汉诺坝玄武岩中辉石岩类包体Nd、Sr、Pb同位素及其成因信息

Nd,Sr AND Pb ISOTOPIC COMPOSITIONS AND THEIR PETROGENETIC INFORMATION OF PYROXENITE XENOLITHS FROM HANNUOBABA SALTS,CHINA1

对汉诺坝地区的１２个辉石岩和１个麻粒岩包体进行了Ｎｄ、Ｓｒ、Ｐｂ同位素测定，发现辉石岩组成有很大变化，１４３Ｎｄ／１４４Ｎｄ比值为０．５１１６０—０．５１３１４，８７Ｓｒ／８６Ｓｒ比值为０．７０２９—０．７０８６，２０６Ｐｂ／２０４Ｐｂ比值为１５．９４２—１８．６８３，２０７Ｐｂ／２０４Ｐｂ比值为１５．２６４—１５．５６９，２０８Ｐｂ／２０４Ｐｂ比值为３６．２１３—３８．７４４，显示了其复杂成因ｑ推测具有高Ｓｒ、低Ｎｄ和低Ｐｂ同位素组成的辉石岩是地幔早期富集的产物，与麻粒岩、辉长岩包体有类似成因；具有弱至中等亏损的Ｎｄ。

Nd,Sr and Pb isotopic compositions of 12 pyroxenitic and 1 granulitic xenoliths in basalts from Hannuoba area,China were determined.The results show that they have wide variattions in composition( 143 Nd/ 144 Nd=0.51160—0.51314; 87 Sr/ 86 Sr=0.7029—0.70 86 ; 206 Pb/ 204 Pb=15.942—18.683; 207 Pb/ 204 Pb=15.264—15.569; 208 Pb/ 204 Pb=36.213—38.744)implying their sophisticated origin.It is postulated that pyroxenitic xenoliths which have high 87 Sr/ 86 Sr,low 143 Nd/ 144 Ndandlow 206 Pb/ 204 Pb ratios are products of mantle enrichment events at very early time probably in Archean or Proterozoic,and they have petrogenesis similar to gabbroic and granulite xenoliths.Pyroxenites with BSE or moderate depleted Nd and Sr and high radiogenic Pb isotopes are metasomatic or enriched products of evolved depleted mantle in recent time not very long before eruption.Most pyroxenites are probably located at shallower level in the lithospheric mantle compared to the lherzolites.