Multistage Metamorphic Evolution and P-T-t Path of High-T Eclogite from the North Dabie Complex Zone during Continental Subduction and Exhumation

Objective High-T eclogites from the North Dabie complex zone （NDZ）, central China underwent a complex metamorphic evolution involved in ultrahigh-pressure （UHP） and high- pressure eclogite-facies metamorphism, and subsequent granulite-facies overprinting and amphibolite-facies retrogression during the Mesozoic continental deep subduction and exhumation. As a consequence, the eclogites were strongly affected by multiple decompression and re-crystallization processes during exhumation. Some eclogites have even been wholly transformed to garnet granulite, or garnet amphibolite, or even garnet-absent amphibolite.

北大别的多阶段高温变质作用与部分熔融及其地球动力学过程和大地构造意义

北大别经历了三叠纪高温超高压变质作用和多阶段折返历史,因而榴辉岩中广泛发育多期减压结构,极少保留早期的超高压变质记录,这为它们不同变质阶段的温度条件估算带来了巨大困难。然而,目前流行的微量元素温度计为北大别榴辉岩的峰期及之后的退变质阶段温度的确定提供了可能性。根据锆石中Ti和金红石中Zr温度计,结合传统矿物对温度计的计算数据,获得了北大别榴辉岩中多阶段高温(>900℃)条件的数据,证明研究区经历了从超高压榴辉岩相→石英榴辉岩相→高压麻粒岩相阶段的高温变质过程。并且,北大别经历了折返初期(207±4Ma)的减压熔融和碰撞后燕山期(约130Ma)的加热熔融作用。长时间的高温变质作用与多期部分熔融也许正是北大别长期难以发现柯石英和有关超高压变质证据等的重要原因。因此,这些成果有助于甄别北大别的岩石成因和演化过程以及大别山多岩片差异折返模型的建立和完善。