东昆仑东段哈日扎石英闪长岩时代、成因及其地质意义

Zircon U-Pb Geochronology and Geochemistry of Harizha Quartz Diorite in the Eastern Section from East Kunlun

哈日扎石英闪长岩出露于东昆仑造山带东段,该地区构造和岩浆活动强烈。LA-ICP-MS锆石U-Pb测年获得哈日扎石英闪长岩年龄为(239.3±2.2)Ma,形成时代为中三叠世,属印支期。石英闪长岩中含镁铁质暗色包体,石英闪长岩w(SiO_2)为61.34%~63.07%,w(Al2O3)为16.12%~16.55%,K_2O/Na_2O比值为0.75~0.82,显示低钾富钠特点,里特曼指数为1.45~1.56,在w(K_2O)-w(Na_2O)关系图上落入中高钾钙碱性系列,A/CNK=0.92~0.95,属于准铝质岩石;稀土元素总量(∑REE=108.38×10^(-6)~124.51×10^(-6))变化不大,为轻稀土元素富集、重稀土元素相对亏损的右倾型。δEu为0.69~0.73,负铕异常明显。在微量元素原始地幔标准化蛛网图上,岩石富集Rb、Ba等大离子亲石元素、LREE和不相容元素(如U),相对亏损Nb、Ta、Ti、P等高场强元素,指示具有弧岩浆特征,Rb/Sr、Nb/Ta比值介于壳幔之间,反映具有壳幔混合成因。结合区域地质背景,认为哈日扎石英闪长岩形成于三叠纪早期俯冲阶段,与阿尼玛卿洋俯冲作用有关。

Harizha quartz diorite is located in the eastern section of East Kunlun orogenic belt.The U-Pb dating of zircons from the quartz diorite using LA-ICP-MS yields an age of（239.3±2.2）Ma,which indicates quartz diorite formed in Triassic and belongs to the Indo-Chinese epoch.Geochemical analysis shows that the SiO_2 ranges from 61.34% to 63.07%,Al_2O_3=16.12%-16.55%,K_2O/Na_2O=0.75-0.82,and it is rich in Na_2O but poor in K_2O,rittmann index ranging between 1.45 and 1.56.The rock is plotted in middle-high K calc-alkaline series in the K_2O-Na_2O diagram,and A/CNK=0.92-0.95.This suggests that the Harizha quartz diorite belongs to the aluminum unsaturated granite.In addition,REE of the quartz diorite content varies little with ∑REE=108.38×10^（-6）-124.51×10^（-6）.REE distribution pattern shows that LREE is strong enrichment and HREE is relative depletion,with obviously Eu negative anomaly.The trace elements of primitive mantle standardization on spider diagram reveal that large ion lithophile elements（Rb,Ba）and LREE and incompatible elements（U）are enriched,strength elements Nb,Ta,Ti and P are relative depleted.Quartz diorite has magnesium iron inclusions,Rb/Sr,Nb/Ta ratio between crust-mantle.This mirrors the characteristics of crust-mantle mixing origin.In combination with regional geological background,quartz diorite has the characteristics of arc magma,while the rock experienced partial melting of lower crust and the crust-mantle mixing origin,formed in the subduction of Anima Ocean.