Structural style and metamorphic conditions of the Jinshajiang metamorphic belt: Nature of the Paleo-Jinshajiang orogenic belt in the eastern Tibetan Plateau

摘要: Abstract The Jinshajiang metamorphic belt is a Barrovian sequence distributed within the Suture Zone (JSZ), which was formed in thickened Paleo-Jinshajiang orogenic after closure of Ocean. We have identified three phases, M1, M2 and M3, corresponding to deformation stages D1, D2 D3, sequences. exhibits field gradient from chlorite biotite, garnet, staurolite–kyanite sillimanite grades. Inclusions garnet staurolite (chlorite, mica, quartz, feldspar, ilmenite graphite) indicate that M1 reflects greenschist facies metamorphism. Pervasive metamorphism dominant S1 schistosity sequence. Peak conditions for metapelites garnet–staurolite grade were ∼580 °C ∼0.65 GPa according petrogenetic grids. ∼635 °C 0.50 GPa ∼650 °C ∼0.61 GPa amphibolites grade. Greenschist retrograde metamorphism, followed deformation, top-down-to-southeast shear JSZ. D3 characterized by well-developed brittle faults with fault gouge breccia. Zircon grains an amphibolite sample cores igneous oscillatory zoning rims. However, rims are too narrow analyze. Laser ablation-inductively coupled plasma mass-spectrometry (LA-ICPMS) analyses zircons yielded crystallization age 242 Ma. 40Ar/39Ar dating white mica garnet-schist gave plateau 224 Ma. peak thus limited be between 242 suggest tectonic shift collision extension Permian Triassic belt.