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.

Fault‐related folds of variable structural styles and assemblages commonly coexist in orogenic belts with competent‐incompetent interlayered sequences. Despite their commonality, the kinematic evolution of these structural styles and assemblages are often loosely constrained because multiple solutions exist in their structural progression during tectonic restoration. We use a sandbox modeling instrument with a particle image velocimetry monitor to test four designed sandbox models with multilayer competent‐incompetent materials. Test results reveal that decollement folds initiate along selected incompetent layers with decreasing velocity difference and constant vorticity difference between the hanging wall and footwall of the initial fault tips. The decollement folds are progressively converted to fault‐propagation folds and fault‐bend folds through development of fault ramps breaking across competent layers and are followed by propagation into fault flats within an upper incompetent layer. Thick‐skinned thrust is produced by initiating a decollement fault within the metamorphic basement. Progressive thrusting and uplifting of the thick‐skinned thrust trigger initiation of the uppermost incompetent decollement with formation of a decollement fold and subsequent converting to fault‐propagation and fault‐bend folds, which combine together to form imbricate thrust. Breakouts at the base of the early formed fault ramps along the lowest incompetent layers, which may correspond to basement‐cover contacts, domes the upmost decollement and imbricate thrusts to form passive roof duplexes and constitute the thin‐skinned thrust belt. Structural styles and assemblages in each of tectonic stages are similar to that in the representative orogenic belts in the South China, Southern Appalachians, and Alpine orogenic belts.