对西昆仑赛力亚克达坂胜利桥岩体再认识

胜利桥岩体是西昆仑库地—麻扎地区出露的面积较大的"浆混"花岗岩,岩性复杂,岩石类型较多。岩石地球化学特征显示,该岩体SiO2含量较高,主要属酸性岩类;里特曼指数σ=2.13~2.89;强不相容元素K、U、Ba、Rb、Th具有明显的富集特征,高场Nb、Ta、P、Ti元素明显亏损,Nb-Ta呈槽状,Sr元素亏损明显;稀土元素总量较低,属轻稀土富集、重稀土亏损型。根据锆石U-Pb法同位素测年,2个U-Pb年龄平均值分别为(229.7±1.4)Ma与(204.65±0.59)Ma,时代确定为晚三叠世。综合分析,认为胜利桥岩体属于过铝高钾钙碱性花岗岩类,属I型花岗岩类,其物质来源主要来自地幔,并有一定地壳物质的加入,是壳幔共同作用的结果。胜利桥单元为陆内俯冲作用的产物,其呈现的火山弧花岗岩特征主要受地壳物质物源影响所致。

The Recognition of Shengliqiao Rock Mass of Saliyakedaban,West Kunlun

With complex lithology and rock types, Shengliqiao rock mass is a large outcrop of mixed granite in Kudi-Mazha area of West Kunlun. Geochemical characteristics of high SiO2 content indicates that the rock mass is mainly acid rock. The value of Rittmann index （a） is between 2.13 and 2.89; strong incompatible elements including K, U, Ba, Rb, Th have obvious enrichment features; high field elements such as Nb, Ta, P, Ti are apparently depletedl the distribu- tion of Nb-Ta is in a groove shape, and Sr element is also in an obvious deficit l the total of rare earth element is fairly low, with LREE enriched while HREE depleted. According to the zircon U-Pb isotopic dating analysis, the average ages are （229.7±1.4） Ma and （204. 65±0.59） Ma, indicating that Shengliqiao rock mass occurred in the Late Triassic age. In summary, the rock is I-type granite of high aluminum potassium calcium alkaline, a result of interaction between crust and mantle. The material resource came mainly from the mantle with a certain amount of crustal material. Combined with the features of regional tectonic position and magmatic evolution of the analysis, it is concluded that Shengliqiao rock unit is a product of intracontinental subduction. The displayed feature of island arc granite is induced by the influence of crustal material resources.