Magnetotelluric Evidence for Distributed Lithospheric Modification Beneath the Yinchuan‐Jilantai Rift System and Its Implications for Late Cenozoic Rifting in Western North China

Abstract

The Yinchuan‐Jilantai rift system (YJRS) is a prominent Cenozoic intracontinental rift zone located along the northwestern margin of the Ordos Block in western North China. Although the absence of volcanism indicates a passive origin, the tectonic driving forces and rift‐related deep processes remain poorly understood. Here we use newly obtained broadband magnetotelluric (MT) data to image the lithospheric electrical structure along a ∼500‐km‐long profile across the YJRS. At middle–lower crustal levels, the resulting model reveals several subvertical, crustal‐scale conductors that spatially correlate with the rift‐parallel, high‐angle normal faults. We attribute these features to a combined effect of saline fluids and partial melt due to recent supply of heat and volatiles into the crust from below. The crustal‐penetrating normal faults that were reactivated during extension serve as permeable pathways for deep fluid migration. In the uppermost mantle, a ∼400‐km‐wide zone of enhanced conductivity is present and requires the presence of partial melt. We interpret this feature as evidence for lithospheric modification through upwelling and decompressional melting of the volatile‐enriched mantle. When compared with the narrow (<100‐km‐wide) mantle conductors imaged beneath the Shanxi rift system along the eastern margin of the Ordos Block, such a feature indicates the YJRS has experienced a larger extent of lithospheric modification. Combined with additional geologic and geophysical observations, we attribute this essential difference to the inherited lithospheric heterogeneity and the eastward decreasing far‐field impacts from the India‐Eurasia collision.

Crustal Electrical Structure of the Ganzi Fault on the Eastern Tibetan Plateau: Implications for the Role of Fluids in Earthquakes

“…The initial model had significant influence on the final model obtained by inversion. It suggested that the conductivity of the final model increased as the conductivity of the initial model increased [33,54]. A series of inversions with varied initial resistivity models and the same other parameters were performed.…”

“…It was considered that the average apparent resistivity of all data points across all periods and sites was approximately 100 Ωm, and so the initial model was set to a 100-Ωm homogeneous halfspace. According to the group of inversions with different smoothing factors (0.1, 0.2, 0.3, and 0.4), the smoothing factors were set to 0.4 for all three directions, because high smoothing factors were more pronounced for the features of high conductors in the lower crust and the high resistances in the shallow [33,54]. The initial value of the regularization parameter (λ) was set to 3000 and divided by 10 when the root mean square (RMS) changed minimally.…”

Spatial heterogeneity of the lithospheric destruction of the North China Craton: Evidence from an extended magnetotelluric sounding profile

“…Consequently, the spatial heterogeneity of lithospheric destruction of the NCC still remains elusive. MT studies have found that there are low-resistivity bodies in the lithospheric mantle beneath the northwestern Ordos Block and the Hetao Graben, which may be related to the upwelling of sulfides produced by deep tectonic activities (Dong et al, 2014;Li C. et al, 2017;Xu et al, 2017;Li et al, 2022). However, there is still well-preserved cratonic lithosphere beneath the southern Ordos Block (Dong et al, 2014;Li C. et al, 2017;Xu et al, 2017;Li et al, 2022).…”

Direct Evidence for Dextral Shearing in the Shanxi Graben System: Geologic and Geomorphologic Constraints From the North Liulengshan Fault

“…As a result of the Indo‐Eurasian continental collision and westward subduction of the Pacific Plate, the North China Craton is neotectonically active (Figure 1; Molnar & Tapponnier, 1975; Tapponnier & Molnar, 1977; Northrup et al., 1995; Yin, 2010). Extensive intracontinental rifting (e.g., the circum‐Ordos graben systems) and intense seismic and igneous activities have made North China one of the most popular sites for geoscientists to explore the mechanism of intracontinental deformation (Clinkscales et al., 2020, 2021; Li et al., 2022; Liu et al., 1983, 2004; Middleton, Walker, Parsons et al., 2016; Middleton, Walker, Rood, et al., 2016; Ren et al., 2002; Zhang et al., 1998, 2016).…”

“…graben systems) and intense seismic and igneous activities have made North China one of the most popular sites for geoscientists to explore the mechanism of intracontinental deformation (Clinkscales et al, 2020(Clinkscales et al, , 2021Li et al, 2022;Liu et al, 1983Liu et al, , 2004Middleton, Walker, Rood, et al, 2016;Ren et al, 2002;Zhang et al, 1998Zhang et al, , 2016.…”