Petrogenesis of Laocheng Granite in South Qinling: Constraints from Zircon U-Pb Age and Sr-Nd Isotopic Composition(PDF)
《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]
- Issue:
- 2017年第05期
- Page:
- 633-651
- Research Field:
- 基础地质与矿产地质
- Publishing date:
Info
- Title:
- Petrogenesis of Laocheng Granite in South Qinling: Constraints from Zircon U-Pb Age and Sr-Nd Isotopic Composition
- Author(s):
- FANG Bo-wen; ZHANG He; YE Ri-sheng; WANG Yan; CHEN Fu-kun
- School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, Anhui, China
- Keywords:
- geochemistry; granite; host rock; enclave; Early Mesozoic; zircon U-Pb age; Sr-Nd isotope; South Qinling
- PACS:
- P588.12+1;P597
- DOI:
- -
- Abstract:
- Laocheng pluton exposed in Ningshan area of South Qinling, together with Wulong pluton, consist of an important part of Early Mesozoic granitoid magmatism in central South Qinling. Abundant mafic enclaves can be found in different units of Laocheng pluton. Analysis results of zircon U-Pb ages show that the host rock from Laocheng pluton is emplaced in 213-219 Ma, and its mafic enclaves are crystallized in 211 Ma, which are more or less simultaneous with the formation of Wulong pluton. Geochemical data show that the host rock from Laocheng pluton is granodiorite and quartz monzonite in composition with the characteristics of low Si, rich alkali, weak peraluminous and high Mg#(52~67), and belongs to high-K calc-alkaline I-type series; mafic enclaves are mainly dioritic, having the characteristics of low SiO2 (52.6%-62.4%), rich alkali and high Mg#(63-72), belonging to shoshonite series. Compared with the host rock, the mafic enclaves have lower initial N(87Sr)/N(86Sr) (0.704 66-0.705 82), highεNd(t) (-4.3--1.6) and higher Mg#, suggesting that the primary magma of the enclaves might have originated from a basaltic magma. Sr-Nd isotope geochemistry suggests that the host rock and mafic enclaves have exchanged prior to the formation of Laocheng pluton, and an equilibrium has been reached. Compared with Sr-Nd isotope ratio of basement rocks exposed in South Qinling, it is suggested that the magma of Laocheng granite originates from Neoproterozoic mafic crustal material. Relationship between host rock and mafic enclaves indicates that a magma mixing between the crystallizing acid magma and the basic magma slightly later injects into the magma chamber; these two magmas are not completely miscible during the mixing process.
Last Update: 2017-10-19