Petrogenesis and geodynamic implications of the Xiema and Ziyunshan plutons in Hunan Province, South China Kai-Xing Wang a,b,c,⇑ , Wei-Feng Chen c , Pei-Rong Chen c , Hong-Fei Ling c , Hui Huang b a Earth Science, East China Institute of Technology, Nanchang 330013, China b State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, Nanchang 330013, China c State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China article info Article history: Received 9 December 2014 Received in revised form 13 August 2015 Accepted 14 August 2015 Available online 15 August 2015 Keywords: Mesozoic Granitoids Geochemistry South China abstract To understand the Mesozoic tectonic settings of the South China Block, samples collected from the Xiema and Ziyunshan plutons were analyzed with respect to zircon age, whole-rock and biotite chemical com- position, whole-rock Sr–Nd and zircon Hf isotopic composition. Petrographic analysis and zircon LA-ICP- MS dating reveal that the Xiema pluton and the outer portion of the Ziyunshan pluton are composed of Late Triassic (Indosinian) biotite granodiorites and quartz monzonites with contemporaneous mafic microgranular enclaves (hereafter MMEs), whereas the inner part of the Ziyunshan pluton consists of Early Jurassic (Yanshanian) biotite granites and two-mica granites. Elemental and isotopic geochemical characteristics demonstrate that the Late Triassic granites are I-type granites and the Early Jurassic gran- ites are S-type granites; furthermore, the data suggest that the two types of granites originated from dif- ferent sources. The Late Triassic granites were mainly derived from the partial melting of Proterozoic meta-greywacke and meta-basalts at temperatures of 758–814 °C and log(fO 2 ) values of 13 to 12. The residual mineral phases contain plagioclase, clinopyroxene/orthopyroxene, and quartz. At melting temperatures of 738–772 °C and log(fO 2 ) values ranging from 15 to 13, the Early Jurassic granites orig- inated from the partial melting of Proterozoic greywacke, with K-feldspar, ilmenite, clinopyroxene/ orthopyroxene, and zircon serving as residues in the source. Geochronology and geochemistry data sug- gest that the Late Triassic granites were formed under the extension environment caused by the Early Mesozoic post multi-plate convergence tectonic setting, whereas the Early Jurassic granites formed in an intracontinental extensional setting. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The South China Block (SCB) is a granite province with strong Mesozoic magma activity and a large number of exposed intrusive and extrusive rocks and related deposits (Zhou et al., 2006). Intru- sive rocks are mainly granitoids, with minor mafic rocks, that can be divided into two periods: the Early Mesozoic (Late Triassic or Indosinian) and the Late Mesozoic (Jurassic and Cretaceous or Yan- shanian). Previous studies have focused intensively on the Late Mesozoic granitoids and their relationship to mineralization, whereas the Early Mesozoic granitoids have not received much attention. In recent years, with the extensive use of high- precision in situ zircon U–Pb isotope dating techniques, some gran- itoids that were previously regarded as Yanshanian granitoids have been confirmed to have formed in the Indosinian period (Sun et al., 2003; Xu et al., 2003; Ling et al., 2005). Moreover, studies on hydrothermal uranium deposits hosted in granitoids and volcanics illustrate that the Indosinian granitoids play a more important role than the Yanshanian granites in South China because most of the basements or wall rocks in hydrothermal-type uranium deposits are Indosinian granitoids (Chen et al., 2000; Chen, 2004; Lu and Wang, 1991; Zhang et al., 2002, 2003; Xu et al., 2003). Therefore, it is useful to re-evaluate the Indosinian granitoids and their spatial distribution in South China for uranium deposit prospecting. Recently, many Indosinian plutons, including the Baimashan, Wawutang, Miaoershan, Weishan and Guandimiao plutons, have been extensively studied in central-west Hunan Province (Ding et al., 2005; Chen et al., 2006, 2007; Y. Wang et al., 2007; Xie et al., 2008), but the Xiema and Ziyunshan plutons have rarely been considered. The Xiema and Ziyunshan plutons are located on the borders of Xiangtan, Xiangxiang, Hengshan, Hengyang and Shuang- feng of Central Hunan Province, with an exposed area of approxi- http://dx.doi.org/10.1016/j.jseaes.2015.08.017 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Earth Science, East China Institute of Technology, No. 418 Guanglan Road, Nanchang 330013, China. E-mail address: xy2gmo02@ecit.cn (K.-X. Wang). Journal of Asian Earth Sciences 111 (2015) 919–935 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes