Upper mantle seismic structure in the Ordos Block, China

E‐W and S‐N Differences in the Sedimentary Cover and Crystalline Crust in the Cratonic Ordos Basin From Receiver Function Analysis

“…This event results in a zone of higher V p/ V s ratio and denser crust‐mantle transition beneath the profile (Wei et al., 2011). The thicker crystalline crust in the southern Ordos may be related to the northward collision of the Yangtze Craton in the south and the NE extension of the Tibet Plateau in the southwest (e.g., S. H. Huang et al., 2022; Peltzer & Tapponnier, 1988; Teng et al., 2008). The observed V p/ V s ratios typical of intermediate‐acid rocks of 1.74 and the ∼40 km thickness of the bedrock (Figure 6), as well as rare strong earthquakes (Figure 1), suggest that the crystalline crust of the Ordos Basin overall has not experienced the mantle material contamination or crustal partial melting and has maintained the cratonic characteristic and stability for a long geological time.…”

“…Based on RF and ambient noise images from E‐W linear profiles, the southern Ordos Basin is speculated to have high S‐wave velocity, large‐scale positive radial anisotropy in the middle and lower crust (Ling et al., 2017), and a sharp crust‐mantle transition zone (Wei et al., 2011), in contrast, the northern Ordos Basin is thought to have relatively low velocity and weak anisotropy in the lower crust (Cheng et al., 2013), and a relatively thick crust‐mantle transition zone (Wei et al., 2011). Roughly divided along 37°–38°N, the southern part of the Ordos Basin is the Loess Plateau composed of thousands of trenches and ravines on the surface, while the northern part is a vast desert (S. H. Huang et al., 2022; Teng et al., 2010). A variety of geophysical studies support the existence of S‐N differences in deep structure in the Ordos Basin.…”

“…In addition, a low‐resistivity layer at a depth of ∼20 km is imaged in the central Ordos Basin by magnetotelluric experiments (G. Z. Zhao et al., 2010). These observations raise doubts about whether the Ordos Basin still retains its originally formed crustal structure after undergoing multistage collision, such as the southward convergence of the ancient Asian Ocean in the north, the northward and northeastward collision of the Yangtze Craton in the south and the Tibetan Plateau in the southwest, respectively (S. H. Huang et al., 2022; Zhai, 2021; Zhang et al., 1998).…”