大兴安岭伊勒呼里山早白垩世碱长花岗岩年龄、地球化学特征及其地质意义

对大兴安岭伊勒呼里山早白垩世碱长花岗岩进行了岩相学、地球化学、LA-ICP-MS锆石U-Pb定年研究。伊勒呼里山地区碱长花岗岩主量元素具有富Si、富碱,贫Mg、Ca的特征;微量元素亏损Sr、P、Eu、Ti,富集K、Rb、Th等不相容元素,元素地球化学特征表明,岩体为铝质A型花岗岩(A/CNK=0.88~1.21,A/NK=0.94~1.49)。测年结果显示,粗中粒碱长花岗岩的锆石年龄为140.3±1.0Ma,细中粒碱长花岗岩锆石年龄为137.9±0.8Ma,均形成于早白垩世。结合区域研究资料,伊勒呼里山地区碱长花岗岩岩体的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展密切相关,其岩浆源区可能为地壳物质的部分熔融。

Geochronology, geochemistry and geological sig-nificance of the Early Cretaceous alkali feldspar granites in the Yilehuli Mountain, Da Hinggan, Mountain

Petrographic and geochemical data and LA-ICP-MS zircon U-Pb ages were obtained for Early Cretaceous alkali feldspar granites of the Yilehuli Mountain. The major elements of Yilehuli alkali feldspar granites are high in Si, ALK, and low in Mg, Ca. Trace elements are enriched in incompatible elements such as K, Rb and Th, and depleted in Sr, P, Eu and Ti. Geochemical features indicate that alkali feldspar granites are aluminum A-type granites (A/CNK=0.88~1.21, A/NK=0.94~1.49). LA-ICP-MS zircon U-Pb age data of coarse-medium alkali feldspar granites and fine-medium alkali feldspar granites are 140.3 ±1.0Ma and 137.9 ±0.8Ma, respectively, indicating that intrusive rocks were formed in Early Cretaceous. Combined with regional geological investiga-tion, the authors hold that the formation of Yilehuli plutons was closely related to lithospheric extension caused by closure of the Mongol-Okhotsk Ocean, and that the primary magma was derived from partial melting of crustal materials.