华北-西伯利亚板块对接带早白垩纪的裂解:来自西拉木伦断裂带中性岩墙群的锆石U-Pb年龄及地球化学证据

Extension of Suture Zone Between North China and Siberia Craton in Early Cretaceous:Insights from Geochronology and Geochemistry of Intermediate Dykes from Xar Moron Fault Belt in Inner Mongolia

在内蒙古林西县西拉木伦断裂带内发育规模较大的中性岩墙群,岩墙多呈NE3°～5°近直立侵入.对岩石进行了锆石LA-ICP-MS U-Pb定年和详细的岩石地球化学特征研究.锆石LA-ICP-MS U-Pb年龄为132.2±2.2Ma,岩石侵位于早白垩世.岩石地球化学特征显示岩石具有高钾钙碱性系列-钾玄岩系列的过渡特征,形成于板内拉张环境,岩浆源区具有壳幔混源的特征,是早期俯冲洋壳遭受幔源岩浆底侵作用的结果.岩墙的产状受左旋剪切机制控制,该机制可能主要与太平洋板块相对亚洲板块的向北运动有关.

A large scale of intermediate dykes developed in Xar Moron fault belt in Linxi county,Inner-Mongolia,with NE3° to 5° angle of strike and nearly vertical trend.LA-ICP-MS zircon U-Pb dating method and whole rock geochemistry test were applied.It is indicated that the intermediate dykes emplaced in Lower Cretaceous with LA-ICP-MS zircon U-Pb age of 132.2±2.2 Ma.The whole rock geochemistry of the dykes reveals transition characteristics between high potassium calc-alkaline series and shoshonite series.They formed in intraplate extensional background and sourced from crust-mantle magmatic mixing,which result from the mantle magma underplating below the early subducted oceanic crust.The strike of the dykes was chronically controlled by a sinistral shear mechanism in the area,which might be related to the northward movement of Pacific plate to Asian plate.