东秦岭松树沟蛇绿岩的形成环境探讨

THE FORMATION ENVIRONMENT OF SONGSHUGOU OPHIOLITE IN THE EASTERN QINLING

东秦岭松树沟蛇绿岩是秦岭造山带中出露于变质基底岩系之上的、形成于中元古代晚期（１０００～１２５０Ｍａ）的异地蛇绿岩构造岩片，与周围变质地层里构造接触关系，为一自南而北的逆冲推覆岩片，于９８３Ｍａ±发生构造侵位及变质作用。蛇绿岩主要由超镁铁岩和镁铁岩两个单元组成，变质橄榄岩（纯橄榄岩、方辉橄榄岩）具地幔残余成因，ΣＲＥＥ低，ＲＥＥ特征为ＬＲＥＥ富集、ＨＲＥＥ近平坦型式。变质基性火山岩的常量元素、微量元素和稀土元素地球化学特征显示以Ｔ－ＭＯＲＢ为主，兼具有ＯＩＢ特征，形成于小洋盆构造环境，于晋宁期北秦岭活动大陆边缘的俯冲－碰撞过程中发生变形变质并侵位于陆壳当中。

The Songshugou ophiolite in the eastern Qinling is a allochthonous lithosheet formed at Middle Proterozoic period (1000￣1250Ma) and accured on metamorphic basement.It has a structural interface with around metastrata and emplaced at 983 Ma and underwent metamorphism. The ophiolite is composed of ultramafic and ma fie rocks.The mantle peridotite (dunite and harzburgite) is mantle relicts, and has REE puttern of LREE-enriched,HREE-flat with lower ΣREE. The features of majon, thace elements and REE of meta basic Volcanic rocks reveal that belong to T-MORB, and have and a charateristic of OIB. The ophiolite might be originated in the small oceanic basin tectonic environmetn.