豫西小秦岭地区太华杂岩中斜长角闪岩地球化学及其大地构造意义

GEOCHEMISTRY OF AMPHIBOLITES WITHIN THE TAIHUA COMPLEX FROM THE XIAO QINLING AREA, WESTERN HENAN AND ITS TECTONIC IMPLICATION

小秦岭地区太华杂岩的斜长角闪岩以多种产状出露于表壳岩系和花岗质片麻岩中，经历了角闪岩相区域变质作用，形成黑云斜长角闪岩、透辉斜长角闪岩、斜长角闪岩和黑云石榴斜长角闪岩等岩石类型。根据它们的主量和微量元素地球化学特征，可将其分为三类：Ａ类较多地显示大陆边缘岛弧的地球化学特征；Ｂ类的地球化学表现为板内玄武岩的特点但仍然记录岛弧玄武岩的组成特征；Ｃ类具有板内玄武岩的特征。这三类斜长角闪岩在空间上的密切共生和地球化学演化特征说明，它们是弧后盆地扩张不同阶段的产物。

An investigation of the major and trace element geochemistry of amphibolites within the Taihua complex from the Xiao Qinling area of western Henan Province has been carried out with a view to the tectonic environment of this late Archaean high-grade terrain. The amphibolites occur as enclaves or bands within the supracrustal sequences and granitic gneisses of the Taihua complex. Their mineral assemblages suggest that they may have been subject to amphibolite facies metamorphism. The amphibolites include biotite-amphibolite, diopside-amphibolite, garnetamphibolite and microcline-amphibolite. They were divided into three types (A, B and C) in terms of geochemical compositions. Type A shows the geochemical features similar to the continental margin arc basalts. Type B has a transitional geological features between arc-related and within-plate basalts, which still recorded more geochemical compositions of arc basalts. Type C displays a close geological affinity of within-plate basalts. The close spatial association of these amphibolites, together with their geological development, suggest that the yrepresented the products formed at different stages of back-arc spreading.