The Late Jurassic extensional event in the central part of the South China Block – evidence from the Laoshan’ao shear zone and Xiangdong Tungsten deposit (Hunan, SE China)

Abstract

International audienceThe Late Mesozoic tectonics strongly reworked the tectonic framework of East Asia. In the South China Block (SCB), the major Late Mesozoic phenomena are featured by numerous magmatic activities, (half-) graben basins opening, and abundant ore deposits formation. The intrinsic relationships of these phenomena with the tectonic regime are still hotly debated, partly due to the lack of structural data. To advance the understanding of these issues, we conducted a detailed structural analysis including field and microscopic observations as well as an Anisotropy of Magnetic Susceptibility (AMS) investigation in the Laoshan’ao shear zone (LSA), which is the northern branch of the major Chaling–Chenzhou–Linwu Fault (CCLF) in the SCB. The new data enable us to reach the following conclusions: the evolution of the LSA can be divided into three deformation phases. D1 is a NW–SE-stretching event featured by the SE-dipping normal fault with a top-to-the-SE shear sense, coeval with the emplacement of the 154 Ma Batuan syn-tectonic pluton that leads to the development of the Xiangdong tungsten deposit and the opening of the Cretaceous Chaling basin; D2 is a NE–SW-striking dextral strike–slip event that dislocated the ore veins formed during the D1 event; D3 is a NW-directed thrusting event that cross-cut the previous gneissic foliation. D1 is the major event of the LSA shear zone, interpreted as the reactivation of the CCLF in response to the Late Mesozoic tectonics in the SCB, and indicates a NW-SE extensional regime since the Late Jurassic in the study area. This study also provides an example for an ore-forming process controlled by both the hydrothermal fluid coming from a syn-tectonic granite and the accommodation of tension gashes opened by the regional extensional event

Magmatic record of the Mesozoic geology of Hainan Island and its implications for the Mesozoic tectonomagmatic evolution of SE China: effects of slab geometry and dynamics in continental tectonics

“…These plutons locally intruded into thick sequences of basaltic, dacitic, rhyolitic volcanic rocks and alkaline basalts, which were also erupted within NE-SW-oriented grabens ( Fig. 12b; Wei et al 2018). The Jurassic magmatism was hence associated with extensional deformation in a~400 km wide belt, characterized by a Basin and Range-type crustal structure, which included lacustrineplaya lake deposits, evaporites and alluvial fan systems interspersed with bimodal volcanic sequences (see Wang & Shu (2012), and references therein, for an overview of the distribution of Mesozoic metamorphic core complexes in SE China, and Ni et al (2013) for the occurrence of a metamorphic core complex in E China).…”

“…Extensional tectonic and magmatic features in SE China include normal fault systems, metamorphic core complexes, and volcanic-plutonic belts with diverse compositions and geochemical affinities (Figs 1, 2;Wang & Shu, 2012;JH Li et al 2014;J Li et al 2016;Wei et al 2018). The main interpretations and models for the origin of these magmatic suites and the extensional fault systems include: (1) post-collisional collapse of thick continental crust (Zhou et al 2006;; (2) large-scale aesthenospheric upwelling associated with the break-up of Gondwanã 190 Ma, leading to lithospheric thinning and magmatism between~180 and 80 Ma (Wilde et al 2003;;…”

“…The post-orogenic collapse models are problematic because: (a) granitic plutons and their volcanic counterparts in E-SE China are much more extensive in their areal coverage beyond the collision zones (i.e. Qinling-Dabie, Sulu, Ailaoshan and Jiang Saho sutures and fault zones), and these plutonic-volcanic rocks are spatially and temporally associated with extensional tectonic features (see, for example, Shu et al (2009) and Wei et al (2018) for Jurassic, and Yang et al (2011), Zhao et al (2019) and for Cretaceous magmatic suites and related extensional tectonics); (b) their emplacement times are at least~60-80 Ma after the collisional events, which represents a very large time window in comparison to an average timespan for the initiation of post-collisional magmatism in other Mesozoic and Cenozoic orogenic belts (for some examples, see Dilek & Moores, 1999;Dilek & Whitney, 2000;Dilek, 2006;Dilek et al 2010;Jamali et al 2010); and (c) there is no viable explanation for the heat source to drive the lithospheric-scale magmatism. Significant variations in the geochemistry and melt origin of the plutonic and volcanic rocks do not support the second and third models above.…”

New Insight into the Genetic Mechanism of Shear Zone Type Gold Deposits from Muping-Rushan Metallogenic Belt (Jiaodong Peninsula of Eastern China)

“…Shear zones are one type of strain localization structures [1], which are widely developed in various structural environments. As weak zones in regions, shear zones are always concentrated for intense magma activities, fluid actions and metamorphism, hence provide favorable transport channels and precipitation spaces for ore-forming elements, e.g., Au, Ag, Cu, Pb, Zn, W, Sn and Mo [2][3][4][5][6][7]. Many gold deposits are host in, or spatially associated with first-and second-order shear zones [8][9][10][11][12][13][14][15], which we call the shear zone type gold deposits (SZTGD).…”

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

“…(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).…”