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Objective The northern margin tectonic zone of the Qaidam Basin underwent a transition from oceanic subduction to continental subduction during the Early Paleozoic, resulting in the formation of the ultrahigh-pressure metamorphic zone known as the northern Qaidam tectonic zone (NQTZ). There has been a longstanding debate regarding the collapse time of the NQTZ. The Maoniushan Formation has long been regarded as a sign of the end of orogeny; however, recent studies show that the Maoniushan Formation has spanned a long time, and it is controversial when the orogenic belt began to collapse. This study aims to determine the age and genetic background of the Maoniushan Formation and to understand the tectonic transition process of the northern Qinghai–Tibet Plateau from the Proto-Tethys to the Paleo-Tethys. Methods Deep-earth samples, including volcanic and intrusive rocks, offer valuable insights into the activity of the crust during this period. In order to investigate the volcaniclastic rocks and granites in the Gahai–Nanshan area, located in the eastern section of the NQTZ, zircon LA–ICP–MS U–Pb chronology and Lu–Hf isotope methods were employed to explore the formation age of igneous rocks and the characteristics of source rocks. Results The zircon U–Pb chronology reveals that the volcaniclastic rocks of the Maoniushan Formation originated approximately 423 Ma. Furthermore, the intrusive granite was formed at 370 Ma, indicating that the volcanic eruption occurred during the Late Silurian, while the subsequent intrusion and crystallization of the granites occurred during the Late Devonian. The zircon Lu–Hf isotope data reveals that the εHf(t) values of the Late Silurian tuffs are concentrated within the range of –11.5 to –8.3, and the corresponding two-stage Hf model ages are primarily between 1945–2133 Ma. These results indicate that the volcanic rocks predominantly originated from partially melting ancient crustal materials. In contrast, the εHf(t) values of the Late Devonian intrusive granites exhibit a distribution within the range of 3.9–9.1, accompanied by two-stage Hf model ages primarily falling within the 792–1118 Ma range. The results suggest that the granites mainly resulted from partially melting Meso-Neoproterozoic crustal materials. Based on a comprehensive analysis of regional geological and petrological data, it is postulated that the Late Silurian–Early Devonian witnessed pronounced orogenesis resulting from continental deep subduction. This event led to substantial crustal thickening in the NQTZ, where the thickened crustal basement of the Oulongbruk experienced partial melting, ultimately giving rise to the volcanic rocks observed during this period. During the Late Devonian, delamination of the thickened crust facilitated the upwelling of the asthenosphere mantle, triggering regional crustal extension. The interaction between mantle material and crust results in the formation of granitic–volcanic rocks. Conclusion The Maoniushan Formation in the region encapsulates a significant period, making it unsuitable to represent the end of orogeny. Late Devonian igneous rocks indicate that the NQTZ entered a period of substantial crustal extension during this time. [ Significance ] The late Devonian igneous rocks of Maoniushan Formation regionally mark the end of orogeny and the beginning of the Paleo-Tethys tectonic domain.

The multi-stage tectonism of compression and extension occurred in the southern part of the Lower Yangtze region in the Mesozoic, which is one of the important factors restricting the breakthrough of oil and gas exploration in this area. This paper aims to reveal the influence of Mesozoic tectonisim on oil and gas preservation in the Lower Yangtze area. Based on the seismic profile interpretation data, field outcrop survey, regional tectonic evolution history analysis and the drilling core data and oil-gas display of the Well Wanjingdi-1, we comprehensively discussed the favorable structural preservation conditions in the southern part of the Lower Yangtze region. The results of seismic interpretation profile and surface survey show that the southern part of the lower Yangtze River has experienced two important tectonic processes since the Late Triassic. The first stage is fold deformation, thrust fault and uplift erosion caused by Indosinian compression, and the second stage is extension since the Late Cretaceous, resulting in the formation of fault basin and normal fault activity. Shale gas display was obtained from the Permian shale in the Well Wanjingdi-1, and light oil was found in the drilling of the Lower Triassic Yinkeng Formation, indicating that the southern Lower Yangtze region has good enrichment conditions and resource potential, which points out a new direction for oil and gas exploration in the region. The analysis of structural preservation conditions shows that the Well Wanjingdi-1 is located in the syncline of the fold-depression belt. The amount of uplift and denudation was small in the Indosinian period. Since the late Cretaceous, the depression has a small amplitude of extension and has good sealing and reservoir forming conditions. It is a favorable structural position for oil and gas preservation in this region. Based on the comprehensive analysis of regional structure and sedimentary basin evolution, it is considered that in the southern Lower Yangtze region, the syncline structural belt in the southern margin of the basin with small erosion amount of Triassic strata or the central zone of fault basin overlying thick Cretaceous-Cenozoic strata should be taken as the key target to search for favorable oil and gas zones.

The ductile shear deformation of Precambrian basement rocks in Wuyishan provides a crucial perspective on intraplate orogeny in the South China Block (SCB). This study focuses on the Longquan‐Badu ductile shear zone in southeastern Zhejiang, employing field observations, thin section analysis, quartz electron backscatter diffraction (EBSD), zircon U–Pb dating and 40Ar/39Ar geochronology. Two distinct phases of deformation, referred to as D1 and D2, have been identified. D1 is primarily characterized by a WNW–ESE striking foliation within a NE‐plunging lineation, indicating top‐to‐SSW shearing. The paragneiss within the Badu complex that experienced D1 deformation has been dated to 247–239 Ma through zircon U–Pb analysis, corresponding to the prevalent high‐pressure metamorphic age in the region. This correlation suggests that the D1 deformation event coincided with crustal thickening during the Early Triassic. D2 deformation exhibits folds, foliation, S‐C fabrics and mylonitic microstructures and is mainly characterized by striking NNE–SSW with steeply dip, demonstrating a dominant dextral strike–slip component. Quartz c‐axis orientations in mylonitic rocks indicate deformation temperatures between 350°C and 550°C with asymmetric girdle patterns suggesting simultaneous basal and prism slip. The plateau ages of muscovite from mylonitic rocks obtained through 40Ar/39Ar dating are approximately ~228 Ma implying that the D2 deformation occurred under retrograde amphibolite to greenschist facies metamorphic conditions during Middle Triassic. Collectively these data along with regional geological evidence signify two distinct intracontinental orogenic processes occurring in eastern SCB. Considering Early Mesozoic tectonothermal events in Cathaysia Block, it can be inferred that intraplate orogeny in Wuyishan resulted from plate‐margin collisions between SCB and peripheral plates following scissors closure of Palaeo‐Tethys from east to west. [ABSTRACT FROM AUTHOR]

The South China region has undergone a complex tectonic history since the Mesozoic era, characterized by significant tectonic regime transformations. However, the mechanism behind these transformations is still subject to debate. This study aims to elucidate the specific manifestations and stress mechanisms driving the tectonic transformations and their geological background. Through field geological surveys, effective stress inversions and analysis of lithofacies palaeogeography in Fujian Province, we have identified six distinct tectonic episodes that occurred during the Mesozoic: (a) late Middle Triassic to early Late Triassic: intense NNE–SSW compression generated an unconformity between the An'ren Formation and Dakeng Formation; (b) middle Late Triassic to early Middle Jurassic: NNE–SSW extension exerted control over the deposition of the Dakeng Formation, Wenbinshan Formation and Zhangping Formation; (c) late Middle Jurassic to early Late Jurassic: NW–SE compression resulted in an unconformity between the Zhangping Formation and Changlin Formation; (d) late Jurassic to early Cretaceous: NW–SE extension influenced the deposition of the Changlin Formation, Nanyuan Formation and Xiaoxi Formation; (e) late Early Cretaceous to Late Cretaceous: a strike–slip stress field caused an unconformity between the Xiaoxi Formation and Shaxian Formation; (f) post‐Late Cretaceous: NE–SW extension occurred. During the late Middle Jurassic to early Late Jurassic period, there was a notable change in the distribution of lithofacies palaeogeography. The coexistence of NE and E‐W‐trending patterns shifted to a predominant NE‐trending pattern, which was controlled by the palaeostress field transitioning from NNE–SSW extension to NW–SE compression. These changes indicate a tectonic regime transformation in Southeast China during this period. Considering the sedimentary, magmatic and tectonic activities, the tectonic evolution of Southeast China was predominantly influenced by the Palaeo‐Tethys tectonic domain from the Early Triassic to early Middle Jurassic and by the Palaeo‐Pacific tectonic domain from the late Middle Jurassic to the Cretaceous. [ABSTRACT FROM AUTHOR]

Key information on sedimentary or tectonic events is recorded in deformation structures formed in unlithified and lithified sediments. Disputes about the classification and identification of the two types of deformation have become increasingly relevant. The present study systematically summarizes, based on consolidation states, the genetic mechanisms of deformation. Consolidation conditions may affect deformation patterns and morphology; this can be a clue to distinguish soft-sediment deformation from tectonic deformation. Liquefaction is a typical state of unconsolidated sediment and can create clastic dikes, liquefied breccia, convolute laminae, load cast, and water-escape structures. Synsedimentary faults may be formed in weakly consolidated sediments. Most deformation structures of lithified sediments are large-scale folds and faults, but small-scale structures – especially microfolds – are difficult to distinguish from slump folds. Tectonic folds can be formed in different strata and induced by tectonic events; they differ from slump folds in morphology, distribution, and related structures. We demonstrated that consideration of liquefaction, folds in different strata – matched with the regional geological regime, related deformation structures, and micro-deformation structures – can be clues to the identification of deformation origins. [ABSTRACT FROM AUTHOR]

The Guang‐Tou‐Shan (GTS) granites, located in the Xing'an Block (XB), record Late Palaeozoic magmatism during the stage of convergence between micro‐blocks in the eastern Central Asian Orogenic Belt (CAOB). We performed a detailed geochronological and geochemical study of GTS granites intending to obtain better constraints on the subduction processes of the Palaeo‐Asian Ocean (PAO) in eastern CAOB. LA–ICP–MS U–Pb dating of zircons from GTS granitic rocks in western XB yielded emplacement ages of 332 ± 2 Ma and 301 ± 2 Ma, respectively, indicating a two‐stage emplacement process. Geochemical analyses show that the Early Carboniferous monzogranite (332 ± 2 Ma) have low values of the A/CNK and A/NK, are enriched in LILE (Rb, Sr, Ba) and LREE (LREE/HREE = 5.6–10.8), and depleted in HFSE (Nd, Ta, Zr, Hf) and P, Ti, which belong to I‐type granites. The Late Carboniferous granodiorite (301 ± 2 Ma) also displays LILE, LREE enrichment, and HFSE depletion with negative Nb–Ta anomalies, and contains relatively high Zr + Nb + Ce + Y contents (495–524 ppm) and high zircon crystallization temperature, indicating the Late Carboniferous granodiorite shows geochemical characteristics similar to those of typical A‐type granites. The two‐stage granitic rocks have εHf(t) values of +7.7 to +11.6 and yield a two‐stage depleted mantle Hf model age of 0.66–0.88 Ga, suggesting that the GTS granitic rocks were derived from partial melting of juvenile arc‐related mafic to intermediate rocks. The results, combined with regional magmatic information, indicate that the eastern CAOB experienced a subduction setting in the Early Carboniferous and extension setting in the Late Carboniferous. This change was most likely caused by the subduction slab break‐off of PAO from the Late Carboniferous. [ABSTRACT FROM AUTHOR]