P-T-T path of metamorphism for the Julin Group and its geodynamical implications in Yuanmou

摘要

The metamorphic complex of the Julin Group occurs in the Yuanmou area of Yunnan Provine on the western margin of the Yangtze platform, and onnects with the kagdian meta- Morphic complex to the north. Based on the detailed petrographic observations and studies of Garnet growth zoning, a P-T-t path has been reconstructed for the staurolite-kyanite zone in the Julin Group. This path is characterized by (1) a counter-clockwise evolutional trend, (2) a quicker Increase of temperature than that of pressure in the initial prograde metamorphism, but slower Near the peak, then temperature and pressure simultaneously reaching the peak metamorphic Conditions, and (3) a slow near-isobaric cooling during the retrograde process.