaustion of residual garnet. This model reproduces the chemical characteristics of all komatiite types in the Barberton belt and can probably be applied to komatiites in other parts of the world.

Description: Peritectic crystals in igneous rocks may be derived from either the source or country rocks, or may have formed by reactive assimilation of source-inherited solids, primary magmatic minerals during self- or magma mixing, or country-rock xenoliths or xenocrysts. Identifying such peritectic crystals is important for constraining the components and textures of igneous rocks and the underlying processes of magmatic evolution. In this study we demonstrate that peritectic olivine formed in melting experiments crystallizes as clusters of euhedral to subhedral crystals. Olivine replacing orthopyroxene, amphibole, and phlogopite forms crystal clusters with distinct crystal to melt ratios, 2D surface area, grain boundary segmentation, and inclusion relations. In our experiments the textures of peritectic crystals are primarily controlled by the stability temperature and decomposition rate of reactive minerals. High-temperature minerals such as orthopyroxene slowly decompose to form high-density clusters of large crystals with long grain boundary segments. The SiO 2 -rich peritectic melt produced favours formation of melt inclusions. Low-temperature minerals such as amphibole and phlogopite rapidly decompose to form low-density clusters of small crystals with short grain boundary segments. The relatively SiO 2 -poor peritectic melt produced results in the formation of fewer melt inclusions. Host melt composition has a minor effect on the textures of peritectic olivine formed in the melting experiments of this study and previous contamination experiments, but affects the assemblages of the peritectic crystal clusters. Cluster density and 2D surface area of peritectic olivine tend to decrease, whereas grain boundary segment length increases with increasing experimental temperature and H 2 O content. Using textural criteria that distinguish olivine formed after different minerals in our melting experiments, we hypothesize that two olivine populations from a basaltic–andesitic lava flow of the Tatara–San Pedro volcanic complex, Chile, may be peritectic crystals formed after amphibole and orthopyroxene. Both amphibole and orthopyroxene are common in xenoliths preserved in some Tatara–San Pedro lava flows. One notable difference between the experimental and natural olivine crystals is that the natural olivine crystals have 2D surface areas and 2D grain boundary segments up to ~1000 and ~100 times larger, respectively, than those produced in our experiments. We propose that this size difference is primarily controlled by comparatively slow heating and decomposition of reactive crystals and textural coarsening of peritectic crystals during prolonged magma residence in the natural system.

Description: Lithium elemental and isotopic compositions of 33 glass and whole-rock samples from nine oceanic island regions were determined to characterize the Li inventory of the deep mantle. The Li contents of the investigated lavas range from 1·5 to 13·3 μg g – 1 , whereas 7 Li ranges from 2·4 to 4·8. There are weak co-variations between the Li/Y, 7 Li, and Sr–Nd–Pb isotope compositions of the lavas, indicating that the Li elemental and isotopic characteristics of ocean island basalt to some extent reflect mantle source heterogeneity. In detail, HIMU-type lavas are characterized by 7 Li values (up to 4·8) slightly heavier than those for average normal mid-ocean ridge basalt (3·4 ± 1·4) and by comparatively low Li contents; EM1-type lavas are characterized by isotopically light Li (average 3·2) and relative Li enrichment, whereas EM2-type lavas tend to heavier 7 Li values (up to 4·4) with high Li concentrations. The Li contents and isotope characteristics of HIMU-type lavas are consistent with recycling of altered and dehydrated oceanic crust, whereas those of the EM1-type lavas can be attributed to sediment recycling. The Li characteristics of EM2-type lavas may reflect reworking of mantle wedge material that has been infiltrated by fluids derived from the subducting plate.

Description: Magmatism in the Cenozoic Central European Volcanic Province (CEVP) has been related to two geodynamic scenarios, either extensional tectonics in the north Alpine realm or upwelling of deep mantle material. The Oligocene (~30–19 Ma) Siebengebirge Volcanic Field (SVF) is a major part of the German portion of the CEVP and consists of erosional remnants of mafic to felsic volcanic edifices. It covers an area of ~35 km (NW–SE) by ~25 km (SW–NE) with eruptive centres concentrated near the eastern shore of the Rhine river in the vicinity of the city of Bonn. Mafic rocks in the SVF comprise strongly SiO 2 -undersaturated basanites to alkaline basalts. Occurrences of alkaline basalts are confined to an inner NW–SE-striking zone, whereas the more SiO 2 -undersaturated basanites dominate the western and eastern periphery of the SVF. Radiogenic isotope compositions ( 87 Sr/ 86 Sr 0·70335–0·70371; Nd +3·1 to +4·5; Hf +6·5 to +8·0; 206 Pb/ 204 Pb 19·46–19·69; 207 Pb/ 204 Pb 15·63–15·66; 208 Pb/ 204 Pb 39·34–39·62) indicate a common asthenospheric mantle end-member with HIMU-like characteristics for all mafic rocks, similar to the European Asthenospheric Reservoir (EAR). A lithospheric mantle source component with a residual K-bearing phase (phlogopite or amphibole) is inferred from negative K anomalies. Incompatible trace element modelling indicates that melting took place in the spinel–garnet transition zone with low degrees of melting at higher pressures generating the basanitic magmas (La N /Yb N = 20–25), whereas the alkaline basalts (La N /Yb N = 14–18) are the result of higher melting degrees at shallower average melting depths. Differentiation of basanitic primary melts generated tephritic to tephriphonolitic magmas that, for instance, erupted at the Löwenburg Volcanic Complex in the central SVF. Latites and trachytes, such as the prominent Drachenfels and Wolkenburg protrusions, are more common in the central portion of the SVF. These compositions originate from parental alkaline basaltic melts. All differentiated samples show evidence for crustal contamination, possibly with lower- to mid-crustal material comprising mafic granulites as found in Eifel basalt xenoliths and metapelites. Based on the spatial and temporal distribution of the various volcanic rock types, a model for the temporal evolution of the SVF can be proposed. During the initial phase of volcanism, low-degree basanitic melts were generated as a result of decompression following tectonic rifting and formation of the Cologne Embayment, a northward extension of the Rhine Graben. In a second stage, alkali basalts were generated at shallower depths and higher degrees of melting as a result of continued lithospheric thinning and passive upwelling of asthenospheric mantle. These conclusions strengthen previous models suggesting that intraplate volcanism in Central Europe is directly linked to regional lithospheric thinning and asthenospheric upwelling. Overall, the SVF constitutes an exceptionally well-preserved magmatic assemblage to illustrate these tectono-magmatic relationships.

Description: Field, petrographic–structural and geochemical data are reported for spinel and plagioclase peridotites from the northern domain of the Lanzo peridotite massif (Western Alps). The North Lanzo peridotites are extremely heterogeneous in terms of mineral mode, texture and chemistry. They can be referred to four major groups: (1) spinel harzburgites with coarse granular to porphyroclastic structures; (2) pyroxene-depleted spinel harzburgites recording olivine-forming or pyroxene-consuming microtextures; (3) spinel lherzolites with porphyroclastic to foliated and banded structures; (4) plagioclase-enriched spinel lherzolites. Major and trace element characterization of whole-rocks and their constituent minerals allows reconstruction of the complex series of pre- to syn-rift events this mantle sector underwent. Sr, Nd and Hf isotope data provide information on the nature of infiltrating melts and time constraints. More depleted harzburgites represent refractory protoliths that after melt extraction, possibly in the presence of residual garnet, underwent a first episode of refertilization by enriched mid-ocean ridge basalt (E-MORB)-like melts, whereas harzburgites and spinel lherzolites with ocean island basalt (OIB) signatures document the successive migration of alkaline melts. The most noticeable feature of this group of rocks is their Nd–Hf decoupling, specifically the very high 176 Hf/ 177 Hf coupled with very low 143 Nd/ 144 Nd. Lu–Hf data for these peridotites define an ~260 Ma errorchron that is interpreted as evidence of mixing during relatively recent times between old (most probably Proterozoic) refractory subcontinental mantle and OIB-type melts. This event most probably occurred during extension (Triassic times) or during the onset of exhumation (Liassic times). Plagioclase peridotites document the last refertilization episode, involving the shallow-level impregnation of harzburgite mantle by evolved MORB melts before its sea-floor emplacement. This Middle Jurassic event caused the almost complete resetting of the original trace element and 87 Sr/ 86 Sr composition. The combination of structural, petrological and geochemical information for a north–south Lanzo traverse, from the North Massif to the South Massif, notwithstanding the effects of the alpine orogeny, allows the study of the complete evolution of a sector of old (Proterozoic?) mantle since the early stages of melt removal and allows reconstruction of the tectonic and magmatic events during continental extension leading to the opening of the Jurassic Ligurian–Piedmontese basin. North Lanzo fundamentally preserves the record of pre-syn-rift ancient episodes, whereas South Lanzo better highlights the processes that deeply modified and refertilized the older lithosphere during subsequent lithosphere extension. Slow to very slow extension led to sea-floor exposure of the subcontinental lithospheric mantle (North Lanzo) at a marginal position, close to the Adria continental margin, and of the deeply melt-modified lithospheric mantle (Lanzo South) in a more distal setting of the basin. In this respect, the Lanzo traverse is closely similar to the ocean–continent transition in slow- or ultraslow-spreading oceanic basins, such as the North Atlantic.

Description: Basanites from the Tertiary Siebengebirge area of Germany (part of the Central European Volcanic Province; CEVP) have high Mg# (〉0·60), moderate to high Cr (〉300 ppm) and Ni (〉200 ppm) contents and strong light rare earth element enrichment, but systematic depletion in Rb and K relative to trace elements of similar compatibility in anhydrous mantle. Rare earth element melting models can explain the petrogenesis of these basanites in terms of partial melting of a spinel peridotite source containing residual amphibole. It is inferred that amphibole, indicated by the relative K and Rb depletion and the melting model, was precipitated in the spinel peridotite lithospheric mantle beneath the Siebengebirge, by metasomatic fluids or melts from a rising mantle diapir or plume. Alkali basalts and more differentiated rocks have lower Mg# and lower abundances of Ni and Cr, and have undergone fractionation of mainly olivine, clinopyroxene, Fe–Ti oxides, amphibole and plagioclase. Most of the basanites and alkali basalts approach the Sr–Nd–Pb isotope compositions inferred for the European Asthenospheric Reservoir component. Trace element constraints (i.e. low Nb/U and Ce/Pb ratios) and the Sr–Nd–Pb isotope composition of the differentiated rocks indicate that assimilation of lower crustal material has modified the composition of the primary mantle-derived magmas. High 207 Pb/ 204 Pb ratios in the differentiated lavas point to assimilation of ancient lower crustal components having high U/Pb and Th/Pb ratios. Relatively shallow melting of inferred amphibole-bearing spinel peridotite sources may suggest an origin from the metasomatized part of the thermal boundary layer. Application of new thermobarometric equations for the basaltic magmas indicates relatively normal mantle potential temperatures (1300–1400°C); thus the inferred mantle ‘baby plume’ or ‘hot finger’ is not thermally anomalous.

Description: We consider an electromagnetic scattering problem produced by a perfect conductor. We pose the problem in a bounded region surrounding the obstacle and impose on the exterior boundary of the computational domain an impedance boundary condition inspired by the asymptotic behaviour of the scattered field at infinity. The operator associated with our problem belongs to a class of operators for which a suitable decomposition of the energy space plays an essential role in the analysis. This decomposition is performed here through a regularizing projector that takes into account the boundary conditions. The discrete version of this projector is the key tool to prove that a Galerkin scheme based on Nédélec’s edge elements is well posed and convergent under general topological assumptions on the scatterer and without assuming special requirements on the triangulations.

Description: Gould and Robinson (2010, SIAM J. Optim. , 20 , 2023–2048; 2010, SIAM J. Optim. , 20 , 2049–2079) introduced a second-derivative sequential quadratic programming method (S2QP) for solving nonlinear nonconvex optimization problems. We proved that the method is globally and locally superlinearly convergent under common assumptions. A critical component of the algorithm is the so-called predictor step, which is computed from a strictly convex quadratic program with a trust-region constraint. This step is essential for proving global convergence but its propensity to identify the optimal active set is paramount for achieving fast local convergence. Thus the global and local efficiency of the method is intimately coupled with the quality of the predictor step. In this paper we study the effects of removing the trust-region constraint from the computation of the predictor step. This is reasonable since the resulting problem is still strictly convex and thus well defined. Although it is interesting theoretically to verify that the same convergence guarantees hold when no trust-region constraint is used, our motivation is based on the practical behaviour of the algorithm. Preliminary numerical experience with S2QP indicates that the trust-region constraint occasionally degrades the quality of the predictor step and diminishes its ability to correctly identify the optimal active set. Moreover, removal of the trust-region constraint allows for re-use of the predictor step over a sequence of failed iterations, thus reducing computation. We show that the modified algorithm remains globally convergent and preserves local superlinear convergence provided that a nonmonotone strategy is incorporated.

Description: We consider a recently proposed finite-element space that consists of piecewise affine functions with discontinuities across a smooth given interface (a curve in two dimensions, a surface in three dimensions). Contrary to existing extended finite element methodologies, the space is a variant of the standard conforming $${\mathbb{P}}_{1}$$ space that can be implemented element by element. Further, it neither introduces new unknowns nor deteriorates the sparsity structure. It is proved that, for u arbitrary in $${W}^{1,p}(\Omega \setminus \Gamma )\cap {W}^{2,s}(\Omega \setminus \Gamma )$$ , the interpolant $${\mathcal{I}}_{h}u$$ defined by this new space satisfies where h is the mesh size, $$\Omega \subset {\mathbb{R}}^{d}$$ is the domain, $$p 〉 d$$ , $$p\ge q$$ , $$s\ge q$$ and standard notation has been adopted for the function spaces. This result proves the good approximation properties of the finite-element space as compared to any space consisting of functions that are continuous across , which would yield an error in the $${L}^{q}(\Omega )$$ -norm of order . These properties make this space especially attractive for approximating the pressure in problems with surface tension or other immersed interfaces that lead to discontinuities in the pressure field. Furthermore, the result still holds for interfaces that end within the domain, as happens for example in cracked domains.

Description: A linear parabolic differential equation on a moving surface is first discretized in space by evolving surface finite elements and then in time by an implicit Runge–Kutta (RK) method. For algebraically stable and stiffly accurate RK methods unconditional stability of the full discretization is proven and the convergence properties are analysed. Moreover, the implementation is described for the case of the Radau IIA time discretization. Numerical experiments illustrate the behaviour of the fully discrete method.

Description: New age and whole-rock 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic data are used to assess petrogenetic and regional geodynamic processes associated with Late Cretaceous subvolcanic intrusions within the sparsely studied Timok Magmatic Complex (TMC) and Ridanj–Krepoljin Zone (RKZ) of eastern Serbia. The TMC and RKZ form part of the Apuseni–Banat–Timok–Srednogorie (ABTS) magmatic belt, a Cu–Au mineralized calc-alkaline magmatic arc related to closure of the Tethys Ocean that extends through Romania, Serbia, and Bulgaria in SE Europe. Zircon ages based on U–Pb laser ablation inductively coupled plasma mass spectrometry supplemented by existing isotope dilution thermal ionization mass spectrometry data respectively range from 89 to 79 Ma and from 76 to 71 Ma for the TMC and RKZ. This age pattern corresponds to cross-arc younging away from the European continent. Adakite-like trace element signatures (Y ≤18 ppm) are linked with samples that extend across the arc. These overlap in space and time with samples that conform to a normal arc differentiation trend. We performed energy-constrained assimilation–fractional crystallization (EC-AFC) modeling of Sr–La–Nd–Yb concentrations and Sr and Nd isotopic data. Results suggest that the two distinct fractionation trends may be explained in terms of a common mantle-derived parental magma but distinct fractionation and assimilation paths in the lower and upper crust. Petrogenesis of the adakite-like magmas is consistent with extensive high-pressure amphibole fractionation in the lower crust followed by ascent and plagioclase-dominant fractionation and assimilation in the upper crust. In contrast, normal arc signatures appear to have evolved exclusively via an upper-crustal differentiation process. Overall, our interpretation supports mantle wedge melting related to weak extension during progressive rollback of a subducting slab.

Description: Late Oligocene to Middle Miocene adakitic andesites are found in the southern part of Okushiri Island, the northern Noto Peninsula and in the Toyama region in the present-day back-arc margin of the SW and NE Japan arcs. On Okushiri Island, adakitic andesite is accompanied by moderately alkaline basalt, whereas on the Noto Peninsula, adakitic andesite has been erupted along with high magnesian andesite (HMA), bronzite andesite and tholeiitic basalt. Adakitic andesites from all three locations are characterized by high Sr/Y and low Y, and have higher MgO contents than adakitic melts generated by experimental melting of metabasalt and amphibolite. They also have higher Ni and Cr contents than either Archaean tonalite–trondhjemite–granodiorite (TTG) suites or Early Cretaceous adakitic granites, which have been attributed to partial melting of subducted oceanic crust. The Noto Peninsula adakitic andesite has Sr and Nd isotopic compositions identical to normal mid-ocean ridge basalt (N-MORB), whereas the Okushiri Island and Toyama adakitic andesites are more isotopically primitive than N-MORB. The Noto Peninsula primary adakitic melt was derived from subducted oceanic N-MORB crust, whereas the Okushiri Island and Toyama primary adakites are interpreted as melts of subducted N-MORB and sediment that have subsequently interacted with the overlying mantle wedge peridotite. To explain the comagmatism of adakite, HMA and basalt, the following model is proposed. A hydrated adakitic diapir ascends from the subducting slab and is heated because it enters the overlying hot mantle wedge. The subsequent establishment of thermal and H 2 O gradients in the adakitic diapir and surrounding mantle wedge peridotite results in concurrent generation of adakitic andesite magma in the inner adakitic diapir region (low temperature and high H 2 O content), HMA and bronzite andesite magmas in the intermediate peridotite region (intermediate temperature and H 2 O content), and tholeiitic basalt magma in the outer peridotite region (high temperature and lower H 2 O content). Comagmatic adakite and mildly alkaline basalt are found in cooler and wetter adakitic diapirs and hotter and drier peridotite regions respectively. The most likely tectono-magmatic situation for the genesis of adakitic magmas in this example of a cool subduction zone involves upwelling of hot asthenosphere into the subcontinental lithosphere beneath the back-arc side of the NE Japan arc and northern end of the SW Japan arc, during the period spanning the pre-Japan Sea opening to syn-opening stages. The unusually high temperature conditions established in the mantle wedge owing to upwelling of hot asthenosphere caused partial melting of the relatively cool subducting Pacific plate, resulting in the generation of adakitic magmas.

Description: The olivine macrocrysts found in oceanites, picrites and magnesian basalts erupted at hotspot volcanoes are generally interpreted either as phenocrysts crystallized from the magma or as xenocrysts extracted from a deforming cumulate. To constrain the origin of these crystals we studied their texture and composition at Piton de la Fournaise volcano, La Réunion. We show that macrocrysts are organized and subdivided into parallel units; this suggests a crystallization by dendritic growth and ripening rather than by a complex combination of paired nucleation, crystal aggregation or synneusis. Dendritic growth is also evidenced by the occurrence of hollow faces, P-rich zones, melt and Cr-spinel inclusions formed from the accumulation of slow diffusing impurities (P, Cr, Al) in the liquid at the contact with rapid-growing olivine. We suggest that early dendritic crystallization may even cause branch misorientations and lattice mismatches, yielding subgrain boundaries, dislocation lamellae and to a certain extent undulose extinction, which have all been formerly interpreted in terms of plastic intracrystalline deformation. We interpret olivine macrocrysts as phenocrysts crystallized under a strong degree of undercooling (–T 〉 60°C), and derived from a harrisitic mush formed on the cold walls of the magma reservoir. Given the growth shapes indicated by P zoning patterns and external faces, the olivine macrocrysts (which consist of groups of several subcrystals) have grown in suspension within the liquid and were neither aggregated into a dense cumulate nor corroded, shocked or deformed before or during their transport to the surface. The major consequence of our study is that most olivine macrocrysts are not xenocrysts, and very few of them, if any, have experienced intracrystalline deformation. The importance of deforming (creeping) cumulate bodies, thought to accommodate the spreading of basaltic volcanoes in La Réunion and Hawaii, may hence have been overestimated.

Description: Tourmaline occurs in peraluminous granites from the Central Iberian Zone associated with two main AFM mineral assemblages: (1) muscovite + biotite ± cordierite ± andalusite in the Araya-type granites; (2) muscovite ± biotite ± garnet in leucogranites from the Alamo complex. When tourmaline is dominant, biotite is an accessory or absent, and vice versa. We present field and petrographic relations, mineral chemistry, and geochemical data for tourmaline-bearing and tourmaline-free granitic rocks from various localities in the Central Iberian Zone. Compositional phase diagrams are used to evaluate the factors controlling the occurrence of tourmaline relative to biotite in granitic rocks, with particular emphasis on the relationships between mineral assemblage and whole-rock chemistry and its petrological implications. Although tourmaline stability in felsic magmas depends on the interplay between rates of changing environmental conditions such as bulk composition, T, aH 2 O, and fO 2 , the principal factor dictating tourmaline formation is the B content of the melt, judging from phase relations. In short, regardless of other variables, granitic melts have to surpass a critical boron threshold to achieve tourmaline saturation. Experimental constraints, combined with petrographic and geochemical data, suggest minimum boron contents in the range of ~500–3000 µg g –1 (depending on temperature) to saturate melt in tourmaline. Acting in concert with boron content, other variables such as Al 2 O 3 , mafic components, T, fO 2 , and so on, control not only the formation of tourmaline during melt crystallization, but also the magnitude of boron loss from the magma to the surrounding rocks. The analysis of phase relations suggests that tourmaline granites usually form units distinct from biotite granites because common granitic melts have restricted accessibility to the three-phase Tur–Bt–Ms field.

Description: We experimentally investigated phlogopite- and C–O–H-bearing lherzolite to model the mantle wedge fluxed by volatiles released from a subducting crustal slab. Experiments have been carried out at 900–1050°C and 1·6–3·2 GPa, at fluid- and carbon-saturated conditions. We used an end-loaded piston cylinder apparatus and a conventional double-capsule technique to constrain the redox state of the experiments, using the nickel–nickel oxide oxygen buffer (NNO). Following thermodynamic calculations, we expect inner f O 2 values to be systematically below NNO, with fluids that are mixtures of CO 2 and H 2 O. Estimated f O 2 in the runs are between FMQ –0·7 at 3 GPa and FMQ –1·1 at 1·8 GPa, values that have been reported for natural mantle-wedge xenoliths. At the conditions investigated, the hydrous phases are phlogopite and pargasitic amphibole. Whereas phlogopite is ubiquitous, amphibole disappears at 3·1 GPa at 900°C and 2·7 GPa at 1050°C, where the solidus is encountered. The amphibole-out reaction also consumes orthopyroxene and liberates water. From low to high P , we observed first carbonate-free, amphibole-bearing assemblages, then carbonate + amphibole-bearing assemblages, and finally amphibole-free, carbonate-bearing assemblages. Carbonate-free assemblages melt to produce trachyandesite at T 〉 1050°C, whereas dolomitic carbonatites have been found beyond the solidus of carbonate-bearing assemblages. Carbonates occur as dolomite at 〈1·9 GPa, 900°C and at 〈2·1 GPa, 1050°C; magnesite at 〉2·4 GPa, 900°C and 〉2·7, 1050°C; between these limits, a magnesite + dolomite-bearing assemblage constitutes a two-carbonate field. P–T pseudosections fail to reproduce the experimental results concerning amphibole breakdown and reaction positions involving carbonates. The amount of COH fluid is thought to have a major role, even in fluid-saturated peridotites. Clinopyroxene and olivine are not expected at fluid-oversaturated conditions, for which dolomite or magnesite are stable respectively. The presented results are useful for unravelling the exhumation history of orogenic lherzolites bearing COH phases and to suggest a way to transfer carbon species to the mantle wedge. We suggest that once carbon-bearing fluids react with mantle-wedge peridotites, a sort of buoyant ‘cold plume’ will form containing low-density phases such as amphibole, carbonates and carbonatitic melt. This plume could represent an important source of CO 2 and H 2 O, and it is one of a series of processes that ultimately lead to arc magmatism.

Description: Jurassic kimberlites in the southern Superior Province in northern Michigan contain a variety of possible lower-crustal xenoliths, including mafic garnet granulites, rare garnet-free granulites, amphibolites and eclogites. Whole-rock major-element data for the granulites suggest affinities with tholeiitic basalts. P–T estimates for granulites indicate peak temperatures of 690–730°C and pressures of 9–12 kbar, consistent with seismic estimates of crustal thickness in the region. The granulites can be divided into two groups based on trace-element characteristics. Group 1 granulites have trace-element signatures similar to average Archean lower crust; they are light rare earth element (LREE)-enriched, with high La/Nb ratios and positive Pb anomalies. Most plot to the left of the geochron on a 206 Pb/ 204 Pb vs 207 Pb/ 204 Pb diagram, and there was probably widespread incorporation of Proterozoic to Archean components into the magmatic protoliths of these rocks. Although the age of the Group 1 granulites is not well constrained, their protoliths appear to be have been emplaced during the Mesoproterozoic and to be older than those for Group 2 granulites. Group 2 granulites are also LREE-enriched, but have strong positive Nb and Ta anomalies and low La/Nb ratios, suggesting intraplate magmatic affinities. They have trace-element characteristics similar to those of some Mid-Continent Rift (Keweenawan) basalts. They yield a Sm–Nd whole-rock errorchron age of 1046 ± 140 Ma, similar to that of Mid-Continent Rift plume magmatism. These granulites have unusually radiogenic Pb isotope compositions that plot above the 207 Pb/ 204 Pb vs 206 Pb/ 204 Pb growth curve and to the right of the 4·55 Ga geochron, and closely resemble the Pb isotope array defined by Mid-Continent Rift basalts. These Pb isotope data indicate that ancient continental lower crust is not uniformly depleted in U (and Th) relative to Pb. One granulite xenolith, S69-5, contains quartz, and has a unique peraluminous composition. It has the lowest Nd and Hf values of the suite. Its isotopic compositions indicate that it is significantly older than the other granulites. Broken zircon cores encased by younger overgrowths suggest that this granulite includes a large component of pre-existing sedimentary rocks. Two distinct populations of zircons from S69-5 were dated by sensitive high-resolution ion microprobe. Abundant rounded zircons yield ages of 1104 ± 42 (2) Ma, which coincide with the Mid-Continent Rift flood basalt eruptions. Their morphology is similar to those found in lower-crustal rocks that have undergone granulite-facies metamorphism and thus they are considered to represent the age of Group 2 granulites. Also present are less abundant elongate zircon grains that yield a mean age of 1387 ± 32 (2) Ma. Their elongate shapes indicate growth from a melt or fluid, possibly associated with 1·3–1·5 Ga anorogenic granite magmatism exposed in the shallow crust to the south in Wisconsin, or related to an initial encroachment of the Keweenawan plume upon the lower crust. Older ages recognized in zircon cores are less well constrained but may be related to tectono-magmatic events in the southern Superior craton. Within the studied suite only S69-5 was recognized as a remnant of the Late Archean lower crust into which the Group 1 and 2 mafic granulite precursor basalts were intruded. Collectively, the data show that the lower crust beneath northern Michigan formed in Archean times and underwent a variety of tectono-magmatic processes throughout the Proterozoic, including orogenesis, partial melting and mafic magmatic underplating in response to upwelling mantle plumes.

Description: Dy/Dy* is the measured value of Dy, a representative middle rare earth element (REE), compared with the value interpolated between La and Yb on a REE plot. It is essentially a measure of the ‘concavity’ of a REE pattern. The use of Dy/Dy* as a proxy for REE pattern shape allows us to compare large amounts of REE data, which can be difficult using standard REE patterns. When Dy/Dy* is combined with Dy/Yb (the slope of the middle-to-heavy REE pattern) REE patterns can effectively be classified by shape. We present a new set of high-quality REE (and other trace element) data for young volcanic rocks from six arcs. When plotted on the Dy/Dy*–Dy/Yb diagram they define a broad negative correlation from LREE-depleted (Tonga–Kermadec) to LREE-enriched (Philippines and Indonesia). This trend corresponds to decreasing Dy/Dy*, reflecting REE patterns varying from concave-down to concave-up respectively. When cogenetic suites from single volcanoes are plotted they define clear trends of decreasing Dy/Yb and Dy/Dy* with differentiation, roughly orthogonal to the general depletion–enrichment trend. The trends for single arc volcanoes are interpreted as most probably reflecting an amphibole control, consistent with the concomitant decreases in Ti/Ti* and increasing SiO 2 . Available distribution coefficients are, however, also permissive of cpx control on arc REE patterns. Estimated compositions of the continental crust fall along these same trends. In contrast, ocean island basalt (OIB) data all fall to high Dy/Yb, suggesting a significant control by garnet. A global consideration of the data suggests that (1) arc magmas are derived from variably depleted asthenospheric (mid-ocean ridge basalt) mantle sources, (2) arc magma (and continental crust) differentiation is controlled by a mineral phase (or phases) that preferentially partitions MREE and (3) OIB genesis appears to always involve garnet control. We propose that Dy/Dy* is potentially a powerful tool for representing the shapes of REE patterns, especially for large datasets. We also note the importance of using cogenetic rock suites to identify petrogenetic processes rather than regional suites.

Description: Spatial and temporal variations in the abundance and biomass of heterotrophic protists and of their grazing impact were investigated during five cruises between July 2006 and February 2009 in the continental shelf waters of the northern East China Sea (ECS). Strongly patchy distributions were observed on all cruises, generally with a higher biomass in the western areas affected by the Changjiang River discharge. An opposite pattern was observed in February when the Kuroshio onshore transport is greatest, with a greater biomass in the eastern area. Small heterotrophic dinoflagellates (〈20 µm) were most abundant numerically, whereas ciliates contributed the most to the biomass, accounting for 28–58% of the total heterotrophic protist biomass. Small heterotrophic dinoflagellates were more strongly correlated with phytoplankton biomass than were other types of protists. The total protist biomass was often most strongly related to amounts of particulate organic carbon of non-phytoplankton origin, suggesting that their abundance distribution often depended on prey other than phytoplankton, such as heterotrophic bacteria. Heterotrophic protists consumed 30.1–91.5% of Chl a production (mean 68.2%), with grazing rates increasing with the phytoplankton biomass. The results suggest that heterotrophic protists were the major consumers of primary production, and that their grazing is one of the most important losses affecting the phytoplankton biomass in the northern ECS.

Description: Larger egg size and body size at lower temperature are widely observed in zooplankton and other groups. Theoretically, considering the increased cost of producing larger eggs, females would produce larger and fewer eggs only if the newborn from such eggs perform better under certain environmental constraints, such as low temperature. In temperate lakes, low water temperature is a fairly reliable cue of future declining dietary conditions for herbivorous zooplankters. Under these conditions, females that produce more resistant offspring are likely to be selected. Nevertheless, it is not efficient for them to do this at high temperature, when the dietary conditions are usually more abundant. In this study, the adaptive significance of temperature-induced plasticity in a planktonic rotifer, Brachionus calyciflorus , was investigated. We found that: first, the egg size and body size were negatively related to temperature; second, neonates from larger eggs induced by low a temperature of 13°C were more resistant to starvation at three different experimental temperatures; third, life table experiments showed that offspring from larger eggs had a higher population growth rate and shorter juvenile period than those from smaller ones at low temperature, and vice versa, which suggests that this may be attributed to some form of anticipatory maternal effect. These differences in population growth rates were mainly due to higher fertility during the first 1 or 2 days after maturation. All of these findings support the view that temperature-induced egg size plasticity has adaptive significance in rotifers.

Description: Ingestion of the large pelagic ciliates Stentor araucanus and S. amethystinus by the cyclopoid copepod Mesocyclops araucanus was independent of light conditions and copepod sex, but rates were twice as high on S. araucanus as on S. amethystinus . Copepods consumed 44–183% of their biomass daily. Absorption efficiency was 5–40%, while 20–30% of the ingested food was found in the faeces. In field samples, 32–93% of Mesocyclops had ingested Stentor, indicating the importance of this food source.

Description: To assess the effect of Microcystis blooms on the crustacean zooplankton community, we conducted a large-scale monthly survey from 2008 to 2010 in Lake Taihu, China. During the sampling period, Microcystis was the dominant genus in the phytoplankton community (〉79% of total biomass), while the crustacean zooplankton community was dominated by small-sized cladocerans (primarily Bosmina coregoni and Ceriodaphnia cornuta ) and copepods. During the study, plankton exhibited significant spatial heterogeneity. The northern and western regions suffered from harmful Microcystis blooms and had higher cladoceran production. In the eastern region where Microcystis blooms seldom occurred, copepods accounted for a relatively larger proportion. Both stepwise multiple linear regression and redundancy analysis demonstrated that Microcystis was the most important factor controlling the spatial dynamics of zooplankton. Linear regression analysis revealed that both cladocera and copepoda were positively correlated with Microcystis and the response of cladocerans ( R 2 = 0.73 , P 〈 0.001) to Microcystis was stronger than that of copepods ( R 2 = 0.44, P 〈 0.001). Our study suggested that cyanobacterial blooms may change competitive relations of small-sized cladocerans and copepoda, favoring small cladocerans (except larger genera).

Description: The scyphozoan Pelagia noctiluca reproduces by direct development without a benthic stage. Typically, this jellyfish is found offshore with a holoplanktonic lifecycle, vertical migration and feeding behaviours. Frequent outbreaks have been well documented on the Mediterranean shores since the 19th century; however, the offshore distribution of this species remains mostly unknown. In this study, we performed a bimonthly monitoring of P. noctiluca surface density, at high resolution, from a sailboat, along a 35-km coastal to offshore transect in the Ligurian Sea, between February and October 2011. During daylight, P. noctiluca was rarely seen. At night, offshore, P. noctiluca was always present, while within 5 km of the coast, P. noctiluca was rarely observed. Pelagia noctiluca aggregations were most abundant within the Northern Current of the Ligurian Sea. Our findings suggest that P. noctiluca outbreaks observed on Mediterranean shores may result from the transport of the permanent offshore population inshore by specific hydrodynamic conditions.

Description: Fecal pellet flux and size distribution at 500, 1500 and 3200 m depths were measured in sediment trap samples collected by the Oceanic Flux Program time-series off Bermuda, December 2006–November 2007. During the study, three mesoscale eddies passed through: a cyclonic eddy in bloom stage (February through mid-April), a decaying post-bloom mode-water eddy (late April through May), and an anticyclonic eddy (August through October). Variability associated with eddy passage masked any seasonal trends in flux or size distributions. At a depth of 1500 m, the fecal pellet flux ranged from a minimum of 100 pellets m –2 day –1 to a maximum of 500 pellets m –2 day –1 during the cyclonic eddy passage, corresponding to ranges in the fecal pellet mass and the carbon flux of 0.5–1.7 mg m –2 day –1 and 0.07–0.25 mg C m –2 day –1 , respectively. Fecal pellets averaged 7 ± 3% of the organic carbon flux, a minimum estimate as disassociated pellets were not quantifiable. Size distribution shifts indicated small zooplankton and immature stages were more abundant within the cyclonic eddy, whereas larger zooplankton were present within the mode water and anticyclonic eddies. The fecal pellet number, flux and size distributions showed no consistent depth trends and indicated extensive fecal pellet reprocessing within the water column.

Description: The build-up of large magmatic complexes can proceed piecemeal over periods of several million years through sequences of complex processes of magma production, differentiation, assimilation, final crystallization and subsequent metasomatic modification. All these stages can produce or modify minerals used as geochronometers, such as zircon, monazite and titanite. The present study exemplifies such complex relationships, also demonstrating how a systematic approach with comprehensive sampling and careful high-resolution U–Pb analyses can yield a coherent picture of the entire magmatic process. The study was conducted on the Pavia pluton, an elongated Variscan intrusion in the Ossa–Morena Zone of Portugal. The geochronological data show that the Pavia pluton was emplaced by the amalgamation of multiple magma pulses into the crust, over a period of c . 11 Myr. An early event at ~340 Ma, revealed by xenocrystic zircon, preceded the magmatic activity at the exposed level of the pluton, but is recognized as the main magmatic event elsewhere in the Ossa–Morena Zone. A second event at 328 Ma formed tonalite, trondhjemite and granodiorite, and subordinate differentiates in the central domains of the pluton (units I and II). A third event at c . 324 Ma emplaced granodiorite in the flanking domains III–V and the contemporaneous and widespread two-mica granite in domain VI, together with late rhyodacite porphyries, microgranodiorites, aplite–pegmatite and pegmatite dikes. A fourth event at 319–317 Ma was characterized by the emplacement of some microgranites and pegmatite dikes. These two last magmatic events also had an effect on the previously emplaced rocks, causing local overgrowths and isotopic resetting of minerals. The occurrence of a fifth magmatic event at depth at 313 Ma is the inferred cause of the hydrothermal activity responsible for local zircon, monazite and titanite resorption and/or recrystallization and for some of the textures exhibited by the main rock-forming minerals. The magmatic episodes were interspersed with periods of quiescence; this cyclicity presumably reflects an external control by the transtensional tectonic regime of the Ossa–Morena Zone.

Description: Igneous rock textures reflect the cooling history of the parental magma. Combined with chemical data, they can provide physical and chemical information about the evolution of a magma body. The petrographic textures and chemical compositions of 21 coarse- and fine-grained granite samples along an ~250 m horizontal outcrop of the Shanggusi granite porphyry are presented in this case study. The coarse-grained granite porphyry is an early intrusion, and the fine-grained granite dykes, mostly intruded into the granite porphyry, are later intrusions. The studied samples have nearly homogeneous major element bulk-rock and mineral compositions, but show large variations in their trace element compositions and textural characteristics. The trace element data suggest the influence of hydrous fluids (possibly enriched in CO 2 , F, and Cl) in the evolution of the plutonic body. Textural analysis of the coarse-grained granite porphyry indicates that the crystal size distribution (CSD) slopes, intercepts and total numbers of groundmass decrease from the center to the margin of the intrusion in contrast to the maximum diameter of the crystals (L max ) (average length of the four largest quartz crystals for each sample); however, most fine-grained samples and the groundmass of the coarse-grained samples show concave-down CSDs, indicating textural coarsening. Quartz CSDs in the coarse-grained samples are kinked, with a steep-sloped log–linear section representing small crystals (〈1 mm) and a shallow-sloped log–linear section representing large crystals (〉1 mm). These two crystal populations are interpreted as resulting from a shift in cooling regime. The straight CSDs of two fine-grained samples may be due to a different cooling history. In general, the spatial variation of the CSD patterns can be attributed to various degrees of overgrowth and mechanical compaction. The quartz phenocrysts in several coarse-grained samples exhibit a high degree of alignment, which may be the result of magmatic flow. By integrating the field geology, geochemistry and quantitative textural data from the horizontal profile of the Shanggusi granite porphyry, it is suggested that hydrous fluids at the top of the intrusion not only controlled the fractionation of elements but also affected its cooling history. Fluid migration-controlled undercooling can explain the solidification processes in the Shanggusi intrusion, and may also be prevalent in other fluid-rich shallow intrusions. Quantitative integration of textural and geochemical data for igneous rocks can contribute to our understanding of the relationships between physical and chemical processes in a magma system, and provide relatively comprehensive insights into the petrogenesis of granites.

Description: Cenozoic volcanism within Mongolia forms part of a large central Asian province of intra-plate magmatism. Numerous small-volume volcanic cones and alkali basalt lava flows have been formed since c . 30 Ma; from c . 12 Ma activity has been focused on the uplifted Hangai dome. A mechanism for melting beneath the dome has, however, thus far remained enigmatic. Some of the oldest basalts on the Hangai dome erupted at its centre at ~6 Ma and their geochemistry suggests a garnet lherzolite source region at 90–100 km depth. These lavas have Pb isotope compositions similar to those of depleted Indian mid-ocean ridge basalts (MORB) ( 206 Pb/ 204 Pb = 17·822, 207 Pb/ 204 Pb = 15·482, 208 Pb/ 204 Pb = 37·767), which may be indicative of the involvement of ambient asthenospheric mantle in their petrogenesis. Younger basalts exhibit a gradual shift in isotopic composition towards a source that has less radiogenic Pb and more radiogenic Sr, evidenced by the eruption of lavas with 206 Pb/ 204 Pb = 16·991 and 87 Sr/ 86 Sr = 0·704704. The youngest lavas, dated as younger than ~8 ka, have the highest K 2 O contents (up to 5·2 wt %) and are characterized by the most enriched trace-element signatures; they are interpreted to represent melting of a metasomatically altered sub-continental lithospheric mantle containing phlogopite. Concurrent with progressive melting of the lithosphere, melting appears to propagate outwards from the centre of the dome to its margins; by 0·7 Ma the marginal magmatism is interpreted to result from melting of a depleted MORB-source mantle component with a smaller contribution from the lithospheric mantle. The spatial and temporal variations in melting beneath the Hangai dome may be explained by either lithospheric delamination or the presence of a small-scale thermal anomaly in the upper mantle. Although it is not possible to distinguish between these models on the basis of geochemistry alone, the lack of a viable mechanism to generate small-scale upwelling lends support to a model involving delamination of the lithospheric mantle beneath the Hangai dome.

Description: The Hidaka Metamorphic Belt, in southeastern Hokkaido, Japan, provides insights into how magmatic sulfide deposits may form through magma mixing deep within arcs. Here, a near-complete cross-section of arc crust is exposed, with large mafic igneous complexes preserved at deeper levels. Magmatic sulfide mineralization occurs within the Opirarukaomappu Gabbroic Complex (OGC), which preserves a record of crustal contamination of mafic magmas via assimilation and magma mixing involving introduction of crust-derived tonalite. Assimilation–fractional crystallization modelling suggests that the gabbro evolved through a combination of approximately 10 wt % mixing and 14 wt % fractional crystallization. Magmatic sulfides and associated gabbros, diorites and tonalites at this locality contain graphite, with carbon isotope signatures consistent with derivation from the surrounding partially melted carbonaceous shales. This indicates that crust-derived carbon was added to the mafic magma through the magma mixing and assimilation process. Sulfur isotope data suggest that sulfur was also added from crustal sources during assimilation and magma mixing. The relationships observed in the OGC suggest that intrusion of basalt into a segment of deep arc crust drove partial melting of carbonaceous metamorphic rocks, producing graphite-bearing felsic magmas with high reducing potential. Redox budget modelling shows that mixing of only small proportions of these magmas is sufficient to lower the oxidation state of oxidized basaltic magmas enough to induce sulfide saturation and consequent exsolution of immiscible sulfide melt. Magmatic sulfide deposits are likely to form by this reduction-induced sulfide saturation mechanism deep within other arcs where magma mixing is thought to be common.

Description: A reactive flow geochemical model based on pMELTS thermodynamic calculations explains the observed modal, major, and trace element variations in the Red Hills peridotite, New Zealand. The model also reproduces the major and trace element chemical variations in mid-ocean ridge basalts (MORB) observed in present-day spreading ridges. The Red Hills peridotite is thought to originate from palaeo-MOR magmatic processes in the mantle–Moho transition zone. The peridotite body consists of a harzburgite matrix and dunite channels. The harzburgite forms the Lower Unit and is intruded by replacive dunite channels in the Upper Unit. This lithology gradually turns into a massive dunite zone in which disseminated to lenticular clinopyroxene aggregates are present. The rare earth element (REE) abundances in the peridotite samples vary greatly depending on their lithologies. In the Lower Unit, REE are extremely depleted, whereas in the Upper Unit they are relatively enriched, in contradiction to the depleted lithologies. Our model consists of two stages. The first stage assumes melting of depleted MORB source mantle in the garnet stability field, and the second assumes reactions between residual solids and the melts from the first stage in the spinel stability field in an open system. The model explains the formation of depleted harzburgite and the formation of dunite channels in the harzburgite matrix well. The major and trace element compositions of the melts calculated by the model vary from ultra-depleted MOR melts in harzburgite to normal MORB in dunite, suggesting that these lithologies are residues of a palaeo-MOR. The model also explains the origins of the local and global geochemical trends observed in MORB and the geochemical variation in abyssal peridotite samples. Our model confirms the important role of reactive flow in the mantle–Moho transition zone beneath MORs.

Description: The islands of Flores and Corvo in the Azores archipelago are the only two of nine subaerial volcanic edifices lying west of the Mid-Atlantic Ridge (MAR). This makes them important for constraining the evolution of this young (〈40 Ma) oceanic plateau. The alkalic basalt suites from Flores and Corvo lie on a single liquid line of descent. Ankaramitic cumulates, with MgO contents up to ~18 wt %, result from clinopyroxene-dominated polybaric crystallization. The parental magmas (MgO ~ 11 wt %) are inferred to be low-degree partial melts ( F = 3–5%) of enriched peridotite generated at depths of ~80–90 km. These primary magmas commenced crystallizing at the lithosphere–asthenosphere boundary and this continued in conduits over a pressure range of ~0·6–1·2 GPa. Only lavas with MgO 〈 3 wt % fractionated at shallow crustal levels. Nd and Sr isotope data reveal variations in the source of both magmatic systems, suggesting variable contributions from both enriched (E-) and depleted (D-) mid-ocean ridge basalt (MORB)-source mantle components. This is supported by the greater variability of incompatible trace-element ratios within the Flores lavas (e.g. Ba/Nd, La/Sm, Th/Nd), whereas those from Corvo exhibit a good correlation between key trace-element ratios [e.g. (La/Sm) N , Th/Nd] and Sr isotope ratios. Lavas from Flores display a greater variability in Sr and Nd isotope compositions and define a mixing array between an E-MORB source and a common Azores mantle source. The latter signature is restricted to lava suites from the north and east of Flores. We concur with the generally accepted notion that Flores and Corvo are derived from the same mantle plume as is responsible for the eastern Azores islands. However, there is evidence (different Nb/Zr, Ta/Hf and La/Sm, but homogeneous Sr and Nd isotopic composition) that these two islands are dominated by a source component that is not as evident in the eastern archipelago.

Description: Significant differences between bulk-rock lithophile trace element budgets and the sum of the contributions from the constituent minerals are common, if not ubiquitous, in peridotite xenoliths. Notwithstanding the possible contributions from fluid inclusions and grain-boundary glass and micro-phases, it is often difficult to reconcile the bulk-rock incompatible element budgets with those of the silicate phases. In the absence of modal metasomatism this discrepancy is often attributed to the ‘catch-all’ yet often vague process of cryptic metasomatism. This study presents comprehensive petrological descriptions, major and trace element and Sr–Nd isotope data for variably metasomatized bulk-rock peridotites, host basalt, and constituent peridotite mineral phases from spinel lherzolite and harzburgite xenoliths from the Kilbourne Hole volcanic maar, New Mexico, USA. Similar measurements were also made on hand-picked interstitial glass from one of the most highly metasomatized samples in an attempt to unravel the sources, effects, and relative timings of multiple metasomatic events. Reaction textures around clinopyroxene grains are evident in the most metasomatized samples. These are accompanied by films of high-SiO 2 interstitial glass, which is not in equilibrium with the primary silicate minerals. Trails of glassy melt inclusions terminate in these films against which the margins of the primary minerals appear partially resorbed. Furthermore, different styles of high field strength element fractionation [e.g. (Nb/Ta) N vs (Zr/Hf) N ] are evident in the bulk-rocks and the clinopyroxenes that they host. In all of the Kilbourne Hole peridotites analysed, hand-picked, optically clean clinopyroxenes preserve a more unradiogenic Sr isotope signature than the corresponding bulk-rock. Hand-picked interstitial glass from KH03-16 reveals the most radiogenic 87 Sr/ 86 Sr of any component recovered from these xenoliths ( 87 Sr/ 86 Sr = 0·708043 ± 0·00009; [Sr] = 81 ppm). Similarly, the 143 Nd/ 144 Nd of the glass is amongst the most evolved of the peridotite components ( 143 Nd/ 144 Nd = 0·512893 ± 0·000012; [Nd] = 10 ppm). However, the host basalt ( 87 Sr/ 86 Sr = 0·703953 ± 0·00012; 143 Nd/ 144 Nd = 0·512873 ± 0·000013), similar in composition to that of the nearby, contemporaneous, Potrillo Volcanic Field basalts, contains nearly an order of magnitude more Sr and more than three times more Nd ([Sr] = 655 ppm; [Nd] = 34 ppm) than the interstitial glass. Despite the high Sr and Nd contents of the host basalt the evidence for basalt infiltration is scant, although the effects of melt–rock interaction, both in antiquity and more recently, are preserved in several xenoliths. Mixing between clinopyroxene and the host basalt cannot account for the full range of bulk-rock Sr–Nd isotope ratios; nearly half of the xenoliths require an additional component that could involve varying amounts of interstitial glass. In detail the behaviour of Sr and Nd isotopes has been decoupled, requiring multiple, temporally distinct, metasomatic events. Several bulk-rock samples require a further, as yet unidentified, component to explain the bulk-rock trace element mass balance and Sr–Nd isotope composition fully, implying that at least three episodes of melt–rock interaction, refertilization and metasomatism must have occurred prior to the arrival of the xenoliths at the surface in their host maar deposits.

Description: Isothermal and isobaric crystallization of plagioclase in a water-saturated synthetic rhyolitic melt is investigated through a time-series of decompression experiments. The experimental variables are the rate at which samples are initially decompressed (30, 150, and 1200 MPa h – 1 ) from 200 MPa and 875°C, final pressure (25–160 MPa), and holding time at final pressure (up to 17 days). Through textural measurements of the crystals, plagioclase crystallization kinetics is characterized in terms of nucleation lag and rates of nucleation and growth. Plagioclase crystallization is markedly dependent on effective undercooling, T eff , and holding time at crystallization pressure. With T eff increasing from 55 to 110°C, (1) nucleation lag decreases from 1–2 days to ~15 min, (2) maximum nucleation rates increase from ~10 – 3 to 10 – 2 mm – 2 s – 1 , and (3) maximum growth rates decrease from ~10 – 6 to 5 x 10 – 7 mm s – 1 . The initial decompression rate (30, 150, and 1200 MPa h – 1 ) has no systematic control on crystallization at final pressure, except for the 1200 MPa h – 1 series in which samples show nucleation difficulties. From the experimental data for T eff -constrained plagioclase number density, proportion, and morphology, we provide means to assess the conditions of nucleation and growth of natural plagioclase microlites from rapidly ascended rhyolitic melts, through the determination of the plagioclase liquidus curve and T eff prevailing during crystallization.

Description: New geochemical and isotopic data are presented for volumetrically minor, depleted low-Ti basalts that occur in the Plateau Basalt succession of central East Greenland (CEG), formed during the initial stages of opening of the North Atlantic at 55 Ma. The basalts have mid-ocean ridge basalt (MORB)-like geochemistry (e.g. depleted light rare earth elements) and are distinct from the high-Ti lavas that dominate the sequence. Rare earth element geochemistry implies derivation from a source more depleted than the typical MORB source, and suggests polybaric melting and contributions from both spinel- and garnet-facies mantle. The low-Ti basalts have Sr–Nd–Pb–Hf isotopic characteristics that are similar to those of depleted magmas from Iceland (e.g. Theistareykir) and adjacent ridges (Kolbeinsey and Reykjanes) and distinct from global MORB (e.g. negative 207 Pb, and Hf and Nd isotope compositions that plot above the mantle reference line). Isotope and trace element data indicate the involvement of two depleted source components. One component has isotopic compositions similar to other depleted components identified in the North Atlantic and has high Rb/Zr and Ba/Nb. The second is isotopically less depleted with lower Rb/Zr and Ba/Nb. Small degrees of crustal contamination (〈 1%) by both amphibolitic and granulitic crust result in relatively large changes in isotopic composition ( c . 1% lower for 206 Pb/ 204 Pb and 0·1% higher for 87 Sr/ 86 Sr depending on the contaminant). Negative Nb suggests a MORB affinity for the low-Ti magmas; however, they are distinguished from global normal (N)-MORB on the basis of vertical deviations from the Northern Hemisphere Reference Line (negative 207 Pb and positive 208 Pb), and relative enrichments in Ba, Sr and Pb. The isotopic compositions of the low-Ti CEG basalts suggest correlation with modern depleted components beneath Iceland and adjacent ridges, considered to be derived from upper mantle sources polluted by the Iceland plume. However, small positive Pb peaks when normalized to MORB, and lower Nb distinguish the CEG low-Ti basalts from depleted Icelandic compositions. The lower Nb (〈 0) and 87 Sr/ 86 Sr, and suggestion of higher 206 Pb/ 204 Pb in crustally uncontaminated parental melts imply a closer affinity to compositions from the oceanic ridges surrounding Iceland (especially the Reykjanes Ridge), yet they are subtly distinct on the basis of available trace element data. We suggest that this depleted component was an integral part of the plume that melted primarily during the rapid lithospheric uplift and extension associated with continental break-up.

Description: The origin and evolution of diamondiferous lithospheric mantle sampled by the Neoproterozoic Renard kimberlites (eastern Superior Province, Quebec) is constrained based on mantle-derived microxenoliths and xenocrysts. The dataset illustrates the wealth of knowledge that can be gleaned from small samples (1·2 mg–2·2 g) through an integration of multiple, mainly single mineral based approaches. Our samples document the presence of an ~200 km thick lithosphere with a ‘cold’ (38 mW m – 2 surface heat flow) model geotherm at the time of kimberlite emplacement ( c . 632 Ma), resulting in a large diamond window from 130 to 200 km (42–60 kbar). On the basis of the mantle xenolith and xenocryst record and excluding megacrysts, the lithospheric mantle beneath Renard was dominated by peridotite (91%), composed of lherzolite (72% of samples), harzburgite (24%) and wehrlite (5%), with minor eclogitic (3%) and websteritic (6%) portions. Comparatively abundant harzburgite probably establishes the principal diamond source, but elevated Na contents in eclogitic garnet suggest the additional presence of diamond-stable eclogites. A number of events have modified the lithospheric mantle underlying the eastern Superior Province, including the following: (1) evolving ‘kimberlitic’ melts pervasively re-fertilized the originally strongly depleted lithospheric mantle with respect to highly and moderately incompatible trace elements; (2) less pervasive fluid style metasomatism is indicated by selective re-enrichment of highly incompatible elements that occurred within a depth range of 125–170 km. In situ Pb isotope data obtained for clinopyroxenes suggest a model age of ~2·7 Ga for the protolith(s) of the cratonic lithospheric mantle beneath Renard. This age coincides with a major phase of continental crust generation within the Superior Province and throughout the Laurentia supercontinent (e.g. Greenland).

Description: In this paper we develop the a priori and a posteriori error analyses of a mixed finite element method for the coupling of fluid flow with nonlinear porous media flow. Flows are governed by the Stokes and nonlinear Darcy equations, respectively, and the corresponding transmission conditions are given by mass conservation, balance of normal forces and the Beavers–Joseph–Saffman law. We consider dual-mixed formulations in both domains, and in order to handle the nonlinearity involved, we introduce the pressure gradient in the Darcy region as an auxiliary unknown. In addition, the transmission conditions become essential, which leads to the introduction of the traces of the porous media pressure and the fluid velocity as the associated Lagrange multipliers. As a consequence, the resulting variational formulation can be written, conveniently, as a twofold saddle point operator equation. Thus, a well-known generalization of the classical Babuska–Brezzi theory is applied to show the well-posedness of the continuous and discrete formulations and to derive the corresponding a priori error estimate. In particular, the set of feasible finite element subspaces includes Raviart–Thomas elements of lowest order and piecewise constants for the velocities and pressure, respectively, in both domains, together with piecewise constant vectors for the Darcy pressure gradient and continuous piecewise linear elements for the traces. Then, we employ classical approaches and use known estimates to derive a reliable and efficient residual-based a posteriori error estimator for the coupled problem. Finally, several numerical results confirming the good performance of the method and the theoretical properties of the a posteriori error estimator, and illustrating the capability of the corresponding adaptive algorithm to localize the singularities of the solution, are reported.

Description: We consider a piecewise linear, discontinuous Galerkin method for the time discretization of a fractional diffusion equation involving a parameter in the range –1 〈 α 〈 0. Our analysis shows that, for a time interval (0, T ) and a spatial domain , the uniform error in L ((0, T ); L 2 ( )) is of order k , where = min g (2, +α) and k denotes the maximum time step. Thus, if –1/2 ≤ α 〈 0, then we have optimal O( k 2 ) convergence, just as for the classical diffusion (heat) equation.

Description: We propose a mixed finite-element method for the motion of a strongly viscous, ideal and isentropic gas. At the boundary we impose a Navier slip condition such that the velocity equation can be posed in mixed form with the vorticity as an auxiliary variable. In this formulation we design a finite-element method, where the velocity and vorticity are approximated with the div- and curl-conforming Nédélec elements, respectively, of the first order and first kind. The mixed scheme is coupled to a standard piecewise constant upwind discontinuous Galerkin discretization of the continuity equation. For the time discretization implicit Euler time stepping is used. Our main result is that the numerical solution converges to a weak solution as the discretization parameters go to zero. The convergence analysis is inspired by the continuous analysis of Feireisl and Lions for the compressible Navier–Stokes equations. Tools used in the analysis include an equation for the effective viscous flux and various renormalizations of the density scheme.

Description: This paper aims to present a unified framework for deriving analytical formulas for smoothing factors in arbitrary dimensions, under certain simplifying assumptions. To derive these expressions we rely on complex analysis and geometric considerations, using the maximum modulus principle and Möbius transformations. We restrict our attention to pointwise and block lexicographic Gauss–Seidel smoothers on a d -dimensional uniform mesh, where the computational molecule of the associated discrete operator forms a (2 d +1)-point star. In the pointwise case, the effect of a relaxation parameter is analysed. Our results apply to any number of spatial dimensions and are applicable to high-dimensional versions of a few common model problems with constant coefficients, including the Poisson and anisotropic diffusion equations, as well as a special case of the convection–diffusion equation. We show that in most cases our formulas, exact under the simplifying assumptions of local Fourier analysis, form tight upper bounds for the asymptotic convergence of geometric multigrid in practice. We also show that there are asymmetric cases where lexicographic Gauss–Seidel smoothing outperforms red–black Gauss–Seidel smoothing; this occurs for certain model convection–diffusion equations with high mesh Reynolds numbers.

Description: We study the stability properties of, and the phase error present in, several higher-order (in space) staggered finite difference schemes for Maxwell's equations coupled with a Debye or Lorentz polarization model. We present a novel expansion of the finite difference approximations, of arbitrary (even) order, of the first-order spatial derivative operator. This alternative representation allows the derivation of a concise formula for the numerical dispersion relation for all even order schemes applied to each model, including the limiting (infinite-order) case. We further derive a closed-form analytical stability condition for these schemes as a function of the order of the method. Using representative numerical values for the physical parameters, we validate the stability criterion while quantifying numerical dissipation. Lastly, we demonstrate the effect that the spatial discretization order, and the corresponding stability constraint, has on the dispersion error.

Description: The aim of this paper is to analyse a numerical method to solve transient eddy current problems with input current intensities as data, formulated in terms of the magnetic field in a bounded domain including conductors and dielectrics. To this end, we introduce a time-dependent weak formulation and prove its well-posedness. We propose a finite element method for space discretization based on the Nédélec edge elements on tetrahedral meshes, for which we obtain error estimates. Then we introduce a backward Euler scheme for time discretization and prove error estimates for the fully discrete problem, too. Furthermore, a magnetic scalar potential is introduced to deal with the curl-free condition in the dielectric domain, which leads to an important saving in computational effort. Finally, the method is applied to solve two problems: a test with a known analytical solution and an application to electromagnetic forming.

Description: In this paper a quadrature method for Cauchy singular integral equations having constant coefficients and index equal to –1 is proposed. A polynomial approximation of the solution is constructed by solving a determined and well-conditioned linear system. Error estimates and numerical tests are also included.

Description: We introduce a novel technique for constructing higher-order variational integrators for Hamiltonian systems of ordinary differential equations. In the construction of the discrete Lagrangian we adopt Hermite interpolation polynomials and the Euler–Maclaurin quadrature formula and apply collocation to the Euler–Lagrange equation and its prolongation. Considerable attention is devoted to the order analysis of the resulting variational integrators in terms of approximation properties of the Hermite polynomials and quadrature errors. In particular, the order of the variational integrator can be computed a priori based on the quadrature error estimate. The analysis in the paper is straightforward compared to the order theory for Runge–Kutta methods. Finally, a performance comparison is presented on a selection of these integrators.

Description: Linear systems of equations Ax = b , where the matrix A has some particular structure, arise frequently in applications. Very often, structured matrices have huge condition numbers and, therefore, standard algorithms fail to compute accurate solutions of Ax = b . We say in this paper that a computed solution is accurate if being the unit roundoff. In this work we introduce a framework that allows many classes of structured linear systems to be solved accurately, independently of the condition number of A and efficiently, that is, with cost For most of these classes no algorithms are known that are both accurate and efficient. The approach in this work relies on first computing an accurate rank-revealing decomposition of A , an idea that has been widely used in the last decades to compute singular value and eigenvalue decompositions of structured matrices with high relative accuracy. In particular, we illustrate the new method by accurately solving Cauchy and Vandermonde linear systems with any distribution of nodes, that is, without requiring A to be totally positive for most right-hand sides b .

Description: This paper is concerned with a staggered discontinuous Galerkin method for the curl–curl operator arising from the time-harmonic Maxwell equations. One distinctive feature of the method is that the discrete operators preserve the properties of the differential operators. Moreover, the numerical solution automatically satisfies a discrete divergence-free condition. Stability and optimal convergence of the method are analysed. Numerical experiments for smooth and singular solutions are shown to verify the optimal order of convergence. Furthermore, the method is applied to the corresponding eigenvalue problem. Numerical results for rectangular and L-shaped domains show that our method is able to produce nonspurious eigenvalues.

Description: We propose a general framework that allows for a new natural coupling of boundary element and a wide class of finite element methods (FEMs) for a model second-order elliptic problem. This class of FEMs includes mixed methods, discontinuous Galerkin methods and the continuous Galerkin method. We provide sufficient conditions guaranteeing the well-posedness of the methods and give several examples that include new as well as old methods.

Description: The Lippmann–Schwinger integral equation describes the scattering of acoustic waves from an inhomogeneous medium. For scattering problems in free space, Vainikko proposed a fast spectral solution method exploiting the convolution structure of this equation's integral operator and the fast Fourier transform. Although the integral operator of the Lippmann–Schwinger integral equation for scattering in a planar three-dimensional waveguide is not a convolution, we show in this paper that the separable structure of the kernel allows to construct fast spectral collocation methods. The numerical analysis of this method requires smooth material parameters; for discontinuous materials there is no theoretical convergence statement. Therefore, we construct a Galerkin variant of Vainikko's method avoiding this drawback. For several distant scattering objects inside the three-dimensional waveguide this discretization technique would lead to a computational domain consisting of one large box containing all scatterers and hence many unnecessary unknowns. However, the integral equation can be reformulated as a coupled system with unknowns defined on the different parts of the scatterer. Discretizing this coupled system by a combined spectral/multipole approach yields an efficient method for waveguide scattering from multiple objects.

Description: The aim of this paper is to investigate the stability of time integration schemes for the solution of a finite element semi-discretization of a scalar convection–diffusion equation defined on a moving domain. An arbitrary Lagrangian–Eulerian formulation is used to reformulate the governing equation with respect to a moving reference frame. We devise an adaptive -method time integrator that is shown to be unconditionally stable and asymptotically second-order accurate for smoothly evolving meshes. An essential feature of the method is that it satisfies a discrete equivalent of the well-known geometric conservation law. Numerical experiments are presented to confirm the findings of the analysis.

Description: Stochastic collocation methods facilitate the numerical solution of partial differential equations (PDEs) with random data and give rise to long sequences of similar linear systems. When elliptic PDEs with random diffusion coefficients are discretized with mixed finite element methods in the physical domain we obtain saddle point systems. These are trivial to solve when considered individually; the challenge lies in exploiting their similarities to recycle information and minimize the cost of solving the entire sequence. We apply stochastic collocation to a model stochastic elliptic problem and discretize in physical space using Raviart–Thomas elements. We propose an efficient solution strategy for the resulting linear systems that is more robust than any other in the literature. In particular, we show that it is feasible to use finely-tuned algebraic multigrid preconditioning if key set-up information is reused. The proposed solver is robust with respect to variations in the discretization and statistical parameters for stochastically linear and nonlinear data.

Description: We address numerically the question of the asymptotic stability of equilibria for a Gurtin–MacCamy model with age-dependent spatial diffusion. The problem reduces to the study of a finite number of simpler models without diffusion, which are parametrized by the eigenvalues of the Laplacian operator. Here the approach in Breda et al. (2007, Stability analysis of age-structured population equations by pseudospectral differencing methods. J. Math. Biol. , 54 , 701–720; 2008, Stability analysis of the Gurtin–MacCamy model. SIAM J. Numer. Anal. , 46 , 980–995), which is based on pseudospectral methods, is adapted to the reduced models and the error analysis is revisited in order to prove the preservation of convergence of infinite order.

Description: The moving least squares (MLS) method provides an approximation û of a function u based solely on values u ( x j ) of u on scattered ‘meshless’ nodes x j . Derivatives of u are usually approximated by derivatives of û . In contrast to this, we directly estimate derivatives of u from the data, without any detour via derivatives of û . This is a generalized MLS technique, and we prove that it produces diffuse derivatives as introduced by Nyroles et al. (1992, Generalizing the finite element method: diffuse approximation and diffuse elements. Comput. Mech. , 10 , 307–318). Consequently, these turn out to be efficient direct estimates of the true derivatives, without anything ‘diffuse’ about them, and we prove optimal rates of convergence towards the true derivatives. Numerical examples confirm this, and we finally show how the use of shifted and scaled polynomials as basis functions in the generalized and standard MLS approximation stabilizes the algorithm.

Description: The differential linear variational inequality consists of a system of n ordinary differential equations (ODEs) and a parametric linear variational inequality as the constraint. The right-hand side function in the ODEs is not differentiable and cannot be evaluated exactly. Existing numerical methods provide only approximate solutions. In this paper we present a reliable error bound for an approximate solution x h ( t ) delivered by the time-stepping method, which takes all discretization and roundoff errors into account. In particular, we compute two trajectories x j h ( t )± j h ( t ) to determine the existence region of the exact solution for each . Moreover, we have . Numerical examples of bridge collapse, earthquake-induced structural pounding and circuit simulation are given to illustrate the efficiency of the error bound.

Description: We present a comprehensive convergence analysis for discontinuous piecewise polynomial approximations of a first-kind Volterra integral equation with smooth convolution kernel, examining the attainable order of (super-) convergence in collocation, quadrature discontinuous Galerkin (QDG) and full discontinuous Galerkin (DG) methods. We introduce new polynomial basis functions with properties that greatly simplify the convergence analysis for collocation methods. This also enables us to determine explicit formulae for the location of superconvergence points (i.e., discrete points at which the convergence order is one higher than the global bound) for all convergent collocation schemes. We show that a QDG method, which is based on piecewise polynomials of degree m and uses exactly m + 1 quadrature points and nonzero quadrature weights, is equivalent to a collocation scheme, and so its convergence properties are fully determined by the previous collocation analysis and they depend only on the quadrature point location (in particular, they are completely independent of the accuracy of the quadrature rule). We also give a complete analysis for QDG with more than m + 1 quadrature points when the degree of precision (d.o.p.) is at least 2 m + 1. The behaviour (but not the approximation) is the same as that for a DG scheme when the d.o.p. is at least 2 m + 2. Numerical test results confirm that the theoretical convergence rates are optimal.

Description: The contact between two membranes can be described by a system of variational inequalities, where the unknowns are the displacements of the membranes and the action of a membrane on the other one. A discretization of this system is proposed in Part 1 of this work, where the displacements are approximated by standard finite elements and the action by a local postprocessing, which admits an equivalent mixed reformulation. Here we perform the a posteriori analysis of this discretization and prove optimal error estimates. Then we present numerical experiments that confirm the efficiency of the error indicators.

Description: In this paper we design high-order accurate and stable finite difference schemes for the initial–boundary–value problem associated with the magnetic induction equation with resistivity. We use summation-by-parts finite difference operators to approximate spatial derivatives and a simultaneous approximation term technique for implementing boundary conditions. The resulting schemes are shown to be energy stable. Various numerical experiments demonstrating both the stability and the high order of accuracy of the schemes are presented.

Description: Time-stepping procedures for the solution of evolution equations can be performed on parallel architecture by parallelizing the space computation at each time step. This, however, requires heavy communication between processors and becomes inefficient when many time steps are to be computed and many processors are available. In such cases parallelization in time is advantageous. In this paper we present a method for parallelization in time of linear multistep discretizations of linear evolution problems; we consider a model parabolic problem and a model hyperbolic problem and their, respectively, A ()-stable and A -stable linear multistep discretizations. The method consists of a discrete decoupling procedure, whereby N +1 decoupled Helmholtz problems with complex frequencies are obtained; N being the number of time steps computed in parallel. The usefulness of the method rests on our ability to solve these Helmholtz problems efficiently. We discuss the theory and give numerical examples for multigrid preconditioned iterative solvers of relevant complex frequency Helmholtz problems. The parallel approach can easily be combined with a time-stepping procedure, thereby obtaining a block time-stepping method where each block of steps is computed in parallel. In this way we are able to optimize the algorithm with respect to the number of processors available, the difficulty of solving the Helmholtz problems and the possibility of both time and space adaptivity. Extensions to other linear evolution problems and to Runge–Kutta time discretization are briefly mentioned.

Description: The community of bacteria associated with the fecal pellets of planktonic copepods and those free living in surrounding seawater were investigated by denaturing gradient gel electrophoresis (DGGE) during a 10-day laboratory fecal pellet degradation experiment. Generally, fecal pellets containing bacteria were composed of different phylogenetic groups compared with those living in seawater. Bacteria in fecal pellets were dominated by -Proteobacteria and Sulfitobacter ( α-Proteobacteria ), whereas bacteria in seawater had higher species richness and mainly consisted of α-Proteobacteria . Remarkable bacterial community shifts occurred in the first 2 days of the experiment along with the apparent increase in dissolved organic carbon and decrease of dissolved oxygen in the incubation bottles. Throughout the incubation, bacteria that were initially unique to fecal pellets were never found in surrounding seawater, while the communities of bacteria in fecal pellets and seawater became more similar, indicating colonization of bacteria from seawater to fecal pellets during the degradation process. These results suggest that the colonization of free-living bacteria took place rapidly and that they might contribute significantly to the degradation of planktonic copepod fecal pellets.

Description: The diel behavior and feeding ecology of three coexisting species of chaetognaths in two shallow subtropical bays in the northeastern part of Hong Kong were studied in summer 2005 and winter 2005–2006. Average densities of adult Flaccisagitta enflata , Aidanosagitta delicata and Aidanosagitta neglecta ranged from 21 to 48 ind. m –3 in the semi-enclosed Tolo Harbour, but densities of the two Aidanosagitta species were low in Mirs Bay, which is deeper and opens into the South China Sea. Adult F. enflata , the largest of the three species, exhibited the most pronounced diel vertical migration (DVM) and diel feeding rhythm. The smaller juvenile F. enflata and adult A. delicata did not exhibit DVM. Although copepods were the most abundant component of the mesozooplankton, they were not preferred prey of chaetognaths. Predation impacts on copepods were generally 〈0.3% of the standing stock. Larvaceans, on the other hand, were highly preferred, with predation impact as high as 〉30%. As prey abundances in Tolo Harbour could be 〉9 x 10 4 ind. m –3 , there was no evidence of resource partitioning behavior by the coexisting chaetognaths.

Description: The Easter Seamount Chain and Nazca Ridge are two of the most conspicuous volcanic features on the Nazca plate. Many questions about their nature and origin have remained unresolved because of a lack of geochronological and geochemical data for large portions of both chains. New 40 Ar– 39 Ar incremental heating age determinations for dredged rocks from volcanoes east of Salas y Gomez Island show that, with very few exceptions, ages increase steadily to the east from 1·4 to 30 Ma, confirming that the two chains are parts of the same hotspot trail and indicating a hotspot location near Salas y Gomez rather than beneath Easter Island some 400 km farther west. Most of the volcanoes appear to have been erupted onto seafloor that was 5–13 Myr old, and no systematic variation in seafloor age at the time of seamount formation is apparent. At about 23 Ma, the formation of the Nazca Ridge ceased and that of the Easter Seamount Chain began, corresponding to a change in the direction of motion of the Nazca plate. Most of the studied rocks are moderately alkalic to transitional basalts. Their geochemical characteristics suggest that they represent relatively small mean amounts of partial melting initiating in garnet-bearing mantle and ending in the spinel facies. Nd–Sr–Pb isotopic compositions are within the range of values previously observed for volcanoes of the Easter Seamount Chain, west of Easter Island; moreover, most of our data cluster in a rather small part of this range [e.g. Nd (t) is between +6·0 and +4·0]. The results indicate that the mantle source has consisted of the same two principal components, a C/FOZO-type component and a high- Nd , incompatible-element-depleted Pacific mid-ocean ridge basalt-source-type component, since at least 30 Ma. The lack of any geochemical gradient along the chain east of Salas y Gomez implies that no systematic change over time has occurred in the proportions of these end-members.

Description: The sea ice diatom biomarker IP 25 has been detected and quantified in bulk zooplankton obtained from the Amundsen Gulf (Canada) in 2008. This study represents the first example of the detection of this biomarker in the pelagic food web. Concentrations of IP 25 ranged from ~5 to 15 ng g –1 dry weight with peak values occurring broadly at the same time as those found for this biomarker in sea ice samples determined previously from the same region; a 25–30 day lag between the sea ice bloom and zooplankton IP 25 profiles is interpreted in terms of a predator–prey relationship. IP 25 concentrations in zooplankton declined towards the end of the spring sea ice algal bloom and during the main period of ice melt. At this point, concentrations of n -C 21:6 , a common biomarker of general marine diatoms, increased substantially in the zooplankton, indicative of a switch in feeding patterns. This detection of IP 25 in one of the first trophic levels of the Arctic marine ecosystem has potentially important implications for the investigation of polar food webs and the impacts that changes to sea ice conditions will have on these.

Description: This study aimed at describing changes in the stable isotopic composition of late copepodite stage V (CV) subarctic marine copepods ( Calanus finmarchicus and C. hyperboreus ) during overwintering non-feeding periods. Diapausing stage CVs sampled in deep waters of the Lower St. Lawrence Estuary (Québec, Canada) in late-September 2009 were monitored for 4 months under controlled laboratory conditions. CVs and newly moulted adults were analyzed for 13 C and 15 N signatures as well as lipid, carbon and nitrogen content. Lipids were extracted in half of the samples to compare 13 C of individuals with and without lipids and to evaluate the accuracy of mass balance correction models for 13 C under lipid influence. Lipid content generally decreased with time for both species, which was reflected in an increase of 13 C values of CVs but a constant 13 C in newly moulted adults. Accordingly, lipid extraction resulted in an increase of 13 C in CVs and adults. The mean 13 C signature of lipid-extracted individuals remained constant through the time for CVs of both species and for C. finmarchicus adults. 15 N signatures of individuals increased after lipid extraction, but this did not result in a constant value over time, suggesting that several endogenous metabolic processes affected nitrogen isotopic content. The accuracy of the mass balance model differed between species and stages, suggesting that lipid extraction should always be performed prior to applying mathematical corrections.

Description: The composition of ultraphytoplankton (〈10 µm) sampled in surface waters (1 m depth) was investigated during summer 2010 in the Bay of Marseille (NW Mediterranean) using flow cytometry. In addition to groups of Synechococcus , Prochlorococcus , picoeukaryotes and nanoeukaryotes, an unidentified additional cluster was observed. The particles forming this cluster had a high abundance (〉7 x 10 4 events mL –1 ), with both orange and red fluorescence intensities like Synechococcus , but with a size signal larger than that of 2 µm fluorospheres (beads). These unknown particles were sorted out by flow cytometry and then observed by epifluorescence microscopy: they appeared to be chain-forming microorganisms, just like trichomes of some diazotroph cyanobacteria with one heterocyst, but not unambiguously distal. The chains observed after cell sorting were not straight, but rather folded. To our knowledge, this is the first report of a possible bloom of such free trichomes. The small sample volume available for the delayed analysis and the limited resolution of our photomicrography did not allow for species identification. The brief occurrence of free trichomes in the Bay of Marseille with such a high abundance remains to be explained. High temperature in summer, induced stratification of the water column and nitrate depletion may be related to this event. High-frequency surveys of ultraphytoplankton assemblages at the single cell level appear to be necessary to observe such phenomenon more efficiently and document their dynamics.

Description: In the rotifer genus Brachionus , the proportion of mictic females in the offspring is significantly related to the population density experienced by their mother. In the present study, we examined whether population densities experienced by mothers could affect the propensity of their offspring to produce mictic females in Brachionus calyciflorus . Results showed that when the mother experienced a high population density, her offspring produced a significantly higher proportion of mictic daughters, 8.5–81.5% higher than those from a low maternal population density, along a gradient of population densities (1 ind. mL –1 to 0.025 ind. mL –1 ). The effect of maternal crowding on the propensity of offspring to produce mictic females was more significant when the offspring faced lower population densities.

Description: The two Cape hake species of the southern Benguela ecosystem, the shallow-water and deep-water hakes Merluccius capensis and M. paradoxus , are economically the most important marine resources in South Africa. Recruitment is a key process in the dynamics of marine organisms, yet very little is known about the early life history of Cape hakes, especially the location of spawning grounds and transport of eggs and larvae. For each species, ichthyoplankton dispersal off South Africa is simulated by coupling oceanographic simulations to an individual-based model in order to track virtual individuals. Results indicate that the most favorable spawning areas for transport to nursery areas are located off the south-western coast and the eastern Agulhas Bank, and highlight partly different drift routes followed by the two ichthyoplankton species off Cape Columbine. Transport from spawning to nursery areas is the highest in austral winter for a spawning depth ranging between 0 and 100 m. These modeling results are in broad agreement with available knowledge on the ecology of Cape hakes. The present work on Cape hakes complements previous modeling studies on anchovy and sardine in the same area. Taken together, these studies underline the correspondence between cross-shore (for hakes) or alongshore (for anchovy and sardine) transport mechanisms and the spawning strategies used by these key species of the southern Benguela ecosystem.

Description: Controlling noxious phytoplankton blooms by biomanipulation largely depends on the presence of large-sized (〉3000 µm) generalist grazers, not common in the tropics. Therefore, we compared the ability of small (≤2000 µm) microcrustaceans Ceriodaphnia dubia, Moina macrocopa, Daphnia pulex, Simocephalus vetulus and Heterocypris incongruens to feed and grow on cyanobacterial diets. We studied their feeding preferences on phytoplankton from natural lake water with a dominance of Microcystis sp., Fragilaria sp. or Planktothrix sp. to which we added Scenedesmus acutus . Also tested were the ability of D. pulex , S. vetulus and H. incongruens to reduce cyanobacterial densities by grazing, and the rate of grazing and demographic responses of S. vetulus and H. incongruens on diets of S. acutus, Microcystis sp. and Planktothrix sp. All species fed on small colonies of Microcystis sp., but not on filamentous Planktothrix sp. or colonial Fragilaria sp. Simocephalus vetulus and H. incongruens were generalists and most capable of reducing cyanobacterial densities. Demographic variables of S. vetulus , but not H. incongruens , were significantly lower on the cyanobacterial diet; for instance, the population growth rates were between 0.07–0.2 day –1 on cyanobacterial diets, but 0.31 on S. acutus while for H. incongruens they ranged between 0.07 and 0.08 day –1 , regardless of whether the diet was a cyanobacteria or S. acutus . Our study warrants further tests on the ostracod H. incongruens in order to test its efficacy in reducing cyanobacterial densities in shallow tropical ponds.

Description: Silicic magma systems are of great scientific interest and societal importance owing to their role in the evolution of the crust and the hazards posed by volcanic eruptions. MELTS is a powerful and widely used tool to study the evolution of magmatic systems over a wide spectrum of compositions and conditions. However, the current calibration of MELTS fails to correctly predict the position of the quartz + feldspar saturation surface in temperature, pressure and composition space, making it unsuitable to study silicic systems. We create a modified calibration of MELTS optimized for silicic systems, dubbed rhyolite-MELTS, using early erupted Bishop pumice as a reference. Small adjustments to the calorimetrically determined enthalpy of formation of quartz and of the potassium end-member of alkali feldspar in the MELTS calibration lead to much improved predictions of the quartz + feldspar saturation surface as a function of pressure. Application of rhyolite-MELTS to the Highland Range Volcanic Sequence (Nevada), the Peach Spring Tuff (Arizona–Nevada–California), and the late-erupted Bishop Tuff (California), using compositions that vary from trachydacite to high-silica rhyolite, shows that the calibration is appropriate for a variety of fluid-bearing silicic systems. Some key observations include the following. (1) The simulated evolutionary paths are consistent with petrographic observations and glass compositions; further work is needed to compare predicted and observed mineral compositions. (2) The nearly invariant nature of silicic magmas is well captured by rhyolite-MELTS; unusual behavior is observed after extensive pseudo-invariant crystallization, suggesting that the new calibration works best for relatively small (i.e. 〈50 wt %) crystallization intervals, comparable with what is observed in volcanic rocks. (3) Our success with rhyolite-MELTS shows that water-bearing systems in which hydrous phases do not play a critical role can be appropriately handled; simulations are sensitive to initial water concentration, and although only a pure-H 2 O fluid is modeled, suitable amounts of water can be added or subtracted to mimic the effect of CO 2 in fluid solubility. Our continuing work on natural systems shows that rhyolite-MELTS is very useful in constraining crystallization conditions, and is particularly well suited to explore the eruptive potential of silicic magmas. We show that constraints placed by rhyolite-MELTS simulations using late-erupted Bishop Tuff whole-rock and melt inclusion compositions are inconsistent with a vertically stratified magma body.

Description: Jeju is a volcanic field that has erupted from around 1·8 Myr to c. 1 kyr ago. Activity began with dispersed, basaltic, monogenetic, phreatomagmatic eruptions. Continuing monogenetic volcanism was later joined by more voluminous lava effusion events building a central composite shield. Samples from older (〉0·7 Ma) and younger (〈0·2 Ma) monogenetic centres were analysed for their whole-rock major element, trace element and Sr–Nd–Pb isotopic compositions. Pyroclastic products from the monogenetic centres are dominantly alkali basalt to trachybasalt, whereas the more voluminous lava flows and domes of the central edifice consist of subalkali basalt and alkali basalt to trachyte. Lavas from the Early Pleistocene monogenetic centres are depleted in MgO, Cr and Ni, reflecting considerable olivine fractionation. By contrast, Late Pleistocene–Holocene monogenetic centre magmas fractionated clinopyroxene + olivine at deeper levels. Isotopic compositions show little variation across the suite; however, the Late Pleistocene–Holocene monogenetic centres have generally lower 87 Sr/ 86 Sr and 208 Pb/ 204 Pb and higher 143 Nd/ 144 Nd than the older centres and subalkali lavas. Major and trace element and isotope data suggest a common, shallower source for the high-Al alkali and subalkali lavas, in contrast to a deeper source for the low-Al alkali magmas. We propose that mantle melting was initiated under partially hydrous conditions at a pressure of near 2·5 GPa, followed by drier conditions and extension of the melting zone to 3–3·5 GPa, with a concomitant increase in the volume of melt derived from the shallower part of the system to produce subalkaline magmas. Increasing melt production at shallow depths may be related to accelerated heat transfer resulting from deepening of the melting zone, or increased mantle upwelling. Mantle lenses were uplifted, probably lubricated by shear zones created during the opening of the Sea of Japan c. 15 Myr ago, and reactivated during rotation of the Philippine Sea plate direction of subduction at around 2 Ma. This is the first hypothesized link between subduction processes and intraplate volcanism at Jeju.

Description: Partial melting of deep continental crust may occur during either prograde heating or decompression. Although the effect of temperature on crustal melting has been widely investigated, few experimental studies have addressed the question of the influence of pressure on crustal anatexis. To understand the influence of decreasing pressure on partial melting processes, the thermodynamic approach of isochemical phase diagrams has been applied to garnet–K-feldspar–kyanite–sillimanite anatectic gneisses (Barun Gneiss) from the Higher Himalayan Crystallines (HHC) of eastern Nepal. The main melt-producing reactions, the amount of melt produced during heating vs decompression, and the effects of melt loss on the mineral assemblages and compositions have been investigated along four ideal P–T trajectories, dominated by either heating or decompression. Based on these results, the observed microstructures and mineral compositions of the Barun Gneiss have been interpreted in terms of melt-producing vs melt-consuming reactions (e.g. growth of peritectic garnet with preserved ‘nanogranite’ inclusions vs microstructures related to back-reactions between solids and melt), and used to derive the metamorphic evolution of the studied samples. The P–T pseudosection modelling predicts that at least 15–20 vol. % of melt was produced at peak P–T conditions through dehydration melting of both muscovite and biotite, and that melt production was mainly triggered by heating, with or without the combined effect of decompression. The preserved granulitic peak metamorphic assemblage, however, is consistent with a significant loss of most of this melt. The P–T evolution inferred for samples from different, strategically located, structural levels of the Barun Gneiss is consistent with the expectations of a ‘channel flow’ model, including: (1) the clockwise shape of the P–T paths; (2) the estimated P at peak T (new data: 10–8 kbar at 800°C; model: 13–7 kbar at 800°C); (3) the decreasing P structurally upward, which defines a ‘normal’ metamorphic sequence, in contrast to the inverted metamorphic sequence occurring in the lowermost Main Central Thrust Zone; (4) the nearly isothermal exhumation of the structurally lowest sample, reflecting the progressive exhumation of rocks that have been entrained in the deep, high-T region of the channel, versus the nearly isobaric heating of the structurally uppermost sample, reflecting the evolution of those rocks that flowed outwards with the underlying channel.

Description: Embryogenesis (single cell to twitching stage) and early larval stages (nauplius to calyptopis 3) internal morphology of the sac-spawning species Nyctiphanes simplex was investigated to explore its temporal association with gonad development and molt development cycles. Krill were collected and incubated shipboard in July 2007 and March 2010 in the Gulf of California. Cleavage patterns were similar to what is observed in broadcast-spawning species, suggesting a close phylogenetic consistency between krill species with distinct spawning strategies. Nyctiphanes simplex , like broadcast-spawning krill species, had eight Kranzzellen (K 1 –K 8 ) cells during the blastula stage. The gonad of ovigerous females with embryos in the cell division stage is in the multiplication stage (Stage I). From the nauplius stage, most females are in previtellogenesis (Stage II). Only females with metanauplii occasionally have gonads in vitellogenesis (Stage III). Gonad maturity (Stage IV) occurs only after the release of the embryos from the ovigerous sac. Females with an ovigerous sac were invariably at the intermolt stage, suggesting a precise synchronization among processes of molting, gonad development and embryo release to produce consecutive broods. Lipid and carbohydrate storage decreased exponentially throughout embryonic and early larval development, depending on their endogenous reserves. When metanauplii leave the ovigerous sac, they have low storage lipid (〈2%) and carbohydrate (〈5%). These proportions suggest a theoretically short period-of-no-return (〈2 days), when they transform into the first feeding stage (calyptopis 1).

Description: One of the problems concerning studies of fish egg distribution is the weak spatial and temporal resolution due to the workload that examination of a large number of samples would demand. Recently, the development of a new laboratory imaging system, the ZooScan, capable of obtaining relatively good resolution images enables automated zooplankton identification using supervised learning algorithms. This new approach was applied to formalin-fixed fish egg samples collected during French winter IBTS (International Bottom Trawl Surveys) in the Eastern English Channel and the Southern North Sea. Fish egg spatial distributions of seven species based on the microscope and ZooScan identifications were compared. Abundance and distribution maps of winter-spawning areas of plaice, long rough dab, cod and whiting were similar for both methods. Low identification accuracy for small size eggs was due to microscope misidentification of standards used for the ZooScan learning (dab and flounder). The potential input of such a tool to quickly acquire valuable data on identification, enumeration, size frequency distribution of fish eggs and map spawning areas is of great interest for understanding and forecasting fisheries recruitment and will support ecosystem-based management.

Description: P–T–X(composition) pseudosections constructed for natural monzodioritic to peridotgabbroic rock compositions using T hermocalc in the model system Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–TiO 2 –O (NCKFMASHTO) illustrate the dependence of granulite and eclogite assemblages on whole-rock composition at mid-crustal to upper-mantle conditions. Increasing ferric iron content results in a marked contraction of garnet–plagioclase assemblages, and an expansion of orthopyroxene, kyanite, quartz and ilmenite stability across the compositional range of monzodioritic–gabbroic protoliths, and the expansion of plagioclase stability up-pressure in gabbroic–peridotgabbroic compositions. Omphacite granulite defines a transitional stage between garnet granulite and eclogite in monzodioritic to gabbroic compositions. Silicate liquid compositions calculated for a monzodioritic protolith using the haplogranite melt model do not accurately reflect trends in comparable experimental data, and refinement is needed for its application to the modeling of intermediate and mafic equilibria involving more than a few per cent partial melt. Omphacite-bearing granulite mineral equilibria in dioritic protoliths are far less sensitive to changes in whole-rock oxidation state than gabbroic protoliths; a doubling of whole-rock oxygen content displaces the modeled granulite–eclogite transition in gabbroic assemblages by 0·4 GPa up-pressure. Results of low-H 2 O, high-O equilibria modeling best validate natural assemblages from Breaksea Sound, Fiordland, New Zealand, where co-facial monzodioritic granulite and peridotgabbroic eclogite formed at P 1·8 GPa and T 850°C.

Description: A new perspective on the role of lipids in zooplankton is proposed, with solid–liquid phase transitions of lipids being a factor regulating their buoyancy. These phase transitions are controlled by zooplankton in relation to their physical environment, through the selective accumulation of specific lipids with optimum levels of unsaturation. The necessity to control buoyancy and maintain an optimum depth is a fundamental evolutionary force, driving anatomical, biochemical and behavioural adaptations of all organisms within the aquatic realm. It is hypothesized that each species adjusts the amount, composition and anatomical location of lipids, to maximize fitness according to their preferred habitat and life history traits. Recent discoveries regarding the role of phase transitions of lipids in marine zooplankton and their role in regulating buoyancy will require re-interpretation of existing data and stimulate future scientific endeavours in zooplankton research.

Description: The accurate identification of individuals in zooplankton samples is a crucial step in many plankton studies. Up to now, this has been done primarily by microscopic analysis of morphological characters, and new molecular methodologies are still relatively rarely applied. Another promising technology is matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), which has had a major impact in applied and systematic microbiology, where it is used for routine high throughput identification of bacteria and fungi. For the present study, we developed a protocol for the rapid acquisition of mass spectra from whole individual copepods. The final protocol enabled us to obtain mass spectra with more than 100 distinct peaks in the mass range of 2000–20 000 Da. A comparison of the mass spectra of three species of Eudiaptomus showed that they could all be clearly discriminated, whereas the mass spectra of different developmental stages and sexes of each particular species were highly similar. Further, a discrimination of con-specific individuals from different habitats was achieved, at least partly, even without extensive optimization of the analytical and statistical procedures. These results indicate the feasibility of identifying copepods by a rapid and simple MALDI-TOF MS analysis, e.g. for population ecology studies.

Description: The range in An content of plagioclase in grain mounts of igneous cumulates provides a measure of diversity that is uniquely preserved in plagioclase because of its well-known refractory nature. To a first approximation such data provide, when calibrated, an estimate of the residual porosity or fraction of trapped liquid, in each specimen. The ensemble of specimens then provides a model for the stratigraphic variation of residual porosity. The raw data, however, include pre-cumulus zoning that can be isolated from in situ zoning by textural analysis in thin section. The baseline of residual porosity determinations was earlier determined for the Lower Zone of the Kiglapait intrusion from the content of excluded components in the solid rock compared with their content in the melt as calculated by summation and Rayleigh fractionation. The baseline equation was then used to calibrate the residual porosity obtained from the An range in grain mounts. This calibration is now extended to the remainder of the intrusion. The An range and the calculated residual porosity decrease to zero at 99% solidified (PCS) and then rise to the end of crystallization. The data suggest initial porosities smaller than 0·35. Allowing for pre-cumulus zoning, the data suggest a dominance of adcumulates in the intrusion and these impermeable barriers occupy 75% of the rocks in the Lower Zone. They occur at intervals of 1 to rarely 15 m and thereby restrict the likelihood of compaction over thick mushy zones. Variations in the Fo range of olivine are also observed in grain mounts and they follow those in plagioclase. However, they are in part due to subsolidus equilibration with Fe–Ti oxides and augite. The new calibration is successfully applied to the Skaergaard intrusion to supplement the published results from excluded components, with some interesting contradictions.

Description: High-Mg ultrapotassic volcanic rock occurrences of lamproitic affinity are exposed in southwestern Anatolia, mostly within the Menderes Massif. From north to south the lamproitic volcanism shows increasingly younger ages ranging from 20 to 4 Ma. Volcanism is contemporaneous with more voluminous shoshonitic, high-K calc-alkaline, and ultrapotassic magmatic activity in the Simav–Selendi, Usak, Kirka, Köroglu, Afyon and Isparta–Gölcük areas. The southward decrease in the age of the volcanism correlates with changes in geochemical composition, particularly a decrease in 87 Sr/ 86 Sr, 207 Pb/ 204 Pb, Zr/Nb and Th/Nb, and an increase in 143 Nd/ 144 Nd, 176 Hf/ 177 Hf, 206 Pb/ 204 Pb, 208 Pb/ 204 Pb and Ce/Pb, thus delineating a systematic change from orogenic (crust-like) to anorogenic (convecting mantle-like) signatures. Rare earth element compositions of clinopyroxene phenocrysts demonstrate an increasing role for residual garnet for locations in the central parts of the Menderes Massif, indicating a lithosphere thickness greater than 80 km. In contrast, K 2 O abundances remain nearly constant at around 7%, indicating buffering by phlogopite in the mantle source. Magma genesis in southwestern Anatolia is controlled by post-collisional extensional events initiated after major lithospheric thickening. Geochemical constraints suggest that the mantle source experienced two main geodynamic stages. The first stage caused ultradepletion of the mantle and subsequent metasomatic enrichment, which allowed coupling of the geochemical signatures of ultradepleted harzburgite with those of crust-derived sediments. This happened during the final closure stages of the southern Neotethys Ocean and the accretion of forearc oceanic lithosphere (island-arc type), as shallowly subducted material to the Anatolian lithosphere. The second stage is post-collisional, and is related to the collapse of the orogenic belt and the development of extension-related horst and graben structures. This stage is concurrent with the initiation of a thermal anomaly originating from a gap, identified by seismic tomography, in the subducted slab under western Anatolia. We propose that the lithospheric mantle underwent intense ‘asthenospherization’ owing to lithosphere–asthenosphere interaction, caused by the southward expansion of this gap during slab roll-back. The geochemical resemblance of the lamproites to more voluminous, contemporaneous shoshonitic magmas implies their derivation from a heterogeneous mantle source that had been affected by similar processes. These mantle processes may be closely associated with the major episode of uplift in the Menderes Massif.

Description: We identify olivine grains with compositions up to Fo 99 ·8 , which are found in multiple primitive basaltic lava flows from a monogenetic volcano in the Big Pine Volcanic Field, California, USA. In this study, we show that the forsterite in these basalts formed by subsolidus recrystallization in a high- f O 2 environment. Olivine compositions are bimodal, with flows having either all normal compositions (Fo 74 ·9 – 94 ·4 ) or highly forsteritic (Fo 97 ·2 – 99 ·8 ) compositions. In many grains, the subhedral forsteritic olivine has a hematite and clinopyroxene rim, and internal parallel-oriented planes of hematite, clinopyroxene and orthopyroxene. Results of isotopic, chemical, crystallographic, petrographic and mineralogical analyses show that the forsterite formed through subsolidus oxidation of olivine phenocrysts. The forsteritic olivines generally occur in the thinner flows. We infer that a rapidly emplaced sequence of thin, vesicular, spatter-fed flows allowed the original olivine phenocrysts to become repeatedly reheated while exposed to air. Our study required sampling each flow, so it was difficult to avoid the altered portions of the thinner flows. Other studies would tend to avoid such flows, which may account for why such forsteritic olivines have not been more widely recognized.

Description: Albitization is a common process during which hydrothermal fluids convert plagioclase and/or K-feldspar into nearly pure albite; however, its specific mechanism in granitoids is not well understood. The c . 1700 Ma A-type metaluminous ferroan granites in the Khetri complex of Rajasthan, NW India, have been albitized to a large extent by two metasomatic fronts, an initial transformation of oligoclase to nearly pure albite and a subsequent replacement of microcline by albite, with sharp contacts between the microcline-bearing and microcline-free zones. Albitization has bleached the original pinkish grey granite and turned it white. The mineralogical changes include transformation of oligoclase (~An 12 ) and microcline (~Or 95 ) to almost pure albite (~An 0 · 5 – 2 ), amphibole from potassian ferropargasite ( X Fe 0·84–0·86) to potassic hastingsite ( X Fe 0·88–0·97) and actinolite ( X Fe 0·32–0·67), and biotite from annite ( X Fe 0·71–0·74) to annite ( X Fe 0·90–0·91). Whole-rock isocon diagrams show that, during albitization, the granites experienced major hydration, slight gain in Si and major gain in Na, whereas K, Mg, Fe and Ca were lost along with Rb, Ba, Sr, Zn, light rare earth elements and U. Whole-rock Sm–Nd isotope data plot on an apparent isochron of 1419 ± 98 Ma and reveal significant disturbance and at least partial resetting of the intrusion age. Severe scatter in the whole-rock Rb–Sr isochron plot reflects the extreme Rb loss in the completely albitized samples, effectively freezing 87 Sr/ 86 Sr ratios in the albite granites at very high values (0·725–0·735). This indicates either infiltration of highly radiogenic Sr from the country rock or, more likely, radiogenic ingrowth during a considerable time lag (estimated to be at least 300 Myr) between original intrusion and albitization. The albitization took place at ~350–400°C. It was caused by the infiltration of an ascending hydrothermal fluid that had acquired high Na/K and Na/Ca ratios during migration through metamorphic rocks at even lower temperatures in the periphery of the plutons. Oxygen isotope ratios increase from 18 O = 7 in the original granite to values of 9–10 in completely albitized samples, suggesting that the fluid had equilibrated with surrounding metamorphosed crust. A metasomatic model, using chromatographic theory of fluid infiltration, explains the process for generating the observed zonation in terms of a leading metasomatic front where oligoclase of the original granite is converted to albite, and a second, trailing front where microcline is also converted to albite. The temperature gradients driving the fluid infiltration may have been produced by the high heat production of the granites themselves. The confinement of the albitized granites along the NE–SW-trending Khetri lineament and the pervasive nature of the albitization suggest that the albitizing fluids possibly originated during reactivation of the lineament. More generally, steady-state temperature gradients induced by the high internal heat production of A-type granites may provide the driving force for similar metasomatic and ore-forming processes in other highly enriched granitoid bodies.

Description: The rapid and efficient analysis of plankton samples (e.g. enumeration, identification, biomass determination) has been an important driver for recent technological developments in (semi-) automated analysis and imaging instruments. Most focus has been on identification and abundance estimates, while less attention has been given to viability, i.e. the assessment of whether the organisms are dead or alive. However, a wide spectrum of scientific applications requires accurate viability determinations, e.g. the monitoring of invasive species in ship ballast water. The transfer of species through ballast water forms a major threat to marine ecosystems, resulting in significant environmental and economic losses. A variety of viability stains and viability assessment methods are available, but there has been no systematic investigation how these methods perform for larger organisms (≥50 µm). We review the current procedures for viability determination for large plankton and present a cross-comparison of three methods: cell digestion assay (CDA), SYTOX ® Green nucleic acid staining and Neutral Red vital staining. The CDA and SYTOX ® Green methods did not perform well and gave various problems linked to the multicellular nature of zooplankton, autofluorescence and/or constraints set by the definition of cell death. Although some issues remain and there is no universal method, the Neutral Red vital stain proved the most robust viability method in this study and is broadly applicable to both phytoplankton and zooplankton larger than 50 µm.

Description: Changes in the tintinnid community were studied in the neritic area of the middle Adriatic Sea from January 1998 until November 1999. Variability in tintinnid abundance showed a clear seasonal pattern with winter–spring and autumn maxima. The vertical distribution of tintinnid populations was affected by their taxonomic structure. A total of 51 taxa belonging to 11 families and 20 genera were identified. Helicostomella subulata , Codonellopsis schabi , Stenosemella nivalis and Salpingella decurtata were the dominant species. Species richness was positively related to overall abundance temporally at each station, and was also affected by environmental trophic state. The total tintinnid abundance, the dominant species abundance and the dominance grade increased significantly with increasing trophic state, while the diversity indices decreased. Hence we conclude that abundance and dominance may be straight indicators of ecosystem trophic state. In addition to environmental trophic state and food availability, tintinnid species distribution was strongly affected by temperature, which was the most important environmental factor determining their seasonality.

Description: Transects of CTD (to 1000 m) and zooplankton stations (to 200 m in 50 m strata) were made across an anticyclonic eddy in the southern Gulf of California during October 2007 to determine its influence upon the three-dimensional distribution of larval fish assemblages. The eddy was ~90 km in diameter and ~70 m deep. A larval fish assemblage, representing a mix of oceanic and coastal species, was defined mainly in the eddy from 200 m depth to the surface. Mesopelagic species, such as Vinciguerria lucetia , were dominant. Coastal reef ( Diplectrum sp.) and pelagic ( Auxis spp.) species were found mainly in the surface layer. This suggests that, because of the Gulf's relative narrowness, the eddy trapped coastal fish larvae during its formation and trajectory southward, retaining larvae of different adult habits. Another larval fish assemblage was defined off the eastern coast; its high larval abundance and specific richness was probably associated with coastal upwelling. Mesopelagic species (e.g. Triphoturus mexicanus ) dominated this assemblage, and coastal demersal species that were absent from the eddy (e.g. Symphurus williamsi ) were recorded in the surface layer, suggesting that the thermocline was a vertical boundary in this assemblage. The 3D differentiation of planktonic habitats was the result of the mesoscale hydrodynamics in the area sampled, in particular that associated to the eddy life history and characteristics (radius, depth and velocity), and to coastal upwelling, promoting larval retention of a mix of species of different adult habits.

Description: The most commonly used biomass estimate for microalgae is obtained from cell biovolume, usually calculated from microscopically measured linear dimensions. Although reliable, this is a highly time-consuming and specialized technique. Automated sampling devices that acquire images of cells and use pattern recognition techniques to identify the images have been developed as an alternative to microscopy-based methods. There are some aspects of automatic sampling and classification methods, however, which can be improved for the analysis of field samples including living and non-living particles. In this work, we demonstrate how the accuracy of a state-of the-art technique for plankton classification (Support Vector Machine) can be improved up to 86% if a previous automated step designed to remove non-living images is included. There is a tendency with the currently applied automatic methods to misestimate cell biovolume due to the two-dimensionality of the images. Here, we present a data set of more than 500 samples to show that the greatest effect is caused by the incorrect estimation of biovolume of the chain-forming diatoms. This results in an overestimate of biomass of between 20 and 100% where chain-forming diatoms represent more than the 20% of the biomass of the sample. We show how the classification method can be adapted to provide not only taxonomic but also the morphological classification of cells in order to obtain a more reliable estimate of biovolume according to the predicted cell shape, in a way comparable with microscopy-based estimates.

Description: We evaluate the feasibility of estimating zooplankton biomass using acoustic Doppler profilers (ADP) as deployed on autonomous ocean gliders. A Sontek Spray ADP mounted on a Mocness net was used for simultaneous collection of zooplankton and measurement of acoustic backscatter (ABS). Zooplankton biomass was estimated from optically scanned plankton samples. We found a direct proportionality between ABS and the summed cross-sectional area of the zooplankton as well as with the estimated zooplankton carbon biomass. ABS at 750kHz was most closely related to the summed cross-sectional area of zooplankton and micronekton greater than 1.6 mm equivalent circular diameter.

Description: Recent observations have confirmed the presence of dense accumulations of the diatom Aulacoseira islandica within surface lake ice on Lake Erie. MERIS (Medium Resolution Imaging Spectrometer) full-resolution satellite imagery is shown to clearly distinguish the optical signature of these phytoplankton blooms. The MERIS Level 1 maximum chlorophyll index is applied to Lake Erie under winter, partially (〉50%) ice-covered conditions, demonstrating for the first time the potential for satellite detection of blooms within, or surrounding, surface lake ice.

Description: A rare occurrence of a chill sequence in drill core from the eastern Bushveld Complex has been discovered at the base of a thick succession of ultramafic rocks that forms part of the Lower Zone. The lowest 10 m of the section preserves a variety of rock types including a true chill against quartzite floor rock, crystalline quench-textured and spinifex-textured rocks as well as high-temperature olivine and orthopyroxene cumulates. It represents the first stage of magma emplacement into the Bushveld chamber and gives an insight into the nature of the parental magmas to the Bushveld, the processes that took place at that early stage, and how rocks with a high original interstitial liquid content give way to more normal cumulates higher in the section. The chill sequence also provides insight into the variety of rock types that are encountered in marginal sills that are regarded as representing early stage magmas intruded as the chamber developed but that are incompletely understood because of inadequate field exposures. Olivine compositions (up to Mg# 0·912) in a pyroxene dunite in this section are the highest recorded for the Bushveld Complex and cores of associated orthopyroxene have Mg# 0·93. Zoned orthopyroxenes in the quench- and spinifex-textured units range from Mg# 0·91 to 0·72 and preserve core compositions close to the original liquidus. Small single chromite crystals have Cr/(Cr + Al) of 0·85 and Cr/Fe(Total) of three; these are also the most primitive compositions found to date in the Bushveld Complex. The chill and quench zones represent the earliest magmas to be emplaced in the Bushveld Complex; however, these are relatively evolved and similar to the B1 liquid, long assumed to be the most primitive magma that gave rise to the Lower Zone. Major and trace element geochemistry and mineral compositions show that the true parental magmas to the Lower Zone were of komatiite composition, with the most primitive containing 19% MgO. The liquid compositions have a strong crustal signature but are also enriched in K, Rb, Pb and especially Cs and Cl. The olivines in this section are highly Ni enriched, consistent with a component of mantle pyroxenite derived from recycled ocean crust in the source of the parental magmas. It is suggested that this source, combined with PGE-fertile subcontinental lithospheric mantle, was melted within a rising mantle plume and the resultant melts then interacted with the basement rocks of the Kapvaal Craton.

Description: Tofua volcano is situated midway along the Tonga oceanic arc and has undergone two phases of ignimbrite-forming activity. The eruptive products are almost entirely basaltic andesites (52·5–57 wt % SiO 2 ) with the exception of a volumetrically minor pre-caldera dacite. The suite displays a strong tholeiitic trend with K 2 O 〈1 wt %. Phenocryst assemblages typically comprise plagioclase + clinopyroxene ± orthopyroxene with microlites of Ti-magnetite. Olivine (Fo 83 – 88 ) is rare and believed to be dominantly antecrystic. An increase in the extent and frequency of reverse zoning in phenocrysts, sieve-textured plagioclase and the occurrence of antecrystic phases in post-caldera lavas record a shift to dynamic conditions, allowing the interaction of magma batches that were previously distinct. Pyroxene thermobarometry suggests crystallization at 950–1200°C and 0·8–1·8 kbar. Volatile measurements of glassy melt inclusions indicate a maximum H 2 O content of 4·16 wt % H 2 O, and CO 2 –H 2 O saturation curves indicate that crystallization occurred at two levels, at depths of 4–5·5 km and 1·5–2·5 km. Major and trace element models suggest that the compositions of the majority of the samples represent a differentiation trend whereby the dacite was produced by 65% fractional crystallization of the most primitive basaltic andesite. Trace element models suggest that the sub-arc mantle source is the residuum of depleted Indian mid-ocean ridge basalt mantle (IDMM-1% melt), whereas radiogenic isotope data imply addition of 0·2% average Tongan sediment melt and a fluid component derived from the subducted altered Pacific oceanic crust. A horizontal array on the U–Th equiline diagram and Ra excesses of up to 500% suggest fluid addition to the mantle wedge within the last few thousand years. Time-integrated ( 226 Ra/ 230 Th) vs Sr/Th and Ba/Th fractionation models imply differentiation timescales of up to 4500 years for the dacitic magma compositions at Tofua.

Description: Fonualei is unusual amongst subaerial volcanoes in the Tonga arc because it has erupted dacitic vesicular lavas, tuffs and phreomagmatic deposits for the last 165 years. The total volume of dacite may approach 5 km 3 and overlies basal basaltic andesite and andesite lavas that are constrained to be less than a few millennia in age. All of the products are crystal-poor and formed from relatively low-viscosity magmas inferred to have had temperatures of 1100–1000°C, 2–4 wt % H 2 O and oxygen fugacities 1–2 log units above the quartz–fayalite–magnetite buffer. Major and trace element data, along with Sr–Nd–Pb and U–Th–Ra isotope data, are used to assess competing models for the origin of the dacites. Positive correlations between Sc and Zr and Sr rule out evolution of the within-dacite compositional array by closed-system crystal fractionation of a single magma batch. An origin by partial melting of lower crustal amphibolites cannot reproduce these data trends or, arguably, any of the dacites either. Instead, we develop a model in which the dacites reflect mixing between two dacitic magmas, each the product of fractional crystallization of basaltic andesite magmas formed by different degrees of partial melting. Mixing was efficient because the two magmas had similar temperatures and viscosities. This is inferred to have occurred at shallow (2–6 km) depths beneath the volcano. U–Th–Ra disequilibria in the basaltic andesite and andesite indicate that the parental magmas had fluids added to their mantle source regions less than 8 kyr ago and that fractionation to the dacitic compositions took less than a few millennia. The 165 year eruption period for the dacites implies that mixing occurred on a similar timescale, possibly during ascent in conduits. The composition of the dacites renders them unsuitable candidates as contributors to average continental crust.

Description: We consider two algorithms to approximate the solution Z of a class of stable operator Lyapunov equations of the form AZ + ZA * + BB * = 0. The algorithms utilize time snapshots of solutions of certain linear infinite-dimensional differential equations to construct the approximations. Matrix approximations of the operators A and B are not required and the algorithms are applicable as long as the rank of B is relatively small. The first algorithm produces an optimal low-rank approximate solution using proper orthogonal decomposition. The second algorithm approximates the product of the solution with a few vectors and can be implemented with a minimal amount of storage. Both algorithms are known for the matrix case. However, the extension of the algorithms to infinite dimensions appears to be new. We establish easily verifiable convergence theory and a priori error bounds for both algorithms and present numerical results for two model problems.

Description: We study several discontinuous Galerkin methods for solving the Signorini problem. A unified error analysis is provided for the methods. The error estimates are of optimal order for linear elements. A numerical example is reported to illustrate numerical convergence orders.

Description: This paper considers the stability of both continuous and discrete time-varying linear systems. Stability estimates are obtained in either case in terms of the Lipschitz constant for the governing matrices and the assumed uniform decay rate of the corresponding frozen time linear systems. The main techniques used in the analysis are comparison methods, scaling and the application of continuous stability estimates to the discrete case. Counterexamples are presented to show the necessity of the stability hypotheses. The discrete results are applied to derive sufficient conditions for the stability of a backward Euler approximation of a time-varying system and a one-leg linear multistep approximation of a scalar system.

Description: The classical error analysis for Nédélec edge interpolation requires the so-called regularity assumption on the elements. However, in Nicaise (2001, SIAM J. Numer. Anal. , 39 , 784–816) optimal error estimates were obtained for the lowest order case under the weaker hypothesis of the maximum angle condition. This assumption allows for anisotropic meshes that become useful, for example, for the approximation of solutions with edge singularities. In this paper we prove optimal error estimates for the edge interpolation of any order under the maximum angle condition. We also obtain sharp stability results for that interpolation on appropriate families of elements. mixed finite elements; edge elements; anisotropic finite elements.

Description: This paper deals with a fluid–solid interaction problem inspired by a biomechanical brain model. The problem consists of determining the response to prescribed static forces of an elastic solid containing a barotropic and inviscid fluid at rest. The solid is described by means of displacement variables, whereas displacement potential and pressure are used for the fluid. This approach leads to a well-posed symmetric mixed problem, which is discretized by standard Lagrangian finite elements of arbitrary order for all the variables. Optimal-order error estimates in the H 1 - and L 2 -norms are proved for this method. A residual a posteriori error estimator is also proposed, for which efficiency and reliability estimates are proved. Finally, some numerical tests are reported to assess the performance of the method and that of an adaptive scheme based on the error estimator.

Description: A numerical method of second order of accuracy for computing conditional Wiener integrals of smooth functionals of a general form is proposed. The method is based on the simulation of a Brownian bridge via the corresponding stochastic differential equations (SDEs) and on ideas of the weak-sense numerical integration of SDEs. A convergence theorem is proved. Special attention is paid to integral-type functionals. A generalization to the case of pinned diffusions is considered. Results of some numerical experiments are presented.

Description: In this paper we utilize affine biquadratic elements and a two-step temporal discretization to develop a finite volume element method for parabolic problems on quadrilateral meshes. The method is proved to have an optimal order convergence rate in L 2 (0, T ; H 1 ()) under the ‘asymptotically parallelogram’ mesh assumption. Numerical experiments that corroborate the theoretical analysis are also presented.

Description: An error analysis is given for a discretization of the Gross–Pitaevskii equation by Strang splitting in time and Hermite collocation in space. A second-order error bound in L 2 for the semidiscretization error of the Strang splitting in time is proven under suitable regularity assumptions on the exact solution. For the semidiscretization in space, high-order convergence is shown, depending on the regularity of the exact solution. The analyses of the semidiscretizations in time and space are finally combined into an error analysis of the fully discrete method.

Description: In this paper we consider the finite-volume-element method for general second-order quasilinear elliptic problems over a convex polygonal domain in the plane. Using reasonable assumptions, we show the existence and uniqueness of the finite-volume-element approximations. It is proved that the finite-volume-element approximations are convergent with , where r 〉 2, and in the H 1 -, W 1, - and L 2 -norms, respectively, for u W 2, r () and u W 2, () W 3, p (), where p 〉 1. Moreover, the optimal-order error estimates in the W 1, - and L 2 -norms and an estimate in the L -norm are derived under the assumption that u W 2, () H 3 (). Numerical experiments are presented to confirm the estimates.

Description: We present guaranteed , robust and computable a posteriori error estimates for nonconforming approximations of elliptic problems. Our analysis is based on a Helmholtz-type decomposition of the error expressed in terms of fluxes. Such a decomposition results in a gradient term and a divergence-free term, that are the exact solutions of two auxiliary problems. We suggest a new approach to deriving computable two-sided bounds of the norms of these solutions. The a posteriori estimates obtained in this paper differ from those that are based on projections of nonconforming approximations to a conforming space. Numerical experiments confirm that these new estimates provide very accurate error bounds, and can be efficiently exploited in practical computations.

Description: The numerical solution for a class of sub-diffusion equations involving a parameter in the range – 1 〈 α 〈 0 is studied. For the time discretization, we use an implicit finite-difference Crank–Nicolson method and show that the error is of order k 2+ α , where k denotes the maximum time step. A nonuniform time step is employed to compensate for the singular behaviour of the exact solution at t = 0. We also consider a fully discrete scheme obtained by applying linear finite elements in space to the proposed time-stepping scheme. We prove that the additional error is of order h 2 max(1, log k –1 ), where h is the parameter for the space mesh. Numerical experiments on some sample problems demonstrate our theoretical result.

Description: The inf–sup stability and optimal convergence of an isogeometric C 1 discretization for the Stokes problem are shown. In this discretization the velocities are the pushforward through the geometrical map of cubic C 1 non-uniform rational B-spline (NURBS) functions and the pressures are the pushforward of quadratic C 1 NURBS. This paper follows the work in Bazilevs et al. (2006, Math. Models Methods Appl. Sci. , 16 , 1031–1090) where the authors showed the numerical result of this discretization and proved the inf–sup stability for C 0 NURBS functions. The use of more regular functions is useful to decrease the degrees of freedom and thus the computational cost. The analysis is performed by means of the Verfürth trick, the macro-element technique, some approximation properties and the inf–sup condition for tensor products of B-spline spaces.