华北中部造山带南缘华山地区太华变质杂岩中锆石U-Pb定年

摘要

Exposed in the Huashan Mountains, southern margin of the Trans-North China Orogen, the Taihua Metamorphic Complex is an appropriate window from which the Precambrian tectonic evolution of the basement of the Trans-North China Craton can be deciphered. Intercalated TTG gneisses, amphibolitic gneisses, felsic gneisses and metapelitic gneisses are widely distributed elsewhere in the Huashan Taihua Metamorphic Complex, and three deformationai events and different metamorphic mineral assemblages formed during the three metamorphic stages have been recognized. SIMS and LA-ICP-MS U-Pb chronological measurements of zircons separated from the metamorphic rocks suggest that the protoliths of the amphibolites were formed at about 2. 29 Ga and the metamorphic event occurred at about 1. 94 -~1. 82 Ga, respectively. The available geochronologic data imply that the Precambrian metamorphism of the Huashan Taihua Metamorphic Complex not only occurred earlier than, but also lasted longer than that of the other metamorphic terranes within middle and northern Trans-North China Craton.%华山太华变质杂岩出露于华北克拉通中部造山带最南缘,区内斜长角闪片麻岩呈“透镜状”或“似层状”产出于黑云斜长片麻岩或TTG片麻岩中.大多数含有石榴子石变斑晶的变质岩中,保留了至少3期变形形迹和3个阶段的变质矿物组合.本文对斜长角闪片麻岩和黑云斜长片麻岩中的锆石,进行了SIMS和LA-ICP-MSU-Pb定年.斜长角闪片麻岩的岩浆锆石年龄为2.29 Ga,表明其原岩形成于古元古代.斜长角闪片麻岩、黑云斜长片麻岩中的变质锆石及锆石变质增生边年龄为1.94～1.82 Ga,表明华山地区比华北克拉通中部造山带中段及北段其他地区普遍记录的约1.85 Ga的变质事件,不仅早了约0.1 Ga,且变质事件持续达0.1 Ga之久.这说明华北中部造山带前寒武纪期间的构造-变质事件是一个比较漫长的复杂过程.