辽北辉绿岩墙(床)群及二道沟组玄武岩锆石年龄及其构造意义

辽东半岛北部铁岭市泛河流域位于郯庐断裂北段,归属于中朝板块华北块体的东北端。此地区发育巨厚的玄武岩(二道沟组)及辉绿岩墙(床)群,过去认为系中元古代时期的基性岩浆活动。对玄武岩及辉绿岩锆石SHRIMP年龄测定,获得二道沟组玄武岩喷发定位的时间在古近纪始新世((36.4±1.8)Ma);辉绿岩浆侵位结晶时间为晚白垩世((93.5±1.4)Ma)。辽北基性岩岩浆定位年龄明确显示,分割中朝板块内部华北块体与胶辽朝块体的北部边界——郯庐断裂北段在晚白垩世处于东西向伸展拉张构造环境,导致辉绿岩侵位;古近纪发育了近南北向的拉张构造,伸展作用进一步发展,形成二道沟组巨厚玄武岩。新的SHRIMP锆石U-Pb年龄不支持辉绿岩及二道沟组玄武岩形成年代为中元古代的传统认识。

Ages of the zircons from basalt of the Erdaogou Formation and diabase dyke warms in Northern Liaoning, and their significances.

The drainage area of Fanhe river around the Tieling city in the north part of Liaodong peninsula is located in the north part of the Tancheng-Lujiang Fault, which belongs to the northeastern end of North China Block in the Sino-Korean plate. In this area, there are huge thick basalt (the Erdaogou Formation) and diabase wall (bed) clusters, which have been thought as the Mesoproterozoic basic magmatism. By means of dating zircons with SHRIMP, the eruption time of the Erdaogou Formation basalt were obtained as (36.4±1.8) Ma, the Eocene Pliogene; and the emplacement time of the diabase swarms as (93.5±1.4) Ma, the Late Cretocesous.That the basic dyke swarms and basalts in Northern Liaoning were determined as the Mesozoic and Cenozoic, respectively, reveals that the northern boundary which divides North China Block and Jiao-Liao-Korean Block within Sino-Korean Plate, i.e. the northern part of the Tancheng-Lujiang fault, was in a stretch-tensile tectonic environment in east-west direction in the Late Cretaceous. And this tectonic environment resulted in the intrusion of the diabase swarms. In the Paleogene Period, the stretching direction was changed to near SN, and the development of the stretching tectonics led to the eruption of the huge-thick Erdaogou Formation basalt. The new SHRIMP zircon U-Pb ages doesn't support the traditional opinion that the Erdaogou Formation basalt was formed in the Mesoproterozoic.