In the Cretaceous, the subduction of the Izanagi/Paleo-Pacific plates beneath the South China Block (SCB) created a wide back-arc domain characterized by numerous extensional basins coeval with voluminous magmatism. The SCB witnessed the whole evolution by records of widespread extensional structures to accommodate the lithospheric stretching. In the interior of the SCB, the Yuechengling (YCL) Massif preserves a large, low-angle detachment fault, the Ziyuan Detachment (ZYD) at the western margin, and a high-angle ductile normal fault, the Tianhu Fault (THF), in the middle of the massif. Both faults display ductile shearing with top-to-the west kinematics but play different roles in two stages of extension. In the early stage at 140-120 Ma, the THF deformed the eastern YCL pluton at a temperature of~350°C, but the ZYD shows limited movement at this time. On the contrary, the later stage (100-85 Ma) is characterized by pervasive middle-to high-temperature deformation (~400-500°C) and rapid exhumation along the ZYD, but the THF only underwent a near-surface brittle overprint. Across the SCB, the two-phase extension is widely recorded in other extensional structures and coincides with magmatic flare-ups at its eastern margin, suggesting episodic changes in the subduction dip. Combined with two compressional events that took place between the intervals of extension, the SCB experienced two cycles of compression-extension at 155-120 and 120-85 Ma. This periodicity is tentatively interpreted as a combined effect from the Izanagi/Paleo-Pacific subduction angle change and a thickening-foundering process in the arc region.

This work first presents field structural analysis, anisotropy of magnetic susceptibility (AMS) measurements, and kinematic and microstructural studies on the Neoproterozoic Pengguan complex located in the middle segment of the Longmenshan thrust belt (LMTB), NE Tibet. These investigations indicate that the Pengguan complex is a heterogeneous unit with a ductilely deformed NW domain and an undeformed SE domain, rather than a single homogeneous body as previously thought. The NW part of the Pengguan complex is constrained by top‐to‐the‐NW shearing along its NW boundary and top‐to‐the‐SE shearing along its SE boundary, where it imbricates and overrides the SE domain. Two orogen‐perpendicular gravity models not only support the imbricated shape of the Pengguan complex but also reveal an imbrication of high‐density material hidden below the Paleozoic rocks on the west of the LMTB. Regionally, this suggests a basement‐slice‐imbricated structure that developed along the margin of the Yangtze Block, as shown by the regional gravity anomaly map, together with the published nearby seismic profile and the distribution of orogen‐parallel Neoproterozoic complexes. Integrating the previously published ages of the NW normal faulting and of the SE directed thrusting, the locally fast exhumation rate, and the lithological characteristics of the sediments in the LMTB front, we interpret the basement‐slice‐imbricated structure as the result of southeastward thrusting of the basement slices during the Late Jurassic‐Early Cretaceous. This architecture makes a significant contribution to the crustal thickening of the LMTB during the Mesozoic, and therefore, the Cenozoic thickening of the Longmenshan belt might be less important than often suggested.

The South China Block (SCB) experienced a polyphase reworking by the Phanerozoic tectonothermal events. To better understand its Late Mesozoic tectonics, an integrated multidisciplinary investigation has been conducted on the Dayunshan–Mufushan composite batholith in the north‐central SCB. This batholith consists of two major intrusions that recorded distinct emplacement features. According to our structural analysis, two deformation events in relation to batholith emplacement and subsequent exhumation are identified. The early one (D1) was observed mostly at the southern border of the batholith, characterized by a top‐to‐the‐SW ductile shearing in the early‐stage intrusion and along its contact zone. This deformation, chiefly associated with the pluton emplacement at ca. 150 Ma, was probably assisted by farfield compression from the northern Yangtze foreland belt. The second but main event (D2) involved two phases: (1) ductile shearing (D2a) prominently expressed along the Dayunshan detachment fault at the western border of the batholith where the syntectonic late‐stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top‐to‐the‐NW kinematics; and (2) subsequent brittle faulting (D2b) further exhumed the entire batholith that behaved as rift shoulder with half‐graben basins developed on its both sides. Geochronological constraints show that the crustal ductile extension occurred during 132–95 Ma. Such a Cretaceous NW–SE extensional tectonic regime, as indicated by the D2 event, has been recognized in a vast area of East Asia. This tectonism was responsible not only for the destruction of the North China craton but also for the formation of the so‐called “southeast China basin and range tectonics.”

International audienceThe Late Mesozoic granitic belt in the northeastern Hunan province (situated in the south of the middle Yangtze region) represents the western front of the large magmatic province of SE China. In order to determine their ages and petrogenesis, we carried out zircon U–Pb dating, Hf isotope and whole-rock geochemical analyses for four granitic plutons, namely Taohuashan, Dayunshan-Mufushan, Wangxiang and Lianyunshan. Our SIMS zircon U–Pb ages, together with previously published data, reveal that the magmatic activities in this area can be roughly subdivided into three phases at 151–146 Ma, 132–127 Ma and ca. 117 Ma, and the Dayunshan-Mufushan batholith therein is a composite pluton. These four plutons are mainly composed of weakly to strongly peraluminous biotite or two-mica monzogranites, with a minor amount of biotite granodiorites. Their geochemical features are similar to S-type as well as fractionated S-type granites, with enrichment in LREEs and negative Ba, Sr, Nb, P and Ti anomalies. All samples show negative zircon εHf(t) values ranging from −12.5 to −3.6, corresponding to crustal Hf model (TDMC) ages of 1.4–2.0 Ga. It is inferred that these granitoids were derived from partial melting of metasedimentary rocks analogous to the Neoproterozoic Lengjiaxi Group, predominantly with psammitic component. Fractional crystallization probably played an important role in the magma evolution, while input of mantle-derived magma was insignificant. Combined with other geological evidence, our new data allow us to propose that the Cretaceous (132–127 Ma and ca. 117 Ma) magmatism might be response to episodic slab rollback of the Paleo-Pacific plate, while the early-stage (151–146 Ma) magmatism that overlapped the epilogue of Jurassic magmatic flare-up and subsequent magmatic quiescence probably foreshadowed the transformation from foundering of a subducted flat-slab to slab rollback. Alternatively, slab foundering after a SE-directed intracontinental subduction in the central SCB cannot be ruled out for geodynamic interpretation of the Jurassic magmatism in SE China

We conducted a paleomagnetic study on the Early Permian volcanic and sedimentary rocks, and the Neoproterozoic mafic dikes in the Yili Block, NW China. Magnetite and hematite were proven to be the principal magnetic remanence carriers. Demagnetizations revealed stable characteristic remanence magnetizations with a sole reversed magnetic polarity. The magnetic remanence of only the Early Permian strata turned out to be primary based on positive fold tests; meanwhile, the magnetic remanence age of the mafic dikes is ambiguous. Accordingly, the first Early Permian paleomagnetic pole for the Yili Block is calculated at λ = 81.5°N, φ = 256.5°E, N = 11, and A 95 = 10.9°. Comparisons of this new pole with published ones from the Yili, Tarim, and South Junggar blocks provide new quantitative constraints on late Paleozoic kinematic evolution of the SW Central Asian Orogenic Belt: (1) Between the Yili and Tarim blocks, significant relative movement took place along major strike-slip faults during the Late Carboniferous to Early Permian (580 ± 290 km) and the Early to Late Permian (585 ± 340 km), and the displacement rate increased from the Late Carboniferous to Early Permian (~19.3 ± 9.7 mm/yr) to the Early to Late Permian (~29.3 ± 17.0 mm/yr); (2) a significant relative rotation of 28.3°± 18.3°in the Late Permian, and a lateral displacement of 630 ± 295 km after the Late Permian occurred between the Yili and South Junggar blocks. The significant strike-slip movements played an important role in the formation of the Central Asian Orogenic Belt and should be considered with great attention in tectonic and paleogeographic reconstructions. ZHU ET AL.

The Longmenshan Thrust Belt in Eastern Tibet resulted from a Mesozoic orogeny and Cenozoic reworking. It is generally believed that the Cenozoic tectonics along the Longmenshan Thrust Belt are mostly inherited from the Mesozoic. Reconstructing the Mesozoic tectonics of the Longmenshan Thrust Belt is therefore important for understanding its evolutionary history. On the basis of detailed structural analysis, we recognized a Main Central Boundary that divides the Longmenshan Thrust Belt into a Southeastern Zone and a Northwestern Zone. Both zones underwent a main D1 event characterized by D1E top-to-the-SE thrusting in the Southeastern Zone and D1W top-to-the-NW/N thrusting in the Northwestern Zone. In the Southeastern Zone, a D2 top-to-the-NW/N normal faulting that cuts the D1E structures is developed along the NW boundary of the basement complexes. Newly obtained and previous geochronological data indicate that the D1E and D1W events occurred synchronously at ca. 224−219 Ma, and the D2 top-to-the-NW/N normal faulting was episodically activated at ca. 166−160 Ma, 141−120 Ma, 81−47 Ma, and 27−25 Ma. Episodic and synchronously activated top-to-the-NW normal faulting and top-to-the-SE thrusting along the northwestern and southeastern boundaries of the basement complexes, respectively, leads us to propose that the basement slices were episodically imbricated to the SE during the Late Jurassic−Early Cretaceous and Late Cretaceous−earliest Paleocene. The D1 amphibolite facies metamorphic rocks above the basement complexes recorded fast exhumation during the Late Jurassic−Early Cretaceous. We propose that the early Mesozoic northwestward basement underthrusting along a crustal “weak zone” was responsible for the D1 double-vergent thrusting and amphibolite facies metamorphism. Subsequent basement-slice imbrications reworked the Longmenshan Thrust Belt and exhumed the amphibolite facies rocks. Our results highlight the importance of basement underthrusting and imbrication in the formation and reworking of the intracontinental Longmenshan Thrust Belt in Eastern Tibet.

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In the Southern French Massif Central, the Late Paleozoic sedimentary sequences of the Montagne Noire area provide clues to decipher the successive tectonic events that occurred during the evolution of the Variscan belt. Previous sedimentological studies already demonstrated that the siliciclastic deposits were supplied from the northern part of the Massif Central. In this study, detrital zircon provenance analysis has been investigated in Early Devonian (Lochkovian) conglomerate and sandstone, and in Carboniferous (Visean to Early Serpukhovian) sandstone from the recumbent folds and the foreland basin of the Variscan Southern Massif Central in Montagne Noire. The zircon grains from all of the samples yielded U-Pb age spectra ranging from Neoarchean to Late Paleozoic with