Kinematic evolution of fold-and-thrust belts in the Yubei-Tangbei area:Implications for tectonic events in the southern Tarim Basin

The Yubei-Tangbei area in the southern Tarim Basin is one of the best-preserved Early Paleozoic northeast-southwest trending fold-and-thrust belts within this basin.This area is crucial for the exploration of primary hydrocarbon reservoirs in northwestern China.In this study,we constructed the structural geometric morphology of the Yubei-Tangbei area using geophysical logs,drilling,and recent two-and three-dimensional(2-D and 3-D)seismic data.The Early Paleozoic fault-propagation folds,the Tangnan triangle zone,fault-detachment folds,and trishear fault-propagation folds developed with the detachment of the Middle Cambrian gypsum-salt layer.According to a detailed chronostratigraphic framework,the growth strata in the Upper Ordovician-Lower Silurian layer formed by onlapping the back limb of the asymmetric fault-propagation folds,which therefore defines the timing of deformations.The changes in kink band hinges and amplitudes in the Permian-Carboniferous and Cenozoic folding strata suggest that the evolution of the fold-and-thrust belts followed a sequential evolution process rather than a simultaneous one.Above the pre-existing Precambrian basement structure,the Yubei-Tangbei fold-and-thrust belts can be divided into four tectonic evolution stages:Late Cambrian,Late Ordovician to Early Carboniferous,Carboniferous to Permian,and Cenozoic.The northwestern-verging Cherchen Fault is part of the piedmont fold-and-thrust system of the southern Tarim foreland basin.We interpreted its strata as a breakthrough trishear fault-propagation fold that developed in three phases:Mid-Late Ordovician,Silurian to Middle Devonian,and Triassic to present.These tectonic events are responses of the Altyn-Tagh and Kunlun collisional orogenic belts and the Indian-Eurasian collision.The inherited deformation and structural modification in the southern Tarim Basin may be an indicator of the growth and evolution of peripheral orogens.