Cretaceous exhumation of the Triassic intracontinental Xuefengshan Belt: Delayed unroofing of an orogenic plateau across the South China Block?
Résumé
A large plateau can be produced by crustal thickening in convergent zones such as continental collision belts and Andean-type subduction zones, but the life cycles of such plateaux are not well-understood. In particular, it is not clear how long they persist after construction, before other tectonic processes or erosion reduce crustal thickness and elevation to near-normal levels. Triassic subduction- and collision-tectonics produced intense deformation, magmatism and metamorphism across the entire South China Block. This large-scale crustal shortening created a broad orogenic belt, uplifted most parts of the South China Block, and probably initiated the growth of an orogenic plateau. Our study presents low-temperature thermochronology data from the Xuefengshan Belt in the interior of the South China Block. There was along-strike variation in exhumation. The north orogenic core was subjected to Triassic (~245–210 Ma), and Late Cretaceous (~100–80 Ma) exhumation, whereas the cooling path of the south orogenic core reflects a two stage Cretaceous evolution. The variable exhumation pattern reflects non-uniform tectonics in different regions, but both regions were subject to Late Cretaceous extension. We tentatively reconstruct the original plateau paleo-elevation to be ~1.5 km above sea level, based on the amount of exhumation (~10 km) and the present crustal thickness (~35 km). The T-t trajectories of the Xuefengshan Belt and other Triassic belts highlight the significance of Cretaceous extension and exhumation in shaping the tectonic configuration of the South China Block. Large-scale extension was probably triggered by rollback of the Paleo-Pacific subduction zone.
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