辽西建平马场义县组火山岩LA-ICP-MS锆石U-Pb年龄及其地质意义

U-Pb Isotopic Age of the Volcanic Rocks of the Yixian Formation in Jianping Machang of Western Liaoning and Its Geological Significance

辽西建平马场地区出露大量的义县组火山岩,通过对其剖面测制研究发现,义县组火山岩可分为早、中、晚三期。对不同时期火山岩样品进行锆石LA-ICP-MS U-Pb测年,获得本区义县组早期火山岩形成年龄为(127.7±1.8)^(124.3±1.8)Ma,中期火山岩形成年龄为(122.3±1.4)^(121.8±1.3)Ma,晚期火山岩形成年龄为(114.9±1.8)Ma,时代均为早白垩世。通过与义县—北票、阜新—彰武、凌源—建昌地区的义县组对比得知,本区火山岩开始活动较晚,属于义县组活动的中—晚期;其年代学特征显示辽西各个地区义县组顶、底界是不等时的,是形成于太平洋板块向欧亚大陆俯冲后的伸展环境中。

Yixian Formation volcanic rocks widely exists in Jianping Machang in western Liaoning. Through the study of the measured sections,three volcanic eruption cycles（early,middle and late）have been recognized.A new LA ICP MS zircon U Pb dating of the volcanic rocks in different cycle presents three ages for the three cycles：（the early age （127.7±1.8）（124.3±1.8）Ma,the middle age （122.3 ± 1.4） （121.8 ± 1.3）Ma,and the late age （1 14.9 ± 1.8）Ma.All three cycles fall into the period of Early Cretaceous.In comparison with the different region in western Liaoning,the volcanic＆amp;nbsp;activity of this area occurred in the middle to late cycle according to the chronological characteristics. Yixian Formation in different region of western Liaoning was formed asynchronously,in an extension environment of the related subduction of the Paleo-Pacific plate towards the Eurasian continent.