A multidisciplinary study of the emplacement mechanism of the Qingyang-Jiuhua massif in Southeast China and its tectonic bearings. Part II: Amphibole geobarometry and gravity modeling

Abstract : The Late Mesozoic geology of the Lower Yangtze area is characterized by extensional sedimentary basins, numerous granitic plutons and several world-class ore deposits. Regionaly, the coeval tectonic and geodynamic framework remains inadequately investigated. In order to provide a more comprehensive understanding of the regional tectonic context, we performed a multidisciplinary study of the emplacement mechanism of the Qingyang-Jiuhua massif. It consists of the granodioritic Qingyang and the monzogranitic Jiuhua plutons, U-Pb dated at 142 ± 1.0 Ma and 131 ± 2.6 Ma, respectively. Biotite and amphibole cooling ages are 5-8 myr younger. Results deduced from field structural observation, petrographic and magnetic fabrics, paleomagnetism show that this massif was probably vertically emplaced by permissive intrusion coeval with weak regional extension. However, detailed information on the characteristics of this tectonic event and its emplacement depth was not documented. Therefore, we carried out an investigation of amphibole geobarometry and gravity modeling in order to address the emplacement mode of the plutons within their regional tectonic framework. Amphibole data show that the Qingyang-Jiuhua massif was emplaced in the upper crust at a depth between 5 and 12 km. Gravity modeling indicates that the massif is laccolithic. It is characterized by several NE-SW-striking linear thickening zones that we interpret as the feeder roots of the massif. These results led us to conclude that (1) the Qingyang-Jiuhua massif was fed by vertical, NE-SW striking tension gashes; (2) consequently the late Early Cretaceous tectonics in the study area was characterized by NW-SE extension.
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Wei Wei, Guillaume Martelet, Nicole Le Breton, Yonghong Shi, Michel Faure, et al.. A multidisciplinary study of the emplacement mechanism of the Qingyang-Jiuhua massif in Southeast China and its tectonic bearings. Part II: Amphibole geobarometry and gravity modeling. Journal of Southeast Asian earth sciences, Elsevier, 2014, 86, pp.94-105. ⟨10.1016/j.jseaes.2013.09.021⟩. ⟨insu-01005623⟩

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