西天山尼勒克地区浅成花岗质侵入体的地球化学特征及形成时代  

Geochemistry and dating of the hypabyssal granite body in Nilka County of Western Tianshan Mountains

作　　者：李晓英[1,2] 徐学义 孙吉明 李智佩 白建科 张晓博 

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]中国地质调局西安地质调查中心,陕西西安710054 [3]长庆油田第八采油厂,陕西西安710026

出　　处：《地质通报》2012年第12期1939-1948,共10页Geological Bulletin of China

基　　金：中国地质调查局项目<天山-兴蒙成矿带火山岩浆作用对成矿制约的综合研究>(编号:1212011085475);<天山成矿带基础地质综合研究>(编号:1212011085055)和<西北综合研究>(编号:1212011220649)

摘　　要：尼勒克西部出露的依兰巴斯套岩体的和乌郎达坂岩体的岩性分别为花岗闪长玢岩和花岗斑岩。详细的岩石学和地球化学研究显示,2个岩体属弱过铝质、富钠花岗岩体,稀土元素球粒陨石标准化分配型式显示2个岩体均显示LREE富集、HREE亏损,发育弱的Eu正异常的特征,具有与埃达克质岩石相似的富Na2O和Al2O3,高Sr,低Yb、Y的特点。对2个岩体中的锆石进行了LA-ICP-MS U-Th-Pb同位素测定,得到其形成年龄分别为291.8Ma±3.7Ma(MSWD=1.13)和303.6Ma±4.0Ma(MSWD=0.95),表明其形成于晚石炭世末—早二叠世早期。结合区域地质证据,认为依兰巴斯套岩体和乌郎达坂岩体是天山古生代洋盆闭合后大陆伸展阶段岩浆作用的产物。Granodiorite porphyrite and granite porphyry are respectively exposed in Yilanbasitao and Wulangdaban of western Nilka County, Xinjiang. Detailed petrologic and geochemical studies have shown that the two rock bodies are characterized by weak peraluixfinous nature, rich Na and LREE, deficiency of HREE and weak positive Eu anomalies, geochemically similar to adakite rocks in such aspects as rich Na2O and Al2O3, high St, low YB and Y, and loss of HREE. Zircon U-Pb dating shows that ages of the two rock bodies are respectively 291.8Ma±3.7Ma （MSWD=l.13） and 303.6Ma±4.0Ma （MSWD=0.95）, suggesting a period from the end of late Carboniferous to the beginning of early Permian. According to their petrological and geochemical characteristics as well as regional geological evidence, the authors have reached the conclusion that the two granite bodies are products of magmatic invasion at the continental extension stage after the closure of Tianshan Paleozoic oceanic basin, and that they were formed by partial melting of the lower crust.

关 键 词：西天山 尼勒克 浅成花岗质侵入体 地球化学 形成时代 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]