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.

In order to reveal the tectonic evolution of the South Chinese Tianshan orogenic belt, we conducted structural, geochemical, and geochronological studies and identifi ed granitic and volcanic rocks along the northern margin of the Tarim block. Zircon laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of two samples from granitic plutons yielded crystallization ages from 404.8 ± 2.0 Ma to 388.1 ± 2.2 Ma, and two samples of dacite and rhyolite yielded ages of volcanism at ca. 404 Ma, highlighting a middle Paleozoic igneous event. Geochemical data suggest that these Devonian igneous rocks are metaluminous, high-K calc-alkaline felsic volcanic and plutonic rocks. All the samples display relatively enriched light rare earth element (LREE) contents, weak or no negative Eu anomalies, and relative depletion in Nb, Ta, Ti, and P, but they show enrichment in K, Rb, and Ba. In situ zircon Hf isotopic results show a positive range of ε Hf (t). These geochemical and isotopic features suggest that this magmatic event probably occurred in an Andean-type arc. Combined with zircon U-Pb and Hf isotopic studies on the basement rocks, the results indicate multiphase Precambrian (ca.

International audienceIn orogenic belts, a basal de'collement 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 de'collement 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 de'collement, 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-Pbtot 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 fromthe continental underthrusting to the SE of the South China block in response to northwestdirected subduction of the Paleo-Pacific plate