辽宁清河断裂以北新太古代变质表壳岩的发现及其地质意义

Discovery of the Late Archean Supracrustal Rock to the North of Qinghe Fault in Liaoning Province and Its Geological Significance

通过详实的地质填图,在辽宁开原地区清河断裂以北新发现一套变质表壳岩组合,主要岩性为斜长角闪岩、黑云角闪斜长变粒岩、黑云角闪斜长片麻岩、浅粒岩及角闪石岩的岩石组合,与红透山岩组基本可以对比。岩石地球化学特征表明,其原岩主要为一套中、中基性的火山岩建造,形成于岛弧环境。该套岩石组合普遍发生强烈的构造变形作用,常见构造样式包括透入性片麻理、石香肠构造、变质分异条带、肠状褶皱等一系列的固态流变构造。对该套变质表壳岩组合中的斜长角闪岩进行LA-ICP-MS锆石U-Pb测年,结果表明其形成于(2 524±18)Ma,变质年龄为(2 477±21)Ma,从形成到发生变质相隔约为47Ma。该套变质表壳岩组合的发现,表明了清河断裂以北也曾存在太古宙结晶基底,清河断裂与寇河断裂之间的区域在构造环境上与清原地区一样,均属于新太古代绿岩带。

By detailed geological mapping in Kaiyuan area,Late Archean supracrustal rocks have been discovered for the first time in the north of the Qinghe fault,which are mainly composed of amphibolite,hornblende-plagioclase leptynite,hornblende-biotite-plagioclase gneiss and hornblendite.Geochemical characteristics of these rocks indicate that their metamorphic original rocks were intermediate or intermediate-basic volcanic rocks which formed in the island arc environment.Suchmetamorphic structural styles as penetrative schistosity,boudin structure,metamorphic differentiation strip and ptygma fold are commonly found in these metamorphic supracrustal rocks.LA-ICP-MS zircon U-Pb dating of the amphibolite show that these newly discovered Late Archean supracrustal rocks were formed at 2 524±18 Ma and metamorphosed at 2 477±21 Ma.The time interval between emplacement and metamorphism is about 47 Ma.These Late Archean supracrustal rocks confirm that the Archean crystalline basement once existed to the north of the Qinghe fault,and that the structural environment between the Qinghe fault and the Kouhe fault was actually the Late Archean greenstone belt,the same as the Qingyuan area.