Late Carboniferous high-Mg dioritic dikes in Western Junggar, NW China: Geochemical features, petrogenesis and tectonic implications

Late Paleozoic High-Mg dioritic dikes widely occur in western Junggar, NW China. Ar–Ar dating on rock chips of the dikes has yielded a plateau age of 321 ± 3 Ma, indicating an early Carboniferous age for the dikes. The dikes are enriched in SiO2 (52–57 wt.%), and characterized by high MgO (5.13–7.41 wt.%), Cr (134–204 ppm), Ni (59–141 ppm), Sr (468–724 ppm) and Ba (316–676 ppm) contents, with geochemical features analogous to those of sanukite of Setouchi volcanic belt, Japan. These dikes contain hornblende and biotite and generally have high Ba/La (27–124) and La/Nb (2.9–4.3) ratios and positive Eu anomalies, consistent with an origin from hydrous partial melting of a mantle source metasomatised by slab-derived component. The occurrence of sanukitic dikes, together with the coeval slab-related adakite in the area, implies that the western Junggar had been affected by hot, subduction-related regime, which gave rise to not only massive magmatism in the late Carboniferous, but also intensive Cu–Au mineralization in the area.