标题:
西藏普兰蛇绿岩体中基性岩脉的地球化学和年代学特征Geochemistry and Geochronology of Mafic Rocks in the Purang Ophiolite, Tibet
作者:
陈洪凯, 李旭平, 陈爽, 赵令权
关键字:
蛇绿岩, 基性岩脉, N-MORB, 地球化学, 年代学, 西藏普兰Ophiolites, Basic Dikes, N-MORB, Geochemistry, Chronology, Purang, Tibet
期刊名称:
《Advances in Geosciences》, Vol.6 No.1, 2016-02-26
摘要:
西藏普兰岩体位于雅鲁藏布江缝合带的西段、西藏自治区西南部、喜马拉雅山南侧的峡谷地带。本文对普兰蛇绿岩中的基性岩脉做了详细地球化学和年代学研究，普兰岩体基性岩脉主要是细粒辉长岩。岩石具有中等含量Al2O3和CaO，低K2O、低P2O5、高Na2O和中等含量TiO2的特征，辉长岩稀土元素球粒陨石标准化配分模式的轻稀土元素亏损，ΣREE含量较高，与MOR型环境特征相似。微量元素标准化图解中可以发现微量元素具有Ba、U等LILE元素富集和Nb、Ti等轻微元素亏损的特点，似乎与岛弧有成因联系。综合来看，辉长岩的主量、微量和稀土元素的特征与弧后盆地的N-MORB的地质环境特征相符合。对辉长岩中的锆石进行LA-ICP-MS U-Pb定年测定，获得两组较好的206Pb/238U年龄数据，得出加权平均年龄为119.4 ± 5.2 Ma~122.1 ± 7.1 Ma，代表辉长岩形成的年龄，也是普兰蛇绿岩形成的年龄。
The Purang ophiolite is located in the west section of the Yarlung Zangbo suture zone, southwestern of Tibet autonomous region, and on the south side valley of Himalayan mountain. This article focuses on geochemistry and chronological studies of the rocks, which are mainly fine-grained gabbros. The gabbro is fine-grained with a massive texture. The gabbros contain low K2O and P2O5, moderate Al2O3, CaO and TiO2, and high Na2O contents. Normalized REE patterns are characteristic of high ΣREE, depleted LREE; normalized spider diagrams show enrichment of LILE (Ba, U) and slight depletion of some HFSE (Nb, Ti). In conclusion, gabbros of the Purang ophiolite exhibits N-MORB feature or affiliate to back arc expansive environment. Zircons from Purang gabbros yields well defined weight mean 206Pb/238U ages at 119.4 ± 5.2 Ma and 122.1 ± 7.1 Ma. These ages represent the formation of the ophiolite complexes along the Yarlung Zangbo Suture Zone.