华北北缘固阳二叠纪闪长岩-石英闪长岩-英云闪长岩套SHRIMP年代学

摘要

应用岩石地球化学方法,笔者在内蒙古二叠纪索伦山蛇绿岩缝合带南100～180 km、华北克拉通北缘固阳地区,识别出了一个闪长岩-石英闪长岩-英云闪长岩套.这些花岗质岩石为钠质,与岛弧深成岩在化学成分上一致.SHRIMP年代学研究表明:2件闪长岩的SHRIMP U-Pb锆石年龄为(293±4)Ma和(266±4)Ma；1件石英闪长岩的锆石年龄为(272±7)Ma;1件英云闪长岩的锆石年龄为(277±3)Ma.这些二叠纪花岗质岩石因此在形成时代上没有间断,它们与索伦山SSZ (supersubduction zone)型蛇绿岩(299～290Ma)大致同时或略晚.基于其特定的构造背景及其与索伦山蛇绿岩的时代关系,所研究的二叠纪钠质深成岩套(293～266 Ma)与大致同时代的安山质火山岩一起,构成一个大陆边缘岛弧.%Using a petrogeochemical means, we recognize a diorite-quartz diorite-tonalite suit in the northern margin of the North China craton, some 100-180 km south of the Permian Solonker ophiolite-decorated suture. The granitoid rocks are all sodic, consistent in composition with a plutonic arc. SHRIMP dating of zircons from two diorites yielded weighted mean 206Pb/238U ages of 293±4 Ma and 266±4 Ma. A quartz diorite and a tonalite are dated at 272 ±7 Ma and 277 ±3 Ma respectively. These Permian granitoid rocks were thus emplaced continuously. They are nearly coeval with, or slightly younger than, the Solonker SSZ (supersubduction zone)-type ophiolite. On the basis of a specific tectonic setting and an age relationship with the Permian Solonker SSZ-type ophiolite, we interpret the sodic granitoid suit investigated, together with near-contemporaneous andesites of the area, to form a continental margin arc.