西藏日喀则地区雅鲁藏布蛇绿岩地球化学特征及其源区性质

摘要

日喀则地区的蛇绿岩是西藏南部雅鲁藏布蛇绿岩带出露较好的蛇绿岩之一。对日喀则地区白朗蛇绿岩的主量、微量元素及 Sr-Nd 同位素研究表明，其基性岩石为钙碱性系列，主要氧化物具有低钛（0.6％～1.1％）和富镁（6.6％～8.7％）、高铝（15.3％～16.0％），以及烧失量普遍较高（2.8％～4.6％）的特征。岩石微量元素配分型式与 N-MORB 类似，又具有岛弧玄武岩的地球化学特征，表明蛇绿岩受到了俯冲作用的影响。Sr-Nd 同位素特征表明源区为略富集的MORB 型地幔。白朗蛇绿岩所代表的特提斯地幔域与印度洋地幔域具有相似的地球化学性质，进一步证实了现今的印度洋继承了特提斯地幔域的地球化学特征。%Ophiolite from Xigaze is one of well-outcropped rocks in the Yalung Zangpo ophiolite,southern Ti-bet.Elemental and Sr-Nd isotopic compositions of the basaltic rocks from Bainang ophiolite in Xigaze were studied in this paper.The rocks are calc alkalic series,with low TiO2 (0.6% -1 .1 %),high MgO(6.6% -8.7%),Al2 O3 (1 5.3% -1 6.0%)and LOI(2.8% -4.6%).The primitive mantle-normalized multi-element pattern of basaltic rocks is similar to that of the normal Mid-Ocean Ridge Basalt(N-MORB)with the characteris-tics of island arc,which suggests that the rocks are related to subduction processes.The geochemical character-istics of Sr-Nd reflect that mantle source of Bainang ophiolite is a little enriched MORB mantle.The geochemi-cal characteristics of Tethyan Ocean are similar to those of the Indian sub-oceanic mantle,which further con-firms that the Indian sub-oceanic mantle is inherited from the Tethyan Ocean geochemical domain.