秦岭造山带松树沟元古宙蛇绿岩及其大地构造背景

THE SONGSHUGOU PROTEROZOIC OPHIOLITE AND ITS TECTONIC SETTING IN THE QINLING OROGENIC BELT

秦岭造山带松树沟蛇绿岩大约是在９８３Ｍａ，构造就位于秦岭杂岩（Ｐｔ１）之上的异地构造岩片．由变质橄榄岩、堆积橄榄岩和火山岩系组成。变质橄榄岩以纯橄榄岩为主。堆晶岩分为单斜辉石型和斜方辉石型两类。火山岩由拉斑玄武岩和低铝安山岩组成，εＮｄ（Ｔ）为＋４．１～＋６．４，表现出Ｎ、Ｔ、Ｐ三种稀土分配型式和非正常洋脊玄武岩地球化学的特征。综合分析认为，这个古老蛇绿岩是在一种位于洋中脊之上的洋岛环境中形成的，代表了晋宁期华北板块与扬子板块之间古洋盆的残骸。

The Sonshugou ophiolite in the Qinling orogenic belt is an allochthonous block tectonicaly emplaced over the Qinling Complex (Pt1)about 983 Ma ago. The ophiolite is composed of metamorphic peridotite,accumlative peridotite and volcanic rocks series. The metamorphic peridotite is in dominance of dunite.The accumlative rocks are divided into Cpx-type and Opx-type. The volcanic rocks are composed of tholeiite and icelandite,εNd(T)=+4.1～+6.4,showing N, T, P geochemical patterns of REE and characteristics of non-normal MORB geochemistry. All this implies that the ancient ophiolite formed in oceanic island occurs in an oceanic spreading ridge,representing the relics of ocean basin between the North-China plate and the Yangtze plate in the Jining period.