The NE striking Longmen Shan Thrust Belt (LSTB) forms the northeastern margin of Tibetan Plateau and merges northward with the southwestern Qinling orogenic belt. The LSTB is characterized by the Late Cenozoic SE‐ward overthrusting and a current 60‐ to 70‐km crustal thickness. Structural constraints link the Late Cenozoic deformation and crustal thickening of the LSTB to the formation of the Tibetan plateau. However, although older Mesozoic deformations are widely identified, including Triassic shortening, they remain underappreciated in the development of the LSTB as the Cenozoic history has been the recent research focus. Thus, it is important to document the early Mesozoic tectonics of the LSTB to better understand the Cenozoic orogeny along the northeastern margin of the Tibetan plateau. Here we synthesize existing and new mapping, structural analyses and geochronology of three regions of the northern LSTB: the Bikou, Tangwangzhai, and Longwangmiao regions. Our observations suggest that the Bikou, Tangwangzhai, and Longwangmiao thrust complexes have similar kinematic styles of southward foreland fold‐and‐thrust propagation. New ⁴⁰Ar/³⁹Ar dating results show that these thrust complexes have deformational ages at circa 237 Ma to circa 180 Ma, respectively, and diachronously emplaced before 201–174 Ma. Triassic shortening structures involving metamorphic rocks are unconformably overlain by Lower to Middle Jurassic strata. We propose a new kinematic model in which Middle to Late Triassic, top‐to‐the south, in‐sequence imbricate thrusts developed in the northern and central LSTB, suggesting that the LSTB was initially built in the early Mesozoic by the southward propagation of the foreland belt of the SW Qinling orogenic belt.

Eastern China underwent structural evolution from N-S contraction to NW-SE contraction and then ESE-ward crustal thinning during Mesozoic-Cenozoic time; however, the mechanisms are still poorly understood. The Western Hills of Beijing are located at the junction among the E-W–trending Yinshan-Yanshan tectonic belt, the NNE-trending Taihang Mountain belt, and the Late Cretaceous–Cenozoic North China Basin. During Jurassic–Cretaceous time, three deformational events, including one compressional and two extensional deformation stages, were superimposed on Middle–Early Triassic south-vergent thrusts and folds in this region. These include (1) WNW-vergent thrusting and fold deformation, (2) ESE-ward crustal thinning with 110°–120°ESE stretching lineations, and (3) E-dipping, high-angle normal faulting. During these deformation stages, muscovite and sericite were produced as synkinematic minerals, and most of these micas are aligned parallel to the stretching lineation or deformed surfaces associated with contractional/extensional deformation. U-Pb zircon dating, as well as ⁴⁰Ar/³⁹Ar hornblende, muscovite, biotite, K-feldspar, and sericite dating, clearly provides the following age constraints in the Western Hills: (1) N-S contraction at ca. 250–200 Ma; (2) WNW-vergent compression at ca. 170–150 Ma; (3) granodiorite and diorite dike intrusion at ca. 136–135 Ma, followed by intrusion of the Fangshan granitic pluton at ca. 130–128 Ma; and (4) ESE-trending stretching lineation at ca. 130–110 Ma. East-dipping, high-angle normal faults developed at ca. 70–60 Ma. The N-S contraction overlaps temporally with the formation and evolution of the Inner Mongolia orogenic belt during late Paleozoic–early Mesozoic time. WNW-vergent thrusting and folding, similar to that in the Taihang Mountain belt, was controlled by the initial formation of the west Pacific plate and its westward subduction beneath the Eurasian plate. ESE-ward crustal thinning in the area was probably controlled by eastward extrusion of the northern margin of the North China craton, driven by final closure of the Mongol-Okhotsk Ocean. The E-dipping, high-angle normal faulting was related to ongoing eastern Asian detachment since Late Cretaceous time. We propose that the main mechanism for the multiple deformation events resulted from the closure of the paleo–Asian Ocean, initial formation of the paleo–Pacific plate, and its subduction, combined with closure of the Mongol-Okhotsk Ocean.

The basaltic pillow lavas in the Liuyuan region of NW China, considered to be part of an ophiolitic suite, have been central to the models on tectonic setting, evolution and timing of the final closure of the Palaeo-Asian Ocean. New field evidence on the sedimentary units associated with the basalts reveals comparable sequences in the northern and southern flanks of the Liuyuan Volcanic Belt with coarse to fine sediments from periphery to the centre. The dacites and rhyolites formed coevally with the pillow basalts. The pillow basalts are interlayered with lacustrine sandstone, claystone and clayey lake deposits. Detrital zircons from these sediments yield zircon U–Pb ages of 291–285 Ma. Andesites, dacites and rhyolites from the basaltic sequence yield U–Pb ages of 280–277 Ma, similar to the 282–280 Ma ages of gabbros that intrude the pillow lavas. All these rocks cover the 460–440 Ma granite and greenschist basement and have been intruded by gabbros ofc.272 Ma age, with subsequent (230–227 Ma) north–south contractional thrusting and folding. The data from our study are incompatible with the existing models that consider the basalts as part of an ophiolitic suite. Along the northern continental margin of China from west to east, the Tarim, Dunhuang-Alxa and North China cratonic areas all show evidence for regional extension through rifting during early–middle Permian time. These rift features and basaltic eruptions occurred coevally with the assembly of various microcontinental blocks against the Siberian craton atc.300–250 Ma, synchronous with amalgamation of the Central Asian Orogenic Belt (CAOB) on the northern side of the Liuyuan Rift. These events were also broadly synchronous with formation of the global supercontinent Pangea.