## 5 Discussion
### Exhunation and Deformation History
#### 5.1.5 Early Cretaceous (130-109 Ma)  
Based on previous analytical procedures (AFT age data, ZFT age data, and the inverse modeling of thermal history), the denudation event between 130 and 110 Ma of HTB is confirmed to represent a significant geological episode in the Late Mesozoic. The Jurassic sandstones are unconformably overlain by the lower Cretaceous strata, constrained by the West Piedmont Fault of the HTB. The Late Jurassic Fengfang River Formation is interbedded with sandstone, and the Lower Cretaceous overlies conglomerate to the southeast of Yinchuan Basin [23]. In addition, a series of angular unconformity interfaces between the pre-Cretaceous and the Late Cretaceous formation is found in the southern HTB [65]. Early Cretaceous strata in Bayinhaote Basin to the west of the HTB were controlled by the West Piedmont Fault of the HTB. Meanwhile, the East Piedmont Fault restricted the development of Cretaceous formation in the Yinchuan Basin [3]. Therefore, both of these two faults were active during the Early Cretaceous. The maximum principal stress direction shifted from a nearly N-S trend in the Mid-Late Jurassic on the eastern margin of Ordos Basin [66], to an E-W oriented extension of the HTB in the Early Cretaceous. Furthermore, the basalt geochronological data obtained from Gugutai in the HTB provides evidence of the extensional tectonic setting and dynamic during the Early Cretaceous [25; 67].  
In addition to the HTB, the presence of angular unconformity between the Late Jurassic strata and the Early Cretaceous strata has been identified in several adjacent regions, including northern North China Craton [68], South China [69; 70], and the Korean Peninsula [71]. Tectonic and geochronological data indicate that the NW-SE-trending extensional event occurred throughout the NCC and its adjacent area during the Early Cretaceous. Liupanshan Basin, restricted by the normal faults, was characterized by the 3 km thickness of sediments, indicating a strong rapid uplift event in the Early Cretaceous, supported by the FT age of \(\sim\)130 Ma [52]. The Early Cretaceous (140-120 Ma) saw fast cooling events, using the feldspar multi-diffusion domain approach and the AFT method [48] in the West Qinling Orogenic Belt. Meanwhile, the MDD technique revealed the same 140-120 Ma ages in the East Kunlun Orogenic belt [72]. The weak young trend of Late Mesozoic crustal extension initiated in Mongolia and northern China (ca. 150-145 Ma) [73; 74; 75], then progressively developed southeastwards (140-130 Ma) [76; 77], and finally spread throughout all of NE Asia (130-120 Ma) [78].  
Based on the above evidence, the HTB and the North China Craton were affected by uniform geodynamics during the Early Cretaceous. Prior numerous investigations prefer to link the Early Cretaceous extension of the HTB with the northwestward subduction of the Paleo-Pacific Plate ([3; 6]). However, the fast conversion of structural settings should not be ignored. Specifically, the lithospheric thickening caused by the Late Jurassic compression implies the Early Cretaceous extension deformation in North China Craton (including HTB) [8; 74; 79]. Therefore, we conclude that the Early Cretaceous extension of the HTB and the North China Craton is not influenced by a solitary factor. Since the remote effect from the rollback of the Paleo-Pacific Plate in the east, the collapse of the thickened lithosphere also played a significant role.