An early extensional event of the South China block during the late Mesozoic recorded by the emplacement of the late Jurassic syntectonic hengshan composite granitic massif (Hunan, SE China)

Wei Wei (1, 2, 3) , Yan Chen (2, 3) , Michel Faure (2, 3) , Guillaume Martelet (4, 2) , Wei Lin (5, 6) , Qingchen Wang (6) , Quanren Yan (1) , Quanlin Hou (1)

1 Key Laboratory of Computational Geodynamics
2 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
3 Géodynamique - UMR7327
4 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
5 Kochi Institute for Core Sample Research
6 SKL - State Key Laboratory of Lithospheric Evolution

Continental scaled extension is the major Late Mesozoic (Jurassic and Cretaceous) tectonic event in East Asia, characterized by faulting, magmatic intrusions and half-grabens in an area with a length of > 5000 km and a width of > 1000 km. Numerous studies have been conducted on this topic in the South China Block (SCB), However, the space and time ranges of the compressional or extensional regimes of the SCB during the Jurassic are still unclear, partly due to the lack of structural data. The emplacement fabrics of granitic plutons can help determine the regional tectonic background. In this study, a multidisciplinary approach, including Anisotropy of Magnetic Susceptibility (AMS), macro and micro structural analyses, quartz c-axis preferred orientation, gravity modeling and monazite EPMA dating, was conducted on the Hengshan composite granitic massif in SCB that consists of the Triassic Nanyue biotite granitic pluton and the Late Jurassic Baishifeng two-mica granitic pluton. The magnetic fabrics are characterized by a consistent NW-SE oriented lineation and weakly inclined foliation. A dominant high temperature deformation with a top-to-the-NW shear sense is identified for both plutons. The deformation increasing from the center of the Baishifeng pluton to its western border is associated to the development of the West Hengshan Boundary Fault (WHBF). The gravity modeling shows a “saw tooth-shaped” NE–SW oriented structure of the Baishifeng pluton, which may be considered as NE–SW oriented tension-gashes formed due to the NW-SE extension. All results show that the Triassic Nanyue pluton was deformed under post-solidus conditions by the WHBF coeval with the emplacement of the Late Jurassic Baishifeng pluton. All these observations comply with the NW-SE extensional tectonics coeval with the emplacement of the Baishifeng pluton, which argues that the NW-SE crustal stretching started since the Late Jurassic, at least in this part of the SCB.

Mots clés: South China Block; Hengshan composite granitic massif; syntectonic pluton; Anisotropy of Magnetic Susceptibility (AMS); gravity modeling; Mesozoic extensional tectonics

Domaines: Planète et Univers [physics]

Wei Wei, Yan Chen, Michel Faure, Guillaume Martelet, Wei Lin, et al.. An early extensional event of the South China block during the late Mesozoic recorded by the emplacement of the late Jurassic syntectonic hengshan composite granitic massif (Hunan, SE China). Tectonophysics, 2016, 672-673, pp.50-67. ⟨10.1016/j.tecto.2016.01.028⟩. ⟨insu-01265788⟩