ALBERT

Notizen: Microstructures in slate belt rocks at the Elura Mine, near Cobar, south-eastern Australia, indicate that volume loss by syntectonic dissolution is coupled with mass accretion by reprecipitation of the dissolved material in dilational sites. The mass accretion is sustained primarily by repetitive tensile microfracturing at high pore-fluid pressures. Oriented growth in the inter- and intragranular microcracks is locally host-controlled, creating lattice- and shape-preferred orientations. The grain-scale crack-seal features throughout the rock reflect rhythmic fluid pressure fluctuations; a balance is achieved between the fracture-induced permeability (and consequent flushing rates), and the rate of fluid build-up in a relatively sealed environment.Instability in the balancing factors can lead to localization and intensification of tensile failure (and hence, tension vein formation) in the grain aggregate. Growth of veins by crack-seal also reflects a steady state, but with more localized fluctuations of fluid flow on the aggregate scale. Still larger imbalances between flushing and fluid accumulation (i.e. pressure variations) induce breccia veining. The larger pressure gradients over greater distances, associated with dilation localization (from pervasive microfracturing to spaced breccia domains), allow fluid channelling with an increased potential for chemical fluid/rock disequilibrium. Therefore, large breccia vein systems tend to be sites of extensive fluid/rock interaction and replacement, as spectacularly illustrated by the syntectonic sulphide orebodies at Elura. The huge amounts of silicate, carbonate and sulphide accumulated during folding at Elura illustrate the large scale of source and sink couples possible in solute mass transfer.

Notizen: The Internal Zone of the Betic Cordilleras consists of several superimposed major thrust sheets with different P-T-t evolutions. On the basis of an integrated field, microscopic and laboratory study, the tectono-metamorphic history of the Mulhacen Complex and Almanzora Unit has been reconstructed in detail. The Mulhacen Complex has been affected by at least five phases of penetrative deformation, which have been labelled Dx-1, Dx, Dx+1, Dx+2 and Dx+3. Dx-1, and Dx are related to continent-continent collision, which is indicated by high pressure-low temperature (HP/LT) and subsequent intermediate P/T metamorphic conditions. Dx+1 is related to crustal thinning and heterogeneous extension. During this event the Almanzora Unit was juxtaposed against the Mulhacen Complex. This phase was succeeded by the establishment of low pressure-high temperature (LP/HT) conditions and at least two phases of folding and overthrusting. The Almanzora Unit shows a comparable tectono-metamorphic evolution post Dx+1. However, the P/T conditions prior to Dx+1 indicate a higher crustal position with respect to the Mulhacen Complex during the collisional event.

Notizen: Following the Middle Devonian Acadian deformation an extensive belt of high grade metamorphism was formed in New England. In south-western Maine, at the northern end of this belt, there occurs a transition along the strike from regional low-pressure/high-temperature metamorphism to contact metamorphism in low-grade rocks. Petrological studies indicate that this transition occurs along a surface plunging to the north-east at about 3.5°, with respect to the Middle-to-Late Devonian erosion surface. In addition, detailed petrological mapping has defined a history of temporally separate, localized metamorphic events associated with plutonism and occurring at increasingly deeper levels to the south-west. Geochronological studies constrain ambient temperatures in the transition zone at the time of metamorphism to be less than 300° C in the north-east and between 350° C and 500° C in the south-west. They also establish a pattern of diachronous cooling due to differential uplift and erosion, with cooling occurring later and most rapidly to the south-west. Geophysical evidence suggests that along with this spatial variation in metamorphic style the shapes of the plutons in Maine undergo a transition from laterally extensive sheet-like bodies in the high grade terrane to more equant-shaped bodies in the low-grade terrane. Using the results of these petrological, geochronological and geophysical studies, as well as those of stratigraphical and structural studies we construct a thermal model for the transition zone. The model suggests that the Acadian metamorphism in south-western Maine is a result of deep-level contact metamorphism near laterally extensive granitic sills dipping to the north-east with respect to the present erosion surface. The plutons themselves are interpreted to be a result of lower crustal melting in response to crustal thickening in the presence of normal or slightly augmented mantle heat flux.

Notizen: All along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher Himalaya crystalline and the crystalline nappes of the Lesser Himalaya. The salient points of the metamorphism, as deduced from data collected in central Himalaya (central Nepal and Kumaun), are:〈list xml:id="l1" style="custom"〉1The Higher Himalaya crystalline, also called the Tibetan Slab, displays a polymetamorphic history with a first stage of Barrovian type overprinted by a lower pressure and/or higher temperature type metamorphism. The metamorphism is due to quick and quasi-adiabatic uplift of the Tibetan Slab by transport along an MCT ramp, accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover. The resulting metamorphic pattern is an apparent (diachronic) inverse zonation, with the sillimanite zone above the kyanite zone.2Conversely, the famous inverted zonation of the Lesser Himalaya is basically a primary pattern, acquired during a one-stage prograde metamorphism. Its origin must be related to the thrusting along the MCT, with heat supplied from the overlying hot Tibetan Slab, as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust.3Thermal equilibrium is reached between units above and below the MCT. Far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the Tibetan Slab during the second metamorphic stage; but closer to the MCT front, the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the Tibetan Slab.

Notizen: South of the Main Mantle Thrust in north Pakistan, rocks of the northern edge of the Indian plate were deformed and metamorphosed during the main southward thrusting phase of the Himalayan orogeny. In the Hazara region, between the Indus and Kaghan Valleys, metamorphic grade increases northwards from chlorite zone to sillimanite zone rocks in a typically Barrovian sequence. Metamorphism was largely synchronous with early phases of the deformation. The metamorphic rocks were subsequently imbricated by late north-dipping thrusts, each with higher grade rocks in the hanging wall than in the footwall, such that the metamorphic profile shows an overall tectonic inversion. The rocks of the Hazara region form one of a number of internally imbricated metamorphic blocks stacked, after the metamorphic peak, on top of each other during the late thrusting. This imbrication and stacking represents an early period of post-Himalayan uplift.

Notizen: Crustal thickening along the northern margin of the Indian plate, following the 50 Ma collision along the Indus Suture Zone in Ladakh, caused widespread high-temperature, medium-pressure Barrovian facies series metamorphism and anatexis. In the Zanskar Himalaya metamorphic isograds are inverted and structurally telescoped along the Main Central Thrust (MCT) Zone at the base of the High Himalayan slab. Along the Zanskar valley at the top of the slab, isograds are the right way-up and are also telescoped along northeast-dipping normal faults of the Zanskar Shear Zone (ZSZ), which are related to culmination collapse behind the Miocene Himalayan thrust front. Between the MCT and the ZSZ a metamorphic-anatectic core within sillimanite grade rocks contains abundant leucogranite-granite crustal melts of probable Himalayan age. A thermal model based on a crustal-scale cross-section across the Zanskar Himalaya suggests that M1 isograds, developed during early Himalayan Barrovian metamorphism, were overprinted during high-grade MCT-related anatexis and folded around a large-scale recumbent fold developed in the hanging wall of the MCT.

Notizen: The intracrystalline diffusion rate of oxygen in diopside was constrained based on natural isotopic variations from a granulite facies marble from Cascade Slide, Adirondacks (New York, USA). The oxygen isotope compositions of the diopsides, measured as a function of grain size, are nearly constant (20.9 ± 0.3‰ vs. SMOW) over the entire measured size range (0.3–3.2 mm diameter). The δ18O values of the cores of calcite grains are 23.0‰. Temperature estimates based on the Δ18O(calcite-diopside) are 800d̀C, in agreement with the highest previous thermometric estimates for these rocks.The lack of isotopic variation in the diopsides as a function of grain size requires that the oxygen intracrystalline diffusion rate in diopside from the Adirondack samples was very slow. The maximum diffusion rates (D800d̀C parallel to the c-axis) were calculated with an infinite reservoir model (IRM) and a finite reservoir model (FRM) that incorporates mineral modal abundances and initial isotopic variations. For an assumed activation energy (Q) = 100 kJ/mol, the IRM diffusion rate estimate of 1.6 times 10-20cm2/s is two orders of magnitude faster than from the FRM; at Q=500kJ/mol, the D800d̀C estimate for both methods is c. 5.6 times 10-20 cm2/s. The present results require that a hydrothermal fluid significantly enhances the diffusion rate of oxygen in diopside if previous data are correct.The δ18O(SMOW) and δ13C(PDB) values of the calcite, measured in situ with a CO2 laser, are 22.9 ± 0.3, 0.1±0.3‰ in the grain cores, 22.1 ±0.3, 0.2 ±0.1‰ at the grain boundaries and 21.7 ±0.4, -0.6±0.1‰ abutting diopside grains. The δ18O and δ13δC values measured conventionally are: crystal cores, 22.96, -0.95‰; abutting diopside grains, 22.38, -0.93‰; bulk, 22.79, -0.95%. Use of the bulk δ18O(calcite) values for thermometry yields unreasonably high temperatures. The lower δ18O values at the calcite grain boundaries are not due to retrograde diffusional exchange with the diopside, they are thought to be a result of a late retrograde fluid infiltration.

Notizen: Clay mineral crystallinity and crystallite (domain) size data determined by X-ray diffraction (XRD) are methods extensively used in the characterization of very low-grade metamorphic conditions. However, the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained, a consequence of the different machine conditions, measurement methods and sample preparations used during analysis. A calibration approach to the standardization of data using rock chip standards is presented, which allows data sets produced by different research groups to be directly and quantitatively compared. A standardized scale, the crystallinity index standard (CIS), is proposed, with illite crystallinity anchizonal boundary limits of 0.25d̀Δ2θ and 0.42d̀Δ2θ, and equivalent illite crystallite sizes of 52 and 23 nm, respectively, determined by the Warren-Averbach method. Calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments, and should improve the accuracy and reliability of correlations made between XRD data and other indicators of very low-grade metamorphism, hence increasing the value of such clay mineral studies.

Notizen: The Chicago mineral-carbonate oxygen isotope fractionation curves have been combined with mineral-water fractionation data for jadeite, zoisite and rutile and new data for grossular-water to provide a set of self-consistent mineral-pair calibrations. The A coefficients in the equation 1000 In α=A× 106T-2 of the new mineral-pair fractionations areJadeite Zoisite Grossular RutileQuartz 1.69 2.00 3.03 5.02Jadeite 0.31 1.34 3.33Zoisite 1.03 3.02Grossular 1.99The isotopic fractionation properties of natural pyralspite garnet [(Ca, Fe, Mg, Mn)3Al2Si3O12] can be approximated by those of the grossular end-member. Appropriate substitutions also yield coefficients for the solid-solution minerals: sodic pyroxene and epidote, e.g. A quartz-sodic pyroxene= 2.75 - 1.06Xjd, A quartz-epidote= 2.00 + 0.75Xpswhere XJd and XPs are the mole fractions of the jadeite and pistacite components, respectively.The new data set is particularly suitable for the geothermometry of metamorphic rocks. δ18O data from minerals of the high-pressure metamorphic rocks of the Sesia Zone of Italy and Cyclades Complex of Greece yield well-constrained mean temperatures of 572 and 478d̀ C, respectively. Type III blueschist metabasalts of the Franciscan Formation of California give mean quartz-garnet temperatures of 354d̀ C.

Notizen: Quantitative modelling of oxygen exchange by diffusion during slow cooling has been compared to the observed oxygen isotope distributions from high-grade metamorphic and granitic rocks of the High Himalayan Crystallines, Langtang Valley, central Nepal, in order to investigate the effect of retrograde diffusional exchange on the preservation of high-temperature, oxygen isotope systematics.Modelled fractionations, using water-present diffusion data reported in the literature, predict quartz-mica fractionations to be much larger than those at peak metamorphic and igneous conditions due to low closure temperatures for micas. Quartz-feldspar fractionations may be less than those at peak conditions, and in some samples may even be slightly negative.The observed oxygen isotope fractionations in the metamorphic rocks are small and largely appear to record equilibrations close to peak conditions determined by other methods. Hence these rocks clearly do not conform to predictions of fluid-present diffusional retrograde exchange. It is suggested that their retrograde history was therefore within an anhydrous closed system in which diffusion was slow and hence mineral closure temperatures were high. The granitic rocks record rather larger quartz-biotite fractionations, approaching those predicted by the diffusion modelling. However, quartz-feldspar fractionations are large and hence, although significant retrograde exchange has clearly occurred, simple diffusion alone is not sufficient to explain the observed data and open-system exchange may be required. The presence of fluids during the retrograde history of this part of the section is supported by petrographic evidence.The different retrograde oxygen exchange histories recorded between the regional metamorphic and magmatic regimes of the Langtang section would appear to support the importance of water on the kinetics of such exchange, and suggests that in its absence, diffusional exchange may become insignificant, allowing oxygen isotope thermometry to record meaningful high-temperature data.

Notizen: The assemblages chlorite-pumpellyite-lawsonite-albite-quartz, chlorite-lawsonite-quartz-epidote and chlorite-epidote-albite-quartz occur in metabasaltic blocks and veins in a metamorphosed tectonic mélange in the structurally highest unit of the autochthonous and parautochthonous section underlying the Semail ophiolite in Saih Hatat, north-east Oman. The pre-Permian basement of this section contains mafic units characterized by the assemblage crossite-epidote-chlorite-quartz-albite /el actinolite. These assemblages indicate a down-section increase in metamorphic grade from ‘lawsonite-albite facies' conditions in the mélange to ‘epidote-blueschist’ facies conditions in the basement.Application of empirically and experimentally based thermobarometers as well as petrogenetic grids calculated for a model basaltic system indicates that the P-T conditions of metamorphism ranged from 3 to 6 kbar and 250 to 300d̀ C for the mélange and P 〉 6.8 kbar, T 〉 310d̀ C for the basement units. Textural relations interpreted in the context of petrogenetic grids indicate that these units followed clockwise P-T paths of evolution. The estimated P-T conditions and down-section increase in metamorphic grade in central, western and northern Saih Hatat are consistent with the hypothesis relating metamorphism to the Late Cretaceous tectonic loading of the continental margin by an ophiolite slab 〈 18 km in thickness. These results contrast with field and petrological observations documented for blueschists and eclogites exposed along the eastern coast of Saih Hatat which may have formed at an earlier stage in response to an Early Cretaceous collisional event.

Notizen: Books reviewed in this article: Perspectives on Biodiversity: Case Studies of Genetic Resource Conservation and Development. Christopher S. Potter, foci 1. Cohen, and Dianne Janczewski, editors

Notizen: To evaluate reclamation success on the Wooley Valley phosphate mine in southeastern Idaho, we compared vegetation structure and soil physical, chemical, and elemental properties of several different reclamation treatments with those of a nearby reference area (a native Artemisia tridentata vaseyana/Festuca idahoensis association) after 14 years. Vegetation data had been collected four years after reclamation, and we were able to compare differences in biomass and species composition between dates on the reclaimed area. Four years after reclamation there were no differences in total biomass between topsoil or spoil or between seed only, seed + mulch, or control treatments on the different soil types. Most treatments were dominated by seeded perennial grasses. Fourteen years after reclamation there were no differences in biomass or cover between spoil and topsoil plots, but on spoil plots the seeded and mulched treatment had higher total biomass and vegetation cover than on control or seed-only treatments. The seeded perennial legume Medicago sativa was codominant with the seeded forage grasses on all of the treatments. High initial fertilization rates probably facilitated the early establishment and dominance of the forage grasses; once nutrient levels, especially nitrogen, began to decline, the legume increased in abundance. Similarity between the reclaimed area and the reference or native area was low. Reclaimed treatments had higher biomass but lower species richness. The topsoil and spoil plots had similar soil texture, bulk density, pH, cation exchange capacity, electrical conductivity, and phosphorus. Differences in organic carbon, total nitrogen, carbon: nitrogen ratios, and available moisture were related more to treatments than to soil type. High biomass and, thus, litter input on the seed + mulch treatment on spoil plots resulted in both higher OC and TN than any on other soil/treatment combination. The reclaimed area had lower OC, TN, and available moisture than did the reference area on all but seed + mulch spoil plots. Bulk density was higher on reclaimed plots. The long-term differences observed between the reclaimed and reference areas parallel those obtained for other western reclamation sites. Although successional trajectories depend on the attribute measured, similarity to native reference areas depends on the initial reclamation methods. We discuss reclamation methods that would increase the structural and functional similarity of reclaimed and reference areas on the Wooley Valley phosphate mine.

Notizen: In land restoration it is imperative to study the potential role of disturbances, biotic or abiotic, that may provide sites for colonization by specific plants. Disturbances can alter community composition by removing species or allowing others to become established. In communities where animal-generated disturbances open sites for seedling establishment, animals may have important indirect effects on several aspects of plant community structure. Animal disturbances in Quercus havardii communities of western Texas appear to open sites for colonization by herbaceous species. These animal disturbances vary in spatial distribution, density, and abiotic and biotic characteristics. The abundance of herbaceous plant seedlings is positively related to bare ground and the number of distinct disturbances. Thus, the density and the spatial distribution of these disturbances may be expected to have an important influence on the abundance and dispersion of plant species. Therefore, successful restoration efforts of sand shinnery oak communities and other similar habitats must consider the effects of animal disturbances and the role of plant-animal and plant-soil microbe interactions on plant community composition and the maintenance of plant species diversity.

Notizen: The rates of seston elimination by zooplankton and primary production were measured in Funada-ike Pond, typical of human-made impoundments in Japan, from April to September in order to evaluate various treatments of the pond aimed at improving water quality by reducing seston abundance. The treatments included draining the pond water, dredging the bottom mud, eliminating the wastewater inflow, and biomanipulation through removal of all fish. After the treatment, seston abundance was reduced from more than 10 to 0.4–2.5 mg C/liter, and large daphnid species, Daphnia similis and D. magna, occurred and predominated in the zooplankton community. Seston abundance remained at a relatively low level from June to August but increased markedly in late August, while the biomass of zooplankton became high from June to mid-August and then decreased. A decrease in seston abundance was found when the elimination rate exceeded the primary production rate. The results indicate that the development of daphnid populations was effective in keeping seston abundance at a low level. The relationship between the rate of primary production and the zoo-plankton biomass required to offset this rate, however, suggests that biomanipulation aimed at increasing zooplankton biomass alone is less effective in a pond with a high primary production. The success in improving water quality in this pond seems to depend not only on the increase in biomass of large daphnid species that resulted mainly from the removal of fish, but also on the decrease in nutrient load that was realized by the other treatments.

Notizen: This essay reviews the recent attempts by the Northwest Power Planning and Conservation Council (NPPC) to conserve and restore wild salmon lost to hydroelectric development along the Columbia River and its tributaries. The restoration of the wild salmon is predicated on cooperation between myriad stakeholders in a planning process that includes the NPPC, 11 state and federal agencies, 13 Indian tribes, 8 utilities, and numerous interest groups. The two goals of the essay are (1) to review the recent amendments to the NPPC's fish and wildlife program, and (2) to describe the political barriers to restoration versus restocking of wild salmon in the Columbia River. The failure of political and administrative entities to deal with the problem of restoring wild salmon may result in drastic requirements being imposed by the imperatives of the Endangered Species Act.

Notizen: An environmental revolution is urgently needed that will lead to a post-industrial symbiosis between man and nature. This can be realized only if the present unrestrained biological impoverishment and neotechnological landscape degradation are replaced by the creation of healthy and attractive landscapes. Restorationists can fulfill a vital role in this process. They must broaden their scales from biodiversity restoration in small, protected nature islands to the large-scale restoration of natural and cultural landscapes. To achieve this they must restore not only the patterns of vegetation but also the processes that create these patterns, including human land uses. Their goal should be to restore the total biological, ecological, and cultural landscape diversity, or “ecodiversity,” and its intrinsic and instrumental values of highly valuable, endangered seminatural, agricultural and rural landscapes. For this purpose it is essential to maintain and restore the dynamic flow equilibrium between biodiversity, ecological, and cultural landscape heterogeneity, as influenced by human land uses, which occur at different spatial and temporal scales and intensities. Recent advances in landscape ecology should be utilized for broader assessment of ecodiversity, including proposed indices of ecodiversity, new techniques such as Intelligent Geographical Information Systems (IGIS), and Green Books for the holistic conservation and restoration of valuable endangered landscapes. Restoration ecology can make an important contribution to an urgently needed environmental revolution. This revolution should lead to a new symbiosis between man and nature by broadening the goal of vegetation restoration to ecological and cultural landscape restoration, and thereby to total landscape ecodiversity.

Notizen: A study of spider (Araneae) communities was conducted in rehabilitated bauxite mines at the Jarrahdale mine site of Alcoa of Australia Ltd. and in the nearby native jarrah (Eucalyptus marginata) forest in southwest Western Australia. The study was conducted from March to August 1993 in five rehabilitated sites of different age and method of rehabilitation and in two forest sites. A variety of collection methods was used, including pitfall trapping, litter sampling, sweep netting, tree beating, and visual searching. These methods were the same as those carried out in a previous study of some of these areas in 1983. We collected 151 spider species belonging to 102 genera and 34 families. We examined the relationship between various habitat features, including the age and method of rehabilitation, of the spider communities present. It was found that leaf litter depth and cover and vegetation density had a significant positive influence on recolonization by the various spider guilds. The age and method of rehabilitation were found to influence different vegetational and habitat features; these, in turn, influenced the spider communities. Thus, the older a rehabilitated site the greater the species richness of both plants and spiders. We compared these results with those of the 1983 study to determine the spider succession of the aging rehabilitation. The spider communities and guild composition were found to change as the vegetation matured, from a dominance of pioneer species to a community of species requiring less harsh conditions. By comparison with the pre-1983 rehabilitation, the latest method of rehabilitation increased the rate of recolonization by both plants and spiders.

Notizen: Peak flowering activity among woody species in the tropical dry forests of St. John, U.S. Virgin Islands, coincided with the brief spring rainy season but continued at moderate levels for six months, abating with the autumn rains. Fruit maturation showed a major peak in the long winter dry season and a minor crest during the summer dry season. Seeds of wind-dispersed species disseminated mainly during the winter dry season, while animal dispersal of seeds (74% of all woody species) followed the bimodal pattern (for wet and dry seasons) described for the community as a whole. Under shadehouse conditions, most dry forest tree species germinated well (〉 80%) and emerged promptly (within four weeks of planting) and synchronously (90% emergence within a four-week interval). Nine of 29 species tested in the shadehouse manifested dormancy of at least six weeks. Seed germinability varied among tree species, and the viability of most species began to decline following six months of dry storage. Few species retained high germinability after nine months of dry storage. The species composition of soil seed banks did not correspond closely with above-ground communities on three forested sites of varying stand age. In the youngest stand (35 years old), dominated by the weedy, arborescent legume Leucaena leucocephala, the soil seed bank was also dominated by this species, but no seeds of any other tree species were found in the soil samples. Seeds of native trees were scarcely encountered (only one indigenous species) in soil seed bank samples of three forest sites. Local seed rain from less disturbed forest may not be sufficient for prompt recovery of the dry forest community on degraded sites.

Notizen: I present an integrated survey of management strategy, which examines organizational design, competitive strategy, and public policy considerations. In addition, 1 offer suggestions on how economic analysis can be applied in unifying and developing management strategy as a field of study.

Notizen: Under prospective pricing, payers for health care essentially use price regulation of hospitals as a way of indirectly regulating the provision of treatment intensity. This paper presents a theory of how a nonprofit hospital selects treatment intensities for its products given the payer's choice of prices and then determines how the payer should select prices in light of this theory. The main result is that, in equilibrium, the ratio of price to marginal cost will vary across products inversely with the elasticity of demand with respect to treatment intensity. This means that, generally, the hospital will earn positive (negative) accounting profit on products with low-(high-) intensity elasticities of demand.

Notizen: Legislation to create optional no-fault insurance (ONFL) programs has recently been enacted in Florida and Virginia. ONFI programs provide compensation to patients when certain medical complications arise, provided the patient agrees not to sue the doctor for additional damages. The optimal design of ONFI programs is explored in this paper, focusing on the incentive effects of ONFI programs. The question of whether ONFI programs should be funded entirely by participating doctors, or whether social subsidies are optimal, is examined.

Notizen: Experiments up to water pressures of 21 kbar have been undertaken to bracket the reactions chlorite + quartz = talc + kyanite + H2O, chlorite + quartz = talc + cordierite + H2O, and talc + kyanite + quartz = cordierite ± H2O by reversed runs in the system MgO-Al2O3-SiO2-H2O (MASH). These reaction curves intersect at an invariant point (IP1) at PH2O = 6.4 ± 0.2 kbar and a temperature of 624 ± 4°C. The curve of the chlorite + quartz breakdown to talc + kyanite + H2O at water pressures above 6.4 kbar shows a negative dP/dT, with the slope decreasing with rising pressure, whereas the slope of the breakdown curve to talc + cordierite + H2O at water pressures is clearly positive.The composition of the chlorite solid solution reacting with quartz has been estimated to be approximately Mg4.85Al1.15[Al1.15Si2.85O10](OH)8 over the entire pressure range investigated. The composition of the talc solid solution forming by the breakdown of chlorite + quartz appears to be Mg2.94Al0.06[Al0.06Si3.94O10](OH)2 at PH2O = 2kbar. With increasing pressure, the Al content of talc decreases, reaching a value of about 0.06 atoms per formula unit at P,H2O = 21 kbar.As a consequence of the new experimental data, the existing phase topologies of the MASH-system and K2O-MASH-system have been revised. For example, the invariant point IP1 and the univariant reaction curve kyanite + talc + H2O = chlorite + cordierite are stable. For this reason, the development of medium- to high-temperature metamorphic rocks compositionally approximating the MASH-system must be reconsidered. The whiteschists from Sar e Sang, Afghanistan, are treated as an example. The application of the present experimental data to metamorphic rocks of more normal composition requires the examination of the influence of further components. This leads to the conclusion that the introduction of Fe2+ into magnesian chlorite extends its stability field in the presence of quartz by 10°-15°C in comparison with pure Mg-chlorite.

Notizen: A reaction producing jadeitic pyroxene in metagreywackes of the northern Diablo Range has been identified on the basis of mineral distribution, isograd patterns and composition of coexisting minerals. The appearance of jadeitic pyroxene (∼Jd80) is closely followed by the disappearance of pumpellyite, which indicates that pumpellyite plays a major role in the pyroxene-producing reaction. A new projection from hematite, lawsonite, chlorite, quartz and H2O on to the NaAlO2-FeO-MgO ternary confirms the role of pumpellyite in pyroxene production and suggests a reaction of the form: 1.00 pumpellyite + 0.31 chlorite + 8.71 albite + 0.70 hematite + 2.00 H2O = 8.54 jadeite + 0.57 glaucophane + 3.09 lawsonite + 5.26 quartz. Metagreywackes of the northern Diablo Range were metamorphosed under conditions of PH2O=Ptotal at 200-300 °C and 7.5-10.0 kbar. Despite the low temperatures attained during metamorphism, the assumption of equilibrium yields results consistent with field observations and phase relations.

Notizen: Metabasites and metagreywackes from the Pelona and Rand Schists of southern California were analysed using three different electron microprobes. For all three instruments, the estimated Fe3+ contents of calcic amphibole, chlorite and epidote are positively correlated. For some samples, there is an additional correlation between high estimated Fe3+ and the presence of magnetite. These results imply that microprobe analyses can be used to discern relative differences in Fe3+. However, microprobe data and calculations on the sensitivity of the correction procedures to systematic analytical errors indicate that estimated values of Fe3+ are not significant in an absolute sense. Thus, estimates of Fe3+ are meaningful when comparing samples analysed with a single microprobe, but must be used with caution when comparing analyses obtained on more than one probe.

Notizen: All the Mesozoic and Cenozoic volcanic rocks of the Central Andes (from southern Ecuador to central Chile), except Recent ones, have been affected by episodes of regional metamorphism, without change in texture and structure. The metamorphism, which ranges from low zeolite to greenschist facies, can be classified as burial metamorphism because there is an overall increase in metamorphic grade with stratigraphic depth in the individual volcanic sequences separated by regional unconformities. Some sequences display metamorphic patterns transitional to ocean-floor and to geothermal field types, reflecting variations along and across the Andes in tectonic setting and thermal gradients.Volcanism was closely followed by metamorphism during each cycle characterizing the geological history of the Central Andes. The episodic nature of the metamorphism has led to breaks in metamorphic grade at regional unconformities and repetition of facies series, where strata of higher grade may even overlie those of lower grade. The existence of permeability-controlled distribution patterns of secondary minerals within individual flows shows that gradients of chemical activity, rate of reaction and Pfluid were acting, in addition to temperature and P,tot overall gradients, during the regional metamorphism. The alteration is accompanied by chemical changes and disturbances of the K-Ar and Rb-Sr isotope systems. Similarities between Mesozoic facies series in the western and eastern flanks of the Andes are consistent with a mechanism of ensialic spreading-subsidence.

Notizen: An analytical study to evaluate quantitatively weak zoning of a garnet from a high-grade kinzigite has been performed with an electron microprobe. The technique consists of the reconstruction of a profile step-by-step by successive analyses performed during relatively long counting times (30 s), along a radial profile of 2,500 μm length. The successive analytical data along this profile are statistically treated by Fisher's test and compared with the χ2 values (Pearson's law). These statistical tests were applied to assess microprobe stability and analysis homogeneity, and as a consequence to assure high credibility of the radial variations of the garnet. From core to rim, and for each element, zoning appears as the radial juxtaposition of stationary Poissonian samples. These samples being associated, the garnet appears to be constituted of successive concentric domains with stationary compositions. Different substitutions between Mg, Fe, Mn and Ca are evidenced. Such an analytical approach to chemical zoning can be useful for understanding growth mechanisms, and the possible diffusion reactions with the environment at each growth step. In addition, such a procedure can be used to evaluate accurately the fluid content of cordierite, and to appreciate the nature of the fluids concerned. As an example, the fluid content of a cordierite from a similar high-grade kinzigite has been evaluated.