辽西地区太古宙—古元古代岩石组合及其研究进展

MAIN PROGRESS IN THE STUDY OF ARCHEAN-PALEOPROTEROZOIC ROCK ASSEMBLAGES OF THE WESTERN LIAONING PROVINCE

辽西地区是华北克拉通东部陆块的一部分,大面积出露了太古宙—古元古代的古老岩石,是研究华北地壳早前寒武纪演化的重点地区之一。辽西地区太古宙岩石组合以TTG质和花岗质变质深成岩为主,少量变质表壳岩以包体或构造残片形式赋存在变深成岩中;古元古代(2.5~1.6Ga)岩石组合包括长城系裂谷沉积岩和碱性侵入杂岩。最新的区调成果以及地质—地化数据表明,辽西地区记录的太古宙岩浆—变质事件主要集中在约2.55~2.50Ga之间,其形成与洋壳俯冲有关;该区缺乏约2.50~1.85Ga构造—热事件的记录,约1.72~1.70Ga是该区另外一期强烈的岩浆活动,其形成与华北东、西部陆块最终碰撞(约1.85Ga)之后的构造伸展有关。

The Western Liaoning Province（WLP）,one of the major Archean-Paleoproterozoic terranes in China,is located at the northeastern margin of the Eastern Block of the North China Craton（NCC）.The region is composed dominantly of early Precambrian ancient rocks as one of the important terranes for studying the Neoarchean-Paleoproterozoic evolution of the NCC.The Archean rock assemblages include a large number of plutonic TTG gneisses and granitoid gneisses and a small amount of supracrustal rocks and the supracrustal rocks are frequently preserved as enclaves or tectonic blocks within the plutonic gneisses.The Paleoproterozoic（2.5-1.6Ga）rocks belong to two major lithological units,namely the rift-related supracrustal rocks of the Changcheng Group and the alkaline plutonic complex.Geochemical and zircon U-Pb-Hf isotope data reveals the Neoarchean-Paleoproterozoic geologic succession of the WLP,and the major Archean magmatic and metamorphic event at^2.55-2.50 Ga was recorded,which resulted from a subduction-related environment.The zircon U-Pb ages between ~2.50-1.85 Ga were absent,but a late magmatic episode at^1.72-1.70 Ga was recorded in the WLP.The geochemical features of these^1.72-1.70 Ga magmatic rocks suggest that they are probably emplaced within a post-collisional setting that postdated the final amalgamation of the NCC.