Several tectonic events in the North China Craton (NCC) since the Archean have been documented, and the available geological evidence explains the various phases of NCC. Three major tectonic events that occurred during the late Paleoproterozoic were reported by many scholars (Kusky et al., 2016; Li S et al., 2015; Zhai and Santosh, 2011; Zhao et al., 2005, 2012, 2013). The western NCC (WNCC) was formed by the amalgamation of the Yinshan block and the Ordos block at ∼1.95 Ga, while the eastern NCC (ENCC) was formed by the collision between Longgang and Nangrim blocks at ∼1.90Ga. Furthermore, WNCC and ENCC amalgamated as a result of a tectonic event at ∼1.85Ga to form the uniform basement of NCC along a central orogenic belt (Trans-North China Craton, TNCO) (Zhao et al., 2001; 2005). The NCC remained stable for a long time until the significant Mesozoic lithospheric thinning. Numerous ancient tectonic structures have been transformed due to the collision between India and Eurasia plates and the subduction of the Pacific plate, which resulted in the elevation of the Tibetan Plateau (Zhu et al., 2011; 2012). This indicates the vulnerability of the amalgamation belts to the subsequent tectonic disturbances. This Paleoproterozoic evolution process has also resulted in a unique tectonic background at the boundary between the eastern side of the Khondalite belt and the northern part of TNCO (Figure 1A). The central tectonic belt and Khondalite rock belt are connected along the Huai’an-Zhangjiakou area in Hebei province, China. The Shanxi–Hebei–Inner Mongolia basin tectonic belt, comprising a series of parallel Holocene faults and basins, characterizes the current surface structures and activities that are relatively distinctive (Figure 1B&c).The tectonic environment in the area is responsible for the relatively high tectonic activity (Li Z et al., 2015), as evidenced by the earthquake with ML = 6.2 triggered in Zhangbei in 1998 (Yang et al., 2002). The potential of this area for the occurrence of strong earthquakes is also evidenced by the GNSS observation data (Wu et al., 2021). The Huai’an-Zhangjiakou is a highly significant area of TNCO due to the area’s paleotectonic and neotectonic activities. From northwest to southeast, the area comprises Yinshan block, Khondalite series, Huai’an complex, and Hengshan complex which are the subdivisions of metamorphic outburst classification (Wang et al., 2016). The temperature and pressure environment at a depth of 35–40 km at the bottom of the Paleoarchean lower crust is evidenced by the high pressure in the mafic granulites. The subduction–collision–exhumation events of Paleoproterozoic orogenic tectonic development transported these high-pressure granulites and eclogites into the core crust (Zhang et al., 2019).Geophysical methods can effectively understand the current deep structures and the tectonic processes. Several scholars have reported the strong concordance of surface topographic changes in the area and the E-W variations in the crustal and lithospheric structures (e.g., Chen, 2010; Cheng et al., 2013; Wei et al., 2015; Zheng et al., 2017). NCC and several other cratons in the world have restructured as a result of subduction (Zhu et al., 2021), and the pre-existing structures in the lithosphere primarily control such continental reconfiguration. However, deep imaging results of satisfactory scales in this local area are still lacking. In this context, the reconfiguration of the ancient tectonic amalgamation belt was investigated by procuring the higher precision imaging results of deep structures. For this purpose, a short-period array was deployed in the Huai’an-Zhangjiakou area to apply the receiver function method for exploring deep structures. The present tectonic activity explained the activation of the ancient tectonic structures based on the imaging results.

The reliable signals in the receiver functions are stable with variations in time and alp. A smaller alp factor provides the Moho basic and smoothed interface data, while a larger alp factor provides more crustal information (Wei et al., 2016). Even though the signal of the Moho is about 5 s (depth of approximately 40 km), it has a distinct segmented pattern from south to north. The profile is subdivided into three characteristic segments based on the shape of the Moho signal: (Ⅰ) 39°N–39.8°N (south of F7), where the Moho is clear and continuous in the staking profile, gradually descending from south to north; (Ⅱ) 39.8°N–40.7°N (between F7 and F1), where the morphology is complex with weak continuity, exhibiting no single layer; and (Ⅲ) 40.7°N–42°N (north of F1), where the Moho is relatively stable and flat. In addition, some relatively stable negative signals shallower than 25 km depth observed in the range of 36.7°N–41.5°N may represent a low-velocity zone (LVZ) within the crust. A comparative analysis of topographic elevation, surface structure, receiver function results, and CCP results are shown in Figure 4. Based on the CCP results, the Moho exhibits a uniform pattern. However, the Moho in region Ⅰ is curved downward, while that in region Ⅱ is relatively complex and that in region Ⅲ is relatively flat. The LVZ is mainly concentrated in region Ⅱ and is discontinuous. The complex features of the Moho represent a series of surfaces closely related to structural features and deep structures and are visible below the densely constructed basin ridges.

NCC is regarded as the most severely damaged craton on earth (Carlson et al., 2005; Zhu et al., 2011). The tectonic belts around cratons are relatively mechanically weak zones compared to the cratons and are primary sites of intense heating and strain localization (Hu et al., 2018; Liu et al., 2021). Based on the imaging results, the average depth of the Moho beneath the profile is 40 km. A comparative study was carried out on the basic crustal conditions under the adjacent regions in North China by the receiver function method and by using the broadband seismograph data (Zheng et al., 2007; Chen, 2009; Tang et al., 2010; Lou et al., 2017; Si et al., 2017; Wei et al., 2020; Zuo et al., 2020), which are comparable with crustal thickness obtained by the measured receiver functions. The imaging results of the Moho obtained from region Ⅰ and region Ⅲ are comparable to the results from the western Khondalite belt (Wan et al., 2020). Moreover, the results of wide-angle reflection and refraction profile data of deep seismic sounding indicate the existence of a deep crust-scale fault zone extending to the Moho beneath the Zhangjiakou area, as well as the presence of LVZ within the crust (Zhu et al., 1999), which may suggest the presence of intense magmatic activity.

Numerical experiments demonstrate that inheritance is the primary controlling factor of lithospheric rifting and layer stiffness. The rift styles mostly depend on the inherited weaknesses embedded in the model (Chenin and Beaumont, 2013). The study area crosses through Yuguang and Wanquan basins from south to north and crosses a series of Holocene normal faults, making the area active. The normal faults are distributed in the east of the western parts, and their characteristic stress conditions are generally in a north–south extensional environment. On the other hand, the combined analysis of previous tomographic results using the receiver function shows that the Moho in region Ⅱ is discontinuous (Figure 5). Also, the complex deep structure in region Ⅱ corresponds rather well with the distribution of the faults and basins, implying that the surface topography variation is generally congruent with the deep dynamic processes. Faults 1 and 7 seem to represent two boundaries of the whole fault and basin system, governed by the migration of deep material on both sides. Frequently, the axis of lithosphere extension and continental breakup is parallel to the orogenic belts and suture zones (van Wijk, 2005). This area is probably related to the weak zone formed by the collage of Yinshan and Ordos blocks, which is evidenced by the combined analysis of the area with the E-W trend of the surface structure.

F1-Huai’an–Wanquan Basin northern margin fault; F4-Huai’an Basin southern margin fault; F5-Yangyuan basin northern margin fault; F6-Liulengshan basin northern margin fault; F7-Yuguang basin southern margin fault.

Based on the tomography results, subduction of the western Pacific has extended westward into the central and WNCC toward the Datong volcano (Wei et al., 2012; Liu Z et al., 2017; Zhao, 2017; Lei et al., 2018), with a large mantle wedge in the middle and upper mantle. The depth profile of the S-wave perturbation velocity along the latitude of 40°N is illustrated in Figure 6 based on the topography results reported by Tao et al. (2018).

The Pacific plate is deeply subducted toward the west, forming a large mantle wedge, and its influence extends westward, up to a longitude of 110°E. The uneven mantle flow in the upper mantle caused by the subducting slab front poses strong action on the upper lithosphere, thereby influencing the tectonic evolution of the crustal and upper mantle structure beneath NC (Tian et al., 2019). The high calorific value in North China at a depth of ∼100 km is also evidenced by the geothermal results reported by Wang and Cheng, (2012). The low-velocity anomalies in the crust and upper mantle below the Zhangjiakou area are shown by the local ambient noise (Jiang et al., 2021). The aforementioned findings show that certain Cenozoic tectonic deformation and fault development in the study area are strongly connected to the internal restructuring of the craton caused by the subduction of the western Pacific plate. The area is tectonically characterized by the western subduction of the Pacific plate and the distinct local restructuring evidenced by the formation of a large mantle wedge. The tomography images from ambient noise also reveal that the crust and upper mantle beneath the Shanxi fault depression belt, Zhangjiakou, and Datong volcanic areas are characterized by low-velocity anomalies associated with a large area of intense Cenozoic magmatic activity in Datong triggered by the upwelling of hot materials from the mantle (Zuo et al., 2020), and the slow movement of the magma surface causing negative signals.

LVZ-low-velocity zone; F1-Huai’an–Wanquan Basin northern margin fault; F4-Huai’an Basin southern margin fault; F5-Yangyuan basin northern margin fault; F6-Liulengshan basin northern margin fault; F7-Yuguang basin southern margin fault.

The results of the receiver function and tomographic imaging were combined to generate a conceptual diagram of the tectonic process of this area, as shown in Figure 7. Since region Ⅱ in Figure 3 and Figure 4 was relatively weak in the ancient craton collage belt earlier, it is more sensitive to get impacted by the mantle wedge (Zuo et al., 2020). These weak zones are reactivated by the mantle plume resulting in the upwelling of the Moho as channels, which ultimately restructures the crust. The shallow crust’s materials are pushed to move on both sides by the circulatory power of deep materials, resulting in a series of normal faults and grabens on the earth’s surface. As a result, region Ⅰ and region Ⅲ may still retain the shape of the ancient Moho without substantial changes.

In the present study, a short-period dense array is used to generate the receiver function image of two ancient tectonic belt boundaries of NCC. The extensive continental restructuring of the area might have affected the structure and properties of the continental lithosphere and impacted both surface processes and mantle dynamics regionally. For example, the series of nearly parallel E-W basins and lithospheric scale normal faults in the study area demonstrate their relationship with the pre-existing weak zone apart from the signatures representing current tectonic processes. The present study proposed a model illustrating the damage of the ancient weak zone caused by the dynamic processes of western Pacific subduction. The mantle wedge activates the local thermal circulation in the lithosphere to reactivate the weak zone to enter the crust as a channel which forms an extensional environment. This is evidenced by the slowly cooling magma upwelling of LVZ at the bottom of the upper crust in Zhangbei-Huai’an and Yangyuan basins.