藏南米拉山地区林子宗火山岩LA-ICP-MS锆石U-Pb年龄和起源  

LA-ICP-MS zircon U-Pb age and origin of the Linzizong volcanic rocks from Milashan, southern Tibet

作　　者：刘安琳[1] 朱弟成[1] 王青[1] 张立雪[1] 李世民[1] 张亮亮[1] 赵志丹[1] 

机构地区：[1]中国地质大学地球科学与资源学院/地质过程与矿产资源国家重点实验室,北京100083

出　　处：《地质通报》2015年第5期826-833,共8页Geological Bulletin of China

基　　金：中国科学院青藏高原专项(B类)(编号:XDB03010301);国家973项目(编号:2011CB403102);国家自然科学基金杰出青年基金项目(批准号:41225006);地质过程与矿产资源国家重点实验室科技部专项

摘　　要：大规模的林子宗火山岩呈带状展布于拉萨地体中南部地区,记录了新特提斯洋壳晚期俯冲和随后印度—欧亚大陆碰撞的重要信息,因而受到广泛关注,但迄今对区域性的林子宗火山岩仍然缺乏可靠的年龄数据约束。为此,本文对南部拉萨地体东部米拉山地区林子宗火山岩中的含角砾流纹岩样品进行了LA-ICP-MS锆石U-Pb定年和Hf同位素、全岩地球化学测试。获得了60.1±0.9Ma的锆石206Pb/238U年龄,与林周盆地典中组底部安山质岩浆活动的时代相当。测试样品以亏损中稀土元素和低的重稀土元素丰度为特征,锆石εHf(t)为正值(+8.5^+18.8),可能来源于较厚新生下地壳物质在角闪岩相/榴辉岩相过渡条件下的部分熔融。目前还很难论证呈带状分布的约60Ma林子宗火山岩稀土元素含量差异的构造含义。Much attention has been paid to the Linzizong volcanic rocks which are extensively developed along the strike of southern and central Lhasa Terrane because these rocks are generally considered to document the history of late subduction of the Neo-Tethyan ocean lithosphere and subsequent India-Asia collision. However, reliable age data for the Linzizong volcanic in a regional scale rocks remain very insufficient. In this paper, the authors performed zircon U-Pb dating, zircon Hfisotope determination, and wholerock element geochemical study of a volcanic breccia-bearing rhyolite sample collected from the Linzizong volcanic rocks in Milas- han, eastern segment of the southern Lhasa Terrane. Eighteen analyses of zircons from this sample yielded a zircon 206Pb/238U age of 60.1 ±0.9Ma, coeval with the andesitic volcanism documented in the lowerest Dianzhong Formation in Linzhou Basin. This sample is characterized by significant depletion of middle rare earth element （MREE） and low abundances of heavy REE, with positive zircon He（t） values ranging from ＋8.5 to ＋ 18.8. Such geochemical characteristics indicate that this sample probably originated from partial melting of thick and juvenile lower crust materials under a transitional condition from amphibolite to eclogite facies. At present, it is still difficult to explore the tectonic implications of the differences in R_EE abundances observed from the ca.60Ma Linzizong volcanic rocks along the strike of the Lhasa Terrane.

关 键 词：LA-ICP-MS锆石U-PB年龄 HF同位素 岩浆起源 林子宗火山岩 西藏米拉山 

分 类 号：P588.14[天文地球—岩石学]