Metamorphic P-T conditions and ages of garnet-biotite schists in the Dahongshan Group from the southwestern Yangtze Block

摘要

The Dahongshan Group, situated at the southwestern margin of the Yangtze Block, represents a geological unit characterized by relatively high-grade metamorphism in the region. This paper investigates the garnet-biotite schist from the Laochanghe Formation of the Dahongshan Group, employing an integrated approach that includes petrological analysis, phase equilibrium modeling, and zircon U-Pb dating. The schist is mainly composed of garnet, biotite, plagioclase, quartz, rutile, and ilmenite. Phase equilibrium modeling revealed the peak metamorphic conditions of 8-9 kbar and 635-675 degrees C. By further integrating the prograde metamorphic profile of garnet and geothermobarometric results, a clockwise P-T metamorphic evolution path is constructed, which includes an increase in temperature and pressure during the prograde stage. LA-ICP-MS zircon U-Pb dating and zircon Ti thermometry constrains the post-peak metamorphic age of 831.2 +/- 7.2 Ma. Integrated with previously reported results, it is revealed that the southwestern margin of the Yangtze Block experienced a large-scale regional metamorphism during the Neoproterozoic (890-750 Ma), which is related to the collisional orogenic process. This may be associated with the late-stage assembly of the Rodinia supercontinent or with local compression and subduction processes during the breakup of the Rodinia supercontinent.