东秦岭富水基性杂岩体地球化学特征及其形成环境

GEOCHEMISTRY AND FORMATION SETTING OF FUSHUI COMPLEX,EASTERN QINLING

富水基性杂岩体以浅色辉长岩为主，是侵入于早元古代秦岭群变质杂岩南部的岩浆侵入体。浅色辉长岩富Ａｌ、ＬＩＬＥ、ＬＲＥＥ，贫ＨＦＳＥ，为高铝辉长岩，具钙碱性演化趋势。Ｔｈ／Ｔａ值高，表明源区受到来自消减组分的影响。（１４３Ｎｄ／１４４Ｎｄ）ｉ值低（０．５１１４３—０．５１１６２），εＮｄ（ｔ）＝－３．５—＋０．２；（８７Ｓｒ／８６Ｓｒ）ｉ值高（０．７０９４２—０．７１３２８），εｓｒ（ｔ）＝＋８１—＋１３５，反映源区可能是富集地幔与消减组分混合形成的。（２０６Ｐｂ／２０４Ｐｂ）ｉ值较低（１６．２２—１７．２５），（２０７Ｐｂ／２０４Ｐｂ）ｉ和（２０８Ｐｂ／２０４Ｐｂ）ｉ变化大（分别为１４．６８—１５．６５和３４．．２２—３７．３４）；δ１８Ｏ值高（＋８．２‰—＋８．９‰）。上述证据表明该杂岩体是形成于活动陆缘构造环境的基性岩浆侵入体，以源区混染为主，存在消减组分的影响。

Fushui basic complex,which intruded into Qinling Group,is mainly lightcolored gabbros.They enriche in Al,LILE,LREE,and deplet in HFSE and belong to the high-Al gabbro with calc-alkaline evolution trend.Their high Th/Ta ratios in dicate that the source magma was influenced by the subducted components.These gabbros have low( 143 Nd/ 144 Nd) i ratios(0.51143—0.51162) and high( 87 Sr/ 86 Sr) iratios (0.70942—0.71328),and their ε Nd (t)=-3.5—+0.2, ε Sr (t)=+81—+135,which maybe related to the mixing between enriched mantle and components from subductionzone.In addition,these gabbros have high δ 18 O(+8.2‰—+8.9‰),low( 206 Pb/ 204 Pb) iratios (16.22—17.25),large variation of( 207 Pb/ 204 Pb) i ratios (14.68—15.65) and ( 208 Pb/ 204 Pb) i ratios(34.22—37.34).The evidences above suggest that Fushui complex is a basic magmatic intrusive which was formed at the active continental margin setting.The source magma was influenced by the components from subduction zone.