北大别变质带高温变质作用的证据和时限:龚家岭地区刚玉片麻岩及其围岩的记录  

High‑temperature metamorphism and time limit in the North Dabie metamorphic belt:A record of corundum gneisses and its enclosing rocks in the Gongjialing area

作　　者：彭春蕾 石永红[1] 王娟[1] 侯振辉[2] 腊晓峰 刘晓宇 王智慧 Peng Chunlei;Shi Yonghong;Wang Juan;Hou Zhenhui;La Xiaofeng;Liu Xiaoyu;Wang Zhihui(School of Resource and Environment Engineering,Hefei University of Technology,Hefei 230009;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]中国科学技术大学,合肥230026

出　　处：《地质科学》2023年第3期810-836,共27页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目(编号:41972059)资助。

摘　　要：长期以来,大别造山带的超高压变质作用一直是研究的热点,而有关该造山带的高温或超高温变质作用的研究则相对有限,且主要集中于北大别变质带中残存的特征性岩石--榴辉岩和变基性岩,对于普遍发育的长英质和泥质片麻岩的变质属性和时限则极少涉及,制约了人们对该造山带形成与演化过程的充分解读。为此,本次研究以北大别龚家岭地区广泛出露的刚玉片麻岩和含辉石花岗闪长片麻岩、黑云角闪斜长片麻岩为研究对象,展开了详细的野外调查、岩相学、矿物化学分析、热力学评价和年代学研究。研究显示,这些片麻岩经历了麻粒岩相、角闪岩相和绿片岩相3个阶段的变质作用,温压条件分别为:(1)T=724℃~762℃和P=0.3~0.4 GPa;(2)T=586℃~595℃和P=0.3~0.4 GPa;(3)T=382℃~395℃和P=0.1~0.3 GPa,总体显示了近等压降温的特征。其中条件(1)基本达到了高温变质作用范畴,为北大别变质带中普遍发育的片麻岩的主期变质条件。锆石U-Pb定年结果显示,刚玉片麻岩具Group-Ⅰ和Group-Ⅱ两组锆石年龄,分别为709±19 Ma~677±19 Ma和207±2 Ma。含辉石花岗闪长片麻岩则记录了Group-Ⅰ、Group-Ⅱ和Group-Ⅲ等3组锆石年龄,分别为602±23 Ma~237±11 Ma、217±4 Ma和192±5 Ma。结合锆石CL图和Th/U比值分析,这两个片麻岩的Group-Ⅰ组锆石Th/U比均大于0.1(多数>0.4),均为岩浆继承锆石,该年龄反映了早期多岩浆事件。Group-Ⅱ组锆石的Th/U比均<0.1,显示了变质成因特征,其217~207 Ma年龄对应于主期麻粒岩相变质时限。Group-Ⅲ组锆石的Th/U比均<0.1,表现变质增生特征,其192 Ma年龄相当于角闪岩相变质时限。本次研究表明北大别变质带主体经历了浅层次的高温变质作用,缺乏高温超高压变质的“记录”。For a long time,UHP metamorphism in the Dabie orogenic belt has been a research hotspot,while the research on HT or UHT in this orogenic belt is relatively limited,and mainly concentrated on the characteristic rocks remaining in the North Dabie metamorphic belt eclogite and metabasic rocks.Thus the metamorphic properties and time limit of felsic and argillaceous gneiss are rarely lack of attention.It restricts people􀆳s full understanding of the formation and evolution process of the orogenic belt.In this study,we took corundum gneiss,pyroxene‑bearing granodiorite gneiss and biotite plagioclase gneiss widely exposed in Gongjialing area of North Dabie as the research object,carried out detailed field investigation,petrography,mineral chemical analysis,thermodynamic evaluation and chronology research.The research shows that these gneisses have undergone three metamorphism stages of granulite facies,amphibolite facies and greenschist facies and the P‑T conditions are①T=724℃~762℃and P=0.3~0.4 GPa;②T=586℃~595℃and P=0.3~0.4 GPa;③T=382℃~395℃and P=0.1~0.3 GPa respectively,which showing a characteristic of near isobaric cooling.Among them,the P‑T‑①basically reached the category of HT metamorphism,which is the main metamorphic condition of gneiss records widely developed in North Dabie metamorphism belt.Zircon U‑Pb dating shows that corundum gneiss have Group‑Ⅰand Group‑Ⅱages of 709±19 Ma~677±19 Ma and 207±2 Ma,respectively.However,pyroxene‑bearing granodiorite gneiss records zircon ages of Group‑Ⅰ,Group‑Ⅱand Group‑Ⅲ,which are 602±23 Ma~237±11 Ma,217±4 Ma and 192±5 Ma,respectively.Combined with the CL diagram of zircons and Th/U ratio analysis,The Th/U ratio of zircons of Group‑I group of the two gneisses is more than 0.1(most of them more than 0.4),which are magmatic inherited zircons,reflecting early multiple magmatic events.The Th/U ratio of zircons in Group‑Ⅱgroup is less than 0.1,which show metamorphic recrystallization characteristics,and their 217~20

关 键 词：北大别变质带 高温变质作用 刚玉片麻岩 主期变质条件 锆石U-PB定年 

分 类 号：P588.3[天文地球—岩石学] P597[天文地球—地质学]