东秦岭商丹断裂南侧变质基性火山岩的时代和岩石地球化学特征

Sm-Nd AGE AND GEOCHEMICAL CHARACTER OF META-BASIC VOLCANIC ROCKS IN SOUTH SIDE OF THE SHANGNAN-DANFENG FAULT FROM EAST QINLING

对东秦岭商丹断裂南侧变质基性火山岩进行了全岩Ｓｍ－Ｎｄ同位素研究，获得等时线年龄为１３８２±３０Ｍａ，εＮｄ（ｔ）＝＋６．５１，代表了其原岩的形成时代。岩石的主元素、微量元素和稀土元素地球化学特征表明，变质基性火山岩成分相当于板内（大陆）拉斑玄武岩，形成于板内（大陆）拉张裂陷构造环境，其源区可能是亏损地幔（ＤＭ）和富集地幔（ＥＭ）组分的混合物，与中元古代时秦岭造山带的裂谷→小洋盆的发生和北秦岭活动大陆边缘的发育有密切成因联系。

The meta-basic volcanic rocks in south side of the Shangnan-Denfeng fault from east Qinling are taken to be measured by Sin--Nd radioactive isotope method in this study, Sin-Nd whole rock isochron gives an age of 1382t 30 Ma. ENd(t) of samples is +6.51. This age is interpreted as the time of the protolith-formation. The geochemical features of major element, trace element and REE compositions indicate that compositions of the meta-basic volcanic rocks correspond to continental tholeiite and that the rocks formed in tectonic environment of intraplate extension, and may be derived from the mixing between depleted mantle(DM) and enriched mantle(EM) and may be related to development of Mid-Proterozoic rift →micro-ocean basin and active continental margin in the Qinling orogenetic belt.