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Arne P Willner - One of the best experts on this subject based on the ideXlab platform.

  • the geodynamics of collision of a microplate chilenia in devonian times deduced by the pressure temperature time evolution within part of a collisional belt guarguaraz complex w argentina
    Contributions to Mineralogy and Petrology, 2011
    Co-Authors: Axel Gerdes, Hans-joachim Massonne, Arne P Willner, Alexander Schmidt, Masafumi Sudo, Stuart N Thomson, Graciela I Vujovich
    Abstract:

    The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde garnet growth in metapelite and Metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s2-foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2σ) was determined from three four-point Lu–Hf mineral isochrones from metapelite and Metabasite samples and represents the time of collision. Peak pressure conditions are followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration of mineral compositions at the rims and also aided Ar diffusion. An 40Ar/39Ar plateau age of white mica at 353 ± 1 Ma (1σ) indicates the time of cooling below 350–400°C. These temperatures were attained at pressures of 0.2–0.3 GPa, indicative of an average exhumation rate of ≥1 mm/a for the period 390–353 Ma. Late hydrous influx at 0.1–0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica. At 284–295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm of 10–12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent–continent collisional setting.

  • conditions and timing of pumpellyite actinolite facies metamorphism in the early mesozoic frontal accretionary prism of the madre de dios archipelago latitude 50 20 s southern chile
    Journal of Petrology, 2009
    Co-Authors: Hans-joachim Massonne, Arne P Willner, Fernando A Sepulveda, Francisco Herve, Masafumi Sudo
    Abstract:

    The Madre de Dios Metamorphic Complex (MDMC) in southern Chile is a fossil frontal accretionary prism, which is mainly composed of metapsammopelitic rocks, intercalations of oceanic rocks (greenstone and metachert) and platform carbonate. We concentrated on the Metabasite to decipher the metamorphic evolution. This rock type contains assemblages of the pumpellyite-actinolite facies: pumpellyite +/- actinolite-chlorite +/- grandite +/- phengite +/- epidote-albite- quartz-titanite +/- K-feldspar +/- calcite. The metamorphic phases mainly grew by prograde hydration reactions during various episodes of restricted fluid influx. Fundamental phase relations of the pumpellyite-actinolite facies and adjacent facies were reproduced by pseudosections calculated for the system K2O-Na2O-CaO-FeO-O-2-MgO-Al2O3-TiO2-SiO2-H2O- CO2 at 200-400 degrees C and 1-9 kbar. The calculated stability fields of the metamorphic assemblages as realized in the MDMC Metabasite indicate highest metamorphic conditions restricted to 290-310 degrees C, 4-6 kbar for the MDMC, presumably as a result of the main fluid influx at these conditions. Nevertheless, earlier local equilibria are still preserved as a result of strongly kinetically controlled mineral reactions and a lack of recrystallization and compositional homogenization at thin-section scale. Hence, thermodynamic calculations of local multivariant mineral equilibria using the entire compositional variation of minerals in the MDMC show that the prograde PT path evolved from 4 +/- 1 kbar, 200-220 degrees C to 5 +/- 1 kbar, 290-330 degrees C. The prograde PT path reflects nearly horizontal particle paths after reaching the maximum depth typical for frontal accretionary prisms. Long residence at maximum depth resulted in thermal re-equilibration. Ar-40/Ar-39 spot ages were measured by in situ UV laser ablation of local phengite concentrations in a deformed metapelite at 233 center dot 2 +/- 1 center dot 8 Ma and in an undeformed Metabasite at 200 center dot 8 +/- 2 center dot 4 Ma. Whereas the first age represents an age of accretion, the latter age can be attributed to mineral growth either during a younger stage of accretion or during a retrograde stage. Ar-40/Ar-39 isotopic analyses of two further Metabasite samples reflect a prominent resetting of ages at 152 center dot 0 +/- 2 center dot 2 Ma and white mica growth during external fluid access triggered by either a local intrusion or a late Jurassic extensional episode.

Alfredo Caggianelli - One of the best experts on this subject based on the ideXlab platform.

  • The lawsonite-glaucophane blueschists of Elba Island (Italy)
    Lithos, 2019
    Co-Authors: Caterina Bianco, Gaston Godard, Alison M. Halton, Andrea Brogi, Domenico Liotta, Alfredo Caggianelli
    Abstract:

    Abstract Evidence for high-P blueschist-facies metamorphism was found in Metabasites embedded in calcschists of Eastern Elba Island (Northern Apennines, Italy). Study of immobile trace elements (REEs and HFSEs) in the Metabasites indicates an affinity with T- and E-MORBs, and they are interpreted as sill or dykes intruded in the western margin of the Adria continental plate. The minerals are heterogeneously distributed in the rock, constituting mafic and Ca-Al-rich microdomains inherited respectively from the magmatic pyroxene- and plagioclase-rich zones of the original doleritic rock. The peak pressure paragenesis consisted of lawsonite, aegirine-omphacite, glaucophane and chlorite. Former rhombic prisms of lawsonite have been replaced by pseudomorphic clinozoisite (0.1 mm in size) with inclusions of Ms. ± Ab ± Qz. The inclusions are preferentially oriented parallel to one of the diagonals of the basal rhombic sections, indicating that the two diagonals were not crystallographically equivalent. This implies that the protocrystals were orthorhombic prisms with {110} faces, which is the case of lawsonite. The different compositions shown by white mica and epidote in the pseudomorphs (muscovite and Fe3+-poor clinozoisite) and in the matrix (phengite and Fe3+-rich epidote) also suggest the former presence of Mg- and Fe-poor lawsonite in these rocks. Thermodynamic modelling, using the THERMOCALC software and dataset, suggests that Metabasites experienced a clockwise P-T path from the lawsonite-blueschist to epidote-blueschist subfacies, down to greenschist facies. The estimated peak pressure conditions are P ≥ 1.6 GPa and 450

Masafumi Sudo - One of the best experts on this subject based on the ideXlab platform.

  • the geodynamics of collision of a microplate chilenia in devonian times deduced by the pressure temperature time evolution within part of a collisional belt guarguaraz complex w argentina
    Contributions to Mineralogy and Petrology, 2011
    Co-Authors: Axel Gerdes, Hans-joachim Massonne, Arne P Willner, Alexander Schmidt, Masafumi Sudo, Stuart N Thomson, Graciela I Vujovich
    Abstract:

    The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde garnet growth in metapelite and Metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s2-foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2σ) was determined from three four-point Lu–Hf mineral isochrones from metapelite and Metabasite samples and represents the time of collision. Peak pressure conditions are followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration of mineral compositions at the rims and also aided Ar diffusion. An 40Ar/39Ar plateau age of white mica at 353 ± 1 Ma (1σ) indicates the time of cooling below 350–400°C. These temperatures were attained at pressures of 0.2–0.3 GPa, indicative of an average exhumation rate of ≥1 mm/a for the period 390–353 Ma. Late hydrous influx at 0.1–0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica. At 284–295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm of 10–12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent–continent collisional setting.

  • conditions and timing of pumpellyite actinolite facies metamorphism in the early mesozoic frontal accretionary prism of the madre de dios archipelago latitude 50 20 s southern chile
    Journal of Petrology, 2009
    Co-Authors: Hans-joachim Massonne, Arne P Willner, Fernando A Sepulveda, Francisco Herve, Masafumi Sudo
    Abstract:

    The Madre de Dios Metamorphic Complex (MDMC) in southern Chile is a fossil frontal accretionary prism, which is mainly composed of metapsammopelitic rocks, intercalations of oceanic rocks (greenstone and metachert) and platform carbonate. We concentrated on the Metabasite to decipher the metamorphic evolution. This rock type contains assemblages of the pumpellyite-actinolite facies: pumpellyite +/- actinolite-chlorite +/- grandite +/- phengite +/- epidote-albite- quartz-titanite +/- K-feldspar +/- calcite. The metamorphic phases mainly grew by prograde hydration reactions during various episodes of restricted fluid influx. Fundamental phase relations of the pumpellyite-actinolite facies and adjacent facies were reproduced by pseudosections calculated for the system K2O-Na2O-CaO-FeO-O-2-MgO-Al2O3-TiO2-SiO2-H2O- CO2 at 200-400 degrees C and 1-9 kbar. The calculated stability fields of the metamorphic assemblages as realized in the MDMC Metabasite indicate highest metamorphic conditions restricted to 290-310 degrees C, 4-6 kbar for the MDMC, presumably as a result of the main fluid influx at these conditions. Nevertheless, earlier local equilibria are still preserved as a result of strongly kinetically controlled mineral reactions and a lack of recrystallization and compositional homogenization at thin-section scale. Hence, thermodynamic calculations of local multivariant mineral equilibria using the entire compositional variation of minerals in the MDMC show that the prograde PT path evolved from 4 +/- 1 kbar, 200-220 degrees C to 5 +/- 1 kbar, 290-330 degrees C. The prograde PT path reflects nearly horizontal particle paths after reaching the maximum depth typical for frontal accretionary prisms. Long residence at maximum depth resulted in thermal re-equilibration. Ar-40/Ar-39 spot ages were measured by in situ UV laser ablation of local phengite concentrations in a deformed metapelite at 233 center dot 2 +/- 1 center dot 8 Ma and in an undeformed Metabasite at 200 center dot 8 +/- 2 center dot 4 Ma. Whereas the first age represents an age of accretion, the latter age can be attributed to mineral growth either during a younger stage of accretion or during a retrograde stage. Ar-40/Ar-39 isotopic analyses of two further Metabasite samples reflect a prominent resetting of ages at 152 center dot 0 +/- 2 center dot 2 Ma and white mica growth during external fluid access triggered by either a local intrusion or a late Jurassic extensional episode.

Sung Won Kim - One of the best experts on this subject based on the ideXlab platform.

  • petrochemistry of garnet bearing Metabasite in marble at shinri area in hongseong and its tectonic implication
    The Journal of the Petrological Society of Korea, 2010
    Co-Authors: Sung Won Kim, Heejae Koh
    Abstract:

    The Shinri area near the Yedang Lake, the eastern part of the Hongseong area in SW Gyeonggi Massif, consists of the Neoproterozoic Duckjeongri granodiorite-tonalite, mylonitized amphibole-bearing orthogneiss and impure marble with lens-shaped garnet-bearing Metabasites. In this paper, we report mineralogical and geochemical data of Neoproterozoic lens-shaped garnet-bearing Metabasites within marble of the Shinri area. The contents of garnet-bearing Metabasites in marble vary between ~46.98 and 51.17 wt%, and the + contents fall between ~1.95 and 2.85 wt%, similar to the tholeiitic sub-alkaline basaltic rocks. In the Zr/Y vs. Zr diagram, garnet-bearing Metabasites also plot in the subalkaline basaltic rocks. The chondrite-normalized REE patterns for Shinri garnet-bearing Metabasites show relatively flat patterns to that of chondrite. They show slight LREE-enriched and depleted patterns. The major and trace element data from lens-shaped garnet-bearing Metabasites in marble of the Shinri area suggest that these rocks were formed in within plate. In contrast, previous major and trace element data of high pressure type garnet-bearing Metabasites from the mafic-ultramafic complex in the Baekdong and Bibong areas suggest that these rocks were formed in a nascent arc to backarc spreading center within subduction zone setting. Based on mineral assemblage and mineral chemistry, P-T estimates for Shinri garnet-bearing Metabasites are 9.6-12.7 kb, for inclusions in the core, and 9.6-13.6 kb, for those in the rim. These P-T estimates are distinct from those of the Baekdong and Bibong garnet-bearing Metabasites with isothermal decompressional retrograde P-T path. In addition to Triassic tectonic activity previously reported in the Shinri area of Hongseong, the details of metamorphic history such as protolith age and Neo-Proterozoic metamorphic episode need to be solved.

  • first finding of eclogite facies metamorphic event in south korea and its correlation with the dabie sulu collision belt in china
    The Journal of Geology, 2005
    Co-Authors: Sung Won Kim, Seon Gyu Choi, Mingguo Zhai, Jinghui Guo, Sajeev Krishnan
    Abstract:

    Abstract Metabasite lenses occur within granitic gneiss at Bibong in the southwestern part of the Gyeonggi massif, South Korea. Bibong Metabasites experienced an initial eclogite facies metamorphism (17.0–20.9 kbar, 835°–860°C), which was succeeded by a granulite facies metamorphism (11.5–14.6 kbar, 830°–850°C) and finally overprinted by an amphibolite facies metamorphism (6.7–11.0 kbar, 570°–740°C). The Metabasites have Sm‐Nd internal isochron ages at 225–258 Ma, and the major elements of the Metabasites display an island arc affinity. The petrochemical and geochronological data suggest the southwestern part of the Gyeonggi massif as an extension of the Triassic Dabie‐Sulu collision belt in China.

  • metamorphic evolution of the baekdong Metabasite in the hongseong area south korea and its relationship with the sulu collision belt of china
    Gondwana Research, 2004
    Co-Authors: Chang Whanoh, Seon Gyu Choi, Suk Hwan Song, Sung Won Kim
    Abstract:

    Abstract Ultramafic rocks in the Hongseong area, southwest Gyeonggi massif, South Korea, occur as lenses within Precambrian granitic gneiss. The ultramafic bodies contain Metabasite boudins that have undergone at least three stages of metamorphism. The first stage mineral assemblage is garnet + augite (X Jd+Aeg = 0.06–0.11) + hornblende + plagioclase + rutile + titanite, and represents a transitional condition between the eclogite (EG), high-pressure granulite (HG) and amphibolite facies (AM). The second stage is characterized by an assemblage of garnet + augite (X Jd+Aeg = 0.01–0.06) + hornblende + plagioclase + titanite, representing the transitional condition between low-pressure granulite facies (LG) and AM. A third stage is identified by an AM assemblage of hornblende + plagioclase ± garnet in symplectites formed during garnet breakdown. The P-T conditions of the first, second, and third stages are 11.8–16.3 kb 690–780°C, 8.2–8.7 kb 660–820°C, and 4.0–6.3 kb 490–610°C, respectively. Cores and rims of two garnets in the country rock granitic gneiss give P-T estimates of 8.9–13.5 kb 640–815°C and 5.5–6.3 kb 575–680°C, indicating a retrograde P-T path similar to that of the Metabasite boudins. Ti-Zr-Y data indicate that the Baekdong Metabasites probably had an island arc paleotectonic setting. While it may be concluded that the Hongseong area in the Gyeonggi massif is a possible extension of the Sulu collision belt in China, Sm-Nd whole-rock - garnet isochron ages of the Baekdong Metabasites (268–297 Ma) are significantly older than the age of UHP metamorphism (208–245 Ma) in the Dabie-Sulu collision belt. Hence, collision between the North and South China blocks may have occurred earlier in the Korean peninsula than in China.

Metcalf, Mendeley K Data) - One of the best experts on this subject based on the ideXlab platform.