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Scarlato P. - One of the best experts on this subject based on the ideXlab platform.
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Clinopyroxene and Titanomagnetite cation redistributions at Mt. Etna volcano (Sicily, Italy): Footprints of the final solidification history of lava fountains and lava flows
'Elsevier BV', 2015Co-Authors: Mollo S, Giacomoni, Pier Paolo, Andronico D, Scarlato P.Abstract:For a better understanding of the final solidification history of eruptions at Mt. Etna volcano (Sicily, Italy), we have investigated cation redistributions at the interface between sub-millimetre-sized clinopyroxene and Titanomagnetite crystal rims and coexisting melts. The studied products were scoria clasts from lava fountains and rock samples from pahoehoe and aa lava flows. Our data indicate that scoria clasts from lava fountaining were rapidly quenched at the contact with the atmosphere, preserving the original crystal textures and compositions inherited during magma dynamics within the plumbing system. Kinetics and energetics of crystallization were instantaneously frozen-in and post-eruptive effects on mineral chemistry were negligible. The near-equilibrium compositions of clinopyroxene and Titanomagnetite indicate that lava fountain episodes were supplied by high-temperature, H2O-rich magmas ascending with velocities of 0.01-0.31 m/s. In contrast, magmas feeding lava flow eruptions underwent a more complex solidification history where the final stage of the crystal growth was mostly influenced by volatile loss and heat dissipation at syn- and post-eruptive conditions. Due to kinetic effects associated with magma undercooling, clinopyroxenes and Titanomagnetites formed by crystal attachment and agglomeration mechanisms leading to intricate intergrowth textures. The final compositions of these minerals testify to closure temperatures and melt-water concentrations remarkably lower than those estimated for lava fountains. Kinetically-controlled cation redistributions at the crystal-melt interface suggest that the solidification of magma was driven by degassing and cooling processes proceeding from the uppermost part of the volcanic conduit to the surface. (C) 2015 Elsevier B.V. All rights reserved
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Clinopyroxene and Titanomagnetite cation redistributions at Mt. Etna volcano (Sicily, Italy). Footprints of the final solidification history of lava fountains and lava flows
'Elsevier BV', 2015Co-Authors: Mollo Silvio, Andronico D, Giacomoni P. P., Scarlato P.Abstract:For a better understanding of the final solidification history of eruptions at Mt. Etna volcano (Sicily, Italy), we have investigated cation redistributions at the interface between sub-millimetre-sized clinopyroxene and Titanomagnetite crystal rims and coexisting melts. The studied products were scoria clasts from lava fountains and rock samples from pahoehoe and aa lava flows. Our data indicate that scoria clasts from lava fountaining were rapidly quenched at the contact with the atmosphere, preserving the original crystal textures and compositions inherited during magma dynamics within the plumbing system. Kinetics and energetics of crystallization were instantaneously frozen-in and post-eruptive effects on mineral chemistry were negligible. The nearequilibrium compositions of clinopyroxene and Titanomagnetite indicate that lava fountain episodes were supplied by high-temperature, H2O-rich magmas ascending with velocities of 0.01–0.31 m/s. In contrast, magmas feeding lava flow eruptions underwent a more complex solidification history where the final stage of the crystal growth was mostly influenced by volatile loss and heat dissipation at syn- and post-eruptive conditions. Due to kinetic effects associated with magma undercooling, clinopyroxenes and Titanomagnetites formed by crystal attachment and agglomeration mechanisms leading to intricate intergrowth textures. The final compositions of these minerals testify to closure temperatures and melt–water concentrations remarkably lower than those estimated for lava fountains. Kinetically-controlled cation redistributions at the crystal–melt interface suggest that the solidification of magma was driven by degassing and cooling processes proceeding from the uppermost part of the volcanic conduit to the surface
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Clinopyroxene and Titanomagnetite cation redistributions at Mt. Etna volcano (Sicily, Italy): Footprints of the final solidification history of lava fountains and lava flows
'Elsevier BV', 2015Co-Authors: Mollo S, Andronico D, Giacomoni P. P., Scarlato P.Abstract:For a better understanding of the final solidification history of eruptions at Mt. Etna volcano (Sicily, Italy), we have investigated cation redistributions at the interface between sub-millimetre-sized clinopyroxene and Titanomagnetite crystal rims and coexisting melts. The studied products were scoria clasts from lava fountains and rock samples from pahoehoe and aa lava flows. Our data indicate that scoria clasts from lava fountaining were rapidly quenched at the contact with the atmosphere, preserving the original crystal textures and compositions inherited during magma dynamics within the plumbing system. Kinetics and energetics of crystallization were instantaneously frozen-in and post-eruptive effects on mineral chemistry were negligible. The nearequilibrium compositions of clinopyroxene and Titanomagnetite indicate that lava fountain episodes were supplied by high-temperature, H2O-rich magmas ascending with velocities of 0.01–0.31 m/s. In contrast, magmas feeding lava flow eruptions underwent a more complex solidification history where the final stage of the crystal growth was mostly influenced by volatile loss and heat dissipation at syn- and post-eruptive conditions. Due to kinetic effects associated with magma undercooling, clinopyroxenes and Titanomagnetites formed by crystal attachment and agglomeration mechanisms leading to intricate intergrowth textures. The final compositions of these minerals testify to closure temperatures and melt–water concentrations remarkably lower than those estimated for lava fountains. Kinetically-controlled cation redistributions at the crystal–melt interface suggest that the solidification of magma was driven by degassing and cooling processes proceeding from the uppermost part of the volcanic conduit to the surface.European Observing System Infrastructure Project (EPOS) Grant agreement no. 262229Published45–543V. Dinamiche e scenari eruttiviJCR Journalreserve
Hiroki Kamata - One of the best experts on this subject based on the ideXlab platform.
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magnetic petrology of the 1991 1995 dacite lava of unzen volcano japan degree of oxidation and implications for the growth of lava domes
Journal of Volcanology and Geothermal Research, 2007Co-Authors: Takeshi Saito, Naoto Ishikawa, Hiroki KamataAbstract:Abstract To understand the oxidation state and process of oxidation of lava domes, we carried out magnetic petrological analyses of lava samples obtained from domes and block-and-ash-flow deposits associated with the 1991–1995 eruption of Unzen volcano, Japan. As a result, we recognize three different types of magnetic petrology, each related to deuteric high-temperature oxidation during initial cooling. Type A oxides are characterized by homogenous Titanomagnetite and titanohematite, indicating a low oxidation state and high Titanomagnetite concentrations. Type B oxides are weakly exsolved and contain titanohematite laths and rutile lenses, indicating a higher oxidation state. Type C oxides, which represent the highest oxidation state, are completely exsolved and composed of Ti-poor Titanomagnetite, titanohematite, rutile, and pseudobrookite, indicating high hematite concentrations. Some grains in Types A and B show indications of reduction, which was related to interaction with volcanic gases subsequent to high-temperature oxidation. In terms of geological occurrence, the oxidation processes probably differed for endogenous and exogenous domes. Endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome: samples from the surface are strongly oxidized and classified as Type C, while the inner part is unoxidized and classified as Type A. Exogenous dome lavas are unoxidized and assigned to Type A. Some samples show signs of reduction, which may have occurred around fumaroles. We propose that location within the dome and the process of dome growth are the factors that control oxidation.
Takeshi Saito - One of the best experts on this subject based on the ideXlab platform.
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magnetic petrology of the 1991 1995 dacite lava of unzen volcano japan degree of oxidation and implications for the growth of lava domes
Journal of Volcanology and Geothermal Research, 2007Co-Authors: Takeshi Saito, Naoto Ishikawa, Hiroki KamataAbstract:Abstract To understand the oxidation state and process of oxidation of lava domes, we carried out magnetic petrological analyses of lava samples obtained from domes and block-and-ash-flow deposits associated with the 1991–1995 eruption of Unzen volcano, Japan. As a result, we recognize three different types of magnetic petrology, each related to deuteric high-temperature oxidation during initial cooling. Type A oxides are characterized by homogenous Titanomagnetite and titanohematite, indicating a low oxidation state and high Titanomagnetite concentrations. Type B oxides are weakly exsolved and contain titanohematite laths and rutile lenses, indicating a higher oxidation state. Type C oxides, which represent the highest oxidation state, are completely exsolved and composed of Ti-poor Titanomagnetite, titanohematite, rutile, and pseudobrookite, indicating high hematite concentrations. Some grains in Types A and B show indications of reduction, which was related to interaction with volcanic gases subsequent to high-temperature oxidation. In terms of geological occurrence, the oxidation processes probably differed for endogenous and exogenous domes. Endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome: samples from the surface are strongly oxidized and classified as Type C, while the inner part is unoxidized and classified as Type A. Exogenous dome lavas are unoxidized and assigned to Type A. Some samples show signs of reduction, which may have occurred around fumaroles. We propose that location within the dome and the process of dome growth are the factors that control oxidation.
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magnetic petrology and its implication for magma mixing of the 1991 1995 dacite at unzen volcano japan
Earth Planets and Space, 2007Co-Authors: Takeshi Saito, Naoto IshikawaAbstract:Magnetic petrologic analyses were carried out on lava samples from the lava dome of the 1991–1995 eruption of Unzen volcano, Japan. As a result, three kinds of Titanomagnetites with different Curie temperatures were identified and the difference between the samples from the lava dome which grew exogenously and endogenously were revealed. Titanomagnetites with Tc of 460–500°C and 380–400°C are the predominant magnetic minerals. In addition, a Titanomagnetite with Tc of ∼540°C, but in low concentration, is also present. The exogenous lava samples contain more Titanomagnetite with Tc of 380–400°C and less microphenocrysts of Titanomagnetites than the endogenous samples. The equilibrium temperature of 900–920°C, 780–820°C and 720°C is estimated from Titanomagnetite with Tc of 380–400°C, 460–500°C and 540°C, respectively. We suggest that these titanomag-netites are probably formed by magma mixing and eruption processes. Titanomagnetite with Tc of 460–500°C was derived from felsic magma (780–820°C) in a shallow chamber. Titanomagnetite with Tc of 380–400°C was produced from the mixed magma (900–920°C). After being squeezed out from the reservoir, a small amount of Titanomagnetite with Tc of ∼540°C was crystallized.
Mei-fu Zhou - One of the best experts on this subject based on the ideXlab platform.
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Disequilibrium iron isotopic fractionation during the high-temperature magmatic differentiation of the Baima Fe–Ti oxide-bearing mafic intrusion, SW China
Earth and Planetary Science Letters, 2014Co-Authors: Ping-ping Liu, Mei-fu Zhou, Béatrice Luais, Damien Cividini, Claire Rollion-bardAbstract:Iron isotopic compositions of olivine, clinopyroxene and Titanomagnetite of the Baima Fe–Ti oxide-bearing layered mafic intrusion, SW China, are used to investigate Fe isotopic fractionation during the formation of the Fe–Ti oxide ore bodies and to constrain the origin of silicate minerals and Fe–Ti oxides. The Baima intrusion comprises the Lower Zone of interlayered troctolite, clinopyroxenite and oxide ores and the Upper Zone of gabbros. Significant differences of Fe isotope values between olivine (δ56 Fe = -0.01to + 0.11‰), clinopyroxene (δ56 Fe = + 0.11to + 0.22‰), and Titanomagnetite (δ56 Fe = + 0.20to + 0.31‰) were observed in rocks and ores of the Lower Zone. Iron isotopic fractionation between olivine and clinopyroxene, olivine and Titanomagnetite and clinopyroxene and Titanomagnetite exhibits large variations of 0.06‰ to 0.22‰, 0.12‰ to 0.27‰, and 0.00‰ to 0.20‰, respectively, suggesting disequilibrium fractionation. This disequilibrium cannot be explained by thermal or chemical gradient-induced kinetic fractionation or by possible subsolidus exsolution of granular ilmenite from Titanomagnetite. Instead, it could be attributed to crystallization of silicates and Titanomagnetite from two immiscible Si-rich and Fe-rich liquids. Continuous segregation of the Fe-rich liquid changed the Fe isotopic composition of the Si-rich liquid and thus the Fe isotopic compositions of olivine and clinopyroxene crystallized from it, resulting in disequilibrium Fe isotopic fractionation between them. The effect of oxygen fugacity on the crystallization order of Titanomagnetite and ilmenite from the Fe-rich melts, on the other hand, gave rise to the disequilibrium Fe isotope fractionation between Titanomagnetite and olivine/clinopyroxene.
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interaction of magma with sedimentary wall rock and magnetite ore genesis in the panzhihua mafic intrusion sw china
Mineralium Deposita, 2008Co-Authors: Clement Ganino, Mei-fu Zhou, Nicholas T Arndt, Fabrice Gaillard, Catherine ChauvelAbstract:In SW China, several large magmatic Fe-Ti-V oxide ore deposits are hosted by gabbroic intrusions associated with the Emeishan flood basalts. The Panzhihua gabbroic intrusion, a little deformed sill that contains a large Titanomagnetite deposit at its base, concordantly intrudes late- Proterozoic dolostones. Mineralogical and chemical studies of the contact aureole in the footwall dolostones demonstrates that the metamorphism was largely isochemical, but for the release of large quantities of CO2 as the rocks were converted to marble and skarns during intrusion of the gabbroic magma. Petrological modelling of the crystallization of the intrusion, using H2O-poor Emeishan basalt as parent magma, shows that under normal conditions Fe-Ti-oxides crystallize at a late stage, after the crystallization of abundant olivine, clinopyroxene and plagioclase. In order for Titanomagnetite to separate efficiently to form the ore deposit, this mineral must have crystallized earlier and close to the liquidus. We propose that CO2-rich fluids released during decarbonatization of sedimentary floor rocks passed up through the magma. Redox equilibria calculations show that when magma with the composition of Emeishan basalt is fluxed by a CO2-rich gas phase, its equilibrium oxygen fugacity (fO2) increases from FMQ to FMQ+1.5. From experimental constraints on magnetite saturation in basaltic magma under controlled fO2, such an oxidizing event would allow magnetite to crystallize near to the liquidus, leading to the formation of the deposit.
Naoto Ishikawa - One of the best experts on this subject based on the ideXlab platform.
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magnetic petrology of the 1991 1995 dacite lava of unzen volcano japan degree of oxidation and implications for the growth of lava domes
Journal of Volcanology and Geothermal Research, 2007Co-Authors: Takeshi Saito, Naoto Ishikawa, Hiroki KamataAbstract:Abstract To understand the oxidation state and process of oxidation of lava domes, we carried out magnetic petrological analyses of lava samples obtained from domes and block-and-ash-flow deposits associated with the 1991–1995 eruption of Unzen volcano, Japan. As a result, we recognize three different types of magnetic petrology, each related to deuteric high-temperature oxidation during initial cooling. Type A oxides are characterized by homogenous Titanomagnetite and titanohematite, indicating a low oxidation state and high Titanomagnetite concentrations. Type B oxides are weakly exsolved and contain titanohematite laths and rutile lenses, indicating a higher oxidation state. Type C oxides, which represent the highest oxidation state, are completely exsolved and composed of Ti-poor Titanomagnetite, titanohematite, rutile, and pseudobrookite, indicating high hematite concentrations. Some grains in Types A and B show indications of reduction, which was related to interaction with volcanic gases subsequent to high-temperature oxidation. In terms of geological occurrence, the oxidation processes probably differed for endogenous and exogenous domes. Endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome: samples from the surface are strongly oxidized and classified as Type C, while the inner part is unoxidized and classified as Type A. Exogenous dome lavas are unoxidized and assigned to Type A. Some samples show signs of reduction, which may have occurred around fumaroles. We propose that location within the dome and the process of dome growth are the factors that control oxidation.
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magnetic petrology and its implication for magma mixing of the 1991 1995 dacite at unzen volcano japan
Earth Planets and Space, 2007Co-Authors: Takeshi Saito, Naoto IshikawaAbstract:Magnetic petrologic analyses were carried out on lava samples from the lava dome of the 1991–1995 eruption of Unzen volcano, Japan. As a result, three kinds of Titanomagnetites with different Curie temperatures were identified and the difference between the samples from the lava dome which grew exogenously and endogenously were revealed. Titanomagnetites with Tc of 460–500°C and 380–400°C are the predominant magnetic minerals. In addition, a Titanomagnetite with Tc of ∼540°C, but in low concentration, is also present. The exogenous lava samples contain more Titanomagnetite with Tc of 380–400°C and less microphenocrysts of Titanomagnetites than the endogenous samples. The equilibrium temperature of 900–920°C, 780–820°C and 720°C is estimated from Titanomagnetite with Tc of 380–400°C, 460–500°C and 540°C, respectively. We suggest that these titanomag-netites are probably formed by magma mixing and eruption processes. Titanomagnetite with Tc of 460–500°C was derived from felsic magma (780–820°C) in a shallow chamber. Titanomagnetite with Tc of 380–400°C was produced from the mixed magma (900–920°C). After being squeezed out from the reservoir, a small amount of Titanomagnetite with Tc of ∼540°C was crystallized.
