Upper mantle tomography of the Western Junggar: Implications for its geodynamic evolution

A high-resolution 3-D P-wave velocity model of the upper mantle beneath the Western Junggar is determined by inverting a large number of relative travel-time residuals of teleseismic events. Our results reveal a prominent high-velocity (high-V) anomaly beneath the western Junggar basin and a low-velocity (low-V) anomaly beneath the Darbut belt. The NE-SW striking high-V anomaly at depths of 50–200 km beneath the western Junggar basin dips toward the northwest, which represents a fossil oceanic slab. The low-V anomaly may reflect an intraoceanic arc-related terrain that has experienced strong metasomatism by hot upwelling asthenosphere in the late Paleozoic, resulting in adakitic intrusions and concentration of porphyry CuAu deposits in the Darbut belt. These results shed new light on the geodynamic evolution of the Western Junggar and formation mechanisms of the adakites and porphyry CuAu deposits.