西藏西南部休古嘎布蛇绿岩的Sm-Nd年龄及Nd-Sr-Pb同位素特征  

Sm-Nd ages and Nd-Sr-Pb isotope signatures of the Xiugugabu ophiolite, southwestern Tibet

作　　者：徐德明[1] 黄圭成[1] 雷义均[1] 

机构地区：[1]宜昌地质矿产研究所,湖北宜昌443003

出　　处：《中国地质》2008年第3期429-435,共7页Geology in China

基　　金：中国地质调查局资源评价项目(1212010530108);国家自然科学基金项目(40572052)资助

摘　　要：休古嘎布蛇绿岩位于雅鲁藏布江蛇绿岩带西段,属于SSZ型蛇绿岩。用Sm-Nd法测定了该蛇绿岩中辉长辉绿岩的结晶年龄,辉石、斜长石和两个全岩样品的等时线年龄为(126.2±9.1)Ma,代表新特提斯洋在该区俯冲消减的时限。同时,对辉长辉绿岩的Nd-Sr-Pb同位素的测定结果表明,辉长辉绿岩的初始εNd(t)值高(6.7～9.1),反映原始岩浆起源于强烈亏损的地幔源区,未受大陆地壳物质的混染;初始206Pb/204Pb比值较低(17.412～17.523),但初始208Pb/204Pb比值较高(37.352～37.706),并具有较高的ISr值(0.70278～0.70383),指示休古嘎布蛇绿岩源于印度洋MORB型地幔域。The Xiugugabu ophiolite is situated in the western segment of the Yarlung-Zangbo ophiolite belt, southwestern Tibet, belonging to SSZ-type ophiolites. The crystallization age of gabbro-diabase in the ophiolite was determined using the Sm-Nd method. The internal isochron age of plagioclase, pyroxene and two wholerock samples is 126.2±9.1 Ma, which represent the time range for the subduction of the Tethys Ocean. In addition, Nd-Sr-Pb analysis of gabbro-diabase indicates that the gabbro-diabase has high initial ε Nd （t） values （6.7-9.1）, suggesting that the primitive magma was derived from a strongly depleted mantle and had not undergone contamination with continental crustal materials. The ophiolite has lower initial ^206Pb/^204Pb values of 17.412-17.523 but higher ^208Pb/^204Pb values of 37.352-37.706 and shows higher Is, values of 0.70278-0.70383, indicating that the Xiugugabu ophiolite originated from the Indian MORB mantle domain.

关 键 词：休古嘎布蛇绿岩 SM-ND定年 Nd-Sr-Pb同位素 西藏西南部 

分 类 号：P597.3[天文地球—地球化学]