ORIGINAL PAPER Yuejun Wang Æ Weiming Fan Æ Touping Peng Æ Feng Guo Elemental and Sr–Nd isotopic systematics of the early Mesozoic volcanic sequence in southern Jiangxi Province, South China: petrogenesis and tectonic implications Received: 2 October 2003 / Accepted: 27 August 2004 / Published online: 14 October 2004 Ó Springer-Verlag 2004 Abstract Elemental and Sr–Nd isotopic results are pre- sented for the early Mesozoic volcanic sequence (172 Ma) in southern Jiangxi Province, South China. The sequence is voluminously composed of 45% sub- alkaline basaltic rocks (group 1), <5% high-mg andes- ite–dacites (group 2) and 50% rhyolites (group 3). The group 1 rocks are characterized by (La/Yb) cn = 3.8–7.2, Eu/Eu* = 0.65–1.15, Nb/La = 0.64–0.99, 87 Sr/ 86 Sr(t) = 0.70602  0.70822 and  Nd (t) = 1.63 to +0.11, similar to those of an EMII-like source. The group 2 rocks have mg=0.42  0.60, SiO 2 =60.24  66.71%, MgO =2.65  5.54%, Ni=24  102 ppm and Cr=84 266 ppm, classified as high-mg andesitic rocks. These rocks are more enriched in LILEs and LREE with more signifi- cant negative Eu anomaly (0.630.79), are more de- pleted in HFSEs with Nb/La ratios of 0.40–0.56 and have lower  Nd (t) (9.44 to 7.78) and higher 87 Sr/ 86 Sr(t) (0.70985  0.71016), in comparison with the group 1 rocks. They most likely originated from meta- somatised veins in the lithospheric mantle. The origi- nation of the group 1 and group 2 magma suggests the development of a peridotite-plus-vein lithospheric man- tle during early Mesozoic era beneath the interior of the Cathaysian block. The group 3 rhyolites are character- ized by high SiO 2 (72.75  77.97%), Zr (99  290 ppm), Hf (3.9  9.7 ppm) and Ga/Al (2.76  3.87) and significant Nb–Ta, Ba–Sr and P–Ti depletions. These rhyolites exhibit Sr–Nd isotopic compositions ( 87 Sr/ 86 Sr(t) = 0.709620.71104,  Nd (t) = 4.63 to 5.80) similar to the contemporaneous Zhaibei and Pitou A-type granites in the area. Such characteristics suggest that they might be derived from the underplating basaltic magma contaminated by crustal materials. Therefore, an early Mesozoic rifting model in response to intracontinental lithospheric extension is proposed to account for the early Mesozoic volcanism in southern Jiangxi Province, South China. Keywords Elemental and Sr–Nd isotopic systematics Æ Early Mesozoic volcanism Æ Peridotite-plus-vein lithospheric mantle Æ Intracontinental lithospheric extension Æ South China Introduction The Cathaysian block, which is also termed the ‘‘Hua- nan block’’ (Hsu¨ et al. 1990), is a major part of the South China Block (SCB). The block includes the ‘‘Southeast China Caledonian fold belt’’ and the ‘‘Southeast China maritime fold belt’’, which are separated by the Zhen- ghe-Dapu fault as illustrated in Fig. 1a (Chen and Jahn 1998), and has a complex history of tectono-magmatic evolution. Over the past 20 years, the tectonic nature of the Cathaysian block and the early Mesozoic tectonic history of the SCB have been debated (Hsu¨ et al. 1990; Faure et al. 1996; Rodgers 1989). Two distinct view- points can be summarized. One suggests that the early Mesozoic tectonic evolution of the region is related to either westward subduction of a Mesozoic Pacific plate, or the closure of an oceanic basin in the interior of the SCB, and as such, considers the region an Andean-type active continental margin (Holloway 1982; Faure et al. 1996), Alps-type collision belt (Hsu¨ et al. 1990) and a lithospheric subduction zone with underplating of mafic magma (Zhou and Li 2000). The other viewpoint favors an intracontinental lithospheric extension scenario in response to asthenospheric upwelling (Gilder et al. 1996; Li et al. 2003, 2004; Wang et al. 2003a, b). This view- point also proposes that the Cathaysian block is an old continental block, and the consolidation between the Cathaysian and Yangtze blocks took place during the Present address: Y. Wang (&) Æ W. Fan Æ T. Peng Æ F. Guo Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, 510640, Peoples Republic of China E-mail: yjwang@gig.ac.cn; wangyj6@21cn.com Tel.: +86-20-85290527 Fax: +86-20-85290708 Int J Earth Sci (Geol Rundsch) (2005) 94: 53–65 DOI 10.1007/s00531-004-0441-4