辽东半岛～2.2Ga岩浆事件及其地质意义

Liaodong Peninsula ～2.2 Ga Magmatic Event and Its Geological Significance

本文报道了辽东半岛古元古代胶—辽—吉活动带内辽河群变质火山岩和辽吉花岗岩的锆石LA-ICP-MS U-Pb年代学和地球化学数据。变质安山岩的锆石具典型的岩浆振荡环带结构和较高的Th/U值（〉0.5）,锆石U-Pb年龄为（2 182±6）Ma和（2 229±22）Ma,该年龄可代表安山岩的形成年龄。辽吉花岗岩的锆石同样具有典型的岩浆振荡环带结构和较高的Th/U值（〉0.3）,锆石U-Pb年龄为（2 199±10）Ma,代表花岗岩的侵位时代,在误差范围内与辽河群火山岩喷发时代一致,表明辽吉花岗岩并不是辽河群的基底,二者可能为同一次岩浆作用过程的产物。辽东半岛～2.2Ga岩浆事件的识别及性质,对于正确认识古元古代胶—辽—吉活动带的属性至关重要。结合前人有关辽东半岛前寒武纪岩石的研究成果,本文研究认为胶—辽—吉活动带的形成演化可能与弧-陆碰撞有关。

The geochronology and geochemical studies were carried out on the Paleoproterozoic meta-volcanic rocks and the Liaoji granite from Jiao-Liao-Ji mobile belt in North China craton tounderstand the ~2.2 Ga magmatic event and its geodynamic setting.The zircon LA-ICP-MS U-Pb analyses on the meta-andesites yield 207 Pb/206 Pb ages of（2 182±6）Ma and（2 229±22）Ma.These zircons exhibit oscillatory and sector-zoning and high Th/U ratios（〉0.5）,the typical magmatic origin;thus the ages probably represent the formation ages of the protolith of the meta-volcanic rocks.The zircons from the Paleopr oterozoic Liaoji granite share the similar magmatic characteristics with those from the meta-volcanic rocks,e.g.,oscillatory and sector-zoning,and high Th/U ratios（〉0.3）.The zircon U-Pb isotopic dating by using the LA-ICP-MS method on the Paleoproterozoic Liaoji granite reveals that they formed at（2 199±10） Ma,which are regionally comparable to those of the Paleoproterozoic meta-volcanic rocks.Our age data suggest a synchronism for the two rock units,rather than that the Paleopreoterozoic Liaoji granites were the basement of Liaohe Group volcanic rocks as considered previously.The recognition and the nature of the ～2.2 Ga magmatic event in Liaodong Peninsula are critical for understanding the evolution of Jiao-Liao-Ji mobile belt.Our new data,coupled with recent studies on lithology, metamorphism,geochemistry,and geochronology of ArcheanPaleoproterozoic basement rocks,support the Paleoproterozoic arc-continent collision model.