大别山北部榴辉岩和英云闪长质片麻岩锆石U-Pb年龄及多期变质增生

U-Pb Zircon Ages of the Eclogite and Tonalitic Gneiss from the Northern Dabie Mountains,China and Multi-Overgrowths of Metamorphic Zircons

大别山北部榴辉岩及英云闪长质片麻岩的锆石U Pb年龄分析表明 :北部榴辉岩相峰期变质时代为 2 2 6～ 2 30Ma左右 ;北部塔儿河一带英云闪长质片麻岩经历过印支期变质事件 ;大别山北部与南部超高压岩石中一致的 (2 2 6～ 2 30Ma)高压或超高压变质年龄表明 ,北部镁铁 -超镁铁质岩带中部分岩石也曾作为扬子俯冲陆壳的一部分 ,在印支期发生过高压或超高压变质作用 ;本区锆石发生过两期变质增生事件 ,一是印支期高压或超高压变质 ,另一期是燕山期热变质事件 ;榴辉岩及英云闪长质片麻岩的原岩形成时代为晚元古代 ;锆石U Pb年龄可用多期变质增生模型来解释。

The U?Pb zircon ages of the eclogite and tonalitic gneiss from the Northern Dabie Mountains were presented. The data suggest that: (1) the peak metamorphic age of the eclogite facies from the Raobazhai eclogite is 226～230 Ma; (2) the tonalitic gneiss near Ta'erhe underwent a Triassic metamorphic event; (3) zircon U?Pb ages of 226～230 Ma for the high?or ultrahigh pressure rocks from the Northern Dabie Mountains are similar to those from the Southern UHP metamorphic belt, implying that most of eclogites or tonalitic gneiss here should be a part of Yangtze subducted continental crust and underwent a Triassic HP or UHP metamorphism; (4) the protolith ages of both eclogite and tonalitic gneiss are Late Proterozoic Era; (5) they are both affected strongly by Early Cretaceous thermal event; (6) the zircons from eclogite and gneiss have experienced two episodes of overgrowths on the margin of old zircons during the Triassic HP or UHP metamorphism and the Early Cretaceous thermal metamorphism. The overgrowth model of zircon under multi?metamorphism is very helpful to interpret the U? Pb zircon data from the high?grade metamorphic rocks.