东海大衢岛高压麻粒岩的发现及其构造指示意义  

Discovery of High Pressure Granulite in the Daqu Island,East China Sea and Its Tectonic Implications

作　　者：曹译文 周喜文[1] 刘建辉[1] Cao Yiwen;Zhou Xiwen;Liu Jianhui(Institute of Geology,CAGS,Beijing 100037,China;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《吉林大学学报（地球科学版）》2023年第2期475-490,共16页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项目(42072223);中国地质调查局项目(DD20201116,DD20211116)。

摘　　要：东海陆架作为华夏地块东部的重要块体,其成因问题一直存在争议,关键是对其变质基底情况认识不清。本文通过对东海陆架西部舟山群岛变质表壳岩开展调查与研究,在其中的大衢岛发现了具有“石榴石+单斜辉石+斜长石+石英”特征组合的高压麻粒岩,通过计算压力-温度视剖面图确定其峰期变质温压条件为860~890℃、(1.28~1.32)×10^(6)kPa,具有顺时针样式温压演化轨迹;峰期后经历近等温降压(ITD)过程,反映了加厚地壳的快速减薄过程,其成因很可能与造山作用有关。利用LA-ICP-MS锆石U-Pb定年,获得该高压麻粒岩的变质时代为(247.9±1.7)Ma,代表了峰期后麻粒岩地体抬升阶段年龄。变质表壳岩的碎屑锆石年龄介于963~339 Ma之间,既不属于新元古界陈蔡群,也不属于古元古界八都群,可能是一套独立的变质沉积建造。尽管其变质时代与华夏板块印支期退变榴辉岩相近,但变质过程迥异,可能不是同一造山带产物。The East China Sea shelf is an important part of the Cathaysia block,the origin of which is still controversial because of a lack of understanding of its metamorphic basement.Based on the investigation and study on the metamorphic supracrustal rocks exposed in the Zhoushan Islands in the west of the East China Sea shelf,a high-pressure granulite with a typical mineral assemblage of“garnet+clinopyroxene+plagioclase+quartz”was identified in the Daqu Island for the first time.By calculating the p-T pseudosection,the peak metamorphic p-T conditions were determined as 860-890℃/(1.28-1.32)×10^(6)kPa with a clock-wise p-T path.This clock-wise p-T path,characteristic of a post-peak isothermal decompression(ITD)is consistent with a thinning process of thickened continental crust which may be a result of the collision.Based on LA-ICP-MS zircon U-Pb dating,the metamorphic age of the high-pressure granulite was determined as(247.9±1.7)Ma,which likely represents the age of the uplift stage.The detrital zircon ages of the metamorphic supracrustal rocks range from 963 to 339 Ma,neither belonging to the Neoproterozoic Chencai Group nor the Paleoproterozoic Badu Group,and may be an independent set of metamorphic sedimentary formations.Although its metamorphic age is similar to that of the Indosinian retrograde eclogites in the Cathaysia block,the metamorphic process is quite different,and they may not be the products of the same orogenic belt.

关 键 词：高压麻粒岩 变质作用 锆石U-PB定年 大衢岛 东海陆架 

分 类 号：P588.3[天文地球—岩石学] P597.3[天文地球—地质学]