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.