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Graphical abstract Highlights • Locations and characteristics of five exhumed high-grade hinterland gneissic mylonite shear zone bounding basement nappes that are related to the Zagros thick-skinned tectonics. • Quantitative data on quartz c-axis preferred orientations (LPO), finite strain (R s), kinematic vorticity number (W k) and deformation temperatures. • Construction of the entire crustal-scale balanced and restored cross-sections to illustrate the kinematic evolution of the thick-skinned and thin-skinned tectonics. • The present study leads to a new crustal-scale structural model and subdivisions on both thin-skinned and thick-skinned tectonics of the whole Zagros orogen. Abstract Our understanding of the geological structures and kinematics of thick-skinned and thin-skinned tectonics during the evolution of an orogenic system is strongly related to field evidence of décollement-dominated tectonics or deformation involving the entire middle and lower continental crust. In this paper, we compare thin-skinned and thick-skinned deformation of the Zagros orogen from small to large-scales. In the foreland thin-skinned region sedimentary rocks with several décollement horizons have undergone in-sequence thrusting with dominant NW-striking, NE-dipping and SW-verging displacement. The gneissic basement of the foreland underwent Permo-Triassic rifting and the normal faults were reactivated as thrust or strike-slip faults during subduction-to-collision orogenic system. There is no field exposures of deformed basement windows in this external part of orogen. However, in the internal parts of the orogen, the newly recognized hinterland fold-and-thrust belt and slate belt, there are outcrops of gneissic basement slices, mylonitic shear zones, and granite-gneissic flow. The Tutak granite-gneiss dome is associated with sole thrusts. Therefore, it contains deformed margins of both continents. Thus in deformation in this part of the orogen was thick-skinned. Measurements of quartz c-axis opening angles of the exhumed mylonite nappes document high temperature (∼642°±43° and ∼424°±31 °C). Relationship between kinematic vorticity number (Wk = Wm = 0.76 ± 0.06) of the mylonite nappes which are related to the hinterland fold-and-thrust belt indicate 55 ± 7.8% simple shear and 45 ± 7.4% pure shear components for instantaneous 2D flow which indicate sub-simple shear deformation. On the more thickened side of the Zagros deformed basement-involved contains continuous to discontinuous shear-band boudins of eclogite and slices of blue schist. This provide kinematic indicators suggesting simultaneous dip-slip and strike-slip and shear zones accelerating inclined lateral exhumation of the high-pressure metamorphic rocks of oceanic and continental crustal origin. Both the thin and thick-skinned portions of the Zagros on three major cross sections indicate the intensity of deformation in the NW and SE parts of the belt that display the opposite senses of shear on the two sides. We infer that both senses of shear were developed coevally under a bulk sub-simple shear, regional-scale deformation along a curved inclined transpression. Study of crustal-scale cross sections of the Paleozoic and Mesozoic sequences shows that asymmetrical to symmetrical folding an d thrusting in the central part of the Zagros foreland fold-and-and-thrust belts in the Fars area are gentle in comparison with those in the SE and NW of the orogen. The highest intensity of deformation occurs in the rotated asymmetrical folding and thrusting near the Bandar Abbas Syntaxis. [ABSTRACT FROM AUTHOR]

The crustal deformation beneath the Chuan–Dian rhombic block (CDB) and surrounding regions has been studied in geological and geodetic methods, and provide important insights into the kinematics and dynamics about the clockwise movement of this tectonic block. In this work, we present images of the normalized full gradient (NFG) of the Bouguer gravity anomalies from five gravity profiles across the boundary faults of the CDB measured in recent years, and investigate the distribution characteristics of the crustal anomalous bodies along the profiles. Firstly, an anomalous body with eastward dipping exist beneath the Xianshuihe fault, suggesting that crustal mass move to east. Secondly, near the Xiaojiang fault, two anomalous bodies dip westward with depth increasing. The inferred movement direction of the north one is from west to east, and the south one is from east to west. Thirdly, anomalous bodies on the northeast and southwest sides of the Red River fault suggest the directions of crustal movement is from northeast to southwest. These results are also consistent with GPS solutions, and provide gravity evidence for crustal deformation of the CDB with clockwise rotation. [ABSTRACT FROM AUTHOR]

The North China Plate (NCP) underwent multi-phase intracontinental deformation during the Mesozoic, which is a much-debated research subject. Here we present a case study of this deformation inferred from regional-scale Helanshan superposed folds in the west of the NCP. New structural analyses and fault kinematic analyses in the Helanshan Structural Belt (HSB) indicate a two-stage syn-folding paleo-stress field, comprising early NNE–SSW compression, with mean orientations 190°/01° (plunge direction/plunge) for σ 1 , 283°/26° for σ 2 , and 100°/63° for σ 3 , and later WNW–ESE compression with mean orientations of σ 1 , σ 2 , and σ 3 at 124°/07°, 213°/04°, and 001°/75°, respectively. These results, combined with geochronological analysis, indicate two episodes of shortening in this belt during the Mesozoic. Late Triassic–Early Jurassic NNE–SSW shortening, which produced ∼8.1 km of horizontal shortening, led to the development of open WNW-trending fold structures. Subsequent Late Jurassic–Early Cretaceous WNW–ESE shortening, which produced ∼18.7 km of horizontal shortening, reshaped the early WNW-trending structures and generated close, overprinting NNE-trending folds that resulted in the development of the regional-scale superposed folds in this area. In terms of geodynamics, the early NNE–SSW shortening is likely to be related to Indosinian intercontinental convergence between the North China Plate and the Yangtze Plate, and the later WNW–ESE shortening is likely to have been related to subduction of the Paleo-Pacific Plate. The regional structural analysis indicates that the whole of the western North China Plate experienced two-phase contractional deformation during the Mesozoic, as manifest by the early NNE–SSW and the late WNW–ESE shortening that characterized Mesozoic intracontinental deformation in the western NCP. [ABSTRACT FROM AUTHOR]

The Shanxi Rift, an intracontinental belt along the eastern margin of the Ordos Block, North China Plate, has undergone multi-stage extensional deformation during the late Cenozoic. In this study, new fault kinematic analysis of boundary faults in the Shanxi Rift, constrained by geochronological data, defines a three-stage tectonic stress regime since the late Miocene, providing new structural evidence for deciphering the northeastward growth of the Tibetan Plateau. The earliest stage involved a transtensional stress regime of NW–SE extension and NE–SW compression in the late Miocene–early Pleistocene (ca. 10–1.8 Ma) and characterized by mean principal stress axes of σ 1 at 344.7°/87.2°, σ 2 at 217.6°/01.1°, and σ 3 at 128.1°/01.0°. The early transtensional stress regime was responsible for the opening of the Shanxi Rift and was very likely associated with intensive right-lateral pull-apart activity in the eastern Ordos Block due to the northeastward growth of the Tibetan Plateau. During the second stage, the stress regime changed to less intense NE–SW extension, with mean stress orientations of 323.3°/85.2° for σ 1 , 127.5°/02.9° for σ 2 , and 214.9°/02.6° for σ 3 in the early late Pleistocene (ca. 1.8–0.11 Ma). This stage is marked by a distinct shift from fluvio-lacustrine to fluvio-piedmont sedimentary facies at the end of the early Pleistocene, and the widespread eruption of basalt in the Datong Basin north of the Shanxi Rift. This short-lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the Tibetan Plateau. The third stage was transtensional, characterized by NNW–SSE extension and WNW–ESE compression ( σ 1 at 060°/88.9°, σ 2 at 074.9°/03.9°, and σ 3 at 164°/00°) since the late Pleistocene (ca. 0.11 Ma), causing dextral shear deformation in the Shanxi Rift and the disappearance of its paleo-lake. This stage resulted from regional ENE–WSW shortening due to northeastward growth of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The Xianshuihe fault (XSHF) zone is an important lithospheric structure in east Tibetan Plateau. The Zheduo-Gonggar massif, about 120 km long and 13–18 km wide, developed along its eastern segment. Based on geological mapping, meso- and micro-structure studying and geochronology testing, the massif is divided into 5 units: (1) Intrusions of 216–204 Ma, (2) Intrusions of ∼170 Ma, (3) mid-Jurassic sillmanite-grade metasediments, (4) Oligo-Miocene migmatite zone, (5) Intrusions less than 20 Ma ago. Intrusions of 216–204 Ma related to the Songpan–Garze folding and distributes on the southern segment of the massif. The middle Jurassic intrusions which were found for the first time in the region, includes the syn-kinematic Zheduoshan granite and a suit of leucogranite. The former constrained by the youngest U–Pb age of 171 Ma which provides a minimum shear age of the XSH fault. The latter, U–Pb age of 170 Ma, is a common feature of convergent orogens or intracontinental subduction. The Oligo-Miocene migmatite zone, about 80 km long and 1–3 km wide, developed on the eastern edge of the massif. Intrusions less than 20 Ma ago is located on the northern segment of the massif. It had been widely researched that the latter two units are associated to the Cenozoic deformation of the XSH fault. While the mid-Jurassic syn-kinematic magmatism, anatexis and metamorphism along the XSH fault suggests a more strong Mesozoic tectono-thermal event in the fault zone. The discoveries provide us with a new perspective on understanding the Mesozoic and Cenozoic deformation of the XSH fault zone, southeastern Tibet. [ABSTRACT FROM AUTHOR]