阿尔金山东段阿克塞蛇绿岩地质地球化学特征及形成时代

Age and geochemistry of Aksay ophiolite in East Altun Mountains

北阿尔金蛇绿岩带是分布在阿尔金山北缘的一条蛇绿混杂岩带,超基性蛇纹岩岩块、基性岩墙、辉长岩块及基性熔岩组合是该带东段阿克塞蛇绿岩的典型组合形式。地球化学研究结果显示,阿克塞蛇绿岩超基性蛇纹岩以富MgO、贫Al_2O_3、P_2O_5、CaO和K_2O为特征,球粒陨石标准化稀土元素配分曲线表现较平缓,比值接近于1;基性熔岩类中TiO_2为0.86%～1.80%,Al_2O_3为12.00%～14.85%,CaO介于4.89%～19.23%之间,球粒陨石标准化稀土元素配分型式表现为右倾;基性岩墙中TiO_2介于1.08%～2.44%之间,Al_2O_3含量为11.07%～13.26%,Na_2O(1.20%～2.28%)>K_2O(0.80%～1.38%),稀土元素总量介于48.65×10^(-6)～124.04×10^(-6)之间,平均92.95×10^(-6);轻、重稀土元素比值介于2.22～4.45之间,总体表现为大洋中脊环境,LA-ICP-MS锆石U-Pb年龄显示,阿克塞蛇绿岩形成于514.6±8.8Ma,为寒武纪,表明在早古生代北阿尔金洋已完全打开,并连通了红柳沟—阿克塞。

North Altun ophiolite belt is an ophiolite melange zone located on the northern margin of the Altun Mountains. Rock as.sociations of ultrabasic rock blocks, basic dyke swarms, gabbro rock blocks and basic lava composite the representative ophiolite suitelocated in Aksay of the East Altun Mountains. Geochemical studies of the Aksay ophiolite show that the ultrabasic serpentinite is highin MgO and poor in Al2O3, P2O5, CaO, K2O, the chondrite-normalized REE patterns are relatively flat, and the ratio of sample tochondrite is close to 1. Basic lava rock is recognized by content of TiO2, Al2O3, CaO, with the chondrite-normalized REE patternsbeing relatively right-inclined. Basic dyke swarms are recognized by content of TiO2, Al2O3, with the features of Na2O higher thanK2O, ΣREE, and ΣLREE/ΣHREE（2.22~4.45）. Geochemical studies indicate that the Aksay ophiolite was formed in a Mid Ocean Ridges （MOR） environment and was reformed by subsequent Suprs-Subduction Zone （SSZ）. Geochronologic studies of zir.con U-Pb show that the Aksay ophiolite was generated at 514.6±8.8Ma of Cambrian period.