大别山岳西县石关混合岩锆石SHRIMP定年及其地质意义

SHRIMP U-Pb Dating of Migmatite in Shiguan of Yuexi County,Dabie Mountains and Its Geological Significance

安徽岳西县石关混合岩属于原北大别变质杂岩的一部分。锆石SHRIMPU-Pb定年结果:第一次变质时间为232Ma,相当于晚三叠世早期,第二次变质时间为207Ma,相当于晚三叠世晚期。复合锆石的核部(继承锆石)为发育韵律环带的岩浆碎屑锆石,其年龄值分别为560Ma、444Ma、394Ma、378Ma和331Ma,暗示其原岩非岩浆岩,而应为沉积岩;研究结果还表明,北大别石关混合岩经历了两次变质作用:①超高压变质作用,变质时间为232Ma(n=5加权平均年龄);②退变质作用,时间为207Ma。与苏鲁地区超高压变质和退变质时间一致。

Shiguan migmatite of Yuexi County is part of former North Dabie Complex. The zircon SHRIMP U- Pb dating shows： the first metamorphism occurred at 232 Ma, equivalent to early period of Late Triassic, and the second metamorphic at 207 Ma, equivalent to late period of Late Triassic. Magmatic detrital zircons with well developed rhythmic zoning constitutes the core of the composite zircon and have the ages of ages of 560,444,394,378 and 331 Ma respectively, suggesting that protolith was not magmatic rock instead of sedimentary rock. Research also shows that the Shiguan migmatite of the North Dabie has gone through two metamorphisms： （1） ultra-high pressure metamorphism at the time of 232 Ma （n=5, mean age） and 2） retrograde metamorphism at 207 Ma. The two ages of metamorphism are consistent with the time of ultrahigh-pressure metamorphic and retrograde metamorphism in Sulu region.