青海沟里地区斜长角闪岩锆石U-Pb年代学、Lu-Hf同位素特征及其指示意义  

Zircon U-Pb Geochronology and Lu-Hf Isotope of Amphibolite in Gouli Area,Qinghai Province,and Their Tectonic Implications

作　　者：吴胜宝 孙国胜[1] 李雪 孙九达 齐雨宁 王卓一 马冬 Wu Shengbao;Sun Guosheng;Li Xue;Sun Jiuda;Qi Yuning;Wang Zhuoyi;Ma Dong(College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《吉林大学学报（地球科学版）》2024年第3期862-876,共15页Journal of Jilin University：Earth Science Edition

基　　金：中国地质调查局项目(DD2019015-06)。

摘　　要：东昆仑造山带金水口群的沉积和变质时代一直存在争议。本文利用LA-ICP-MS技术对青海省都兰县沟里地区金水口群中的斜长角闪岩进行了锆石U-Pb年代学、Lu-Hf同位素研究。结果显示:斜长角闪岩中6个测点的碎屑锆石年龄集中在2.1~2.0 Ga之间,碎屑锆石最小年龄为1829 Ma,变质锆石的上交点年龄为(1905±300)Ma,误差较大,但暗示金水口群沉积时间漫长,沉积时代不晚于中元古代早期,故本文认为金水口群沉积时代在1800 Ma左右;年龄集中于2100 Ma的碎屑锆石具有麻粒岩相变质锆石特征。变质锆石年龄集中于450~420 Ma之间,12个点的加权平均年龄为(444.3±5.3)Ma,为早古生代,该年龄与东昆仑造山带响应原特提斯洋俯冲拼合并发生区域深熔作用的年龄基本一致;锆石^(176)Lu/^(177)Hf值较低,变质锆石ε_(Hf)(t)值为-35.41~-3.75,T_(DM2)介于3641~1666 Ma之间,源岩物质为古老地壳再循环的产物;古元古代碎屑锆石ε_(Hf)(t)值为-2.98~25.58,T_(DM2)介于2833~920 Ma之间,源区为来源于亏损地幔的陆壳,与太古宙TTG岩系相似,暗示阿尔金地块的TTG岩系为金水口群提供了部分物质来源。金水口群沉积于活动大陆边缘或初始裂谷盆地,上部沉积盖层冰沟群与万宝沟群沉积于浅海陆棚,沉积过程具有连续性。The sedimentary and metamorphic ages of the Jinshuikou Group in the East Kunlun orogenic belt has been controversial.In this paper,the zircon U-Pb geochronology and Lu-Hf isotope of amphibolite in Jinshuikou Group in Gouli area,Dulan County,Qinghai Province were studied by LA-ICP-MS technique.The results show that the ages of detrital zircons in amphiboliterange from 2.1 to 2.0 Ga,with the youngest detrital zircons dating to 1829 Ma;The upper intersection age of metamorphic zircons is(1905±300)Ma,although with a large error.However,this implies a lengthy deposition time for the Jinshuikou Group,not extending beyond the Early Mesoproterozoic.Therefore,this study proposes a deposition time of about 1800 Ma for the Jinshuikou Group.The detrital zircons with ages of 2100 Ma are characterized by granulite facies metamorphic zircon.Metamorphic zircon ages are concentrated between 450 and 420 Ma,with a weighted average age of 12 points is(444.3±5.3)Ma(Early Paleozoic),consistent with the age of regional anatexis in the East Kunlun orogenic belt in response to the subduction and amalgamation of the Proto-Tethys Ocean.The zircon^(176)Lu/^(177)Hf values are low,theε_(Hf)(t)values of metamorphic zircons are-35.41--3.75,and the T_(DM2)is between 3641-1666 Ma.The source rock materials are the product of ancient crustal recycling.Theε_(Hf)(t)values of the Proterozoic detrital zircons are-2.98-25.58,and the T_(DM2)is between 2833-920 Ma.The source area is the continental crust from the depleted mantle,which is similar to the Archean TTG rock series,suggesting that the TTG rock series of Altyn block provides some material sources to Jinshuikou Group.The Jinshuikou Group was deposited on the active continental margin or the initial rift basin,while the Binggou Group and Wanbaogou Group,the upper sedimentary cover,were deposited on the shallow sea shelf,with a continuous deposition process.

关 键 词：金水口群 斜长角闪岩 锆石U-Pb定年 锆石Lu-Hf同位素分析 东昆仑造山带 

分 类 号：P597[天文地球—地球化学]