榴辉岩相峰期流体活动:来自东昆仑榴辉岩石英脉的证据  

Fluid activity during eclogite-facies peak metamorphism: Evidence from a quartz vein in eclogite in the East Kunlun,NW China

作　　者：贾丽辉[1,2] 孟繁聪[2] 冯惠彬 

机构地区：[1]中国地质大学,北京100083 [2]中国地质科学院地质研究所,大陆构造与动力学国家重点实验室,北京100037

出　　处：《岩石学报》2014年第8期2339-2350,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41272052);中国地质调查局项目(1212010918003;1212011120158;12120114080101)联合资助

摘　　要：本文通过对东昆仑温泉地区榴辉岩中石英脉的锆石U-Pb定年和Lu-Hf同位素的综合研究,为榴辉岩相峰期变质阶段的流体活动提供了一定的证据。石英脉中的锆石晶型较好,具有振荡环带或弱分带,排除了从寄主榴辉岩中捕获锆石的可能性。石英脉和寄主榴辉岩中锆石U-Pb年龄的加权平均值分别为450±2Ma和451±2Ma,说明石英脉中锆石的形成年龄与榴辉岩相的峰期变质阶段一致。两种锆石Hf同位素组成的相似性说明形成石英脉的流体/熔体为内部来源,推测可能为榴辉岩中石英发生溶解以及绿辉石和石榴石分子结构中羟基的出溶作用形成。锆石较低的U、Th含量以及Th/U比值说明石英脉更可能是流体活动形成而非熔体。This paper reports a quartz vein in eclogite from Wenquan area in the East Kunlun, and through a comprehensive research in U-Pb age and Lu-Hf isotope, which provides some evidence about fluid activity in peak eclogite-facies metamorphic stage. The zircon grains in Wenquan quartz vein have perfect euhedral habit and show sector or weak zoning, which precludes the possibility that the zircon crystals were physically introduced into the quartz vein from the country rock. Zircon grains from quartz vein and eclogite yield weighted mean 2~6pb/238U date of 450 _＋ 2Ma and 451 ~ 2Ma, respectively, which describes that the forming age of zircon in quartz vein and the peak eclogite-facies metamorphic stage are consistent. The similarity of/-If isotope composition in the two styles of zircon proves the aqueous fluid/melt that formed veins is internal source, which may be derived from the fused quartz in eclogite, hut we can not preclude the exsolusion of structural hydroxyl in omphacite and garnet. Quartz vein formed more likely in aqueous fluid rather than melt because of the low U, Th contents and Th/U ratios in zircons.

关 键 词：锆石 石英脉 榴辉岩 U-Pb LU-HF 东昆仑 

分 类 号：P588.348[天文地球—岩石学] P597.3[天文地球—地质学]