大兴安岭中部柴河地区晚侏罗世花岗质岩石成因及构造意义

本文对大兴安岭中部柴河地区晚侏罗世花岗质岩石进行了岩石学、同位素年代学、地球化学等研究，探讨了其岩石成因及形成的构造背景。岩石学研究表明，大兴安岭中部柴河地区晚侏罗世花岗质岩石主要岩石组合为花岗闪长岩、二长花岗岩和碱长花岗岩。LA-ICP-MS锆石U-Pb测年结果获得2个二长花岗岩年龄分别为（152±1）Ma和（150±1）Ma。岩石主量元素具有富钾钠、富铝的特点，属铁质碱-钙性岩石。稀土元素相对富集轻稀土元素、亏损重稀土元素，具有弱到中等的Eu负异常，微量元素主要富集大离子亲石元素（Rb、Th、U、K、LREE）和Zr、Hf元素，亏损高场强元素（Nb、Ta、P、Ti）和Ba、Sr元素。地球化学特征指示这些晚侏罗世花岗质岩石来源于新元古代和早古生代期间从亏损地幔新增生的地壳物质部分熔融，形成于蒙古-鄂霍茨克洋闭合陆壳加厚之后挤压到伸展的转换环境。

Genesis and Tectonic Significance of Late Jurassic Granitoids in Chaihe Region,Central Great Xing'an Range,NE China

The authors studied the Late Jurassic granitoids in the Chaihe region of central Great Xing'an Range. The Late Jurassic granitoids consist of granodiorite, monzonitic granite, and alkali-feldspar granite in lithology. We obtained two LA-ICP-MS zircon U-Pb ages of monzonitic granite, they are (152±1) Ma and (150±1) Ma respectively. The chemical analyses show that the Late Jurassic granitoids are classified as ferrous alkali-calcic rocks, and are characterized by enrichment in light rare earth elements (LREEs), large ion lithophile elements (LILEs), Zr, Hf, and depletion of heavy rare earth elements (HREEs), high field strength elements (HFSEs), Ba, and Sr, with weak to moderate Eu negative anomalies. All the geochemical characteristics suggest that the Late Jurassic granitoids were derived from the partial melting of lower juvenile crustal basaltic rocks. We propose that the generation of the Late Jurassic granitoids is related to the transitional environment of extrusion-extension after the final closure of the Mongol-Okhotsk Sea and subsequent continental thickening.