大兴安岭北段呼中西部塔木兰沟组火山岩年代学、岩石地球化学特征及其构造意义

Zircon U-Pb geochronology,petrogeochemistry and tectonic significance of volcanic rocks from Tamulangou Formation in western Huzhong,northern Great Xing'an Range

呼中火山岩位于大兴安岭北段,塔木兰沟组是其喷发较早的一期中基性火山岩。锆石U-Pb年代学研究表明,呼中火山岩形成于(154±1)Ma,属晚侏罗世。呼中火山岩SiO_2为49.80%~55.96%、Al_2O_3为16.70%~18.93%、Na_2O+K_2O为6.35%~9.11%,属中基性高铝碱性岩石。微量元素特征显示,呼中火山岩富集大离子亲石元素Ba,亏损高场强元素Nb、Ta,Nb/Ta=12.44~15.58。呼中火山岩元素含量及其比值的变化显示了本区塔木兰沟组玄武岩浆在分离结晶作用过程中受到了壳源物质的影响,其形成环境为板块边缘岛弧造山带环境,由古亚洲洋和(或)蒙古—鄂霍茨克洋板块俯冲形成。

Huzhong volcanic rock belt lies in the northern part of Greater Khingan Range. Tamulangou For-mation ,which is one of the earlier phases of the eruption, is mainly composed of intermediate - basic volcanic rock. Zircon U-Pb dating shows that the Huzhong volcanic rock formed in the Late Jurassic （154 ± 1 Ma）. SiO2 content of Huzhong volcanic rock is 49. 80% ？55. 9 6% ,Al2O3 is 16. 70%-18. 9 3% ,Na2O ＋ K2O is 6.35% -9. 11% , belonging to intermediate-basic high alumina alkaline rocks. The volcanic rocks are enriched in large ion lithophile elements Ba, and depleted in Nb, Ta, with Nb/Ta = 12. 44-15. 58. The changes of Huzhong volcanic rock element contents and their ratios indicate that the basaltic magma of Tamulangou Formation is influenced by crust - derived material during fractional crystallization process. The formation was formed in the plate margin arc orogen environment related to the subduction of Paleo Asian Ocean plate and （or） Mongolia-Okhotsk Ocean plate.