Structural styles and evolution of a thin-skinned fold-and-thrust belt with multiple detachments in the eastern Sichuan Basin, South China

摘要

The structural deformation of the eastern Sichuan Basin, South China, is characterized by a thin-skinned fold-and-thrust belt with exposed, approximately parallel narrow anticlines and wide synclines. A 196-km long regional cross section has been constructed parallel to the shortening direction to analyze structural styles and evolution of the fold-thrust belt. The stratigraphic succession is composed of competent layers separated by three main incompetent layers which act as detachments. The basal detachment, the Cambrian evaporites, played a dominant role in the deformation; the middle and top detachments accommodated the displacement during deformation. Structural styles are dominated by faulted detachment folds with the breakthroughs of the fore- and/or backlimbs. Balanced restoration shows that the shortening between basal and top detachments is about 26 km with the shortening ratio of 12.4-18.6%. Integrated analyses of kinematics and balanced restoration reveal the evolution succession of kink bands, detachment folds, and faulted detachment folds. Kink bands initiated and evolved into detachment folds above the basal detachment as the shortening took place; with progressive shortening the back- and/or forelimbs of these folds developed thrusts.