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对北大别漫水河和凤凰关2个地区混合岩中的锆石进行了CL显微结构分析和SHRIMP法U-Pb定年.漫水河混合岩中的锆石具有明显的核边结构,核部锆石具有扇形分带或弱分带特征,低的Th/U比值(0.01～0.17),为变质流体中生长锆石,U-Pb年龄为(137±2)Ma;边部锆石具有显示面状分带或云雾状分带特征,高的Th/U比值(0.35～0.69),为变质熔体中生长锆石,U-Pb年龄为(124±2)Ma.凤凰关混合岩中的锆石同样具有核边结构,核部锆石具有弱的岩浆环带或无分带特征,Th/U比值较高(0.21～3.03),年龄为(768±12)Ma,为经历不同程度重结晶作用的原岩岩浆锆石;边部锆石则没有明显的分带特征,Th/U比值很低(0.01～0.09),为变质流体中生长锆石,U-Pb年龄为(137±4)Ma.这些结果表明,大别山存在两期混合岩化变质事件,早期(137±2)Ma事件以变质脱水为主,而晚期(124±2)Ma事件出现部分熔融.部分混合岩的原岩为新元古代中期,与大别-苏鲁造山带超高压变质火成岩原岩年龄一致.因此,大别碰撞造山带山构造从挤压到伸展构造体制转换的最小时间为(137±2)Ma,北大别混合岩化与同时期花岗岩和麻粒岩之间存在着成因联系,它们都是俯冲加厚的扬子地壳部分熔融的产物.
CL microstructure analysis and SHRIMP U-Pb dating of zircons in the mixed rocks of Manchuanshui and Fenghuanguan areas in the North Dabie River have been carried out.The zircons in the Manshuihe mixed rock have obvious nuclear edge structure, Zircon has a fan-shaped or weak zonation with a low Th / U ratio (0.01-0.17) for the zircons grown in the metamorphic fluid and the U-Pb age is (137 ± 2) Ma. The marginal zircons have been shown Surface zonation or cloud-like zonation. The high Th / U ratio (0.35-0.69) is the zircon that was grown in the metamorphic melt and the U-Pb age was (124 ± 2) Ma. Zircon also has a nucleus structure. Nuclear zircons have weak magmatic zoning or no zoning characteristics. The Th / U ratio is high (0.21-3.03) and age is (768 ± 12) Ma, The zircons from the protolith magma show no obvious zonation and the Th / U ratio is very low (0.01-0.09). For the zircons from the metamorphic fluids, the U-Pb age is (137 ± 4) ) Ma. These results show that there are two mixed metamorphic events in the Dabie Mountains, the early (137 ± 2) Ma events are dominated by metamorphic dehydration, and the late (124 ± 2) Ma events are partially melted. For the Neolithic mid-term, Which is consistent with the age of Proterozoic metamorphic igneous rocks in the Dabie-Sulu orogenic belt, so that the minimum time for the Dabie collision orogenic belt to transform from compression to extensional structure is (137 ± 2) Ma, There is a genetic relationship between granite and granulite in the same period, which are all products of partial melting of the subducted Yangtze crust.