We can determine the stress tensor associated with fault movements by analysing fault nature and slip direction. Considering that fault slip data, including dip directions and angles of fault planes, pitch directions and angles of striations, and strike-slip directions, are easy to obtain, this method has been extensively applied to the study of tectonic evolution (Angelier, 1979, 1984; Delvaux et al., 1995; Delvaux and Sperner, 2003; Zhang et al., 2003; Allmendinger et al., 2012; Riller et al., 2017; Lin et al., 2015; Shi et al., 2015, 2020; B.; Zhang et al., 2020). The stress inversion method is usually based on the Wallace-Bott hypothesis, which suggests that the fault-slip vector (s) is parallel to the orientation of the maximum shearing stress (τ) under the influence of a regional uniform stress tensor (Wallace, 1951; Bott, 1959). Some other conditions also need to be considered, for example 1) the stress field remain constant during a tectonic event (Angelier, 1979); 2) the faults do not interfere with each other, with no rotation of the fault planes (Lacombe, 2012); and 3) the protoliths of the deformed rocks are homogeneous and isotropic (Lacombe, 2012). In practice, there is usual an angle between the slip vector (s) and shear stress vector (τ). Therefore, this angle should be kept as small as possible so that the stress tensor we get is more accurate (Chen and Shi, 2015). The stress state or stress ellipsoid can be expressed by three principal stress axes (maximum (σ₁), intermediate (σ₂), and minimum (σ₃) stresses, where σ₁> σ₂> σ₃) and stress difference ratio (R = (σ₂ − σ₃)/(σ₁ − σ₃), 0 ≤ R ≤ 1). Theoretically, we need at least four independent fault-slip data to calculate a stress field (Etchecopar et al., 1981; Chen and Shi, 2015; B. Zhang et al., 2020).

In this work, we use Win-Tensor software (Delvaux et al., 1995; Delvaux and Sperner, 2003) for paleo-stress inversion. 314 fault-slip data were obtained from 34 observation sites in the field (Table 1). The relative sequences of multi-stage tectonic deformation can be determined by identifying the youngest strata that involved in various stages of deformation, by analyzing the superposition relationships of multiple slip vectors on a single fault surface, and by observing the cross-cutting relationships of truncated fault planes (Shi et al., 2015, 2020). According to the above analysis, together with the attitude of the fold hinges and the angular bisector orientations of the X-type conjugate shear fractures from different strata, we are able to reconstruct the evolutionary sequence of the late Mesozoic tectonic stress field in the Shangyi Basin.

In order to carry out the quantitative analysis to tectonic deformation of the basin, we use the technique of balanced cross-section to restore the deformation and structure to its initial state based on the reliable geologic section and related geometrical rules (Dahlstrom, 1969; Hosseck, 1979; Li et al., 2011; Zhang et al., 2011; Nakapelukh et al., 2017; Y. Zhang et al., 2020). Because of the lack of seismic and borehole data in our study area, we mainly based our cross-sections on detailed field geological investigations. Generally speaking, the cross-sections should theoretically be kept orthogonal to the strikes and axes of faults and folds (or parallel to the direction of regional principal stress) (Hosseck, 1979; Song, 1985) so that the deformation behavior and the amount of shortening can be defined more accurately. Taking into account the major structural features of the basin, the sections A-A' with NW-SE-trending and B-B' with NNW-SSE-trending were selected for balancing and restoration (Figures 2A,B). Here we took the 2D-Move software to restore the deformation and estimate the crustal shortening. Meanwhile, the layer length conservation principle and plane strain should be considered during the analysis process (Dahlstrom, 1969; Li et al., 2011; Li et al., 2019).

To constrain the timing of tectonic deformation in the Shangyi Basin, we analyzed zircon grains from two selected rock samples (for sample locations, see Figure 2A) using LA–ICP–MS U–Pb dating. Zircon grains were extracted from crushed blocks using heavy liquid and magnetic separation techniques. Zircons were handpicked under a binocular microscope, mounted in epoxy resin, polished to expose approximately half of the grains, and gold coated. Cathodoluminescence (CL) images of zircon grains were acquired using an Analytical Scanning Electron Microscope (JSM−IT100) connected to a GATAN MINICL system. LA–ICP–MS zircon U–Pb dating was conducted at the Key Laboratory of Paleomagnetism and Tectonic Reconstruction, Ministry of Natural Resources, Beijing. The spot size and laser frequency were set to 32 µm and 5 Hz, respectively. Zircon 91500 was taken as an external standard for the U–Pb dating, and glass NIST610 was used as a standard for the trace-element calibration. The ICPMSDataCal software was used to calibrate the trace-element analysis and U–Pb dating (Liu et al., 2008, 2010). Weighted mean calculations and concordia diagrams were acquired using Isoplot/Ex_ver3 (Ludwig, 2003).

The major faults and related folds are exposed along the north and south edges of the basin. Along the northern boundary of the basin, the SPF from west of Houfugou to east of Daxigou is striking WNW-ESE and dipping towards the north or north-northeast, in spite of its whole orientation in the Yanshan belt as ∼E-W (Figures 1B, 2A). Along the SPF, Neoarchean-Paleoproterozoic basement and a few Mesoproterozoic caprock are overthrust southward onto Late Mesozoic strata. Within the footwall of the SPF, near Dawangmaogou, Xiajing and Hongtuliang, some ∼E-W- and NE-striking secondary thrusts show tectonic vergence towards the south (or the southeast). These secondary faults extend towards the northeast and eventually merge into the SPF (Figure 2A), indicating that the former are controlled by the latter. In the south margin, the BSF from Banshen to Shuiquangou is striking NE, whereas east of Shuiquangou, its direction changes into NNE (Figure 2A), and it finally disappeared in the Tuchengzi Formation of the east of Xiaosuangou. The BSF is generally steeply dipping (>60°) towards the southeast. Along the BSF, the basement rocks are thrust northwestward over the Tuchengzi Formation (Figure 2B). According to the variation trend of the attitude of the rock stratum in geological map, some folds with the NE-trending axes are mainly observed in the north and south parts of the basin, showing the asymmetric syncline or anticline controlled by the boundary faults (Figure 2B). Additionally, a WNW-trending gentle syncline occurs between Yanjiayao and Tumulu (Figure 2A), which represents a structural style different from the asymmetric folds described above.

Based on detailed field measurements from the Shangyi Basin, together with the superposition and cross-cutting relationships of different structures, three-stage deformation can be identified. In this part, we mainly introduced the structural deformation characteristics of each stage, as well as the corresponding inversion results of fault slip data. Relevant interpretations of their deformation sequences were presented in the Discussion section.

According to the analysis of multi-stage deformation, we established a relative evolutionary sequence of the basin during the late Mesozoic, including the early NW-SE compression, the middle NW-SE extension and the later NE-SW compression. The present bulk architecture of the basin was controlled by the early NW-SE compressional stress, and the subsequent two tectonic events only caused limited destruction to the previous tectonic framework.

Some fault striations associated with NW-SE compression and the X-type conjugate shear fractures resulted from NE-SW compression were simultaneously observed in the pyroclastic interlayer at the location of sample SY86 (Figures 11B–D), indicating that both of the two compressional events commenced posterior to 161 Ma. Our structural analysis has revealed that the Tuchengzi Formation is the youngest strata suffered from NW-SE compressional deformation. Many investigations suggest that the Tuchengzi Formation in the Yanshan belt is commonly marked by the molasse-like formations or synorogenic deposits (Zhao, 1990; Zhang, 1999; He et al., 2008), whose lower limit age has been usually constrained to 157–151 Ma (Cope, 2003; Xu et al., 2012; Qi et al., 2015; Fu et al., 2018). Furthermore, despite we failed to define the emplacement age of the NE-oriented mafic dike at the east edge of the basin from our sample SY57, Xu et al. (2016) reported a SHRIMP zircon U–Pb age of 141 ± 1 Ma from the mafic dikes that intrude in the upper part of the Tuchengzi Formation in the eastern Shangyi basin. Many other mafic dikes intruded in the Tuchengzi Formation were widely recognized in North China and Northeast China. Their ages of emplacement are concentrated in 144–140 Ma, indicating a regional extensional tectonic setting during the Early Cretaceous (Xu et al., 2017). Based on the analysis above, the timing of NW-SE compressional deformation can therefore be constrained to ca. 151–141 Ma. In the light of regional tectonic evolution, NW-SE compressional deformation was closely related to the episode B of the Yanshanian movement (Yanshanian B) in the NCC, expressed by territorial Late Jurassic–Early Cretaceous disconformities, series of fold-thrust structures and transpressional fault systems (Wong, 1927; Davis et al., 1998; Zhao et al., 2004; Zhang and Dong, 2008; Li et al., 2016; Zhu et al., 2018; Lin et al., 2019), which has been constrained to 160–135 Ma (Zhao et al., 2004; Zhu et al., 2015; Clinkscales and Kapp, 2019; Lin et al., 2019).

Niu et al. (2003) used the SHRIMP zircons U-Pb dating from the base of the Zhangjiakou Formation volcanics in the basin of the central Yanshan belt to determine the change in regional tectonic regime from compression to extension occurred at 136 Ma. As is well-known, during the Early Cretaceous, regional NW-SE extension was matched with widespread lithospheric extension and destruction in eastern China, manifested by massive magmatism and remarkable NE-trending basin-range structures, which has been normally constrained to 135–110 Ma (Wu et al., 2005; Wang et al., 2012, 2015; Daoudene et al., 2013; Zhu et al., 2018). The Early Cretaceous volcanics are absent in the Shangyi Basin. Whereas, Zhang (2019) recently provided new evidence of the magmatic activity in Shangyi area during the middle–late Early Cretaceous based on the zircons U–Pb ages of 135–123 Ma from the Huangyuwa granitic pluton (or the Xiaodaqingshan granites) at the northeast of Xinghe (Figure 2A). The above descriptions allows us to constrain the timing of NW-SE extension to ca. 135–110 Ma.

In the northern margin of North China, correlational studies of NE-SW compression during the late Mesozoic were rarely reported. Based on the comprehensive analysis of the intracontinental transform structures in the joint part of the Yanshan and Taihang Mountain belts during the Early Cretaceous, Lin et al. (2020) suggested that the Yanshan belt was marked by ∼E-W-oriented sinistral extension after 129 Ma. A local NE-SW compressive stress field may be derived from this sinistral transtensional structure, whereas the multi-stage tectonic evolution sequences established in this paper cannot support this pattern. Actually, C. H. Zhang et al. (2004) investigated the NW-striking Taiying-Lengkou-Shangying Fault Zone in the central part of the Yanshan belt, which has experienced multi-phase tectonic movements in the late Mesozoic, including thrusting, extension and strike-slip faulting. A significant reversal faulting with the top-to-the-SW slip sense along the Taiying-Lengkou-Shangying Fault Zone occurred after the generated age of the late Early Cretaceous Jiufotang Formation, causing an asymmetric syncline with the NE-dipping axial plane was formed in the Jiufotang Formation in the footwall (C. H. Zhang et al., 2004). Moreover, Yang (2015) conducted the analysis of Mesozoic tectonic deformation and palaeostress field in the southern area of Jianchang, Western Liaoning Province, China and established a model of four-phase tectonic evolution. The NW- to NNW-oriented fold and fault system was considered as the result of the latest NE-SW compression, whose activity age was identified as later than the Jiufotang Formation (Yang, 2015). The Jiufotang Formation in the northern NCC is predominantly a set of fossil-bearing lacustrine sediments, whose age constraints was still lacking in reliable geochronology data and was generally defined by the research of Paleontology and Stratigraphy. He et al. (2004) reported the K-feldspars ⁴⁰Ar/³⁹Ar date of 120.3 ± 0.7 Ma from the tuff interlayer within the shale of the Jiufotang Formation at the Shangheshou section in Chaoyang, Liaoning, northeastern China. Another radioisotopic age of the Jiufotang Formation has been dated from Tebch, Inner Mongolia, with a ⁴⁰Ar/³⁹Ar age of 110.59 ± 0.52 Ma got from intrusive basalt within the Jiufotang Formation (Eberth et al., 1993), which may provide a top limit for the Jiufotang Formation. In consequence, NE-SW compression may commence posterior to 110 Ma. Given that the Cenozoic strata in the study area were not involved in NE-SW compressional deformation, this tectonic event may occur at the late Early Cretaceous–Late Cretaceous.

In addition to the Shangyi Basin, the Tuchengzi Formation is also extensively exposed in other typical late Mesozoic basins in the northern margin of the NCC. The origin of the Tuchengzi Formation was variously interpreted to be related to 1) the flexural basin controlled by compression and thrusting (He et al., 2008; J. Liu et al., 2015; Liu et al., 2018; Lin et al., 2019); or 2) intraplate rift environment (Shao et al., 2003; P. Zhang et al., 2014; Y. Q. Liu et al., 2015; Xu et al., 2016). According to this study, integrated with previous achievements, we believe that the Tuchengzi Formation of the Shangyi Basin developed during a compression environment. The reasons are as follows. 1) Abundant chronological data show that the Tuchengzi Formation was formed in the Late Jurassic-Early Cretaceous (157–137 Ma) (Cope, 2003; Zhang et al., 2009；; Xu et al., 2012; Wang et al., 2013; Qi et al., 2015; Li et al., 2016; Fu et al., 2018; Lin et al., 2019; Shi et al., 2019), which is consistent in time with the Yanshanian B. 2) Since the lack of accurate chronological data, P. Zhang et al. (2014) and Xu et al. (2016) assigned the pyroclastic interlayer within the sandstones near the west edge of the basin to the Tuchengzi Formation, and they considered the pyroclastic deposit reflected an extensional environment during the depositional stage of the Tuchengzi Formation. However, our chronological results confirmed this set of pyroclastic rocks was formed at 161 Ma (Figures 3, 12C), corresponding to the sedimentation time of 164–158 Ma from the lower part of the Jiulongshan Formation (Chen et al., 2014; Li et al., 2014; Lin, 2019). Meanwhile, numerous studies have shown that the molasse-like characteristics of the Tuchengzi Formation represent the thrust faulting from the basin-controlling faults (J. Liu et al., 2015; Liu et al., 2018; Lin et al., 2019, Shi et al., 2019). 3) The overall tectonic framework of the basin is controlled by NW-SE compressional stress, and the synsedimentary normal faults associated with the Tuchengzi Formation are not found on the edges of the basin (He et al., 2008). Xu et al. (2016) took the Early Cretaceous mafic dikes intrude in the upper part of the Tuchengzi Formation in the Shangyi basin as the result of syntectonic emplacement during the late sedimentary stage of this formation, suggesting an extensional tectonic setting. Nevertheless, based on our fieldwork, these mafic dikes are not appeared as the interlayers but manifested as evident cross-cutting relationships with the surrounding strata (Figures 11E,F), which implies that the regional extension may later than the Tuchengzi Formation. 4) The stratigraphic succession of the Tuchengzi Formation in Shangyi area is characterized by an upward decrease in grain size (Figure 3), which is inconsistent in sedimentary characteristics with that in others Mesozoic basins (such as the Luanping Basin, the Chicheng Basin, and the Qianjiadian Baisn) in the Yanshan belt, expressed by a sequence with fining-upward first and then coarsening-upward in grain size (J. Liu et al., 2015; Lin et al., 2019; Shi et al., 2019). This difference may be related to the geotectonic location of the study area. Related research reveals that the Taihang Mountains might have experienced two significant tectonic uplifts during the late Middle Jurassic to Early Cretaceous (Wang and Li, 2008; Cao et al., 2013; Yang et al., 2014), which may result in the denudation of the upper part of the Tuchengzi Formation and the lack of late Mesozoic volcanic rocks in Shangyi region.

Of course, we are not ruling out that some transitory tectonic quiet periods (even the short-lived weak extensional episodes) may occur in the depositional phase of the Tuchengzi Formation. Shi et al. (2019) confirmed that the middle and upper part of the Tuchengzi Formation in the Qianjiadian Basin in the western Yanshan fold and thrust belt was controlled by the NE-striking Qianjiadian thrust fault and the SPF. Before that, the basin has experienced an obvious lake transgression event during the early deposition of the Tuchengzi Formation, suggesting a temporary tectonic quiet period (Shi et al., 2019).

Based on restoration of the section B-B', we obtained the minimum crustal shortening ratio of 27% in Shangyi area under the control of NW-SE compression during the late Late Jurassic to earliest Cretaceous. Horizontal shortening of the crust was principally accommodated by vertical crust thickening resulted from the thrust faulting and the buckle folding. Numerous studies confirmed that the Yanshanian movement caused conspicuous thickening of the lithosphere in eastern China during the late Mesozoic (Zhao et al., 2004; Zhang et al., 2008; Dong et al., 2015, 2018). Based on balanced cross-section reconstructions, Zhang et al. (2011) estimated the north-south-directed shortening of the central part of the Yanshan belt before 135 Ma was around 38%, causing crustal thickening up to 12–15 km. Subsequently, the tectonic regime in eastern China and its adjacent areas underwent a remarkable transition from compression to extension, generating extensive lithospheric destruction and thinning. In recent years, some significant evidence of early crustal shortening-thickening has been discovered from some representative low-angle detachment systems or metamorphic core complexes developed in the northern margin of the NCC (Wang et al., 2011; Zhu et al., 2015), indicating an intimate relationship between crustal shortening-thickening and lithospheric destruction. On the one hand, the thickened crust may usually give rise to deep-seated partial melting, and then continuous melting may cause the weakening of deep-seated rocks and may further trigger crust–mantle decoupling (Liu et al., 2009, 2020). On the other hand, lithospheric isostasy and the coeval magmatism caused the thickened crust uplifted significantly accompanied with increasing gravitational potential energy, which incurred the destruction of the original stability of the craton and also provided favorable conditions for the subsequent intense extensional collapse of the middle and upper crust (Zheng and Wang, 2005; Wang et al., 2011; Zhang et al., 2011).

Intracontinental deformation events occurred at pre-Late Jurassic in the north edge of the NCC had been recognized in many studies. For instance, some significant ∼E-W-striking faults in Yanshan belt, including the Fengning-Longhua Fault, the Gubeikou-Pingquan Fault (namely the eastern the Shangyi-Pingquan Fault) (Figure 1B) and so on, were characterized by thrusting towards the south of hanging wall during the pre-Middle Jurassic (J. Liu et al., 2012; Li et al., 2016; S. F. Liu et al., 2021), indicating the ∼N-S crustal shortening. Afterwards, a regional unconformity interface formed between the Tiaojishan Formation and the underlying older stratigraphic units, which reflects the episode A of the Yanshanian movement. Furthermore, a set of molasse-like formations represented by the Longmen Formation conglomerates from the Western Hills of Beijing acted as the crucial sedimentary response of this tectonic movement (Xu et al., 2016). However, in view of limited structural data in this work, here we mainly discuss the Late Jurassic-Cretaceous tectonic deformation in the northern margin of North China.

During the Late Jurassic to earliest Cretaceous (ca. 151–141 Ma), after the short tectonic quiet period, another intense intracontinental deformation event, namely the episode B of the Yanshanian movement, occurred in northern margin of the NCC. The SPF, as the north boundary of the Shangyi Basin, reactivated under the influence of regional NW-SE compression, expressed by obvious dextral strike-slip movement. Meanwhile, the BSF was formed on the southern edge of the basin and was marked by a reverse fault with the top-to-the-NW slip sense. These thrust structures have shown as the basement-involved thick-skinned tectonics, which made all the late Mesozoic strata in the basin subject to folding and thrusting and formed a structural style of facing thrusts (Figure 13A1). In addition, some evidence related to the ∼N-S contraction deformation has also been identified simultaneously in the north margin of the NCC. For example, Zhu et al. (2015) reported that the Sihetang ductile shear zone in the middle of the Yanshan belt was a thrusting zone with the top-to-the-SSW shear sense during the early Early Cretaceous (140–137 Ma); Davis et al. (2001) deemed that the high-angle Gubeikou Fault shown as a thrust fault with the top-to-the-south slip sense during the Late Jurassic to earliest Cretaceous (148–132 Ma). The above information demonstrates that the north edge of the North China might be affected by multiple tectonic domains in this period.

The geodynamics of NW-SE compression in this stage was normally considered as the subduction of the Paleo-Pacific plate beneath the East Asian continent (Liu et al., 2017, 2018; Zhu et al., 2018; Clinkscales and Kapp, 2019; Lin et al., 2019). However, this suggestion cannot explain the simultaneous ∼N-S or NNE compressional deformation in the northern margin of the NCC (Lin et al., 2013), which was usually attributed to the closure of the Mongol-Okhosk Ocean (Zorin, 1999; Davis et al., 2001; Meng, 2003; Donskaya et al., 2008; Wang et al., 2011, 2015; Zhu et al., 2015). Some studies suggest that the Mongol-Okhotsk Ocean began to close from west to east in a scissor-like fashion during the late Mesozoic, and the final collision may occur in the Early Cretaceous (Metelkin et al., 2010). Under the influence of the closure of the Mongol-Okhosk Ocean in the north, series of N-S-directed tectonic shortening were marked in the northern margin of the NCC (He et al., 1998). Therefore, this stage of tectonic event (namely the Yanshanian B) may be driven by a combined effect from both of the subduction of the Paleo-Pacific plate beneath East Asia and the closure of the Mongol-Okhosk Ocean (Figure 13A2).

During the middle–late Early Cretaceous (ca. 135–110 Ma), the NCC underwent widespread lithospheric extension and destruction, expressed by vast magmatism and the development of abundant extensional structures. Due to previous compression and uplifting, the Early Cretaceous volcanics are quite undeveloped in Shangyi area. Nevertheless, under the control of regional NW-SE extension, some outcrop-scale extensional structures were formed in margins and interior of the basin, and some coeval mafic dikes and intermediate-acid granites were also invaded sporadically in the east and west sides (Figure 13B1). Compared with the contemporaneous representative extensional basins and low-angle detachment systems (or metamorphic core complexes) in the northern margin of the NCC (Wang et al., 2011, 2012; Lin and Wei, 2018), the strength and influence of NW-SE extensional deformation in the Shangyi Basin are very limited and are not change the previous tectonic framework, which may reflect the inhomogeneous extension and thinning of the lithosphere (Xu, 2004; Liu et al., 2009). Many researchers linked far-ranging NW–SE extensional deformation in North China during the Early Cretaceous to the roll-back of the Paleo-Pacific subducting plate (Griffin et al., 1998; Davis et al., 2001; Ren et al., 2002; Zhu et al., 2011; Liu et al., 2017; B. Zhang et al., 2020). However, many extensional structures, such as half-graben basins, metamorphic core complexes, and syntectonic plutons bounded by low-angle normal faults, were also recognized in Transbaikalia and adjacent areas in the northern Central Asian Orogenic Belt, whose origin was owed to post-orogenic extensional collapse of the Mongol–Okhotsk belt (Zorin, 1999; Meng, 2003; Donskaya et al., 2008; Wang et al., 2011). These extensional structures show the highly consistent in activity age with the lithospheric extension and thinning of the NCC (Donskaya et al., 2008; Wang et al., 2012, 2015; Daoudene et al., 2013; Lin and Wei, 2018). Furthermore, in terms of the geotectonic position, the distance between the northern margin of the NCC and the subducting edge in the east is roughly the same as the distance from the northern margin of the NCC to the Mongol–Okhotsk belt in the north (Figure 1A). The geodynamic context of this far-ranging NW–SE extensional event is thus likely associated with back-arc extension triggered by the roll-back of the Paleo-Pacific subducting plate and post-orogenic extensional collapse of the Mongol–Okhotsk belt (Figure 13B2).

After the late Early Cretaceous (<110 Ma) (or may be during the late Early Cretaceous–Late Cretaceous), the Shangyi Basin experienced NE-SW compression. This compressional event, whereas, only caused limited destruction and transformation to the early structures, which was shown as local strike-slip displacement along the boundary faults, some outcrop-scale X-type conjugate shear fractures, and NW-trending open fold (Figure 13C1). It should be noted that the Cretaceous faulted basin in Eastern China experienced an important tectonic reverse associated with another NW-SE compressive stress field during the late Early Cretaceous-Late Cretaceous (Y. Q. Zhang et al., 2004; Liu et al., 2017; B. Zhang et al., 2020), which reflects termination of the NCC peak destruction. Here NW-SE compression is inconsistent in orientation with the contemporaneous NE-SW compression, implying a complex tectonic situation of intracontinental multidirectional compressional deformation in the north edge of the NCC during this period.

About the driving mechanism, on the one hand, this stage of NW-SE compression may be linked to the change of velocity and angle of the subducting plate (Zhang et al., 2008; Zhu et al., 2018; B. Zhang et al., 2020). After further analysis, some researchers have argued that an undefined ocean block or plateau collided with the southeast margin of East Asia continent during the Late Cretaceous (ca. 100 Ma) (Yang, 2013; Niu et al., 2015; J. Zhang et al., 2020). Then this unknown block continued moving to the north along the east margin of East Asia, which affected the compression-shear structural environment in the east edge of East Asia. In this process, Paleo-Pacific Plate changed into low-angle subduction again (Figure 13C2) (Yang, 2013; J. Zhang et al., 2020). However, on the other hand, NE-SW compression is almost perpendicular in orientation to the subduction of the Paleo-Pacific plate, so the latter is unlikely to be the geodynamic background of the former. Simultaneously, the Mongol-Okhosk Ocean has closed, suggesting the driving force may not be from the north. Actually, the Qiangtang and Lhasa terranes at the southwest of the NCC (Figure 1A) experienced collision and collage during the Mesozoic (Guynn et al., 2006; Kapp et al., 2007; Ma et al., 2017). The Bangong-Nujiang suture zone, as the boundary between the Qiangtang and Lhasa terranes, represents the relic of the Mesozoic Bangong–Nujiang Tethyan Ocean (Wang et al., 2016). Recently, Peng et al. (2020) conducted a systematic petrologic, geochemical and isotope chronological investigation in Tongka area, which is located in the eastern section of the Bangong-Nujiang suture. They deemed that the initial subduction of the Bangong–Nujiang Tethyan Ocean may start at 190 Ma, and its eventual closure may continue to the Late Cretaceous (Peng et al., 2020). Considering that the subduction and closure of the Bangong–Nujiang Tethyan Ocean is consistent in direction with regional NE-SW compression, we can speculate that the NE-SW compression may be linked to the remote effect of the final collision between the Qiangtang and Lhasa terranes (Figure 13C2).