The pressure-temperature-time path of metasedimentary rocks during the Permian-Triassic collisional orogeny along the northwestern margin of the Gyeonggi Massif, South Korea

초록

Metasedimentary rocks consisting of layered metapelites, quartzites, and calc-silicates in the northwestern Gyeonggi Massif underwent metamorphism and deformation during the Permian-Triassic. As a result, they provide insights into a subduction- and exhumation-related collisional orogeny. However, the metamorphic pressure-temperature-time (P-T-t) paths of the metapelites and calc-silicates remain poorly constrained. Based on petrographic observations, P-T-X-CO2 (CO2/[CO2 + H2O]) modeling, and detrital zircon U-Pb ages, the estimated peak metamorphic P-T conditions of the garnet-biotite schist, kyanite-staurolite-garnet schist, and scapolite-diopside calc-silicate rocks were 7.7-9.2 kbar/560-575 degrees C, 7.0-9.0 kbar/625-670 degrees C, and 6.2-7.5 kbar/550-575 degrees C (at X-CO2 = 0.05), respectively, during the Middle Triassic (244-239 Ma). Subsequently, both the metapelites and calc-silicates underwent retrograde metamorphism at similar to 4 kbar and similar to 500 degrees C. The metapelites and calc-silicates in the northwestern Gyeonggi Massif underwent a clockwise P-T-t path under amphibolite- and greenschist-facies conditions, accompanied by shearing and folding during the Permian-Triassic collisional orogeny. This evolution is almost identical to that experienced by the Neoproterozoic-Devonian metasedimentary rocks in the Hongseong-Imjingang Belt.

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