胶莱盆地西南缘青山群火山岩锆石U-Pb年龄、岩石地球化学特征及意义

Zircon U-Pb age,geochemical characteristics and the geological significance of volcanic rocks of Cretaceous Qingshan group at the Southwest margin of Jiaolai basin

胶莱盆地西南缘发育的青山群火山岩以中中酸性为主,属同源岩浆喷发;岩石具有高硅、高钾、富铝、贫铁钛特征;微量元素Nb、Ta亏损,Zr、Hf较富集,岩浆来源于下地壳,与板块俯冲作用有关;稀土元素配分图具右倾特征,轻稀土富集,Eu异常不明显;岩浆演化特征以部分熔融为主,区内火山岩碱度指数A·R值小于4.0,判断研究区青山群火山活动的构造环境是大陆边缘区,通过U-Pb年龄测试,确定青山群火山岩成岩年龄为113 Ma—119 Ma。

Volcanic rocks of Early Cretaceous Qingshan group at Southwest margin of Jiaolai basin are dominated by intermediate-intermediate acidic rocks.The volcanic are the product of cognate eruption characterized by high Si and K,Al richness and Fe and Ti poorness,relative trace element depletion of Nb,Ta and relative enrichment of Zr and Hf,REE pattern declined to right,LEE enrichment,indistinct Eu anomaly.The Magma is partially melted one related to plate subduction and comes from lower crust.Alkalinity index AR of the volcanic is less than 4.0 suggesting a continent marginal tectonic setting.The zircon U-Pb dating is 113 Ma~119 Ma.