Crustal structure of the southern Dabie ultrahigh-pressure orogen and Yangtze foreland from deep seismic reflection profiling

摘要

A new 140-km-long seismic reflection profile provides a high-resolution crustal-scale image of the southern Dabieshan high-pressure (HP) metamorphic belt and the Yangtze foreland fold-and-thrust belt. The seismic image of the stacked section shows that the southern Dabieshan metamorphic terrane and Yangtze foreland belt are separated by a large north-dipping fault. In the foreland the upper crust is dominated by a series of folds and thrusts formed during the collisional stage in the mid-Triassic; it was reworked by crustal extension resulting in the formation of a late Jurassic and Cretaceous red-bed basin. The southern Dabieshan profile shows stacked crustal slabs developed along the margin of the collisional orogenic belt. The Moho reflectors at 10-11 s (similar to30-33 km) are seismically prominent and segmented by a number of south-verging thrusts that were probably developed by foreland-directed thrusting of the deeply subducted continental crust during exhumation. The seismic reflection profile suggests that structures related to the Triassic-Jurassic subduction and exhumation of the Yangtze plate are preserved despite the severe crustal extension superimposed during the late Mesozoic and Cenozoic.