TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 53, 2019

Petrogenesis and tectonic setting of the Wulong two-mica monzogranite on Liaodong Peninsula, NE China: constraints from zircon U-Pb and Hf-O isotopic data


1Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
2Department of Earth Sciences, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark
3College of Earth Science, University of Chinese Academy of Sciences, Beijing, China
4State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

(Received August 29, 2017; Accepted April 26, 2019)

Abstract: The petrogenesis and tectonic setting of Middle-Late Jurassic granitoids on Liaodong Peninsula, NE China, are debated. To resolve these uncertainties, this study analyzed geochemistry, zircon U-Pb ages and Hf-O isotopic compositions of the Wulong two-mica monzogranite on the Liaodong peninsula. Zircon U-Pb ages indicate that the Wulong monzogranite was intruded at ca. 168-162 Ma, and included an inherited population of Paleoproterozoic zircon grains (ca. 2.5-2.0 Ga). Wulong monzogranite is characterized by quartz, plagioclase, K-feldspar and minor muscovite and biotite. This S-type granitic intrusion has high SiO2 (>70 wt.%) contents, is high-K calc-alkaline, shows high zircon δ18O values (>7.5 ‰), and is weakly peraluminous (A/CNK = 1.01-1.08). The relatively low Sm/Nd (0.13-0.21), Rb/Sr (0.17-0.53) and FeOT/MgO (2.54-8.51) ratios suggest that Wulong monzogranite is weakly fractionated. Geochemical characteristics indicate that the monzogranite is probably derived from partial melting of a clay-poor, plagioclase- and biotite-rich psammitic source, such as metasedimentary rocks of the North China Craton. Moreover, the Wulong monzogranite displays high initial 87Sr/86Sr ratios (0.7099-0.7181), δ18O values (7.8 ‰ - 9.4 ‰), low εHf(t) values (-34.7 to -23.0) with two-stage Hf model ages (TDM2) of 2.67-3.40 Ga and εNd(t) (-24.9 to -21.2) values with two-stage Nd model ages (TDM2) of 2.67-2.96 Ga, suggesting that they may be the product of the melting of the Neoarchen-Paleoproterozoic metasedimentary basement of the North China Craton. Zircon saturation temperature and Ti-in-zircon thermometry indicate that Wulong monzogranite formed at ∼700°C, and high Sr/Y ratio and low HREE imply it was formed at depths within the stability field of garnet in a thickened crust. Taking the regional tectonic and magmatic activities into account, it is proposed that the Wulong monzogranite was generated in an active continental margin that involved the subduction of the Izanagi slab during the Middle-Late Jurassic.
Key words: Zircon U-Pb age; Element geochemistry; Hf-O isotopic composition; Liaodong Peninsula; North China Craton

*Corresponding author E-mail: wangyongbin@mail.iggcas.ac.cn