Abstract:

We have investigated the Xigaze ophiolites (Tibet) in the Yarlung Zangbo ophiolite belt (Tibet), SW China, by using noble gases isotopic compositions. The rocks investigated in this paper include serpentinized peridotites, basalts and dolerites. The 3He/ ? 4He ratios in these basalts are similar, having an average value of 5.36R a, and the He contents closely resemble each other. Two exceptions are basalt samples from Dagzhuka, with 3He/ ? 4He ratios that are lower than atmospheric value

Key words: ophiolite, helium, mantle plume, Yarlung Zangbo River, Xigaze

摘要：

测定了日喀则地区蛇绿岩组合岩石的稀有气体同位素组成。白朗的玄武岩具有比较均一的He同位素组成 ,3He/ 4He平均值为 5 35 9Ra;变橄岩的He同位素比值范围为 1 10 4～ 3 384Ra,平均为 2 383Ra;从东部的仁布和大竹到西部的下鲁和白朗 ,辉绿岩的3He/ 4He由低变高。采于吉定的新鲜辉绿岩平均高达 31 5 7Ra,该值接近于在夏威夷发现的高比值。分步加热法结果显示高R值的He是在低温步释放的 ,根据这种高R值的He可以推测雅鲁藏布江蛇绿岩的成因环境有地幔柱的作用 ,该构造带很可能出现过裂谷洋盆或未能发育成熟的深大裂谷带

关键词: 雅鲁藏布江, 日喀则, 蛇绿岩, 氦, 地幔柱