Petrology, geochemistry, zircon U-Pb age characteristics and significance of Dengfuxian pluton in Hu'nan Province

In this paper, the authors analyzed LA-ICP-MS zircon U-Pb dating, petrology and petro-geochemistry of Mesozoic Dengfuxian pluton in Hu'nan Province. The zircon U-Pb age is 225.1±1.2Ma for granodiorite, which suggests that it was formed in Late Triassic. Combined with the age data available, the authors hold that Defuxian pluton is complex rock which intruded in Indo-sinian(222.9~225.7Ma)and Yanshanian(151.1~159Ma). Granites in Indosinian and Yanshanian Dengfuxian pluton all have high content of SiO₂ and high ratios of A/CNK and contain para-aluminous muscovite and cordierite mineral. In terms of trace elements, large ion element Rb, Th, U are rich, whereas Nb, Ba, Sr, Ti are poor obviously. The REE distribution patterns exhibit right devia-tion, with rich light rare earth elements and relatively poor Eu. As for isotopes, Dengfuxian pluton has low values of ε_Nd(t), and the ratios of ¹⁷⁶Hf/¹⁷⁷Hf are lower than the ratio of chondrite (0.282772). In combination with the above-mentioned characteristics and by means of (⁸⁷sr/⁸⁶Sr)_i-ε_Nd(t) discrimination, the authors consider that the granites in Indosinian and Yanshanian Dengfuxian pluton are of S-type granites, and the source area was formed by partial melting of crustal argillaceous-poor pluton in the region in Paleo-proterozoic and argillaceous-rich pluton. It is considered that the granites in Indosinian and Yanshanian Dengfuxian pluton were formed under the extended tectonic regime, and the granites in Indosinian intruded in the extension setting after the collision of Indo-sinian movement, whereas the granites in Yanshanian period were formed by the subduction of Pacific plate.