Pb Isotopic Compositions of Mafic Lower Continental Crust in Dabie Orogen, China: Constraint from the Eclogites(PDF)
《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]
- Issue:
- 2017年第01期
- Page:
- 34-46
- Research Field:
- 基础地质与矿产地质
- Publishing date:
Info
- Title:
- Pb Isotopic Compositions of Mafic Lower Continental Crust in Dabie Orogen, China: Constraint from the Eclogites
- Author(s):
- GU Xiao-feng; LIU Yi-can; LIU Jia
- 1. Key Laboratory of Crustmantle Materials and Environments, Chinese Academy of Sciences, Hefei 230026, Anhui, China; 2. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, Anhui, China
- Keywords:
- geochemistry; eclogite; Pb isotope; mafic lower continental crust; Neoproterozoic; crustal contamination; continental deep subduction; North Dabie
- PACS:
- P597
- DOI:
- -
- Abstract:
- The eclogites from the North Dabie high-temperature and ultrahigh-pressure complex zone in central China have been previously documented by petrology and geochronology to be transformed from the Neoproterozoic mafic lower continental crust underneath South China block during the Triassic continental deep subduction. An integrated study of Pb isotopic geochemistry on the whole rocks and omphacites of the eclogites from North Dabie was carried out, providing new insight into the Pb isotopic compositions of the mafic lower continental crust. The results show that the eclogites here display low radiogenic Pb isotopic characteristics similar to the surrounding gneisses with even lower N(208Pb)/N(204Pb); (N(206Pb)/N(204Pb))i, (N(207Pb)/N(204Pb))i and (N(208Pb)/N(204Pb))i of the eclogites are 15.217-17.522, 15.077-15.540 and 35.219-38.082, respectively, showing the lowest Pb isotopic compositions in the three eclogite-bearing ultrahigh-pressure metamorphic slices of Dabie orogen, and documenting a mafic lower-crustal origin of their protoliths; the variation range of Pb isotopic compositions of the eclogites is large, and the lowest Pb isotopic compositions are demonstrated to be derived from the Paleoproterozoic to Archean mafic lower continental crust with low w(U)/w(Pb) and w(Th)/w(U), while the relatively higher Pb isotopic compositions are inherited from the Neoproterozoic mantle-drived magma, suggesting the precursors of the eclogites from North Dabie are formed by mantle-drived magma contaminated with variable degrees of ancient mafic lower continental crustal materials during the Neoproterozoic. Compared to the Pb isotopic compositions of the Mesozoic adakitic rocks derived from partial melting of delaminated lower continental crust in Dabie orogen, it is suggested that the recycled lower crustal materials contain both mafic and felsic lower-crustal rocks, implying the lowermost felsic lower continental crust together with the whole mafic lower continental crust in Dabie orogen may have been delaminated and recycled into the underlying convective mantle.
Last Update: 2017-01-20