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 peralu-minous 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 A12O3, high Sr, 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=1.13) 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.%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.
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