Precambrian Research 243 (2014) 39–62 Contents lists available at ScienceDirect Precambrian Research jou rn al h om epa ge: www.elsevier.com/locate/precamres Neoproterozoic arc-related mafic–ultramafic rocks and syn-collision granite from the western segment of the Jiangnan Orogen, South China: Constraints on the Neoproterozoic assembly of the Yangtze and Cathaysia Blocks Jinlong Yao a , Liangshu Shu a,∗ , M. Santosh b , Guochun Zhao c a State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China b School of Earth Sciences and Resources, China University of Geosciences Beijing, No. 29 Xueyuan Road, Haidian District, Beijing 100083, China c Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China a r t i c l e i n f o Article history: Received 25 June 2013 Received in revised form 16 October 2013 Accepted 31 December 2013 Available online 9 January 2014 Keywords: Jiangnan Orogen South China Granite and mafic–ultramafic rocks Neoproterozoic assembly Geochemistry Geochronology a b s t r a c t The Jiangnan Orogen is considered as the trace of the collisional suture between the Yangtze and Cathaysia Blocks in South China. Here we investigate the mafic–ultramafic suites and granitoids exposed in the Yuanbaoshan area along the western segment of the Jiangnan Orogen. We present new LA-ICP-MS zir- con U–Pb data, Hf isotopes and whole rock geochemistry from a suite of granite, gabbro diorite and mafic–ultramafic rocks from this area. Zircons in the mafic rocks yield a U–Pb age of 854.7 ± 5.3 Ma, whereas those from the granites show ages of 822.6 ± 5.2, 830.7 ± 5.0, 823.8 ± 5.3 and 833.0 ± 5.9 Ma. The Neoproterozoic mafic–ultramafic rocks display dominantly tholeiitic features and are characterized by negative Ba, Nb, Ta, Zr, Hf and Sr anomalies and LREE enriched patterns, with a minor negative Eu anomaly. The gabbro diorite also exhibits similar geochemical characters. The mafic suite plots in the field of volcanic arc basalt in tectonic discrimination diagrams and displays distinctive geochemical sig- natures of an arc setting. The zircons from these rocks show εHf(t) values in the range of 3.9–13.8. The granitoids in northern Guangxi are typical S-type granites with high ACNK values (1.15–1.40), and are classified as collision-related granites in tectonic discrimination diagrams. The zircons from these rocks show negative εHf(t) values of -18.99 to -0.84. We correlate the granitoids with the continent–continent collisional orogeny between the Yangtze and Cathaysia Blocks. Our new results suggest a ∼854 Ma vol- canic arc and an 840–820 Ma collisional setting in the western segment of the Jiangnan Orogen, which is different from previous proposals of plume and bimodal magmatic settings and place the timing of assembly of the Yangtze and Cathaysia Blocks at some time ca. 850–800 Ma. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The South China Craton (SCC), one of the major crustal blocks in East Asia, is composed of two distinct tectonic units, namely the Yangtze Block to the northwest and the Cathaysia Block to the southeast (Fig. 1). The role and juxtaposition of the SCC within the Neoproterozoic supercontinent Rodinia have been topics of long debate (e.g., Li et al., 2008a,b; Wang et al., 2006, 2012a; Peng et al., 2012; Xia et al., 2012; Zhang and Zheng, 2013; Zheng et al., 2013). The nature and timing of the initial collision of the Yangtze and Cathaysia Blocks is important to understand the assembly of the Rodinia supercontinent. Recent geological, geochronological and geochemical studies of the magmatic and sedimentary rocks in the ∗ Corresponding author. Tel.: +86 25 89680700. E-mail addresses: Lsshu2003@yahoo.com.cn, lsshu@nju.edu.cn (L. Shu). Jiangnan Orogen suggest that the two blocks collided in the Neo- proterozoic (Fig. 1) (e.g., Chen et al., 1991; Charvet et al., 1996; Guo et al., 1980, 1985; Li et al., 1999, 2003a,b, 2007; Shu, 2006; Shu and Charvet, 1996; Wang et al., 2012b; Xu et al., 2013; Yao et al., 2012; Zhou and Zhu, 1993; Zhang and Zheng, 2013). However, the timing of this assembly has not yet been precisely constrained. Some studies propose the amalgamation at ca. 1000–900 Ma (e.g., Li et al., 1995, 2002, 2007, 2008b; Greentree et al., 2006; Ye et al., 2007), correlating the Neoproterozoic Jiangnan Orogeny in South China (also called the “Sibao” or “Jinning” Orogeny) as part of the global Grenvillian-aged orogenic events (Li et al., 2002, 2008b). However, based on Precambrian stratigraphic sequences and mag- matic records, others suggest that the Jiangnan Orogeny lasted until 830 Ma, or even up to 800 Ma, and is not connected with the main Grenvillian orogeny (e.g., Wang et al., 2006, 2007, 2010, 2012a,b; Yao et al., 2012; Zhao and Cawood, 1999a,b, 2012; Zhao et al., 2011; Zhou et al., 2002). The existence of ca. 860 Ma arcs in both west and 0301-9268/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.precamres.2013.12.027