柴北缘铁石观榴辉岩锆石U-Pb定年及其地质意义  

Zircon U-Pb Dating of Eclogite from Tieshiguan,North Qaidam and Its Geological Significance

作　　者：国显正 王红军 许荣科 郑有业 贾群子[2] 陈鑫[4] 蔡鹏捷[1] 

机构地区：[1]中国地质大学(武汉)地质调查研究院,武汉430074 [2]中国地质调查局西安地质调查中心,西安710054 [3]河南省地质矿产勘查开发局第一地质矿产调查院,河南洛阳471023 [4]中国地质大学(武汉)资源学院,武汉430074

出　　处：《矿物岩石地球化学通报》2017年第6期995-1006,共12页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：中国地质大调查项目(1212011121204;12120113029000);教育部长江学者和创新团队发展计划项目(NOS;IRT14R54;IRT1083)

摘　　要：为查明柴北缘超高压变质带铁石观地区榴辉岩变质时间及流体活动,利用LA-ICP-MS对该区榴辉岩进行了锆石U-Pb定年分析,同时对锆石中包裹体进行了研究。结果表明,榴辉岩中变质锆石^(206)Pb/^(238)U加权平均年龄为426.1±4.9 Ma(MSWD=1.18),与区域上鱼卡、锡铁山、都兰等地榴辉岩变质峰期年龄一致。激光拉曼分析结果显示,包裹体核部矿物为金红石、绿辉石,边部为磷灰石、斜长石,可能为榴辉岩变质峰期捕获的产物。锆石^(176)Hf/^(177)Hf=0.282691~0.282795,^(176)Lu/^(177)Hf=0.000002~0.000228,Hf同位素两阶段亏损地幔模式年龄为769.7~1002.8 Ma,与区域上测得榴辉岩原岩年龄一致。通过搜集区域变质岩年龄数据分析,柴北缘地区超高压变质带年龄可分3期:第1期(470~440 Ma)与洋壳俯冲事件相关,第2期(440~420 Ma)与陆陆俯冲碰撞事件相关,第3期(420~400 Ma)为岩石退变化时期。In order to constrain the timing of eclogite metamorphism and fluid activity in Tieshiguan, North Qaidam UHP metamorphic belt, LA-ICP-MS was performed on U-Pb dating of zircon from eclogite. The metamorphic zircon of eclogite have 206pb/238U weighted average age of 426. 1±4.9 Ma（ MSWD = 1.18） , which is corresponding to eclogite metamorphic peak ages of Yuka, Xitieshan, Dulan. The laser Raman spectroscopy analysis shows that the core of zircon contains inclu- sions of rutile and omphacite, and the rim of zircon bears inclusions including plagioclase and apatite, all of which may have been captured during metamorphic peak of eclogite. Zircon grains havet76 Hf/x77 Hf ratios between 0. 282 691 and 0. 282 795 and176Lu/177Hf ratios varying from 0. 000 002 to 0. 000 228, yielding two stage Hf model age from 769. 7 to 1002.8 Ma, which is consistent with the age of regional source rocks of eclogites. By comparison of metamorphic age da- tum of Northern Qaidam UHP metamorphic belt, the metamorphism can be divided into three stages： The first stage（470±440 Ma）is associated with subduction events; the second （440±420 Ma）is associated with continental subduction and col- lision events and the third（420±400 Ma）is a rock retrogressive period.

关 键 词：榴辉岩 U-PB定年 矿物包裹体 变质年龄 柴北缘铁石观 

分 类 号：P588.3[天文地球—岩石学]