西大别红安地区榴辉岩原岩年龄及Hf同位素组成:对扬子板块北缘中元古代晚期地壳生长作用的显示  

PROTOLITH AGE AND HF ISOTOPE COMPOSITIONS OF ECLOGITE IN HONG’AN AREA,WESTERN DABIE MOUNTAINS:IMPLICATION FOR CRUSTAL GROWTH AT THE LATE MESOPROTEROZOIC IN THE NORTH MARGIN OF THE YANGTZE BLOCK

作　　者：汪晶[1] 吴元保[1,2] 彭敏[1] 焦文放[1] 刘小驰[1] 

机构地区：[1]地质过程与矿产资源国家重点实验室,中国地质大学（武汉）地球科学学院,湖北武汉430074 [2]大陆动力学国家重点实验室,西北大学地质系,陕西西安710069

出　　处：《矿物岩石》2009年第2期108-114,共7页Mineralogy and Petrology

基　　金：国家自然科学基金(批准号:40772042,90714010和40521001);教育部项目(IRT0441,B07039和NCET-06-0659);西北大学大陆动力学国家重点实验室和中国地质大学地质过程与矿产资源国家重点实验室开放基金

摘　　要：西大别红安地区榴辉岩样品的锆石CL图像显示这些锆石为经历了后期变质重结晶改造的岩浆锆石；挑选锆石内部无变质重结晶区域进行微量元素测试，结果表明其具有典型的岩浆锆石微量元素特点；LA—ICPMS锆石U—Pb年龄测定为1068Ma±23Ma（MSWD=1．8），应为该榴辉岩原岩形成年龄，指示该地区在中元古代晚期有岩浆活动发生；而锆石的εHf（t）值为8．2～18．1（加权平均结果为14．06±0．62），TDM为892Ma～1300Ma（加权平均结果为1062Ma±21Ma），表明榴辉岩的原岩来自亏损地慢。这些结果证实，大别地区存在中元古代晚期到新元古代早期的岩浆作用，且这一时期扬子板块有不同程度的地壳生长。CL images, trace element, LA-ICPMS U-Pb age,and Hf isotope compositions of zir cons in an eclogite from the Hong＇an area were analyzed in detail. CL images of the zircons indicated that most of them were magmatic zircons variably modified by metamorphic recrystallization. The inner zircon zone domains without clear recrystallization were chosen for analysis. Since the trace element features of these zircon zones showed typical characteristics of magmatic zircon, their average ^207Pb/^206Pb age of 1 068 Ma± 23 Ma （MSWD =1.8） could be taken as the protolith age of the eclogite. This indicated that the protolith of the eclogite was resulted from the late Mesoproterozoic magmatic activities along the northern margin of the Yangtze block. Their εHf （t） values ranged from 8.2 to 18.1, with a weighted average of 14.06±0.62 （MSWD=4.4）. Their one-stage Hf model ages （TDM1） ranged from 892 Ma to 1 300 Ma, with a weighted average of 1 062 Ma± 21 Ma （MSWD =1.12）,suggesting that its protolith was derived from the depleted mantle. The results showed that the late Mesoproterozoic to early Neoproterozoic magmatic activities occurred in the Dabie area, which might also be a period o{ crustal growth in the Yangtze block.

关 键 词：西大别 榴辉岩 锆石微量元素 锆石U—Pb年龄 地壳生长 

分 类 号：P597.3[天文地球—地球化学]