Geophysics Department Seminar: Jerry Ning
Title: Ordos Block, China: understanding the stability and impending destruction of an intra-continental plateau
The North China Craton (NCC) is Archaean but is atypical in its active tectonics. East North China Craton (ENCC) has been tectonically reactivated since the Mesozoic, manifested by extensive magmatism and devastating intra-continental earthquakes, whereas West North China Craton (WNCC), incorporating the Ordos plateau, seems to retain its stability. The Ordos Plateau is an analog to the Colorado Plateau, and its uplift and stability present similar problems.
Virtual deep-seismic sounding (VDSS) and receiver function analysis of a Peking University broadband seismic array suggest that the crustal thickness changes rapidly from the ENCC to the WNCC reaching a thickness of ~ 60 km on the eastern flank of Ordos, 20 km thicker than previously thought. Our results also reveal a strong interface near ~ 40 km depth, previously thought to be Moho, but more likely the Conrad discontinuity. Mafic lower crust between the Conrad and Moho might maintain crustal isostasy. High-resolution Ambient Noise Tomography around the NCC shows a tadpole-shaped high S- velocity zone at ~60 km beneath Ordos at ~ 38 ºN 109 ºE with its tail pointing SE.
We conclude that the Ordos plateau is being destroyed from the margin while its core remains relatively stable, and speculate on implications for the destruction of NCC.