雅鲁藏布江蛇绿岩的氦、氩同位素组成及其地质意义

笔者测定了稚鲁藏布江地区蛇绿岩的氦、氩同位素组成。白朗的玄武岩He同位素组成比较均一，^3He/^4He平均值为5.359Ra；与之伴生的变橄岩的^3He／^4He比值范围为1.104～3.384Ra，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。吉定的辉绿岩样品^3He／^4He比值平均高达31.57Ra，该值与夏威夷发现的高比值样品接近。分步加热法结果显示，该样品高比值的He是在低温区段释放的，这种高^3He／^4He比值He的捕获表明稚鲁藏布江蛇绿岩

Helium and Argon Isotopic Compositions of the Yarlung Zangbo Ophiolites in Tibet and Their Geological Implications

Helium and argon isotopic compositions of Yarlung Zangbo ophiolites in Tibet have been determined in this paper. Helium isotopic compositions of basalts from Bailang are quite uniform with the average 3He/4He ratio being 5.359 Ra,whereas the 3He/4He ratios of meta-peridotites associated with the basalts vary between 1.104 Ra and 3.384 Ra with an average value of 2.383 Ra. 3He/4He ratios in diabases gradually increase from Renbu in the east to Bailang and Xialu in the west. The average 3He/4He ratio of three diabase samples from Jiding is as high as 31.57 Ra, close to the previously reported values from Hawaii hotspots. Further stepwise heating studies reveal that the highest 3He/4He ratio is obtained from the lower temperature intervals. All this suggests that plume magmatism must have played an important role in the formation of the Yarlung Zangbo ophiolites.