北山古堡泉地区榴辉岩变质作用P-T-t轨迹及构造意义

P-T-t Path and Tectonic Implications of Gubaoquan Eclogite from Beishan Region

北山造山带南部古堡泉地区出露榴辉岩,对榴辉岩变质作用P-T-t轨迹的研究,有助于了解北山地区的构造演化历史。本文对古堡泉地区的榴辉岩开展了岩石学、矿物化学和锆石U-Pb年代学的研究。研究表明,榴辉岩原岩形成时代为860 Ma,进变质或近峰期变质时代为~465 Ma,岩石具有顺时针P-T-t轨迹,经历了较陡的升温升压过程后到达峰期高压榴辉岩相,峰期变质条件分别为P>22 kbar、T=660~700℃,之后经历了近等温降压过程。榴辉岩是大陆地壳快速俯冲形成,俯冲深度达80 km,之后又经历了快速的折返。

The P-T-t path of eclogite from the Gubaoquan area,south of Beishan Orogen,is used to track the tectonic history of the Beishan region.This paper presents novel petrology,mineral chemistry,and geochronology of Beishan eclogite.Zircon U-Pb data show that the protolith of eclogite formed at~860 Ma with a prograde or near-peak metamorphic age of~465 Ma.The P-T-t path of the eclogite was clockwise,with an early steep temperature and pressure rise process,subsequent eclogite-facies metamorphism with conditions of>22 kbar and 660−700℃,and a late isothermal retrograde decompression process.The eclogite was formed by rapid subduction of continental crust,with a depth of 80 km,followed by rapid exhumation.