Geochemistry and petrogenesis of the Huashan granites and their implications for the Mesozoic tectonic settings in the Xiaoqinling gold mineralization belt, NW China

The Huashan complex granitic batholith, occurred in the core of the Xiaoqinling orogen and gold mineralization belt along the south margin of the North China Craton, consists of amphibole monzogranite and biotite monzogranite in the Wengyu and Fangshanyu valleys, respectively. Zircon LA-ICP-MS U–Pb dating yields ages of 205 ± 2 Ma and 132 ± 1 Ma for the Wengyu and Fangshanyu granites, respectively, which represent the two major episodes of Mesozoic magmatism in the region. These rocks are characterized by metaluminous, high silica and total alkalinity, and have high FeOtotal/(FeOtotal + MgO) ratios, high large-ion lithophile elements (LILEs, especially Sr and Ba) and light rare earth elements (LREEs), and low heavy rare earth elements (HREEs) and Y concentrations and insignificant negative Eu anomalies. The Wengyu granites have higher Ba and Sr contents, which can be classified as high Ba–Sr granites, whereas the Fangshanyu granites show much lower Ba and Sr contents and display an adakitic affinity. Elemental and isotopic compositions suggest that the main sources of both the Wengyu and Fangshanyu granites are likely the ancient basement materials of Taihua Group. However, the high Ba and Sr contents of the Wengyu granites require addition of small amounts of enriched lithospheric mantle metasomatised by fluid/melt derived from pelagic sediments-bearing subducted slab in the sources. The Wengyu granites were most likely generated earlier by partial melting of the lowest part of the crust due to the subducted slab break-off under the post-collision extensional stage of the continental collision orogeny. The Fangshanyu granites might be mainly derived later from the partial melting of thickened lower crustal materials, representing by the Taihua Group basement rocks, corresponding to the tectono-magmatism of the post-orogeny to rift extensional environment during the tectonic transition from the Paleo-Tethys subduction-collision system to the Paleo-Pacific regime.

► Two episodes (205 ± 2 Ma and 132 ± 1 Ma) of magmatism are recognized in the Huashan complex, Xiaoqinling district.
► Wengyu granite belongs to high Ba–Sr granite, whereas Fangshanyu granite displays an adakitic affinity.
► The sources of magma are most likely the ancient basement materials of Taihua Group.
► Wengyu granite was generated due to the subducted slab break-off under the post-collision extensional stage.
► Fangshanyu granite was generated during the post-orogeny to rift extensional environment.