Zircon U-Pb Ages, Geochemistry and Sr-Nd-Pb Isotope Characteristics of Menglian Granites and Their Dark Enclaves in Tengchong Block of Western Yunnan, China(PDF)
《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]
- Issue:
- 2018年第05期
- Page:
- 563-581
- Research Field:
- 基础地质与矿产地质
- Publishing date:
Info
- Title:
- Zircon U-Pb Ages, Geochemistry and Sr-Nd-Pb Isotope Characteristics of Menglian Granites and Their Dark Enclaves in Tengchong Block of Western Yunnan, China
- Author(s):
- WAN Xin; YANG Yi-zeng; LI Shuang-qing; CHEN Fu-kun
- 1. Key Laboratory of Crust-mantle 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; granite; dark enclave; zircon U-Pb age; Early Cretacous; Sr-Nd-Pb isotope; Tengchong block; Yunnan
- PACS:
- P588.12+1；P597
- DOI:
- -
- Abstract:
- The Tengchong block in western Yunnan is an important component of East Tethys tectonic belt, and the Mesozoic and Cenozoic magmatism is widely distributed. The zircon U-Pb ages of Menglian granites and their dark enclaves in the southeastern Tengchong block indicate that they are formed in (127±2)Ma and (125±2)Ma, respectively. The main rock types of Menglian granites are quartz monzonite, granodiorite and biotite monzogranite, and the geochemical characteristics show that they are high K calc-alkalinity I-type granites with the aluminum saturation index point to S-type granites. Although the dark enclaves and granites show similar zircon U-Pb ages, the dark enclaves display smaller grain size, higher REE contents ((305.2-322.8)×10-6), higher w(Nb)/w(Ta) (18.2-19.5), lower Pb isotope compositions and depleted εNd(t), indicating that the dark enclaves should be heterogenous, and may be quenched by the mafic and felsic magma mingling or mixing process. The constant Sr-Nd isotope compositions with varying SiO2 contents suggest the crustal contamination is negligible. The Ba-Sr diagram implies the crystallization of plagioclase and K-feldspar for Menglian granites. The two-stage Nd model ages (1.37-1.58 Ga) and similar upper crust Pb isotope compositions indicate that the main material source of Menglian granites should be Mesoproterozoic Gaoligongshan Group. But in contrast to Gaoligongshan granites, the more depleted εNd(t) indicates that some mantle-derived materials should be involved. As a whole, the initial N(87Sr)/N(86Sr) (0.710 020-0.712 001) and εNd(t) (-4.6-2.1) of Menglian granites are similar to the granites in the northern magmatic belt of Lhasa block, suggesting the same formation environment. Combining with the island arc tectonic environment and the heterogenous dark enclaves with high w(Nb)/w(Ta), the Menglian granites and their dark enclaves may be formed by the subduction-collision-closure processes of the middle Tethys ocean.
Last Update: 2018-10-01