Metamorphism and geochronology of high-pressure mafic granulites (retrograded eclogites?) in East Cathaysia terrane of South China: Implications for Mesozoic tectonic evolution

作者：Xia, Yanfei; Yin, Changqing^*; Lin, Shoufa; Zhang, Jian; Qian, Jiahui; Wu, Shangjing; Liu, Jingna

来源：Geological Society of America Bulletin, 2022, 134(3-4): 832-848.

DOI：10.1130/B36025.1

• U-PB GEOCHRONOLOGY
• MINERAL EQUILIBRIA CALCULATIONS
• PARTIAL MELTING EQUILIBRIA
• TEMPERATURE TIME PATHS
• FLAT-SLAB SUBDUCTION
• ND-HF ISOTOPES
• SOUTHWESTERN ZHEJIANG
• ZIRCON GEOCHRONOLOGY
• REACTION TEXTURES
• REGIONAL METAMORPHISM

High-pressure mafic granulites (retrograded eclogites?) were discovered as minor lenses enclosed in garnet-kyanite-cordierite gneiss from the Badu Complex of the East Cathaysia terrane in South China. These rocks consist mainly of garnet, clinopyroxene, hornblende, quartz, and rutile/ilmenite with or without omphacite pseudomorphs that are indicated by clinopyroxene + sodic plagioclase symplectic intergrowths. Mineral textures and reaction relationships suggest three metamorphic stages: (1) an eclogitefacies stage (M-1) characterized by the mineral assemblage of garnet + clinopyroxene (omphacite) + hornblende + rutile + quartz; (2) a high-pressure granulite-facies (M-2) stage mainly represented by garnet + clinopyroxene + plagioclase + hornblende + rutile + quartz in the matrix; and (3) an amphibolite retrograde stage (M-3) defined by hornblende + plagioclase + ilmenite + quartz symplectites surrounding garnet porphyroblasts. Conventional geothermometers and geobarometers in combination with phase equilibria modeling constrain metamorphic P-T conditions of 15.8-18.2 kbar/625-690 degrees C (M-1), 11.8-14.5 kbar/788-806 degrees C (M-2), and 5.4-6.4 kbar/613-668 degrees C (M-3), respectively. Two-staged decompression processes are defined after the peak pressure, which suggests a two-staged exhumation of these deeply buried rocks. Secondary ion mass spectrometry (SIMS) zir con U-Pb dating and trace element analysis show that the high-pressure metamorphism occurred at 240-244 Ma. Complete early Mesozoic orogenic processes characterized by initial subduction and/or crustal thickening and subsequent exhumation followed by rapid uplift are reconstructed for this part of the East Cathaysia terrane, South China.

• 单位
  中山大学; 桂林理工大学; 1