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  • 1
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    Electronic Resource
    Eruption and emplacement of a basaltic welded ignimbrite during caldera formation on Gran Canaria (1995)
    Springer
    Bulletin of volcanology 56 (1995), S. 640-659 
    Details
    ISSN: 1432-0819
    Keywords: Key words Basaltic ignimbrite ; Lava-drop coalescence ; Welding ; Pyroclastic fountain ; Caldera collapse ; Gran Canaria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The 14.1 Ma old composite ignimbrite cooling unit P1 (45 km3) on Gran Canaria comprises a lower mixed rhyolite–trachyte tuff, a central rhyolite–basalt mixed tuff, and a slightly rhyolite-contaminated basaltic tuff at the top. The basaltic tuff is compositionally zoned with (a) an upward change in basalt composition to higher MgO content (4.3–5.2 wt.%), (b) variably admixed rhyolite or trachyte (commonly 〈5 wt.%), and (c) an upward increasing abundance of basaltic and plutonic lithic fragments and cognate cumulate fragments. The basaltic tuff is divided into three structural units: (I) the welded basaltic ignimbrite, which forms the thickest part (c. 95 vol.%) and is the main subject of the present paper; (II) poorly consolidated massive, bomb- and block-rich beds interpreted as phreatomagmatic pyroclastic flow deposits; and (III) various facies of reworked basaltic tuff. Tuff unit I is a basaltic ignimbrite rather than a lava flow because of the absence of top and bottom breccias, radial sheet-like distribution around the central Tejeda caldera, thickening in valleys but also covering higher ground, and local erosion of the underlying P1 ash. A gradual transition from dense rock in the interior to ash at the top of the basaltic ignimbrite reflects a decrease in welding; the shape of the welding profile is typical for emplacement temperatures well above the minimum welding temperature. A similar transition occurs at the base where the ignimbrite was emplaced on cold ground in distal sections. In proximal sections the base is dense where it was emplaced on hot felsic P1 tuff. The intensity of welding, especially at the base, and the presence of spherical particles and of mantled and composite particles formed by accretion and coalescence in a viscous state imply that the flow was a suspension of hot magma droplets. The flow most likely had to be density stratified and highly turbulent to prevent massive coalescence and collapse. Model calculations suggest eruption through low pyroclastic fountains (〈1000 m high) with limited cooling during eruption and turbulent flow from an initial temperature of 1160°  C. The large volume of 26 km3 of erupted basalt compared with only 16 km3 of the evolved P1 magmas, and the extremely high discharge rates inferred from model calculations are unusual for a basaltic eruption. It is suggested that the basaltic magma was erupted and emplaced in a fashion commonly only attributed to felsic magmas because it utilized the felsic P1 magma chamber and its ring-fissure conduits. Evolution of the entire P1 eruption was controlled by withdrawal dynamics involving magmas differing in viscosity by more than four orders of magnitude. The basaltic eruption phase was initially driven by buoyancy of the basaltic magma at chamber depth and continued degassing of felsic magma, but most of the large volume of basalt magma was driven out of the reservoir by subsidence of a c. 10 km diameter roof block, which followed a decrease in magma chamber pressure during low viscosity basaltic outflow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301468
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  • 2
    Electronic Resource
    Electronic Resource
    Models for the origin of accretionary lapilli (1995)
    Springer
    Bulletin of volcanology 56 (1995), S. 626-639 
    Details
    ISSN: 1432-0819
    Keywords: Key words Accretionary lapilli ; Particle binding ; Capillary forces ; Liquid film binding ; Electrostatic attraction ; Experimental agglomeration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Binding between initially cohesionless ash particles to form concentric accretionary lapilli is provided primarily by the capillary forces of liquid bridges from condensed moisture and by electrostatic attraction. Capillary forces are strong bonds if the particles are in close contact, but they decrease rapidly with increasing particle spacing. Electrostatic attraction between charged ash particles is much weaker but effective over larger distances, increasing the frequency of collision between them. Experimental results of liquid film binding of volcanic ash showed that agglomeration was most successful between 15 and 25 wt.%, defining the agglomeration window for the formation of accretionary lapilli. Below 5–10 wt.% and above about 25–30 wt.% of water, concentric agglomeration was inhibited. Particles 〈350 μm could be selected from a wider particle population in the experiments using only small amounts of water, which can explain the growth of accretionary lapilli in pyroclastic surges around agglomeration nuclei. Experiments testing the behavior of volcanic ash in electric fields showed that ash clusters formed instantaneously when the ash entered the field between a corona discharge gun and a grounded metal plate. The maximum grain size incorporated into the artificial clusters was about 180 μm but 〉90 wt.% of ash was 〈45 μm. Accretionary lapilli form in turbulent ash clouds when particles carrying liquid films of condensed moisture collide with each other and when the binding forces exceed the grain dispersive forces. Larger particles 〉500 μm act as agglomeration nuclei in surges, accreting ash 〈350 μm around them. In pyroclastic flows the aggregates are thought to originate from already size-sorted ash at the interface between the lower avalanche part of the flow and its overriding elutriation cloud. The fine-grained rims around accretionary lapilli found close to source are interpreted to be accreted dominantly by electrostatic attraction of very fine ash similar to clustering in elutriation clouds.
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    URL: http://dx.doi.org/10.1007/BF00301467
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  • 3
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    Electronic Resource
    The lateral facies of ignimbrites at Laacher See volcano (1990)
    Springer
    Bulletin of volcanology 52 (1990), S. 271-285 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Valley-fill ignimbrites of the Middle Laacher See Tephra (MLST) in the proximal depositional fan south of Laacher See volcano are laterally continuous with fine-grained overbank-facies deposits, 0.5–1.5 m thick, covering higher elevations and interfluves between the paleovalleys. The overbank deposits consist of up to 12 ash layers, each 4–10 cm thick, which show internal structures typical of ash-flow transport, such as poor sorting, reverse size-grading of pumice, local normal grading of coarse ash-sized lithics above a fine-grained basal layer, cross-stratification behind obstacles, and erosional unconformities. Thickness, median grain-size, and number of individual layers decrease systematically with distance from the vent. Overbank ash layers thicken at the valley slopes and form discrete valley-fill ignimbrite flow units in the paleochannels with median grain size increasing from ≤63 μm to ≤350 μm. Toward the center of paleochannels, however, the well-defined overbank facies is obscured by mutual erosion of individual flow units. Overlapping data fields in ternary grain-size variation diagrams indicate the overbank facies to have evolved from ash flows chiefly through depletion of lapilli and coarse ash. Overbank-facies ash layers do not represent dust layers resulting from elutriation clouds of ash flows (co-ignimbrite ash) or surge deposits developed on higher ground due to low concentration of solids. They are similar in some parameters to Taupo-type ignimbrite veneer deposits, but are interpreted differently. The thin, fine-grained, Laacher See ash layers are thought to have been deposited from diluted portions of the flow proceeding directly from the eruption column while the main pyroclastic flows were confined to the paleovalleys radiating away from the eruptive center. The wide distribution of the thin ash layers is attributed to the balance of deposition from various flow parts and turbulent entraining and heating of ambient air that sustained sufficient mobility of the diluted flows to spread across hills and level ground.
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    URL: http://dx.doi.org/10.1007/BF00304099
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  • 4
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    Electronic Resource
    Polybaric differentiation of alkali basaltic magmas: evidence from green-core clinopyroxenes (Eifel, FRG) (1985)
    Springer
    Contributions to mineralogy and petrology 91 (1985), S. 340-353 
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    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Quaternary foidites and basanites of the West Eifel (Germany) contain optically and chemically heterogeneous clinopyroxenes, some of which occur as discrete zones within individual crystals: Most clinopyroxene phenocrysts are made up of a core and a normally zoned comagmatic titanaugite mantle. Most cores are greenish pleochroic and moderately resorbed (fassaitic augite). Some are pale green and strongly resorbed (acmitic augite). Cores of Al-augite composition and of Cr-diopside derived from peridotite xenoliths are rare. The fassaitic augites are similar in trace element distribution pattern to the titanaugites, but are more enriched in incompatible elements. The acmitic augites, in contrast, are clearly different in their trace element composition and are enriched in Na, Mn, Fe and depleted in Al, Ti, Sr, Zr. A model for polybaric magma evolution in the West Eifel is proposed: Primitive alkali basaltic magma rises through the upper mantle precipitating Al-augite en route. It stagnates and differentiates near the crust/mantle boundary crystallizing Fe-rich fassaitic augites. The magma differentiated at high pressure is subsequently mixed with new pulses of primitive magma from which the rims of pyroxene are crystallized. Sporadic alkali pyroxenite xenoliths are interpreted to represent cumulates of cognate phases formed within the crust and not metasomatized upper mantle material (Lloyd and Bailey 1975).
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    URL: http://dx.doi.org/10.1007/BF00374690
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  • 5
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    Flow directions in Columbia River Basalt flows and paleocurrents of interbedded sedimentary rocks, South-Central Washington (1967)
    Springer
    International journal of earth sciences 56 (1967), S. 992-1020 
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    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract More than 150 flow directions measured mainly in inclined pipe vesicles and, more rarely, vesicle cylinders, spiracles, and inclined foreset beds in pillowpalagonits-complexes) of the upper 12 widespread Yakima Basalt flows on the Columbia River Plateau in south-central Washington indicate rather uniform transport directions from southeast to northwest. This strongly supports former ideas that the large Grande Ronde-Cornucopia dike swarm in northeast Oregon fed the huge lava floods. It is shown that all previous evidence indicating eruption centers for the basalts in the Cascada Range to the west is inconclusive. Cross-bedding directions, maximum pebble sizes, and distribution of heavy mineral suites in sedimentary deposits interbedded with the basalt sheets delineate in more detail two main paleoslopes whose deposits interfinger: a) the Cascade paleoslope to the west with east-southeast paleocurrents and a predominance of volcanic heavy minerals (hornblende, oxyhornblende, hypersthene, and clinopyroxene). b) the Columbia paleoslope with south-southwest paleocurrents and chiefly sphene, epidote, clinozoisite, blue-green hornblende, garnet, sillimanite, kyanite, and staurolite. Distribution of conglomerats, current directions, and heavy mineral suites support former hypotheses that the ancestral Columbia River flowed about 50 km farther west in early Pliocene time than it does today in the area of lower Yakima Valley. The opposed transport directions of basalts and sediments can be tentatively explained as follows: during outpouring of the lower basalts the regional gradients were very low as indicated by thin veneers of fine-grained sediments. The thick, very fluid lava flows were therefore able to overcome very gently opposed slopes for several tens of kilometers. The southwest gradient of the ancestral Columbia River became more pronounced at the time of eruption of the two youngest basalts. These lavas therefore turned and flowed southwest where they met the Columbia paleoslope. Even the youngest flows spread as sheets of wide lateral extent, however, despite accelerated tectonism and rapid sedimentation in synclinal basins.
    Abstract: Résumé Les nappes des basaltes tholeiitiques du Miocène-Pliocène, qui sont les plus jeunes du Columbia River Plateau s'étendent au moins de 3000 à 20 000 km2 chacune. Dans les 12 nappes de la partie supérieure, 150 mesurages de structures réglées indiquent que ces laves ont coulé plus ou moins de SE à NO. Ces basaltes probablement sont originaires des filons du système Grande Ronde-Cornucopia dans le NE-Oregon. Des structures réglées et des dates de pétrographie et de chimie indiquent, que les centres d'éruption ne sont pas situés dans les Montagnes des Cascades à l'ouest du plateau basaltique, comme c'était supposé autrefois; c'est valable au moins pour les laves de la partie supérieure. Il y a deux types de sédiments intercalés dans les basaltes: 1. Sédiments d'origine volcanique qui ont été transportés par des rivières et des lahars des anciens volcans dans les montagnes des Cascades à l'est. 2. Débris des roches plutoniques et métamorphes du N, transportés par la Columbia River dans le Miocène-Pliocène. Les couches sédimentaires entre les 12 nappes analysées augmentent de bas en haut; ils sont plus fines à la base, probablement selon sédimentation sur une plaine d'un pendage assez faible. Les laves d'une épaisseur considérable et d'une viscosité très petite pouvaient couler plusieurs kms vers le pendage de la plaine. Pendant l'éruption des basaltes plus jeunes le plateau commençait à se diviser en anticlinauxet synclinaux, mais le relief restait faible selon la sédimentation rapide dans le bassin. Ainsi même les plus jeunes nappes basaltiques s'épandaient assez loin vers l'ouest. Il y a une différence concernant les 2 nappes les plus hautes: au contraire des directions O-NO des basaltes plus bas ils indiquent par des structures réglées qu'ils ont coulé vers le SO, parallèle au Columbia River du MiocèneePliocène.
    Notes: Zusammenfassung Die jüngsten tholeiitischen Deckenbasalte (Miozän-Pliozän) des Columbia-River-Plateaus haben je eine flächenhafte Ausdehnung von mindestens 3000 bis 20 000 km2. Mehr als 150 Messungen von gerichteten Strukturen der 12 oberen Decken zeigen relativ einheitliche Fließrichtung der Laven von Südosten nach Nordwesten. Die Basaltlaven wurden wahrscheinlich von den teilweise über 50 km langen Gängen des Grande Ronde-Cornucopia Gangschwarms in Nordost-Oregon gefördert. Fließrichtungen und petrographisch-chemische Gründe sprechen gegen vermutete Eruptionszentren, zumindest für die oberen Lavadecken, in den Kaskaden im Westen des Basaltplateaus. H.-U.Schmincke - Flow directions in Columbia River Basalt flows Die den Basalten zwischenlagernden Sedimente gehören zwei verschiedenen, sich verzahnenden Ablagerungsprovinzen an: a) Vulkaniklastische Sedimente (mit Hauptschwermineralien: braun-grüne Hornblende [oft oxydiert], Hypersthen und Klinopyroxen), die von Aschenschauern, Flüssen und Lahars aus den westlichen Kaskaden nach Osten transportiert wurden. b) Der Vorläufer des Columbia River brachte plutonisch-metamorphen Detritus des nördlichen Grundgebirges nach Südosten auf das Lavaplateau. Wesentliche Schwermineralien sind: Titanit, Epidot, Klinozoisit, blau-grüne Hornblende, Granat, Sillimanit, Disthen, Staurolith. Der alte Columbia River floß etwa 50 km westlich, des heutigen Laufes im unteren YakimaRiver-Tal. Die entgegengerichteten Gradienten (die Basalte flossen west-nordwestwärts, die Flüsse ost-süd-südwestwärts) lassen sich folgendermaßen erklären: zwischen den unteren (der zwölf eingemessenen) Basaltdecken sind Sedimente selten und nur feinkörnig, sie wurden daher wahrscheinlich auf einer sehr flachen Ebene mit geringem Gefälle abgelagert. Die Lavaströme waren außerordentlich dünnflüssig und sehr mächtig und konnten deshalb mehrere km gegen das Gefälle dieser Ebene fließen. Während der Eruption der jüngsten Basaltlaven begann sich das Lavaplateau in Antiklinalen und Synklinalen zu zergliedern. Jedoch blieb das allgemeine Relief wegen der raschen Beckensedimentation so niedrig, daß auch die jüngsten Lavaergüsse nach Westen vorstoßen und sich flächenhaft ausbreiten konnten. Abweichend von den W-NW-Fließrichtungen der unteren Basalte zeigen die beiden obersten Ströme SW-gerichtete Strukturen im unteren Yakima-Tal, parallel der Fließrichtung des alten Columbia River. Die zentrale, schüsseiförmige Absenkung des Lavaplateaus war zur Zeit der jüngsten Basalteruptionen nicht bedeutend.
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    URL: http://dx.doi.org/10.1007/BF01848776
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  • 6
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    Editorial (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 157-158 
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    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279600
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  • 7
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    Volatile emission during the eruption of Baitoushan Volcano (China/North Korea) ca. 969 AD (2000)
    Springer
    Bulletin of volcanology 61 (2000), S. 537-555 
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    ISSN: 1432-0819
    Keywords: Baitoushan Volcano ; Melt inclusions ; Peralkaline rhyolites ; Petrologic method ; Mass balance ; Volatile emission ; Climate impact
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: 3 [magma volume (DRE): 24 ± 5 km3]. The main phase (ca. 95 vol.%) is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites. The eruption column is estimated to have reached ca. 25 km and thus entered the stratosphere. A late phase (5 vol.%) is represented by trachyte emplaced chiefly as moderately welded ignimbrites. The comendites contain  ∼ 3, and the trachytes 10–20 vol.% phenocrysts, mainly anorthoclase, hedenbergite, and fayalite. Primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra, whereas those in phenocrysts in the trachytes are devitrified. The comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra. The mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method. The average H2O concentration of the comenditic matrix glass is 1.5 wt.% (probably largely secondary) and of the corresponding melt inclusions  ∼ 5.2 wt.%. Melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm. The comenditic matrix glasses are represented by a fluorine-rich (3992 ppm F) and fluorine-poor group (2431 ppm F), averaging 3853 ppm for chlorine. Only 20% of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of  ≥ 250 ppm S. The difference between pre- and post-eruptive concentration of H2O is at least 3.7 ± 0.6 wt.% H2O taking into consideration re-hydration of the matrix glass and possible leakage of melt inclusions. The difference between pre- and post-eruptive concentrations of the halogens amounts to 909 ± 90 ppm Cl, and 1863 ± 280 ppm and 302 ± 40 ppm F. The difference for S was estimated based on the average of the maximum S concentrations in the melt inclusions (455 ppm S) and the detection limit, resulting in 205 ± 40 ppm S. The calculated mass of volatiles injected into the atmosphere, based on the erupted magma volume and volatile data, is 1796 ± 453 megatons for H2O, 45 ± 10 megatons for chlorine, 42 ± 11 megatons for fluorine, and 2 ± 0.6 megatons for sulfur. The 969 ± 20 AD eruption of Baitoushan Volcano, one of the largest eruptions of the past 2000 years, is thought to have had a substantial but possibly short-lived effect on climate.
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    URL: http://dx.doi.org/10.1007/s004450050004
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  • 8
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    Englacial vs lacustrine origin of volcanic table mountains: evidence from iceland (1999)
    Springer
    Bulletin of volcanology 60 (1999), S. 335-354 
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    ISSN: 1432-0819
    Keywords: Key words Hyaloclastites ; Table mountains ; Subglacial volcanism ; Eruption mechanism ; Eruptive environment ; Iceland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar "hyaloclastite volcanoes" in the Icelandic rift zone contradict a rapid and continuous, "monogenetic", entirely subglacial evolution of most volcanoes studied. The majority of the exposed hyaloclastite deposits formed in large, stable lakes as indicated by widespread, up to 300-m-thick, continuous sections of deep water, shallow water and emergent facies. Salient features include extensively layered or bedded successions comprising mainly debris flow deposits, turbidites, base surge and fallout deposits consisting of texturally and compositionally variable, slightly altered hyaloclastites, as well as sheet and pillow lavas. In contrast, chaotic assemblages of coarser-grained, more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias, as well as scoria and lava are interpreted to have formed under sub- or englacial conditions in small, chimney-like ice cavities or ice-bound lakes. Irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted mainly from rapid changes of the eruptive environment due to repeated build-up and drainage of ice-bound lakes as well as the restricted space between the ice walls. We distinguish a "deep water" facies formed during high water levels of the lake, a hydroclastic shallow water and emergent facies (leakage of the lake or growth of the volcano above the water surface). Our model implies the temporary existence of large, stable lakes in Iceland probably formed by climatically induced ice melting. The highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods in changing environments characterized by contrasting volcanic and sedimentary processes.
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    URL: http://dx.doi.org/10.1007/s004450050237
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  • 9
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    Deposition of rheomorphic ignimbrite D (Mogán Formation), Gran Canaria, Canary Islands, Spain (1999)
    Springer
    Bulletin of volcanology 60 (1999), S. 465-485 
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    ISSN: 1432-0819
    Keywords: Key words Ignimbrite ; Strain and fabric analysis ; Lithification ; Cooling of vitrophyre ; Remobilization ; Deformation history ; Rheomorphic flow model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Rheomorphic ignimbrite D (13.4 Ma, Upper Mogán Formation on Gran Canaria), a multiple flow–single cooling unit, is divided into four major structural zones that differ in fabric and finite strain of deformed pyroclasts. Their structural characteristics indicate contrasting deformation mechanisms during rheomorphic flow. The zones are: (a) a basal zone (vitrophyre) with pure uniaxial flattening perpendicular to the foliation; (b) an overlying shear zone characterized by asymmetric fabrics and a significantly higher finite strain, with an ellipsoid geometry similar to stretched oblate bodies; (c) a central zone with a finite strain geometry similar to that of the underlying shear zone but without evidence of a rotational strain component; and (d) a slightly deformed to non-deformed top zone where the almost random orientation of subspherical pyroclasts suggests preservation of original, syn-depositional clast shapes. Rheomorphic flow in D is the result of syn- to post-depositional remobilization of a hot pyroclastic flow as shown by kinematic modeling based on: (a) the overall vertical structural zonation suggested by finite strain and fabric analysis; (b) the relation of shear sense to topography; (c) the interrelationship of the calculated vertical cooling progression at the base of the flow (formation of vitrophyre) and the related vertical changes in strain geometry; (d) the complex lithification history; and (e) the consequent mechanisms of deformational flow. Rheomorphic flow was caused by load pressure due to an increase in the vertical accumulation of pyroclastic material on a slope of generally 6–8°. We suggest that every level of newly deposited pyroclastic flow material of D first passed through a welding process that was dominated by compaction (pure flattening) before rheomorphic deformation started.
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    URL: http://dx.doi.org/10.1007/s004450050246
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  • 10
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    Evolution of parental magmas of Miocene shield basalts of Gran Canaria (Canary Islands): constraints from crystal, melt and fluid inclusions in minerals (1996)
    Springer
    Contributions to mineralogy and petrology 124 (1996), S. 422-435 
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    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Picritic units of the Miocene shield volcanics on Gran Canaria, Canary Islands, contain olivine and clinopyroxene phenocrysts with abundant primary melt, crystal and fluid inclusions. Composition and crystallization conditions of primary magmas in equilibrium with olivine Fo90-92 were inferred from high-temperature microthermometric quench experiments, low-temperature microthermometry of fluid inclusions and simulation of the reverse path of olivine fractional crystallization based on major element composition of melt inclusions. Primary magmas parental for the Miocene shield basalts range from transitional to alkaline picrites (14.7–19.3 wt% MgO, 43.2–45.7 wt% SiO2). Crystallization of these primary magmas is believed to have occurred over the temperature range 1490–1150° C at pressures ≈5 kbar producing olivine of Fo80.6-90.2, high-Ti chrome spinel [Mg/ (Mg+Fe2+)=0.32–0.56, Cr/(Cr+Al)=0.50–0.78, 2.52–8.58 wt% TiO2], and clinopyroxene [Mg/(Mg+Fe)=0.79–0.88, Wo44.1-45.3, En43.9-48.0, Fs6.8-11.0] which appeared on the liquidus together with olivine≈Fo86. Redox conditions evolved from intermediate between the QFM and WM buffers to late-stage conditions of NNO+1 to NNO+2. The primary magmas crystallized in the presence of an essentially pure CO2 fluid. The primary magmas originated at pressures 〉30 kbar and temperatures of 1500–1600° C, assuming equilibrium with mantle peridotite. This implies melting of the mantle source at a depth of ≈100 km within the garnet stability field followed by migration of melts into magma reservoirs located at the boundary between the upper mantle and lower crust. The temperatures and pressures of primary magma generation suggest that the Canarian plume originated in the lower mantle at depth ≈900 km that supports the plume concept of origin of the Canary Islands.
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    URL: http://dx.doi.org/10.1007/s004100050201
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