西藏尼玛县西拉木那勒地区晚白垩世埃达克岩岩石成因及构造指示  

Genesis and tectonic indication of the Late Cretaceous adakite rocks in the Lamunale area,Nima County,Tibet

作　　者：董宇超[1] 王明[1,2] 解超明 于云鹏[1] 郝宇杰 DONG YuChao;WANG Ming;XIE ChaoMing;YU YunPeng;HAO YuJie(College of Earth Sciences,Jilin University,Changchun 130061,China;MNR Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061 [2]自然资源部东北亚矿产资源评价重点实验室,长春130061

出　　处：《岩石学报》2020年第2期426-442,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41872231、41972236);自然资源部东北亚矿产资源评价重点实验室自主课题基金(DBY-ZZ-18-06)联合资助

摘　　要：青藏高原北拉萨板块上发育大规模的晚白垩世岩浆作用,长期以来,关于其岩石成因及构造属性一直存在较大争论。本次研究对产出于北拉萨板块尼玛县西约150km的拉木那勒晚白垩世岩体开展了锆石U-Pb年代学、地球化学等方面的工作。拉木那勒岩体主要为花岗闪长岩和二长花岗岩,具有较高的SiO2(68.12%~72.21%)、Al2O3(12.28%~17.02%)含量和较高的Sr/Y比值(26.7~145)、La/Yb比值(24.1~28.4),低含量的MgO(0.88%~1.86%)、Y(4.58×10^-6~10.03×10^-6)和Yb(0.33×10^-6~0.73×10^-6),具有埃达克岩的典型特征。本文共对4件年代学样品进行了锆石U-Pb定年,其中2件样品获得了88.4±0.5Ma和88.6±0.4Ma的谐和年龄,另外2件样品获得了89Ma和95Ma的下交点年龄。结合区域地质资料,我们倾向于认为拉木那勒岩体形成于班公湖-怒江洋闭合之后,是陆-陆碰撞加厚下地壳部分熔融的产物。此外,地壳增厚可能是北拉萨板块晚白垩世岩浆岩的一个重要的形成机制。Large-scale Late Cretaceous magmatism occurs in the North Lhasa Block on the Tibet Plateau.For a long time,there have been large debates about its petrogenesis and tectonic properties.This time we carried out zircon U-Pb chronology,geochemistry and other aspects of the Lamunale Late Cretaceous intrusion located about 150km west of Nima County in the North Lhasa Block.The lithology of the Lamunale rock is composed of granodiorite and monzonitic granite with high content of SiO2(68.12%~72.21%),Al2O3(12.28%~17.02%),Sr/Y ratios(26.7~145),La/Yb ratios(24.1~28.4),low content of MgO(0.88%~1.86%),Y(4.58×10^-6~10.03×10^-6)and Yb(0.33×10^-6~0.73×10^-6),which is a typical characteristics of adakite.A total four samples were analyzed to determine their radiometric ages.Two samples achieved a concordant U-Pb age of 88.4±0.5Ma and 88.6±0.4Ma,whereas the other two samples provide the lower intersection ages of 89Ma and 95Ma.Combining regional geological data,we tend to think that the Lamunale rock formed after the closure of the Bangong-Nujiang Ocean Basin was a product of partial melting of the lower crust due to land-land collision thickening.Crustal thickening may be an important mechanism for the formation of the Late Cretaceous magmatic rocks in North Lhasa Block.

关 键 词：青藏高原 晚白垩世 埃达克岩 地壳增厚 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]