Jurassic and Cretaceous (Yanshannian) tectonics, magmatism and metallogenesis in South China: preface

ABSTRACT

South China is famous for its poly-metal deposits, with more than 50% of global W and Sb reserves, 20% of global Sn reserves, as well as abundant Cu-Mo-Pb-Zn-Au-Ag, Ta, Nb, REE and U deposits. This special issue consists of 21 papers, reporting recent progress on Yanshannian tectonic evolution, magmatism and ore deposits in South China, aiming at better understandings on the Mesozoic large-scale magmatism and mineralization events.

KEYWORDS:

• Jurassic-Cretaceous (Yanshannian) tectonics
• magmatism
• poly-metal deposits
• metallogenesis
• South China

Eastern China experienced major geologic events in the Late Jurassic to the Early Cretaceous. Two major unconformities were identified in the Yanshan Mountains northwest of Beijing and named as the Yanshanian Movement 90 years ago (Wong 1927). This term has since been used to describe major Jurassic and Cretaceous tectono-magmatic events all over China. The term is also applied to ore deposits; South China is famous for its poly-metal deposits, with more than 50% of global W and Sb reserves, 20% of global Sn reserves, as well as abundant Cu-Mo-Pb-Zn-Au-Ag, Ta, Nb, REE and U deposits. This special issue consists of 21 papers, reporting recent progress on Yanshannian tectonic evolution, magmatism and ore deposits in South China, aiming at better understandings on the Mesozoic large scale magmatism and mineralization events.

Tectonically, the South China block is classified into two parts, the Yangtze craton and the Cathysia block separated by the central Jiangnan orogenic belt of Meso- to Neo-Proterozioc (c.a. 1100-800Ma) age. South China is famous for strong Jurassic to Cretaceous magmatism and mineralization, with more than 50% of the world’s W and Sb reserves, and 20% of the world’s total Sn reserves, all of which rank No. 1 in the world. Its Ta, Nb and U reserves rank No. 1 in China, whereas heavy REE from S. China Yanshannian weathered granites dominates China’s REE markets. It consists of three major mineralization belts: the Nanling W-Sn, Nb-Ta, HREE belt in the south (Chen et al. 2016; Guo et al. 2018; Cheng et al. 2016; Hsü 1943; Mao et al. 2007), the Lower Yangtze River Cu, polymetallic belt in the north (Mao et al. 2006; Pan and Dong 1999; Sun et al. 2003; Ling et al. 2009; Yang et al. 2011; Yang and Lee 2011; Deng et al. 2016) and the Xiang-Qian-Gui Sb belt in the west (Rao 1999; Zaw et al. 2007; Ding et al. 2013). The Dexing porphyry Cu-Mo-Au and Xiang-Gan Pb-Zn-Ag deposit regions are located between the Nanling and Lower Yangtze River belts (Wang et al. 2006, 2011; Zhang et al. 2013, 2018b). Most of these deposits are closely associated with a large igneous event that started in Jurassic and ended in Cretaceous time (Zhou et al. 2006). For the last several decades, the Chinese government has invested to support research and mineral exploration in this region.

South China is a unique crustal block. It is more like an orogenic belt that experienced multiple episodes of subduction: (1) South China has been located in a backarc setting during multiple subduction episodes since Paleozoic time, which may have pre-enriched the block in ore-forming materials. (2) Pacific plate subduction was a principal factor controlling Mesozoic large scale magmatism and mineralization in South China, through flat subduction, ridge subduction and slab rollbacks.

Several tectonic models have been proposed to account for Yanshanian magmatism and mineralization in South China, including four main points: (1) an Andean-type active continental margin related to the northwestward (Jahn et al. 1990; Zhou and Li 2000; Zhou et al. 2006; Li and Li 2007), or southwestern subduction of the Pacific plate in Mesozoic time (Sun et al. 2007, 2010, 2011, 2012a, 2012b); (2) intraplate lithospheric subduction as a result of closing an oceanic basin in the interior of South China (Hsü et al. 1990); (3) wrench faulting, continental rifting and extension (Gilder et al. 1991); (4) Mesozoic mantle plume activity beneath South China (Deng et al. 2004).

This special issue reports more comprehensive studies on the tectonics, petrology and ore deposits in South China, providing stronger constraints and better understanding of Yanshannian magmatism and mineralization (Figure 1). The contributions are:

1. Petrogenestic and metallogenic implications of Early Cretaceous high-K calc-alkaline magmatism along the Middle-Lower Yangtze Metallogenic Belt. Several scholars concentrated their work on the Tongling, Anqing, Guichi and Ningwu ore-cluster region (Fan et al. 2018; Wu et al. 2018; Yang et al. 2018; Liu et al. 2018a; Wang et al. 2018a). They have detailed work on regional geology, tectonic setting, magmatism and Fe-Cu-Au deposits, providing geochronological and geochemical constraints. Their work documented the genesis of magmatism and Fe-Cu-Au deposits, suggesting that paleo-Pacific plate subduction caused massive igneous activity and poly-metal mineralization (Xie et al. 2017, 2018; Gu et al. 2018; Hu et al. 2018).

2. Magmatism at the north margin of the Yangtze Craton was dominated by subduction of the Yangtze and North China Cratons, leading to special metal mineralization, such as the Cretaceous ore-bearing granitoids in the Beihuaiyang Zone along the northern margin of the Dabie Orogen, which is closely related to massive Mo deposits (Liu et al. 2018b). Recycling of paleo-Pacific subducted oceanic crust related to a Fe-Cu-Au mineralization in the Xu-Huai region of North Anhui-Jiangsu is a unique mineralization system, where a series of Early Cretaceous skarn deposits and genesis of their host diorite/monzodiorite porphyry was proven to be of high oxygen fugacity, suggesting that these Early Cretaceous igneous suites associated with Fe-Cu-Au deposits are related to recycled subducted Pacific oceanic crust (Zheng et al. 2018). There is a special point that favors the origin of Early Cretaceous adakitic pluton in Guandian in North Anhui province as partial melting of delaminated lower continental crust triggered by ridge subduction (Luo et al. 2018).

3. Late Jurassic magmatism in the central part of the South China Block. Studies in the special issue concentrate on the Nanling region, including studies of the Laoshan’ao shear zone and the Xiangdong Tungsten deposit (Wei et al. 2018) and a review of Late Mesozoic A-type granites associated with W–Sn mineralization in the Nanling range (Cao et al. 2018) .

4. Zircon U–Pb age and Hf isotopic compositions and petrogenesis of igneous rocks in the South China Block (Yang et al. 2018), including the Late Cretaceous basalts and rhyolites from the Shimaoshan Group in eastern Fujian Province (Li et al. 2018), adakitic rocks in the Middle-Lower Yangtze Metallogenic Belt formed mainly as slab melts with contributions from enriched mantle (Xie et al. 2017; Gu et al. 2018; Hu et al. 2018). Mid-Late Cretaceous igneous activity on Hainan Island suggests that subduction of the E-W trend Neo-Tethys plate was the main cause (Sun et al. 2018). Cretaceous A-type volcanic–intrusive rocks and contemporaneous mafic rocks along the Gan-Hang Tectonic Belt have been studied to illustrate their petrogenesis and implications for crust-mantle interactions (Wang et al. 2018b).

Figure 1. Localities of the important tectonic belts, ore deposits and igneous rocks related to the special issue ‘Jurassic and Cretaceous (Yanshannian) Tectonics, Magmatism and Metallogenesis in South China’.

It has long been a mystery why more than half of the world’s W and Sb reserves are located in South China. Both W and Sb deposits are located in backarc settings away from the convergent plate margin. Multiple plate subductions in South China may have provided multiple enrichment pulses of W, Sb and also Sn. Southwestward flat subduction and subsequent slab rollback controlled the major magmatism and mineralization events in South China. Decomposition of phengite during the slab rollback may explain the high Li and F granites in the Nanling region and formation of other highly evolved granites.

Authors of the 21 contributions of this SI are from top universities and institutes in China, including in University of Science and Technology of China, University of the Chinese Academy of Sciences(CAS), Nanjing University, Tianjing University, Central China University, Ocean University of China, Hefei University of Technology, Institute of Geology and Geophysics (CAS), Qingdao National Laboratory for Marine Science and Technology (CAS), Guangzhou Institute of Geochemistry(CAS), Chinese Academy of Geoscience, and Institute of Geology of Uranium.

Acknowledgments

Most of the contributions to this special issue were supported by the DREAM project of China. We thank Dr. Bob Stern for super editorial handlings and many referees for constructive review comments.

Disclosure statement

No potential conflict of interest was reported by the authors.