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The Longmenshan thrust belt (LMTB) is one of the best natural laboratories for thin-skinned tectonics and has developed a series of NE-SW trending fold-and-thrust structures represented by a series of nappes and klippes, exemplified by the Tangbazi and Bailuding klippe. However, the timing and emplacement mechanism of these klippes are still in dispute. Three possible mechanisms have been proposed: (1) a Mesozoic-Cenozoic southeastward thrusting, (2) a Cenozoic gravity gliding, and (3) glacial deposition. Almost all of these klippes are tectonic and overlaid on folded Late Triassic sandstone except the Tangbazi klippe, which is located in the center of the LMTB and has a narrow tail extending southeastward and covering Jurassic-Quaternary rocks. This geometric relationship is considered the most important stratigraphic evidence to support the post-Cenozoic emplacement of the Longmenshan klippe. Our structural and petrological observations show that the rocks at the front of the Tangbazi and Bailuding structures are brecciated limestone, which is assumed to have been generated by a gravitational collapse and is not characteristic of the massive Permian strata. Artemisia pollen, which has been exclusively recognized in post-Late Eocene strata in Central Asia, was found in the matrix of this brecciated limestone. Therefore, our discovery indicates that the brecciated limestone was deposited after the Late Eocene rather than during the Permian as annotated on the geological map. In contrast, unbrecciated, massive Permian limestone overlaid on the folded Late Triassic rocks. Hence, the anomalous relationship of Permian strata overlaying Late Triassic rocks cannot be evidence of Cenozoic emplacement. According to currently recognized bulk strata relationships, we can only be sure that the klippe was emplaced in the post Late Triassic. The petrological characteristics of the brecciated limestone show that it was crumbled before the re-sedimentation of the breccia, implying that the LMTB might have experienced a rapid uplift during the Late Eocene. [ABSTRACT FROM AUTHOR]

Abstract: Granitoids play an important role in deciphering both crustal growth and tectonic evolution of Earth. In the eastern end of the Yinshan–Yanshan belt of North China Craton, the Yiwulüshan massif is a typical region that presents the tectonic evolution features of this belt. Our field work on the host rocks has demonstrated two phases of opposite tectonics: compressional and extensional, however, the deformation is almost invisible in the intrusive rocks. To improve the understanding of the tectonic evolution of the Yiwulüshan massif and the Late Mesozoic tectonics of East Asia, a multidisciplinary study has been carried out. In this study, anisotropy of magnetic susceptibility (AMS) and gravity modeling have been applied on these Jurassic plutons (Lüshan, Jishilazi and Guanyindong), which intrude into the Yiwulüshan massif. According to laboratory measurements and microscopic observations on thin sections, the AMS of the Yiwulüshan massif is characterized by secondary fabrics, indicating that the intensive post solidus deformation has reset the (primary) magmatic magnetic fabrics. A relatively gentle NW dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of N34°E and N335°E orientations, namely LM1 and LM2, relatively. Gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif. Integrating all results from structural observation, geochronological investigation, AMS measurement and gravity modeling, two tectonic phases have been identified in the Yiwulüshan massif, posterior to the Jurassic (180–160Ma) magmatism in the Yinshan–Yanshan area. The early one concerns a Late Jurassic–Early Cretaceous (~141Ma) compressional event with a top-to-the-south to southwest sense of shear. The second one shows an Early Cretaceous (~126Ma) NW–SE ductile extensional shearing. At that time, sedimentary basins widened and Jurassic plutons started to be deformed under post solidus conditions. In fact, the NW–SE trend of the maximum stretching direction is a general feature of East Asian continent during Late Mesozoic. [Copyright &y& Elsevier]

Abstract: With a cratonic nucleus, the North China Craton (NCC) experienced a complex tectonic evolution with multiphase compressional and extensional events during Mesozoic times. Along the northern part of the NCC, the Yinshan–Yanshan fold and thrust belt was a typical intraplate orogen. Jurassic and Cretaceous continental sedimentation, magmatism, widespread intraplate characterize the Yinshan–Yanshan orogenic belt. The geodynamic significance of these tectonic events is still in dispute. In the western part of the Liaoning province, the Yiwulüshan massif crops out at the eastern end of the Yinshan–Yanshan orogenic belt. The Yiwulüshan massif presents an elliptical domal shape with a NE–SW striking long axis. The structural evolution of this massif brings new insights for the understanding of the Mesozoic plutonic–tectonic history of the NCC. A multidisciplinary study involving structural geology, geochronology, Anisotropy of Magnetic Susceptibility (AMS) and gravity modeling have been carried out. The presentation of the new results splits into two parts. Part I (this paper) deals with field and laboratory structural observations, and presents the main geochronological results. The AMS, gravity modeling data will be provided in a companion paper (Part II). The early compressional deformation (D1) corresponds to a Late Jurassic to Early Cretaceous southward thrusting. The subsequent deformation is related to the Early Cretaceous exhumation of the Yiwulüshan massif. A detailed structural analysis allows us to distinguish several deformation events (D2, D3, and D4). The Cretaceous extensional structures, such as syntectonic plutons bounded by ductile normal faults, metamorphic core complexes, and half-graben basins are recognized in many places in East Asia. These new data from the Yiwulüshan massif constitute a link between Transbaikalia, Mongolia, North China and South China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region. [Copyright &y& Elsevier]

In orogenic belts, a basal décollement zone often develops at depth to accommodate the shortening due to folding and thrusting of the sedimentary cover. In the Early Mesozoic intracontinental Xuefengshan Belt of South China, such a décollement zone is exposed in the core of anticlines formed by the emplacement of the late-orogenic granitic plutons. Our detailed, multi-scale structural analysis documents a synmetamorphic ductile deformation. In the basal décollement, the Neoproterozoic pelite and sandstone, and the intruding Early Paleozoic granites were deformed and metamorphosed into mylonites and orthogneiss, respectively. The metamorphic foliation contains a NW-SE stretching lineation associated with top-to-the-NW kinematic indicators. The ductile shearing of these high-strained rocks can be correlated with NW-verging folds and thrusts recognized in the Neoproterozoic to Early Triassic sedimentary cover. Monazite U-Th-Pb chemical dating, and zircon SIMS U-Pb dating provide age constraints of the ductile shearing between 243 and 226 Ma, and late-orogenic granite emplacement around 235-215 Ma. In agreement with recent geochronological data, these new results show that the Xuefengshan Belt is an Early Mesozoic orogen dominated by the NW-directed shearing and thrusting. At the southeastern boundary of the Xuefengshan Belt, the Chenzhou-Linwu fault separates the Early Mesozoic domain to the NW from the Early Paleozoic domain to the SE. The tectonic architecture of this belt was possibly originated from the continental underthrusting to the SE of the South China block in response to northwest-directed subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Petrography and geochemistry data are applied in this research. [•] The Dulate arc is the primary source area. [•] REE mixing of provenance modelling method is used to determine the source rocks. [•] The sedimentary rocks deposit in a back-arc basin. [•] The back-arc basin formed by the southward subduction of the Zaysan–Erqis Ocean. [Copyright &y& Elsevier]

Abstract: The Tongcheng massif, a structure lying to the east of the central Dabieshan domain, previously considered a unique unit metamorphosed under Ultrahigh-Pressure (UHP) conditions, similar to those involved in the South Dabieshan and wrenched by the Tan–Lu fault during the Mesozoic. Detailed field survey and laboratory work in the areas of structural geology and petrology indicates that the Tongcheng massif is a tectonic stack of allochthonous sheets. From the bottom to the top, this massif is divided into three units: Lower, Middle and Upper Unit. The Lower Unit suffered an UHP metamorphism with a P-T condition of about 3.21–3.31 GPa and 590–651 °C. Eclogites in the Middle Unit underwent high pressure (HP) and medium temperature metamorphism at 2.46–2.64 GPa and 500–565 °C. In the Upper Unit, the peak metamorphic P-T conditions for eclogites were estimated as 1.54–2.36 GPa and 389–510 °C. These petrological results correspond well to the geometry of the field observation. Structural analysis indicates that the Tongcheng massif has experienced polyphase deformation. The earliest event (D1) corresponds to top-to-north (northeast) shearing associated with the early exhumation stages of HP-UHP rocks during the late Triassic. The D2 deformation overprints D1 and coincides with a domal structure similar to a metamorphic core complex of early Cretaceous age. The D3 deformation is expressed by a pervasive ENE-WSW trending, subvertical foliation and a subhorizontal lineation or penetrative slickenline with a sinistral sense of shear, probably related to the NE-SW contraction during the NW-SE subhorizontal extension, the strike slip deformation raised by the N-S compression during the early Cretaceous. The D4 event is represented by a brittle NE striking, moderately to steeply dipping to the SE fault with down-dip slickenlines. Kinematic indicators show a normal displacement with the east side moving downward. Half-grabens of late Cretaceous to early Cenozoic age are widespread throughout Eastern China. Based on structural analysis, mineral chemistry data and, in particular, the results of P-T calculations for eclogites in different units, a geodynamic scenario for the evolution of the HP-UHP orogenic belt of the Dabieshan is proposed, and the significance of the Tan–Lu fault is also discussed. [Copyright &y& Elsevier]

The anisotropy of seismic velocities in the mantle, when integrated with high-resolution tomographic models and geologic information, can be used to detect active mantle flows in complex plate boundary areas, providing new insights on the impact of mantle processes on the topography of mountain belts. Here we use a densely spaced array of temporary broadband seismic stations to analyze the seismic anisotropy pattern of the western Alpine region, at the boundary between the Alpine and Apenninic slabs. Our results are supportive of a polyphase development of anisotropic mantle fabrics, possibly starting from the Jurassic to present. Geophysical data presented in this work, and geologic evidence taken from the literature, indicate that: (i) fossil fabrics formed during Tethyan rifting may be still preserved within the Alpine and Apenninic slabs; (ii) mantle deformation during Apenninic slab rollback is not compensated by a complete toroidal flow around the northern tip of the retreating slab; (iii) the previously observed continuous trend of anisotropy fast axes near-parallel to the western Alpine arc is confirmed. We observe that this arc-parallel trend of fast axes is located in correspondence to a low velocity anomaly in the European upper mantle, beneath regions of the Western and Ligurian Alps showing the highest uplift rates. We propose that the progressive rollback of the Apenninic slab, in the absence of a counterclockwise toroidal flow at its northern tip, induced a suction effect at the scale of the supraslab mantle. The resulting mantle flow pattern was characterized by an asthenospheric counterflow at the rear of the unbroken Western Alps slab and around its southern tip, and by an asthenospheric upwelling, mirrored by low P wave velocities, that would have favored the topographic uplift of the Alpine belt from the Mont Blanc to the Mediterranean sea. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Huangling massif has an asymmetric domal structures and deformation styles related to its uplifting. [•] Cooling history reveals the Huangling massif underwent distinct uplifting between 160Ma and 110Ma. [•] Structural geology and geochronology improve the knowledge of the Late Mesozoic tectonics of Eastern China. [Copyright &y& Elsevier]

Abstract: Intracontinental orogens remain less understood than accretionary or collisional orogens that are related to plate margin interactions. In the center of the South China block, the Xuefengshan Belt provides a well-exposed example of such an intracontinental orogen of Early Mesozoic age. Detailed field tectonic observations indicate that the Xuefengshan Belt can be divided into a Western Outer Zone characterized by km-scale box-fold structures, and an Eastern Zone, separated from the Western Outer Zone by the SE-dipping Main Xuefengshan Thrust. In the Eastern Zone, NW verging folds coeval with a pervasive slaty cleavage and a NW–SE trending lineation are the dominant structures. From west to east, the dip of the cleavage surface exhibits a fan-like pattern. The bulk architecture of the Xuefengshan Belt results from polyphase deformation: D1 is characterized by a top-to-the-NW ductile shearing; D2 corresponds to SE-directed back thrusting and folding; D3 consists of upright folds with vertical cleavage and lineation. At depth, a high strain zone characterized by greenschist facies metamorphic rocks and a top-to-the-NW ductile shearing corresponds to a ductile décollement zone that accommodated the deformation of the Neoproterozoic to Early Triassic sedimentary series. Kinematic compatibility suggests that the synmetamorphic ductile shearing was coeval with the D1 event in the sedimentary cover. The Xuefengshan Belt is interpreted as an Early Mesozoic intracontinental orogen, which possibly originated from the SE-directed continental subduction of a piece of the South China block in response to northwestwards subduction of the Pacific plate. [Copyright &y& Elsevier]

Abstract: The south-Liaodong peninsula massif is the easternmost Mesozoic metamorphic core complex, recognized in Eastern China. It provides a good example of the combination of ductile shearing, syn-kinematic plutonism and polyphase exhumation. The Jurassic granodioritic plutons, located at the footwall of the detachment normal fault, and dated here at ca 160Ma, recorded two different phases of cooling. A slow cooling regime of about 3–10°C/my prevailing before 122Ma, was followed by a significant increase in cooling rate of about 40–55°C/my after that time. By contrast, a single fast cooling path was recorded by the Cretaceous monzogranite situated in the footwall of the detachment normal fault. This result indicates that the Jurassic and Cretaceous plutons recorded different exhumation processes: a Jurassic slow or negligible exhumation and a Cretaceous fast one assisted by normal faulting. These two cooling stages correspond to distinct geodynamic processes during the Jurassic and Cretaceous. Extensional tectonics seems not significant before Early Cretaceous. The second stage, dominated by an extensional regime which develops after ca 120Ma, is tentatively correlated to the lithosphere removal of the North China Craton. [Copyright &y& Elsevier]

Abstract: The Tarim and Junggar basins in central Asia are capped by a thick pile of conglomerates, called the Xiyu Formation, that are commonly linked to a change in climate and/or accelerated uplift near the Plio-Pleistocene boundary. In order to better understand their origin and significance, we carried out a combined structural and magnetostratigraphic study in the Quilitage syncline (southern Tianshan), where the base of the Xiyu conglomerates is observed at both sides of the syncline. A balanced cross-section shows that, even at a local-scale, the base of the Xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer. On the southern flank of the Quilitage syncline, we collected 172 samples collected for magnetostratigraphic dating identify 17 polarity chrons that date the new section from 5.2 to ~1.7Ma and constrain the base of the Xiyu conglomerate here at ~1.7Ma. This is 4.2Ma younger than the age of the Xiyu previously found on the northern limb of the same syncline. Together with other magnetostratigraphic studies carried out around the Tianshan, our study unambiguously demonstrates that the onset of deposition of the Xiyu conglomerates is diachronous, and that the conglomerates are systematically younger toward the basin. Consequently, the Xiyu Formation should not be considered as a chronostratigraphic marker related to any particular tectonic or climatic event, but is instead a prograding gravel wedge that has prograded over the underthrusting forelands. A synthesis of chronologic and structural results yields progradation rates over the last 10Ma on the order of ~2.0mm/yr and ~3.9mm/yr south and north of the Tianshan Mountains respectively. These rates are comparable to the shortening rate across the Tianshan range, suggesting that underthrusting is the main factor governing the progradation rate of the Xiyu Formation. [Copyright &y& Elsevier]