Ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern Dabie Shan: U/Pb zircon geochronology

摘要: The Dabie Shan contains two rare geologic features. One, the occurrence of ultra-high pressure metamorphic rocks (peak P > 2.7 GPa = UHP) in east-central part this belt, and two, some these UHP are characterized by anomalously 18O-depleted oxygen isotopic compositions. Geochronological data presented that constrain age metamorphism, ages protoliths, potentially hydrothermal alteration believed to be responsible for anomalous metamorphism eastern is dated at 218.5 ± 1.7 Ma using U/Pb zircon separated from host gneisses. This identical within uncertainty with a less precise eclogite (225.5 + 3/−6 Ma) previously published eclogites Shan. Map relationships strongly support an in-situ, as opposed exotic, orgin region. gneisses provides additional interpretation. protolith 772.5 9.5 based on upper intercept zircons which accords well other dates granitic Qinling belt. association mafic felsic magmatism interpreted reflect rifting along northern margin Yangtze block time. These may date circulation meteoric water gave rise protoliths Sulu coincidence early Sinian glaciation South China consonant suggestion highly compositions region imprecisely determined 447 +82/−79 but younger than not