辽东古元古代热液铀矿床形成的大地构造背景

Tectonic Settings of Paleoproterozoic Hydrothermal Uranium Deposits in Eastern Liaoning Province, China

辽东半岛是胶-辽-吉古元古代造山带的一部分,经历了古元古代早期裂谷作用和古元古代末期碰撞造山过程。裂谷阶段形成了A型花岗岩(2.09~2.18 Ga)、辽河群沉积(2.05~1.93 Ga)。1.90~1.93 Ga期间裂谷闭合碰撞造山,辽河群遭受强烈变形、变质。1.83~1.90 Ga造山带构造折返,伴随垮塌、软流圈地幔上涌,发生区域退变质作用,形成造山后环斑花岗岩、斑状花岗岩、碱性正长岩和花岗伟晶岩。1.83 Ga辉绿岩的出现标志地壳进入伸展张裂阶段。尽管辽东地区古元古代铀矿化的类型多样,包括单铀型(3075铀矿床、410铀矿床)、铁-铀型(405铀矿床)、铁-硼-铀型(翁泉沟含铀铁硼矿床),但是铀的成矿时代一致,集中在1.83~1.90Ga。辽东地区古元古代末期的铀成矿作用形成于太古宙龙岗地块与狼林地块碰撞造山之后的伸展环境,可能与碰撞造山晚期俯冲陆块的构造折返和/或造山带垮塌及软流圈地幔上涌加热下地壳有关。

As part of the Paleoproterozoic Jiao-Liao-Ji orogenic belt,the eastern Liaoning peninsula underwent rifting in the early Paleoproterozoic and collisional orogenesis in the late Paleoproterozoic.The A-type granitoids(2.09 to 2.18 Ga)and Liaohe Group(2.05 to 1.93 Ga)were formed in the rifting process.The rift was closed due to collisional oogenesis at 1.90 to 1.93 Ga which led to the extensive deformation and metamorphism of the Liaohe Group.During 1.83 to 1.90 Ga,exhumation took place as a consequence of orogenic collapse and subsequent upwelling of asthenospheric mantle which is marked by the regional retrograde metamorphism,intrusion of post-orogenic rapakivi granites,porphyritic granites,alkaline syenites and granitic pegmatites.The^1.83 Ga diabase dykes indicated a regional crustal extension.The types of uranium mineralization in the eastern Liaoning peninsula are diverse,including single U,Fe-U,Fe-B-U mineralization,however,they are coeval with ages of 1.83 to 1.90 Ga.Therefore,the regional uranium mineralization in the eastern Liaoning peninsula of the Paleoproterozoic Jiao-Liao-Ji orogenic belt was formed in post orogenic extensional setting following the collision between the Archean Longgang and Langlin blocks.