The heterogeneity of carbonate ooze in plane-slice and vertical-slice orientations is usually less than that of clastic ooze and has been reported in fewer types of soft-sediment deformation structures in carbonate rocks. Most soft-sediment deformation structures reported in the literature developed in clastic rocks. Soft-sediment deformation structures developed in the platform-facies dolomites of the Mesoproterozoic Guandaokou Group along the southwestern margin of the Ordos Block in the western North China Craton (NCC). On the basis of their genesis, these structures in the Guandaokou Group can be divided into two major types: (1) soft-sediment deformation structures formed by loading and compaction during diagenesis, including load casts, flame structures, sandstone balls, sandstone pillow structures, and convolute bedding, and (2) soft-sediment deformation structures caused by seismic activity, namely, seismic structures, including structural types such as microfaults, self-clastic breccias, ball-pillow structures, and quasi-ball-pillow structures. Horizontal comparison of the sedimentary facies indicates that the study area should be near the boundary of the Ordos Block. Seismic structures indicate that the area was strongly disturbed by tectonic activity in the surrounding area at 1600–1400 Ma. On the basis of field data and regional geological data analysis, we suggest that the seismic structures in the Guandaokou Group reflect strong extension and that such an extensional tectonic setting is consistent with the synsedimentary faults within the Mesoproterozoic strata under the Mesozoic–Cenozoic cover rocks, the spreading Kuanping Ocean at the southern margin of the Ordos Block, and the homochronous magmatism in the adjacent area west of the Ordos Block. The early Mesoproterozoic Columbia breakup event resulted in different structural responses in the carbonate rocks of the Guandaokou Group in the southern NCC. In the Xiaoqinling area, the presence of acidic tuff indicates continental rifts, whereas soft-sediment deformation structures are observed in the study area.

Accretionary orogens are sites of continental crust growth and reworking and provide an archive of magmatism in both compressional (advancing) and extensional (retreating) plate margin settings, but how this tectonic switching occurs and what the petrological indicator is remain unclear. Here, zircon U-Pb dating results reveal magma emplacement ages of 411–399 Ma for granitic rocks in the central Beishan Orogenic Belt, southern Central Asian Orogenic Belt (CAOB). They have a high proportion of K-feldspar, relatively high (K₂O + Na₂O)/CaO and FeO_t/(MgO + FeO_t) ratios, elevated zircon saturation temperatures, and diagnostic 10,000 × Ga/Al ratios (3.07–3.89). These petrological and geochemical features not only accord with typical ferroan granitoids but also imply a hot and anhydrous origin. In addition, they show relatively depleted zircon Hf isotopic signatures (εHf(t)=−2.9 to +11.1) and are typified by moderate whole-rock Nd isotopes (εNd(t)=−2.7 to +0.5). Consequently, we consider these early Devonian ferroan granitoids formed by variable mixing of crustal components (up to 30%) with juvenile magma in an back-arc basin setting, likely resulting from the slab rollback process. Since early Paleozoic magmatic rocks in this orogenic belt were largely generated by continuous slab subduction, the early Devonian granitoids likely mark the conversion from compressional to extensional settings. Combining this with other geological records, we propose that the early Devonian ferroan granites signaled a switching of the tectonic regime in the southern CAOB from an advancing to a retreating accretionary orogen.