苏北牛山片麻状A型花岗岩及其成因

Gneissic A Type Granite and Its Genesis in Niushan Hill, North Jiangsu

苏北牛山片麻状花岗岩形成于震旦期，富含碱性长石，普遍含有碱性镁铁矿物，具有高硅、富碱、低铝、贫水，富含Ｎｂ、Ｚｒ、Ｙ、Ｇａ、ＲＥＥ及Ｅｕ明显亏损等特征，为Ａ型花岗岩。其Ｙ／Ｎｂ、Ｙｂ／Ｔａ、Ｃｅ／Ｎｂ等比值较高，Ｇａ×１０４／Ａｌ和碱度较低，属Ａ２亚型花岗岩。它是苏胶造山带在晋宁期碰撞造山后的拉张环境下，由地幔热流上涌，致使下地壳岩石部分熔融，产生的岩浆于中地壳侵位而形成。

Formed in the Sinian, Niushan gneissic granite, rich in alkali feldspar and alkali mafic minerals, is characterized by high silicon, low aluminum, short of water and full of alkali, Nb, Zr, Y, Ga, REE as well as evident loss in Eu content. So, the gneissic granite belongs to an A type granite. What is more, as there are higher content of Y/Nb, Yb/Ta, Ce/Nb and lower Ga×10 4/Al and alkalinity, the granite falls in to A 2 subtype granite. It is deduced that after the collision orogenic movement in the Jinning age, the Su Jiao Orogenic Belt was in a pull apart environment. Owing to upwelling mantle heat flow, there caused a partly melting rocks in the lower crust. Then, the emplaced magma in the middle crust formed A 2 type granite. As a batholith, Sinian A type granite in Niushan Hill becomes an ending mark of collision orogenesis of Su Jiao Orogenic Belt during Jinning age.