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±4 Ma）的减压熔融和碰撞后燕山期（约130 Ma）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。

Multistage high-temperature metamorphism and partial melting of the North Dabie complex zone,central China,and their geodynamic processes and tectonic implications

The integrated investigations on eclogites from the Luotian dome in the North Dabie complex zone(NDZ), central China suggest that the NDZ wholly underwent high-T/UHP metamorphism and multistage exhumation history as a coherent slice,resulting in the common formation of peculiar multiple decompression textures and the extremely rare preservation of UHP metamorphic traces. The eclogites were strongly affected by multiple decompression and re-crystallization processes,and modified by multistage partial melting during exhumation,thus making the determination of peak metamorphic conditions particularly challenging. The recently calibrated Ti-in-zircon and Zr-in-rutile thermometers provide new tools to estimate the peak and post-peak temperatures. Multistage high-T(>900 ℃) conditions of the eclogites are indicated by garnet-omphacite thermometer and hypersthene＋quartz lamellae in clinopyroxene. It is also supported by high-T indicators including high Zr and Ti contents in metamorphically grown rutile and zircon,respectively. The temperatures estimated using zircons and rutile inclusions within zircon from the NDZ eclogites reveal a protracted HT metamorphic history with at least three metamorphic stages from UHP eclogite-facies to HP granulite-facies,occurred at significantly different pressures and ages,during Triassic continental subduction and subsequent exhumation. In addition,this study presents field,petrographical and geochemical evidences on multiple partial melting of the NDZ such as decompression melting at 207±4 Ma and heating melting at ～130 Ma. Therefore,the long-lived HT evolution coupled with slow cooling and partial melting may explain the rare preservation of UHP traces such as coesite and related minerals in the NDZ. These observations provide further insights into the petrogenesis and evolution of the NDZ,and processes of multi-slice exhumation,whereby the detachment and decoupling occurred at variable depths within the subducted continental crust and the multi-slices in the Dabie orogen were successively exhumed during the continental collision between the South China and North China Blocks.