Receiver Function Imaging of the Mantle Transition Zone beneath the South China Block

Abstract:

Upper mantle discontinuities are influenced by convection-related thermal heterogeneities arising in complex geodynamic settings. Slab roll-back of the Pacific plate and mantle upwelling in the Meso-Cenozoic caused the extension and spreading of continental segments in the South China Block, leading to profound variations of the local temperature conditions. We processed 201 teleseismic events beneath 87 stations in the Hainan, Guangdong, and Fujian provinces in the South China Block, and extracted 4172 high-quality receiver functions. We imaged topographies of the mantle discontinuities by using phase-weighted common conversion point (PW-CCP) stacking of the receiver functions, which effectively improves the P-to-S converted phases. We found that the average depths of the discontinuities at 410 km and 660 km depth are 429 km and 680 km, respectively, while no clearly defined discontinuity at 520 km depth was detected. We mapped the thickness of the mantle transition zone (MTZ), which can reflect temperature and/or compositional heterogeneities as well as the presence of water, and used our results to discuss possible geodynamic implications. In particular, we found that the MTZ beneath the Leizhou Peninsula in the Hainan province is 43 km thinner than average. This scenario is compatible with a “Hainan plume” responsible for positive temperature anomalies of 380 K and 220 K at the 660 km and 410 km discontinuities, respectively. Prominent uplifting of the 660 km boundary beneath the coast regions may also support a horizontal channel flow of the Hainan plume.