青海省乌拉斯太地区早石炭世花岗质岩体地球化学特征及其地质意义

Geochemical Characteristics and Geological Significance of Early Carboniferous Granitoids in Wulasitai Area in Qinghai Province

摘要:

早石炭世花岗质岩体主要沿昆中断裂带两侧断续分布，多呈岩床、岩株状产出，根据岩性特征可划分为3类，即浅肉红色斑状二长花岗岩、肉红色正长花岗岩、肉红色中细粒碱长花岗岩。主量元素特征显示花岗质岩体全碱含量较高，显示出壳源的特点，为过铝质—偏铝质花岗岩，属Ⅰ型花岗岩。稀土元素特征显示岩石属轻稀土富集型，重稀土相对平坦，轻重稀土分馏明显，具弱—中等铕异常，显示出地壳重熔的特点。微量元素特征显示花岗质岩体中Rb、Sr明显富集，Nb、Ta、P、Ti亏损，显示出壳源型花岗岩特点。研究认为早石炭世花岗质岩体岩浆演化是斑状二长花岗岩—正长花岗岩—碱长花岗岩的过程，早石炭世花岗质岩体主要形成于同碰撞期向后碰撞伸展期转化的构造环境。

Abstract:

Early Carboniferous granitoids are mainly distributed intermittently along both sides of Kunlun fault zone, and most of them occur in the form of batholith and stock. According to the lithologic characteristics, they can be divided into three types, namely, flesh red porphyritic monzogranite, flesh red syenogranite and flesh red medium fine grained alkali feldspar granite. As showed by the characteristics of major elements, total alkali content of granitoids is high. It shows the characteristics of crust source. It is peraluminous meta aluminous granite, and belongs to Itype granite. As showed by the characteristics of rare earth elements, the rock belongs to the enrichment type of light rare earth, and the heavy rare earth is relatively flat. The fractionation of light rare earth and heavy rare earth is obvious with weak to medium europium anomaly. It shows the characteristics of crustal remelting. As showed by the trace element characteristics, the granitoids are obviously enriched in Rb and Sr and depleted in Nb, Ta, P and Ti. It shows the characteristics of crust derived granite. It is considered that the magmatic evolution of early Carboniferous granitoids is a process of porphyry monzogranitesyenogranitealkali feldspar granite. The early Carboniferous granitoids are mainly formed in the tectonic environment transformed from the same collision period to the later collision extension period.