南极乔治王岛中—新生代岩浆岩Sr-Nd-Pb同位素组成及源区特征

Sr Nd Pb Isotopic Compositions and Source Features of Mesozoic to Cenozoic Magmatic Rocks on King George Island,Antarctica

对乔治王岛１１个火山岩和２个侵入岩样品做了Ｓｒ－Ｎｄ－Ｐｂ同位素分析，其中（８７Ｓｒ／８６Ｓｒ）ｉ＝０．７０３２６～０．７０３９２，εＮｄ＝３．０２～６．７２，２０６Ｐｂ／２０４Ｐｂ＝１７．７７６～１８．５１５，２０７Ｐｂ／２０４Ｐｂ＝１５．．５０６～１５．５７１，２０８Ｐｂ／２０４Ｐｂ＝３７．８６８～３８．３０８。根据以上同位素组成及其相互关系并结合岩石学和微量元素特征及火山岩中熔融包裹体成分，得出以下结论：（１）研究的乔治王岛岩浆岩起源于亏损地幔（ＤＭＭ）和地幔流体交代成因的富集地幔ＥＭＩ混合形成的源区；（２）该源区具有广义Ｄｕｐａｌ异常，它正是由于ＥＭＩ组份加入即通过流体交代作用而产生的；（３）流体主要是俯冲深海沉积物脱碳酸盐作用而释放出的富ＣＯ２流体。

Sr Nd Pb isotopic analyses of 11 volcanic and 2 plutonic rock samples from King George Island are presented in this paper.Among them,( 87 Sr/ 86 Sr) i=0 70326～0 70392,ε Nd =3 02～6 72, 206 Pb/ 204 Pb=17 776～18 515, 207 Pb/ 204 Pb=15 506～15 571, 208 Pb/ 204 Pb=37 868～38 308。Based on these new isotopic data and their interrelation,and combined with petrology and trace element geochemistry as well as composition of mineral melt inclusions,we concluded:(1)the studied King George Island igneous rocks were derived from a mixing source of DMM and EMI caused by fluid metasomatism;(2)the mixing source had Dupal anomaly which was produced by EMI addition,i.e.,through fluid metasomatism;(3)metasomatic fluids here are inferred to be CO 2 rich fluids released by decarbonation of subducted pelagic sediments.