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Olivier Bachmann - One of the best experts on this subject based on the ideXlab platform.
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the role of magma mixing mingling and cumulate melting in the neapolitan yellow tuff caldera forming eruption campi flegrei southern italy
Contributions to Mineralogy and Petrology, 2018Co-Authors: Francesca Forni, Olivier Bachmann, Eleonora Petricca, Silvio Mollo, Gianfilippo De Astis, Monica PiochiAbstract:Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, ~ 39 ka and Neapolitan Yellow Tuff, NYT, ~ 15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor Sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., Sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a “mature” (i.e., Sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge.
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The role of magma mixing/mingling and cumulate melting in the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei, Southern Italy)
Contributions to Mineralogy and Petrology, 2018Co-Authors: Francesca Forni, Olivier Bachmann, Eleonora Petricca, Silvio Mollo, Gianfilippo De Astis, Monica PiochiAbstract:Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, ~ 39 ka and Neapolitan Yellow Tuff, NYT, ~ 15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor Sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., Sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a “mature” (i.e., Sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge.
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rhyolite generation prior to a yellowstone supereruption insights from the island park mount jackson rhyolite series
Journal of Petrology, 2017Co-Authors: Juliana Troch, Ben S Ellis, D F Mark, Ilya N Bindeman, Adam J R Kent, Marcel Guillong, Olivier BachmannAbstract:The Yellowstone volcanic field is one of the largest and best-studied centres of rhyolitic volcanism on Earth, yet it still contains little-studied periods of activity. Such an example is the Island Park–Mount Jackson series, which erupted between the Mesa Falls and Lava Creek caldera-forming events as a series of rhyolitic domes and lavas. Here we present the first detailed characterisation of these lavas and use our findings to provide a framework for rhyolite generation in Yellowstone between 1·3 and 0·6 Ma, as well as to assess whether magmatic evolution hints at a forthcoming super-eruption. These porphyritic (15–40% crystals) lavas contain mostly Sanidine and quartz with lesser amounts of plagioclase (consistent with equilibrium magmatic modelling via rhyolite-MELTS) and a complex assemblage of mafic minerals. Mineral compositions vary significantly between crystals in each unit, with larger ranges than expected from a single homogeneous population in equilibrium with its host melt. Oxygen isotopes in quartz and Sanidine indicate slight depletions (δ18Omagma of 5·0–6·1‰), suggesting some contribution by localised remelting of hydrothermally altered material in the area of the previous Mesa Falls Tuff-related caldera collapse. The preservation of variable O isotopic compositions in quartz requires crystal entrainment less than a few thousand years prior to eruption. Late entrainment of rhyolitic material is supported by the occurrence of subtly older Sanidines dated by single-grain 40Ar/39Ar geochronology. The eruption ages of the lavas show discrete clusters illustrating that extended quiescence (>100 kyr) in magmatic activity may be a recurring feature in Yellowstone volcanism. Ubiquitous crystal aggregates, dominated by plagioclase, pyroxene and Fe–Ti oxides, are interpreted as cumulates co-erupted with their extracted liquid. Identical crystal aggregates are found in both normal-δ18O and low-δ18O rocks from Yellowstone, indicating that common petrogenetic processes characterise both volcanic suites, including the late-stage extraction of melt from an incrementally built upper crustal mush zone.
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in defense of magnetite ilmenite thermometry in the bishop tuff and its implication for gradients in silicic magma reservoirs
American Mineralogist, 2016Co-Authors: Bernard W Evans, Olivier Bachmann, Wes Hildreth, Bruno ScailletAbstract:Despite claims to the contrary, the compositions of magnetite and ilmenite in the Bishop Tuff correctly record the changing conditions of T and f O2 in the magma reservoir. In relatively reduced (ΔNNO 1, e.g., Fish Canyon Tuff, Pinatubo), and the d ( a TiO2)/ dT slope can be negative. Biotite, FeTi-oxides, liquid, and possibly plagioclase largely maintained equilibrium in the Bishop Tuff magma (unlike the pyroxenes, and cores of quartz, Sanidine, and zircon) prior to and during a mixing event triggered by a deeper recharge, which, based on elemental diffusion profiles in minerals, took place at least several decades before eruption. Equilibrating phases and pumice compositions show evolving chemical variations that correlate well with mutually consistent temperatures based on the FeTi-oxides, Sanidine-plagioclase, and Δ18O quartz-magnetite pairs. Early Bishop Tuff (EBT) temperatures are lower (700 to ~780 °C) than temperatures (780 to >820 °C) registered in Late Bishop Tuff (LBT), the latter defined here not strictly stratigraphically, but by the presence of orthopyroxene and reverse-zoned rims on quartz and Sanidine. The claimed similarity in compositions, Zr-saturation temperatures and thermodynamically calculated temperatures (730–740 °C) between EBT and less evolved LBT reflect the use of glass inclusions in quartz cores in LBT that were inherited from the low-temperature rhyolitic part of the reservoir characteristic of the EBT. LBT temperatures as high as 820 °C, the preservation of orthopyroxene, and the presence of reverse-zoned minerals (quartz, Sanidine, zircons) are consistent with magma recharge at the base of the zoned reservoir, heating the cooler rhyolitic melt, partly remelting cumulate mush, and introducing enough CO2 (0.4–1.4 wt%, mostly contained in the exsolved fluid phase) to significantly lower H2O-activity in the system.
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implications of equilibrium and disequilibrium among crystal phases in the bishop tuff
American Mineralogist, 2013Co-Authors: Bernard W Evans, Olivier BachmannAbstract:Eruption of the Bishop Tuff magma preserved equilibrium of exchange components and element concentrations among magnetite, ilmenite, biotite, apatite, zircon, and liquid. Orthopyroxene and clinopyroxene were not in exchange equilibrium with the other MgFe-bearing phases, but they appear to have been in equilibrium among themselves. Internally consistent temperatures recorded by the FeTi-oxide, Ti-in-quartz, and Δ 18 O quartz-magnetite thermometers, coupled with evidence for magmatic corrosion of quartz and Sanidine, indicate that an initially low- T (≈700 °C), near-H 2 O-saturated, high-SiO 2 rhyolite magma was heated up to ≥800 °C and its crystal cargo partially melted by recharge of hotter melt from below. Oxygen fugacity and compositions of biotite, ilmenite, magnetite, and silicate liquid initially adjusted by internal rearrangement of components and conservation of oxygen. Partial melting of feldspars liberated Sr and Ba back into the melt. Mixing during recharge eventually re-introduced compatible elements (e.g., Mg, Ba, Sr) as well as foreign crystals of euhedral ortho- and clinopyroxene, which evidently never totally re-equilibrated with the rhyolite liquid. Introduction of CO 2 and accompanying reduction in the a H 2 O during recharge raised crystallization temperatures of quartz and Sanidine in the rhyolite sufficient to allow marginal regrowth of these phases with enhanced contents Ti, Ba, and Sr.
M Dantonio - One of the best experts on this subject based on the ideXlab platform.
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timescales of magmatic processes prior to the 4 7 ka agnano monte spina eruption campi flegrei caldera southern italy based on diffusion chronometry from Sanidine phenocrysts
Bulletin of Volcanology, 2017Co-Authors: Raffaella Silvia Iovine, Gerhard Worner, Lorenzo Fedele, Fabio Carmine Mazzeo, I Arienzo, A Cavallo, G Orsi, L Civetta, M DantonioAbstract:Barium diffusion chronometry applied to Sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (∼4.7 ka) constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera. Backscattered electron imaging and quantitative electron microprobe measurements on 50 Sanidine phenocrysts from representative pumice samples document core-to-rim compositional zoning. We focus on compositional breaks near the crystal rims that record magma mixing processes just prior to eruption. Diffusion times were modeled at a magmatic temperature of 930 °C using profiles based on quantitative BaO point analyses, X-ray scans, and grayscale swath profiles, yielding times ≤60 years between mixing and eruption. Such short timescales are consistent with volcanological and geochronological data that indicate that at least six eruptions occurred in the Agnano-San Vito area during few centuries before the Agnano-Monte Spina eruption. Thus, the short diffusion timescales are similar to time intervals between eruptions. Therefore, the rejuvenation time of magma residing in a shallow reservoir after influx of a new magma batch that triggered the eruption, and thus pre-eruption warning times, may be as short as years to a few decades at Campi Flegrei caldera.
Monica Piochi - One of the best experts on this subject based on the ideXlab platform.
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the role of magma mixing mingling and cumulate melting in the neapolitan yellow tuff caldera forming eruption campi flegrei southern italy
Contributions to Mineralogy and Petrology, 2018Co-Authors: Francesca Forni, Olivier Bachmann, Eleonora Petricca, Silvio Mollo, Gianfilippo De Astis, Monica PiochiAbstract:Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, ~ 39 ka and Neapolitan Yellow Tuff, NYT, ~ 15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor Sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., Sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a “mature” (i.e., Sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge.
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The role of magma mixing/mingling and cumulate melting in the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei, Southern Italy)
Contributions to Mineralogy and Petrology, 2018Co-Authors: Francesca Forni, Olivier Bachmann, Eleonora Petricca, Silvio Mollo, Gianfilippo De Astis, Monica PiochiAbstract:Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, ~ 39 ka and Neapolitan Yellow Tuff, NYT, ~ 15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor Sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., Sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a “mature” (i.e., Sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge.
L Civetta - One of the best experts on this subject based on the ideXlab platform.
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timescales of magmatic processes prior to the 4 7 ka agnano monte spina eruption campi flegrei caldera southern italy based on diffusion chronometry from Sanidine phenocrysts
Bulletin of Volcanology, 2017Co-Authors: Raffaella Silvia Iovine, Gerhard Worner, Lorenzo Fedele, Fabio Carmine Mazzeo, I Arienzo, A Cavallo, G Orsi, L Civetta, M DantonioAbstract:Barium diffusion chronometry applied to Sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (∼4.7 ka) constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera. Backscattered electron imaging and quantitative electron microprobe measurements on 50 Sanidine phenocrysts from representative pumice samples document core-to-rim compositional zoning. We focus on compositional breaks near the crystal rims that record magma mixing processes just prior to eruption. Diffusion times were modeled at a magmatic temperature of 930 °C using profiles based on quantitative BaO point analyses, X-ray scans, and grayscale swath profiles, yielding times ≤60 years between mixing and eruption. Such short timescales are consistent with volcanological and geochronological data that indicate that at least six eruptions occurred in the Agnano-San Vito area during few centuries before the Agnano-Monte Spina eruption. Thus, the short diffusion timescales are similar to time intervals between eruptions. Therefore, the rejuvenation time of magma residing in a shallow reservoir after influx of a new magma batch that triggered the eruption, and thus pre-eruption warning times, may be as short as years to a few decades at Campi Flegrei caldera.
Gerhard Worner - One of the best experts on this subject based on the ideXlab platform.
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timescales of magmatic processes prior to the 4 7 ka agnano monte spina eruption campi flegrei caldera southern italy based on diffusion chronometry from Sanidine phenocrysts
Bulletin of Volcanology, 2017Co-Authors: Raffaella Silvia Iovine, Gerhard Worner, Lorenzo Fedele, Fabio Carmine Mazzeo, I Arienzo, A Cavallo, G Orsi, L Civetta, M DantonioAbstract:Barium diffusion chronometry applied to Sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (∼4.7 ka) constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera. Backscattered electron imaging and quantitative electron microprobe measurements on 50 Sanidine phenocrysts from representative pumice samples document core-to-rim compositional zoning. We focus on compositional breaks near the crystal rims that record magma mixing processes just prior to eruption. Diffusion times were modeled at a magmatic temperature of 930 °C using profiles based on quantitative BaO point analyses, X-ray scans, and grayscale swath profiles, yielding times ≤60 years between mixing and eruption. Such short timescales are consistent with volcanological and geochronological data that indicate that at least six eruptions occurred in the Agnano-San Vito area during few centuries before the Agnano-Monte Spina eruption. Thus, the short diffusion timescales are similar to time intervals between eruptions. Therefore, the rejuvenation time of magma residing in a shallow reservoir after influx of a new magma batch that triggered the eruption, and thus pre-eruption warning times, may be as short as years to a few decades at Campi Flegrei caldera.
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structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in Sanidine a cathodoluminescence and electron microprobe study
Journal of Petrology, 2004Co-Authors: Catherine Ginibre, Gerhard Worner, Andreas KronzAbstract:Microtextures and zoning patterns in Sanidine phenocrysts from the phonolitic Laacher See Tephra (Germany) were investigated in order to constrain processes occurring in the magma chamber before eruption. The Laacher See Tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted, layered magma chamber. Samples from various levels in the deposit were investigated. We used a combination of textural studies (optical microscopy and back-scattered electron (BSE) imaging), electron microprobe (EMP) analysis of major, minor and trace elements (Ca, Na, K, Al, Si, Ba, Sr, Fe and Ti) and element mapping. The samples studied contain two feldspar phases and the ternary composition of the Sanidine thus constrains the temperature of crystallization, whereas its trace element content reflects the melt composition. The large diversity in textures found in the Sanidine crystals can be classified into three types: composite (C-type), pseudooscillatory (PO-type) and resorbed/patchy (R-type). Trace elementpoor, lamellar composite alkali feldspars (C-type) are found in samples inferred to represent the top and the middle part of the magma chamber. They grew as composite crystals from the melt at temperatures as low as 650 � C in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall. Pseudooscillatory zoning with resorption surfaces (PO-type) is found in Sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber. Repeated, large An variations (1–4 mol %) reflect temperature variations of 100–300 � Ca ssociated with changes in water content. Variations of minor and trace elements (Ba, Sr and Ti) in Sanidine, decoupled from the pseudo-oscillations of the major elements, reflect chemical changes in the melt, and are damped by chemicaldiffusioninthemelt.Bothmajorandminorelementvariations inPO-typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic, hotter melt. This may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber; however, the additional role of magma recharge may be required to explain the large temperature variations. Resorbed/patchy-zoned crystals (R-type), found mainly in samples corresponding to the middle part of the magma chamber, reflect early growth in a differentiated boundary layer, followed by resorption and overgrowthinthemainmagmabody.ManyoftheLaacherSeeSanidine crystals did not crystallize for the most part in the melt in which they were erupted. In the presence of preserved major and trace element zonation in the magma, this observation indicates crystal dispersion within a layered magma chamber without large-scale mixing and overturn.
