Petrogenesis and tectonic implications of the Early Carboniferous shoshonitic to calc-alkaline magmatic rocks of the southern Yili terrane, western Tianshan

Abstract In the Yili terrane at Awulale mountain, most shoshonitic lavas are related to post-collision extension and were extruded during the Late Carboniferous to Early Permian (310–280 Ma). Herein, we evaluate a small-volume occurrence of shoshonitic magmas in the southern Yili terrane formed c. 346 Ma ago. The high MgO (Mg#) and positive Hf isotope values of the shoshonitic magmas indicate the input of juvenile mantle-derived material. Still, their high Ba–Sr signatures were likely inherited from the partial melting of previously metasomatized lithospheric mantle. We argue the shoshonitic magmatic activity recorded a syn-subduction extensional history in the Yili terrane. This interpretation is consistent with the magmatic records from Early Carboniferous A-type granite and magnesian andesite found in the Zhaosu–Adentao–Dahalajunshan area of the southern Yili terrane. Combined with the geological development in this area, we propose that the emergence of the shoshonitic rocks records either the retreat of the trench or the rollback of the Junggar oceanic slab that occurred at or before the 346.1 ± 3.1 Ma age of the rocks.