Stage division and origin of Tonglushan pluton in southeast Hubei Province： Evidence from zircon U-Pb ages and Hf isotopes

Abstract：The Tonglushan pluton is mainly composed of quartz-orthoclase diorite porphyry, together with diorite, quartz diorite and diorite porphyry. In this paper, zircon U-Pb ages and Lu-Hf isotopic data were obtained by using LA-ICPMS and LA-MC-ICPMS analysis. The results show that there existed at least three times of intrusive activities in the Tonglushan complex, which occurred at 150 Ma, 145 Ma and 140 Ma, respectively. These magmatic activities successively occurred from west to east and from the depth to the shallow part and formed quartz diorite and Ⅶ Cu-Au ore body at the depth of the Jiguanzui mining area, the diorite and Ⅰ，Ⅱ，Ⅲ Cu-Au ore bodies in the shallow part of the Jiguanzui ore district, as well as the quartz-orthoclase diorite porphyries in and around the Tonglushan mining area and the Tonglushan Fe-Cu deposit, the Jiguanzui Fe-Cu deposit and the Taohuazui Fe-Cu deposit, respectively. The U-Pb ages and Hf isotopic data of igneous zircons and inherited zircons indicate that the Tonglushan complex was mainly derived from Paleoproterozoic (Ca.1730Ma) lower crust with a little depleted mantle components, with the involvement of variable amounts of the Late Mesoproterozoic (1100~1200Ma) and Neoproterozoic (800 Ma) crustal materials. Different rock units had different magmatic sources and were related to different ore-forming processes. The quartz diorite and diorite were associated with Cu-Au mineralization, which probably resulted from the involvement of mantle components in the magma source. The age data of inherited zircons, which include Neoarchean, Mesoarchean, Paleoproterozoic, Late Mesoproterozoic and Neoproterozoic, are comparable with zircon ages of the Kongling Group TTG gneiss in Yichang, lamprophyre pipes in Jingshan, Ningxiang and Zhenyuan, sandstones of Liantuo Formation in Yichang, and tuffs of Xieshuihe Formation (Liantuo Formation) in Shimen, indicating that the crustal evolution of southeast Hubei Province was basically in accordance with that of the other areas in the Yangtze block, and Paleoproterozoic and Archean basement might also exist in the deep crust of southeast Hubei Province.