The Experts below are selected from a list of 210 Experts worldwide ranked by ideXlab platform
Olivier Reubi - One of the best experts on this subject based on the ideXlab platform.
-
a dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc Andesites
Nature, 2009Co-Authors: Olivier Reubi, Jonathan D. BlundyAbstract:Olivier Reubi and Jon Blundy present an alternative view of Andesite petrogenesis and argue that true liquids of intermediate composition (59 to 66 wt% SiO2) are far less common in the subvolcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records. A large proportion of the magmas erupted at continental arc volcanoes are Andesites, which are regarded as a major component in the formation of continental crust — consequently, it is important to understand Andesite petrogenesis. Here, an alternative view of Andesite petrogenesis is presented, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments; this new view resolves several puzzling aspects of arc volcanism. Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust1. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in Andesite petrogenesis2 and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex Andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of Andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO2) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (≥66 wt% SiO2) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.
-
a dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc Andesites
Nature, 2009Co-Authors: Olivier Reubi, Jonathan D. BlundyAbstract:Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in Andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex Andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of Andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.
Yoshiyuki Tatsumi - One of the best experts on this subject based on the ideXlab platform.
-
geochemical modeling of dehydration and partial melting of subducting lithosphere toward a comprehensive understanding of high mg Andesite formation in the setouchi volcanic belt sw japan
Geochemistry Geophysics Geosystems, 2003Co-Authors: Yoshiyuki Tatsumi, Takeshi HanyuAbstract:[1] Possible mechanisms for the production of mantle-derived, high-Mg Andesite magmas, including (1) partial melting of mantle wedge peridotite by addition of aqueous fluids from the subducting lithosphere and (2) partial melting of the subducting sediments and altered oceanic crust, and subsequent melt-mantle interaction, were examined by geochemical formulation of dehydration, partial melting and melt-solid reactions. The modeling results demonstrate that both mechanisms can reasonably explain the incompatible trace element characteristics of high-Mg Andesites in the Setouchi volcanic belt, SW Japan. However, simple hydrous melting of mantle wedge peridotite cannot account for the Sr-Nd-Pb-Hf isotopic compositions of such Andesites. By contrast, the latter mechanism, which is consistent with thermal structures beneath the Setouchi volcanic belt, can well reproduce the isotopic signature of those high-Mg Andesites.
-
the petrology and geochemistry of calc alkaline Andesites on shodo shima island sw japan
Journal of Petrology, 2002Co-Authors: Yoshiyuki Tatsumi, T Nakashima, Yoshihiko TamuraAbstract:Petrographical and geochemical characteristics of calc-alkaline McLennan, 1995) that are produced at convergent plate boundaries and are characterized by lower FeO∗/MgO Andesites on Shodo-Shima Island, SW Japan, having bulk comratios than tholeiitic Andesites (Miyashiro, 1974). An positions largely identical to the continental crust, are presented. understanding of the origin of such orogenic, calc-alkaline The following petrographic observations suggest a role for magma Andesites is thus essential for comprehending not only mixing in producing such Andesite magmas: (1) two types of olivine the magma flux in the modern Earth but also the role phenocrysts and spinel inclusions, one with compositions identical of subduction-related magmatism in the evolution of the to those in high-Mg Andesites and the other identical to those in solid Earth. Since the pioneering work of Eichelberger basalts, are recognized in terms of Ni–Mg and Cr–Al–Fe (1975, 1978), Anderson (1976), Sakuyama (1979, 1981, relations, respectively; (2) the presence of orthopyroxene phenocrysts 1984), and Luhr & Carmichael (1980), the majority of with mg-number >90 suggests the contribution of an orthopyroxenepetrologists have considered mixing of mafic and felsic bearing high-Mg Andesite magma to production of calc-alkaline magmas to be one of the major mechanisms of generation Andesites; (3) reversely zoned pyroxene phenocrysts may not be in of calc-alkaline Andesites. Continental crust formation, equilibrium with Mg-rich olivine, suggesting the involvement of a however, may not be elucidated solely by such magma differentiated Andesite magma as an endmember component; (4) the mixing processes. The reasons for this are twofold. First, presence of very Fe-rich orthopyroxene phenocrysts indicates the calc-alkaline Andesite magmatism typifies continental arcs association of an orthopyroxene-bearing rhyolitic magma. Conat least on the modern Earth, suggesting that the contributions from the above at least five endmember magmas to the calctinental crust itself plays an important role in such Andesite alkaline Andesite genesis can also provide a reasonable explanation of formation, possibly as the source of the felsic endmember the Pb–Sr–Nd isotope compositions of such Andesites. component. Second, there is a slight but significant difference in MgO contents between the bulk continental crust and the typical calc-alkaline Andesite (e.g. Kelemen,
-
geochemical modeling of partial melting of subducting sediments and subsequent melt mantle interaction generation of high mg Andesites in the setouchi volcanic belt southwest japan
Geology, 2001Co-Authors: Yoshiyuki TatsumiAbstract:A possible mechanism for high-Mg Andesite formation, including melting of subducting sediments and subsequent melt-mantle interaction, was examined by geochemical formulation of partial melting and melt-solid reactions. The modeling results demonstrate that a sediment-derived melt produced at 1050 °C and 1.0 GPa changes its composition from rhyolitic to andesitic as it dissolves olivine and clinopyroxene and crystallizes orthopyroxene. The resulting reaction product possesses major and incompatible trace element compositions close to high-Mg Andesites in the Setouchi volcanic belt, southwest Japan.
Jonathan D. Blundy - One of the best experts on this subject based on the ideXlab platform.
-
a dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc Andesites
Nature, 2009Co-Authors: Olivier Reubi, Jonathan D. BlundyAbstract:Olivier Reubi and Jon Blundy present an alternative view of Andesite petrogenesis and argue that true liquids of intermediate composition (59 to 66 wt% SiO2) are far less common in the subvolcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records. A large proportion of the magmas erupted at continental arc volcanoes are Andesites, which are regarded as a major component in the formation of continental crust — consequently, it is important to understand Andesite petrogenesis. Here, an alternative view of Andesite petrogenesis is presented, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments; this new view resolves several puzzling aspects of arc volcanism. Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust1. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in Andesite petrogenesis2 and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex Andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of Andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO2) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (≥66 wt% SiO2) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.
-
a dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc Andesites
Nature, 2009Co-Authors: Olivier Reubi, Jonathan D. BlundyAbstract:Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in Andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex Andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of Andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.
Valery N. Kozhevnikov - One of the best experts on this subject based on the ideXlab platform.
-
an archean quartz arenite Andesite association in the eastern baltic shield russia implications for assemblage types and shield history
Precambrian Research, 2000Co-Authors: P C Thurston, Valery N. KozhevnikovAbstract:Abstract Shallow water sedimentary units are generally considered scarce in Archean greenstone belts. We describe an unusual quartz arenite-subaerial Andesite association within the Archean Hisovaara greenstone belt, a fragment of the Parandovo-Tikshozero belt within the Karelian craton of the Baltic Shield. The Hisovaara greenstone belt consists of several lithotectonic assemblages: (1) a komatiite-tholeiite assemblage>2803 Ma (based on ages of cross-cutting dikes); (2) an Andesite-quartz arenite assemblage cut by similar dikes; (3) an assemblage of coarse volcaniclastic rocks, and (4) an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks. The Andesite-quartz arenite assemblage (100 to ca. 750 m thick) has basal amygdaloidal fragmental Andesites overlain by massive Andesites, then amygdaloidal and plagioclase phyric Andesites. Unconformably overlying the Andesite is a unit of quartz-rich sandstones (6–40 m thick) dominated by quartz arenite extending several km along strike. At the north end, the quartz arenite succession consists of basal Andesite overlain by quartz arenite exhibiting hummocky cross-stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlying tholeiite/komatiite unit. At the south end, the succession is basal Andesite, regolith, cross-bedded quartz arenite, weathered Andesites, a second quartz arenite, argillite and then subaerial rhyolite. REE and HFSE geochemistry has been obtained on the rocks of the Andesite-quartz arenite assemblage. The quartz arenites contain low abundances and chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grain size, with pebbly units having higher abundance and more fractionated patterns. Combined major and trace element geochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistry of the quartz arenites. The Andesites display moderately fractionated spidergrams with negative anomalies at Ti, Ta and Nb typical of arc volcanism. The Andesite-quartz arenite assemblage represents accumulation of shallow water quartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerial at the southern end of the assemblage. However, at the north end, our evidence is interpreted as indicating subaerial andesitic volcanism, subsidence to a shallow marine basin which then deepens and rifts. Therefore the Hisovaara Andesite-quartz arenite assemblage provides a linkage in Archean greenstones between assemblages representing continental volcanism and a platform-to-rift setting. The presence of an erosional interval in>2.8 Ga greenstones suggests possible pre-2.7 Ga orogeny in the Baltic shield. The pre-2.7 Ga quartzrich sedimentation is similar in age to platformal assemblages in the pre-2.7 Ga North Caribou terrane of the Superior Province, Canada.
-
An Archean quartz arenite–Andesite association in the eastern Baltic Shield, Russia: implications for assemblage types and shield history
Precambrian Research, 2000Co-Authors: P C Thurston, Valery N. KozhevnikovAbstract:Abstract Shallow water sedimentary units are generally considered scarce in Archean greenstone belts. We describe an unusual quartz arenite-subaerial Andesite association within the Archean Hisovaara greenstone belt, a fragment of the Parandovo-Tikshozero belt within the Karelian craton of the Baltic Shield. The Hisovaara greenstone belt consists of several lithotectonic assemblages: (1) a komatiite-tholeiite assemblage>2803 Ma (based on ages of cross-cutting dikes); (2) an Andesite-quartz arenite assemblage cut by similar dikes; (3) an assemblage of coarse volcaniclastic rocks, and (4) an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks. The Andesite-quartz arenite assemblage (100 to ca. 750 m thick) has basal amygdaloidal fragmental Andesites overlain by massive Andesites, then amygdaloidal and plagioclase phyric Andesites. Unconformably overlying the Andesite is a unit of quartz-rich sandstones (6–40 m thick) dominated by quartz arenite extending several km along strike. At the north end, the quartz arenite succession consists of basal Andesite overlain by quartz arenite exhibiting hummocky cross-stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlying tholeiite/komatiite unit. At the south end, the succession is basal Andesite, regolith, cross-bedded quartz arenite, weathered Andesites, a second quartz arenite, argillite and then subaerial rhyolite. REE and HFSE geochemistry has been obtained on the rocks of the Andesite-quartz arenite assemblage. The quartz arenites contain low abundances and chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grain size, with pebbly units having higher abundance and more fractionated patterns. Combined major and trace element geochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistry of the quartz arenites. The Andesites display moderately fractionated spidergrams with negative anomalies at Ti, Ta and Nb typical of arc volcanism. The Andesite-quartz arenite assemblage represents accumulation of shallow water quartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerial at the southern end of the assemblage. However, at the north end, our evidence is interpreted as indicating subaerial andesitic volcanism, subsidence to a shallow marine basin which then deepens and rifts. Therefore the Hisovaara Andesite-quartz arenite assemblage provides a linkage in Archean greenstones between assemblages representing continental volcanism and a platform-to-rift setting. The presence of an erosional interval in>2.8 Ga greenstones suggests possible pre-2.7 Ga orogeny in the Baltic shield. The pre-2.7 Ga quartzrich sedimentation is similar in age to platformal assemblages in the pre-2.7 Ga North Caribou terrane of the Superior Province, Canada.
Mysore Santosh - One of the best experts on this subject based on the ideXlab platform.
-
paleoproterozoic crustal evolution in the east sarmatian orogen petrology geochemistry sr nd isotopes and zircon u pb geochronology of Andesites from the voronezh massif western russia
Lithos, 2016Co-Authors: R A Terentiev, K A Savko, Mysore SantoshAbstract:Abstract Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr–Nd isotopes, and zircon U–Pb geochronological data from Andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the Andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe–Ti oxides, we estimate a temperature range of 1179 to 1262 °С, pressures of 11.3 to 13.0 kbar, H2O content of 1–5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) Andesites. Our zircon U–Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for Andesite and dacite–porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic Andesite of the KG. The Andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive eNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two Andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in the case of KG Andesites in contrast to the higher degree of contamination with continental crustal lithologies and/or dacitic melts for the BA Andesites. Furthermore, the upper mantle source of the KG Andesites is inferred to be metasomatically enriched in comparison with the hydrous mantle source of the BA magmas. We propose post-collisional setting for both the high-Mg Andesites of the KG and normal Andesites of the BA, with magma generation through partial melting of enriched mantle sources.