西藏班公湖-怒江缝合带中段江错蛇绿岩岩石学、 地球化学、年代学及地质意义
Petrology, Geochemistry, Chronology and Geological Significance of Jiang Tso Ophiolite in Middle Segment of Bangonghu-Nujiang Suture Zone, Tibet

江错蛇绿岩位于班公湖-怒江缝合带中段,位于切里湖蛇绿岩亚带的最东端,南邻蓬湖西蛇绿岩.江错蛇绿岩岩石组合 相对较全,主要由变质橄榄岩、辉长岩和辉绿岩等组成.江错蛇绿岩辉长岩-辉绿岩与N-MORB相比具有较高的Mg# 、低Ti、 K、Na和P的特征,富集大离子亲石元素Sr、Rb、Ba和亏损高场强元素Th、Hf、Ta、Nb,REE配分图总体显示为平坦型分布模 式.通过地球化学元素分析认为江错蛇绿岩是形成于SSZ之上的弧后盆地扩张脊环境.对其进行辉长岩锆石SHRIMPU-Pb 定年,得出加权平均年龄为189.8±3.3Ma(MSWD=0.97),该结果代表了班公湖怒江缝合带中段江错地区特提斯洋的扩张时 代,与中段东巧地区蛇绿岩年龄一致,但晚于东段洋盆发育时代且早于西段洋盆发育时代,表明整个班公湖-怒江洋盆发育 时代存在东早西晚的特点.
Jiang Tso ophiolite, which belongs to the most eastern part of Qieli Lake ophiolite subzone, is1ocated at the middle segment of the Bangonghu-Nujiang suture zone to the south of Pung Lake ophiolite. The rock association of Jiang Tso ophiolite is relatively complete and mainly composed of metamorphic peridotite, gabbro and diabase. Comparing with N-MORB, the ma- jor and trace elements of Jiang Tso ophiolite are characterized with high content in Mg and1ow contenls in Ti, K, Na, P and the depletion of elements of Nb, Ta, Hf, and Th. In addition, it displays relative enrichment of Rb, Sr, and Ba. Geochemistry characteristics of the Jiang Tso ophiolite indicate it is of supra-subduction zone type ophiolite and formed in the spreading ridge of back arc basin. The zircon SHRIMP U-Pb weighted average ages of gabbro is 189.8士3.3 Ma(MSWD=0.97), which sug- geststhat the extension time of Tethys oceanic basin in Jiang Tso region was consistent with the formation time of the Dongqiao oceanic basin in the middle part, and also corresponding to that of the oceanic basin in the western part, whilelater than the development of oceanic basin in the eastern part of the Bangonghu-Nujiang suture zone. From the geochrono1ogical data, it can be deduced that the development of the Bangonghu-Nujiang oceanic basin was characterized by being gradually later from east to west