The Upper Mantle Seismic Structure in the Ordos Block, China

We present a new seismic model of upper mantle structure in the Ordos Block region in order to test the importance of mantle heterogeneity for topographic differences between Northern Ordos and Southern Ordos. Our model is based on P- and S-wave seismic receiver functions calculated for data from 171 stations, and the data has been analysed by CCP stacking and velocity inversion along selected transects. The model documents the presence of an uppermost mantle low-velocity zone between the Mid Lithospheric Discontinuity (MLD) and the Lehmann discontinuity. Clear converters at the 410 and 660 km discontinuities show constant Mantle Transition Zone (MTZ) thickness within the Ordos Block region, which indicates that no deep mantle thermal anomaly affects its present dynamics. However, the amplitude of the MTZ-converters is larger in the southern than the northern Ordos Block. In contrast, the conversions from MLD and the Lehmann discontinuity are strongest in Northern Ordos, which we interpret as a block with essentially preserved cratonic lithospheric mantle. We speculate that smaller amplitudes of the MLD and Lehmann converters in Southern than Northern Ordos may be related to either rheological weakening of cratonic lithosphere during the Mesozoic convergence between the North and South (Yangtze) China Cratons, or northeast extrusion of Tibetan lower crust and upper mantle in the Cenozoic caused by the India-Asia collision (Huang et al., 2022).

Reference

Huang, S.H., Thybo, H., Dong, S.W., Artemieva, I.M., He, R.Z., Han, B.F., Zhou, Q., Shi, W., 2022. Upper mantle seismic structure in the Ordos Block, China. J Geodyn 151, 101921. doi:https://doi.org/10.1016/j.jog.2022.101921