Contrasting crustal structures crossing the boundary region of the southwest Ordos block and its tectonic implications revealed by dense seismic arrays

Abstract

High-resolution images of the crust were obtained along two high-density temporary seismic arrays that cross tectonic blocks in the southwest boundary of the Ordos block and its adjacent regions. Dense stations with <1-km station spacings allowed teleseismic receiver functions to unveil the unprecedented details of crustal structures from the northeast margin of the Tibetan Plateau and the Qinling orogenic belt to the southwest Ordos block. The observations from nearby broadband seismic stations and two-dimensional numerical simulation were used to verify the reliability and validity of our results from the temporary dense array data. The receiver function profiles and the migration images revealed the contrasting crustal structures beneath the southwest Ordos block and the adjacent regions. Liupanshan mountain is a boundary that resists the lateral growth of the Tibetan Plateau; however, the slight bending of the Moho indicates absence of large-scale deformation in west Liupanshan. The Moho transition zone beneath the Weihe graben and southwest corner of the Ordos block represented by the complicated P-to-S converted phases can be contributed to the eastward extrusion of hot uppermost mantle from the Tibetan Plateau driven by the mantle flow.