西藏普兰蛇绿岩位于雅鲁藏布江缝合带的西段,主要由地幔橄榄岩、辉长岩和玄武岩组成.在拉昂错南侧有一个辉长岩体,面积约1 km2,与其相邻的地幔橄榄岩为侵入接触关系.辉长岩为中细粒辉长结构,块状构造,主要矿物为半自形板柱状基性斜长石和他形-半自形粒状辉石.岩石化学成分显示其具有MOR型岩石特点,表现为中等含量的TiO2(1％～1.77％),低含量的K2O(0.08％～0.21％)和P2O5(0.1％)；轻稀土元素(LREE)轻微亏损的近平坦型稀土元素球粒陨石标准化模型,(La/Ce)N、(La/Sm)N和(La/Yb)N等特征比值分别为0.73～0.80、0.44～0.58、0.53～0.65;岩石的高场强元素(HFSE)为相互平行的具有接近1的平坦型分配型式.微量元素的N-MORB标准化图解显示富集大离子亲石元素(LILE)如Rb,高场强元素(HFSE)轻微亏损.辉长岩锆石的LA-ICP-MS U-Pb年龄为130±3Ma,指示了普兰蛇绿岩形成的时代,与邻区休古嘎布、东波蛇绿岩的形成时代相一致.%The Purang ophiolite in the western part of the Yarlung Zangbo suture zone, is composed of mantle peridotite, gabbro and basalt. A gabbro massif, about lkm in area, occurs south of Lhanag-tso. The gabbro is fine- to medium-grained with a massive texture, and is composed mainly of subhedral tabular to prismatic plagioclase and anhedral to subhedral granular pyroxene. The gabbro has a MOR-type composition with relatively high TiO2 (1. 00% ~ 1. 77% ) and low K2O (0. 08% ~0. 21% ) and P2O5 (0. 1% ). It is characterized by having a nearly flat chondrite-normalized REE pattern with only slightly depleted LREE, as indicated by (La/Ce)N = 0.73-0.80, (La/Sm)N =0.44-0. 58 and (La/Yb)N =0. 53 -0. 65. An N-MORB-normalized spider diagram shows enrichment in LILE (e. G. , Rb) and slight depletion in HFSE. U-Pb dating of zircons from gabbro of the Purang ophiolite yields an age of 130 ± 3Ma. This age is similar to that of the nearby Xiugugabu and Dongbo ophiolite, and is taken as the crystallization age of the Purang ophiolite.
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