孙吴-嘉荫地区早中生代花岗岩的年代学、地球化学与成因

对小兴安岭北部孙吴-嘉荫地区早中生代花岗岩进行了年代学和地球化学研究，据此探讨其成因及形成的构造背景。锆石U-Pb同位素定年结果表明，研究区早中生代花岗岩分为晚三叠世和早侏罗世两期，形成时代分别为210 Ma和187~181 Ma。晚三叠世碱长花岗岩属铝质A型花岗岩，岩浆源区为新元古代从亏损地幔中增生的基性火成岩地壳。早侏罗世英云闪长岩-花岗闪长岩和二长花岗岩属埃达克岩，是由加厚下地壳物质部分熔融形成的；正长花岗岩-碱长花岗岩与同期埃达克岩具明显不同的地球化学特征，岩浆源区为中元古代从亏损地幔中增生的基性地壳物质。结合区域地质构造演化特征，认为晚三叠世花岗岩是华北板块和西伯利亚板块碰撞造山后伸展构造环境下的产物，早侏罗世花岗岩的形成与古太平洋板块俯冲产生的挤压构造环境有关。

Geochronology,Geochemistry and Petrogenesis of the Early Mesozoic Granites in the Sunwu-Jiayin Area,Heilongjiang Province

To determine petrogenesis and tectonic background of the early Mesozoic granites in the Sunwu-Jiayin area, Xiao Hinggan Mountains, U-Pb dating and Hf isotopic composition in zircon grains, major and trace element characteristics in different granites have been analyzed. Due to their zircon U-Pb ages, ages of granites in this area can be classified into two periods: the Late Triassic period(~210 Ma) and Early Jurassic period(187-181 Ma). Geochemical data indicate that the Late Triassic alkali feldspar granite belongs to the aluminous A-type granite, and was originated from partial melting of the newly accreted Neoproterozoic basic igneous crust. The Early Jurassic tonalite-granodiorite and monzogranite have similar geochemical characteristics as the adakite, and were formed by partial melting of the thickened lower crust. The Early Jurassic syenogranite and alkali-feldspar granite are of significantly different characteristics from the cotemporaneous adakite, and were derived from the basaltic crust accreted from depleted mantle during the Mesoproterozoic period. Combining with the regional researching results, it’s suggested that the Late Triassic granite was resulted from the post-orogenic extension after the collision between the North China plate and Siberia plate, whereas the Early Jurassic granites formed in a compressive tectonic setting related to the subduction of the Pacific plate.