东昆仑小灶火地区钼矿化正长花岗岩年代学、地球化学特征及其地质意义

Geochronology,Geochemical Characteristics of Molybdenum Ore-bearing Syenogranite from Xiaozhaohuo Area in East Kunlun and Its Geological Significance

小灶火地区位于昆中岩浆弧北缘,北部与祁漫塔格弧后盆地区相邻,属于拉陵灶火整装勘查区众多铜钼多金属矿(化)点之一,该区含钼岩体为正长花岗岩。采用LA-ICP-MS锆石U-Pb法测得小灶火地区含矿正长花岗岩形成年龄为(226±1)Ma,形成于晚三叠世Carnian期。岩石地球化学分析结果显示,岩石明显具有富硅钾的特点,属高钾钙碱性系列,具有较弱的Eu负异常(0.75~0.86),Nb、Ta、Ti、P、Ba等元素亏损,Rb、Th、U、K等元素富集,Rb/Sr比值平均为1.90,Nb/Ta比值平均为11.33,上述特征均反映了岩石的壳源成因。结合区域上该期的火成岩岩石组合判断小灶火地区成岩成矿背景为晚三叠世后碰撞陆内造山阶段,与整个东昆仑造山带晚三叠世强烈壳—幔相互作用大背景相一致。

Xiaozaohuo area is located in the northern region of the Middle Kunlun magmatic arc,next to the Qimantage back-arc basin in the north,which is one of the large number of copper molybdenum polymetallic mineralized points in Lalingzaohuo monoblock exploration area.The ore-bearing intrusion is syenogranite.Detailed studies on geochronology,element geochemical were carried out for the syenogranite.The results show that the age of syenogranite is(226±1)Ma,geochemical analysis show that it belongs to shoshonitic series,with weaker Eu negative anomaly(0.75~0.86),depleted of Nb,Ta,Ti,P,Ba,rich in Rb,Th,U,K;Rb/Sr ratios of 1.90 on average,Nb/Ta ratios of 11.33 on average,these characteristics are reflected the crust sources of the magma genesis.Combined with studies of igneous diagenetic assemblages in this area,this paper proposed that the diagenetic mineralization setting in Xiaozaohuo area is post-collision intracontinental orogenic stage in the late Triassic.