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Andrew H. Allibone - One of the best experts on this subject based on the ideXlab platform.
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low pressure High Temperature Metamorphism of koettlitz group schists taylor valley and upper ferrar glacier area south victoria land antarctica
New Zealand Journal of Geology and Geophysics, 1992Co-Authors: Andrew H. AlliboneAbstract:Abstract Koettlitz Group metasediments of the Taylor Valley and upper Ferrar Glacier region contain rare horizons of garnet‐bearing and pelitic schist, together comprising 2% of the exposed outcrop. Pelitic schists containing the upper amphibolite facies assemblage quartz‐sillimanite‐cordierite‐biotite‐garnet‐K‐feldspar‐relict andalusite are restricted to The Defile in the lower Taylor Valley. In the upper Taylor Valley, muscovite‐K‐feldspar‐quartz‐plagioclase‐biotite assemblages occur adjacent to anatectic migmatites and quartz‐K‐feldspar‐garnet‐biotite‐plagioclase assemblages, with one sample containing sillimanite as inclusions in garnet At the confluence of the Darkowski and Ferrar Glaciers, quartz‐biotite‐plagioclase‐garnet schists contain rare quartz‐plagioclase‐cordierite leucosomes. Phase relations indicate peak metamorphic Temperatures and pressures of 700 ± 50°C and 4–5 kbars throughout the Taylor Valley and upper Ferrar Glacier area. The presence of relict andalusite in sample 56816 suggests a ...
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Low pressure/High Temperature Metamorphism of Koettlitz Group schists, Taylor Valley and upper Ferrar Glacier area, South Victoria Land, Antarctica
New Zealand Journal of Geology and Geophysics, 1992Co-Authors: Andrew H. AlliboneAbstract:Abstract Koettlitz Group metasediments of the Taylor Valley and upper Ferrar Glacier region contain rare horizons of garnet‐bearing and pelitic schist, together comprising 2% of the exposed outcrop. Pelitic schists containing the upper amphibolite facies assemblage quartz‐sillimanite‐cordierite‐biotite‐garnet‐K‐feldspar‐relict andalusite are restricted to The Defile in the lower Taylor Valley. In the upper Taylor Valley, muscovite‐K‐feldspar‐quartz‐plagioclase‐biotite assemblages occur adjacent to anatectic migmatites and quartz‐K‐feldspar‐garnet‐biotite‐plagioclase assemblages, with one sample containing sillimanite as inclusions in garnet At the confluence of the Darkowski and Ferrar Glaciers, quartz‐biotite‐plagioclase‐garnet schists contain rare quartz‐plagioclase‐cordierite leucosomes. Phase relations indicate peak metamorphic Temperatures and pressures of 700 ± 50°C and 4–5 kbars throughout the Taylor Valley and upper Ferrar Glacier area. The presence of relict andalusite in sample 56816 suggests a ...
Pierre Lanari - One of the best experts on this subject based on the ideXlab platform.
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Permian High-Temperature Metamorphism in the Western Alps (NW Italy)
International Journal of Earth Sciences, 2017Co-Authors: Barbara E. Kunz, Paola Manzotti, Brigitte Von Niederhäusern, Martin Engi, James Darling, Francesco Giuntoli, Pierre LanariAbstract:During the late Palaeozoic, lithospheric thinning in part of the Alpine realm caused High-Temperature low-to-medium pressure Metamorphism and partial melting in the lower crust. Permian Metamorphism and magmatism has extensively been recorded and dated in the Central, Eastern, and Southern Alps. However, Permian metamorphic ages in the Western Alps so far are constrained by very few and sparsely distributed data. The present study fills this gap. We present U/Pb ages of metamorphic zircon from several Adria-derived continental units now situated in the Western Alps, defining a range between 286 and 266 Ma. Trace element thermometry yields Temperatures of 580–890 °C from Ti-in-zircon and 630–850 °C from Zr-in-rutile for Permian metamorphic rims. These Temperature estimates, together with preserved mineral assemblages (garnet–prismatic sillimanite–biotite–plagioclase–quartz–K-feldspar–rutile), define pervasive upper-amphibolite to granulite facies conditions for Permian Metamorphism. U/Pb ages from this study are similar to Permian ages reported for the Ivrea Zone in the Southern Alps and Austroalpine units in the Central and Eastern Alps. Regional comparison across the former Adriatic and European margin reveals a complex pattern of ages reported from late Palaeozoic magmatic and metamorphic rocks (and relics thereof): two late Variscan age groups (~330 and ~300 Ma) are followed seamlessly by a broad range of Permian ages (300–250 Ma). The former are associated with late-orogenic collapse; in samples from this study these are weakly represented. Clearly, dominant is the Permian group, which is related to crustal thinning, hinting to a possible initiation of continental rifting along a passive margin.
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Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for High-Temperature Metamorphism in a forearc zone
Lithos, 2013Co-Authors: Nicolas Riel, Stephan Guillot, Etienne Jaillard, J.-e. Martelat, Jean-louis Paquette, Stephan Schwartz, P. Goncalves, G. Duclaux, N. Thebaud, Pierre LanariAbstract:In the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-Temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing Temperature from 650 to 700 °C. In the biotite dehydration melting zone, Temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak Metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3±2.1 Ma and 224.5±2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the High-pressure low-Temperature (HP-LT) Arenillas-Panupalí unit at 225.8±1.8 Ma. The association of High-Temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. Wepropose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere.
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Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for High-Temperature Metamorphism in a forearc zone
Lithos, 2013Co-Authors: Nicolas Riel, Stephan Guillot, Etienne Jaillard, J.-e. Martelat, Jean-louis Paquette, Stephan Schwartz, P. Goncalves, G. Duclaux, N. Thebaud, Pierre LanariAbstract:International audienceIn the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-Temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing Temperature from 650 to 700 °C. In the biotite dehydration melting zone, Temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak Metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3±2.1 Ma and 224.5±2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the High-pressure low-Temperature (HP-LT) Arenillas-Panupalí unit at 225.8±1.8 Ma. The association of High-Temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. Wepropose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere
M. L. Williams - One of the best experts on this subject based on the ideXlab platform.
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Timescales and significance of High-pressure, High-Temperature Metamorphism and mafic dike anatexis, Snowbird tectonic zone, Canada
Contributions to Mineralogy and Petrology, 2006Co-Authors: R. M. Flowers, S. A. Bowring, M. L. WilliamsAbstract:New geochronological, isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1.9 Ga High pressure, High Temperature Metamorphism along the Snowbird tectonic zone in northern Saskatchewan. High-precision U–Pb zircon dates reveal anatexis of Chipman mafic dikes at 1,896.2 ± 0.3 Ma during syntectonic and synmetamorphic intrusion at conditions of 1.0–1.2 GPa, >750°C. U–Pb zircon dates of 1,894–1,891 Ma for cross-cutting pegmatites place a lower bound on major Metamorphism and deformation at the currently exposed crustal levels. The persistence of elevated Temperatures for ~14 m.y. following peak conditions is implied by younger U–Pb titanite dates, and by Sm–Nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source. Limited melting of the host felsic gneiss at 1.9 Ga despite High Temperature is consistent with evidence for their previous dehydration by granulite facies Metamorphism in the Archean. Spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak Temperature and compositional variability. We correlate 1,896 Ma Chipman mafic dike emplacement and Metamorphism with substantial 1.9 Ga mafic magmatism over a minimum along-strike extent of 1,200 km of the Snowbird tectonic zone. This suggests a significant, continent-wide period of asthenospheric upwelling that induced incipient continental rifting. Extension was subsequently terminated by hinterland contraction associated with Trans-Hudson accretion and orogenesis. Little activity in the lower crust for ca. 650 m.y. prior to Proterozoic Metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1.9 Ga. This episode of destabilization contrasts with the record of long-term stability in most preserved cratons, and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents.
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Petrological and geochronological constraints on High pressure, High Temperature Metamorphism in the Snowbird tectonic zone, Canada
Journal of Metamorphic Geology, 2003Co-Authors: Julia A. Baldwin, S. A. Bowring, M. L. WilliamsAbstract:The upper deck of the East Athabasca mylonite triangle (EAmt), northern Saskatchewan, Canada, contains mafic granulites that have undergone High P-T Metamorphism at conditions ranging from 1.3 to 1.9 GPa, 890-960 � C. Coronitic textures in these mafic granulites indicate a near-isothermal decompression path to 0.9 GPa, 800 � C. The Godfrey granite occurs to the north adjacent to the upper deck High P-T domain. Well-preserved corona textures in the Godfrey granite constrain igneous crystallization and early Metamorphism in the intermediate-pressure granulite field (Opx + Pl) at 1.0 GPa, 775 � C followed by Metamorphism in the High pressure granulite field (Grt + Cpx + Pl) at 1.2 GPa, 860 � C. U-Pb geochronology of zircon in upper deck mafic granulite yields evidence for events at both c. 2.5 Ga and c. 1.9 Ga. The oldest zircon dates are interpreted to constrain a minimum age for crystallization or early Metamorphism of the protolith. A population of 1.9 Ga zircon in one mafic granulite is interpreted to constrain the timing of High P-T Metamorphism. Titanite from the mafic granulites yields dates ranging from 1900 to 1894 Ma, and is interpreted to have grown along the decompression path, but still above its closure Temperature, indicating cooling following the High P-T Metamorphism from c. 960-650 � C in 4-10 Myr. Zircon dates from the Godfrey granite indicate a minimum crystallization age of 2.61Ga, without any evidence for 1 .9 Ga overgrowths. The data indicate that an early granulite facies event occurred at c. 2.55-2.52 Ga in the lower crust (c. 1.0 GPa), but at 1.9 Ga the upper deck underwent High P-T Metamorphism, then decompressed to 0.9-1.0 GPa. Juxtaposition of the upper deck and Godfrey granite would have occurred after or been related to this decompression. In this model, the High P-T rocks are exhumed quickly following the High pressure Metamorphism. This type of Metamorphism is typically associated with collisional orogenesis, which has important implications for the Snowbird tectonic zone as a fundamental boundary in the Canadian Shield.
Nicolas Riel - One of the best experts on this subject based on the ideXlab platform.
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Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for High-Temperature Metamorphism in a forearc zone
Lithos, 2013Co-Authors: Nicolas Riel, Stephan Guillot, Etienne Jaillard, J.-e. Martelat, Jean-louis Paquette, Stephan Schwartz, P. Goncalves, G. Duclaux, N. Thebaud, Pierre LanariAbstract:In the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-Temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing Temperature from 650 to 700 °C. In the biotite dehydration melting zone, Temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak Metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3±2.1 Ma and 224.5±2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the High-pressure low-Temperature (HP-LT) Arenillas-Panupalí unit at 225.8±1.8 Ma. The association of High-Temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. Wepropose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere.
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Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for High-Temperature Metamorphism in a forearc zone
Lithos, 2013Co-Authors: Nicolas Riel, Stephan Guillot, Etienne Jaillard, J.-e. Martelat, Jean-louis Paquette, Stephan Schwartz, P. Goncalves, G. Duclaux, N. Thebaud, Pierre LanariAbstract:International audienceIn the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-Temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing Temperature from 650 to 700 °C. In the biotite dehydration melting zone, Temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak Metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3±2.1 Ma and 224.5±2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the High-pressure low-Temperature (HP-LT) Arenillas-Panupalí unit at 225.8±1.8 Ma. The association of High-Temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. Wepropose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere
Roger L. Gibson - One of the best experts on this subject based on the ideXlab platform.
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sequential syndeformational porphyroblast growth during hercynian low pressure High Temperature Metamorphism in the canigou massif pyrenees
Journal of Metamorphic Geology, 1992Co-Authors: Roger L. GibsonAbstract:The sequence of growth of garnet, staurolite and aluminosilicate in Fe-rich metapelitic rocks from the Canigou massif, Pyrenees, is established using evidence of inclusion, reaction and pseudomorphing textures between the different minerals, compositional zoning patterns in garnet and staurolite (that can be related to the KFMASH reaction grid), and the geometric relations between inclusion trails in the porphyroblasts and the matrix microstructures. The evidence indicates that garnet and staurolite commenced growth before aluminosilicate in all cases, even where all three are in textural equilibrium. Interpretation of the reaction textures between the porphyroblasts and of the compositional zoning in garnet and staurolite in terms of the KFMASH reaction grid indicates the importance of continuous reactions in the development of these phases. Some garnet and staurolite porphyroblasts underwent renewed growth during breakdown, producing rims enriched in Mn and Zn respectively. The presence of aluminosilicate in these assemblages (i.e. the absence of a clear andalusite-absent zone in the field) is attributed to a strong pressure-dependence for the aluminosilicate-producing reactions. Porphyroblast-matrix microstructural relations indicate that Hercynian Metamorphism in the massif was synchronous with the development of the regional subhorizontal foliation (S3).
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Sequential, syndeformational porphyroblast growth during Hercynian low-pressure/High-Temperature Metamorphism in the Canigou massif, Pyrenees
Journal of Metamorphic Geology, 1992Co-Authors: Roger L. GibsonAbstract:The sequence of growth of garnet, staurolite and aluminosilicate in Fe-rich metapelitic rocks from the Canigou massif, Pyrenees, is established using evidence of inclusion, reaction and pseudomorphing textures between the different minerals, compositional zoning patterns in garnet and staurolite (that can be related to the KFMASH reaction grid), and the geometric relations between inclusion trails in the porphyroblasts and the matrix microstructures. The evidence indicates that garnet and staurolite commenced growth before aluminosilicate in all cases, even where all three are in textural equilibrium. Interpretation of the reaction textures between the porphyroblasts and of the compositional zoning in garnet and staurolite in terms of the KFMASH reaction grid indicates the importance of continuous reactions in the development of these phases. Some garnet and staurolite porphyroblasts underwent renewed growth during breakdown, producing rims enriched in Mn and Zn respectively. The presence of aluminosilicate in these assemblages (i.e. the absence of a clear andalusite-absent zone in the field) is attributed to a strong pressure-dependence for the aluminosilicate-producing reactions. Porphyroblast-matrix microstructural relations indicate that Hercynian Metamorphism in the massif was synchronous with the development of the regional subhorizontal foliation (S3).