内蒙古毛登地区碎斑熔岩LA-ICP-MS锆石U-Pb年龄与地球化学特征

LA-ICP-MS zircon U-Pb dating and geochemical characteristics of the porphyroclastic lava in Maodeng area of Inner Mongolia

摘要: 在内蒙古毛登地区发现碎斑熔岩发育，其具有熔岩和熔结凝灰岩的双重结构。毛登碎斑熔岩岩体呈近圆形穹状，可划分出中心相、过渡相和边缘相，不同相带岩石特征明显。LA-ICP-MS锆石U-Pb年龄为139.20Ma±0.73Ma，属早白垩世火山—岩浆活动的产物。岩石富硅、碱，轻稀土元素富集，Eu强烈亏损，富集Rb、Th，亏损Ba、K，与同期流纹岩的地球化学特征相同，研究表明其形成于造山后板内伸展环境。

Abstract: The porphyroclastic lava with the texture of both lava and ignimbrite was found for the first time in Maodeng area of Inner Mongolia. The Maodeng porphyroclastic lava body，occurring as an oval dome，can be divided into internal facies，transitional facies and external facies. Based on the field geological investigation and the LA-ICP-MS zircon U-Pb age，the authors hold that it was produced by volcanic and magmatic activities in Early Cretaceous. The rock is characterized by enriched Si，alkaline and LREE，with relatively strong negative Eu anomaly，high Rb and Th content and low Ba and K. It resembles the liparite of the same period in geochemical characteristics. It is suggested that the porphyroclastic lava body was formed in an intra-plate anorogenic extensional setting.