CCSD超高压变质金红石U-Pb定年及其约束意义

U-Pb Dating and its constraints on genesis of ruffles from UHP metamorphic rocks from CCSD.

本文尝试性地对来自中国大陆科学钻探(CCSD)主孔及地表的超高压(UHP)变质榴辉岩中的金红石进行了U-Pb定年研究,初步获得了211±22Ma的等时线年龄,这是苏北地区榴辉岩型金红石矿床的第一个直接的年龄结果,结合前人在大别山地区获得的首个准确的金红石U-Pb年龄:218Ma及金红石U-Pb体系大约500℃的封闭温度分析,该年龄代表的是UHP变质峰值期后板块折返过程的冷却年龄,峰值期形成的金红石在此时发生了变质重结晶作用。此年龄对整个苏鲁UHP变质地体的俯冲-折返历史及本地区榴辉岩型金红石矿床的形成过程都有重要的约束意义。

U-Pb dating of ultrahigh pressure metamorphic rutiles from CCSD was performed in this study, which yields an isochron U-Pb age of 211 +/- 22Ma. Compared with age of rutiles (218Ma) from Dabie area and the closed temperature around 500 degrees C, it suggested that the age may represent a cooling age, but not the peak age of UHP metamorphism. The rutile mineralization occurs mainly during the peak of UHP metamorphism, and the age around 210Ma may represent the recrystallization during the amphibolite-facies retrogression stage of eclogites. This age also imply that subduction and exhumation of slab was quite quick in CCSD area. In addition, this study also shows that rutile is a suitable accessory mineral for U-Pb dating and rutile age can be used as a complementary method to explain the zircon SHRIMP age.