Mesozoic Contraction Deformation And Its Implications In The Eastern Part Of The Northern Segment Of The Taihang Mountains

Taihang Mountains has long been known as a tectonic-magmatic belt. In recent years, however, some scholars proposed that it is an intraplate orogenic belt. A long-term debate about the mechanism for the formation of Taihang Mountains is that it formed as a result of vertical uplift or horizontal contraction deformations, or different dynamic mechanisms in different stage.This study is focused on the Mesozoic tectonic evolution of the Lingshan area, north of Quyang County and west of Tangxian County, the eastern part of northern Taihang Mountains. Based on detailed mapping in this area and the study on the geometry and kinematics about the Mesozoic contraction deformation, two early NE-NNE trending thrust faults and two late NWW trending thrust faults as well as a series of nappes and tectonic windows have been recognized. They form the Mesozoic contraction tectonic framework of the research area. The geometry and kinematics of these thrust structures and their relationships have been preliminarily defined in this research. Construction of a series of balanced cross-sections and restoration together with the analysis of the structural styles reveal that the deformation intensity in Lingshan area gradually increases from north to south.The zircon SHRIMP U-Pb dating on a small diorite pluton that intruded in the Lingshan fault gives an age of 129±3Ma. The zircon LA-ICP-MS U-Pb dating on the diorite involved in NE trending folds and intruded in NE trending thrust faults to the southwest of Yixian County gives the age of 157±2Ma and 156±2Ma respectively. Related studies indicate that two stage NE-SW directed contraction deformation in 160~150Ma and 137~131Ma existed in the eastern part of the northern segment of the Taihang Mountains at least. The normal faulting represented by Linshan fault occurred before 129Ma, the NNE-SSW directed or almost SN directed contraction deformation revealed by the NWW trending thrust faults lasted after 125Ma.The NE-NNE trending structures serve as the strongest Mesozoic contraction deformation in the eastern part of the northern segment of Taihang mountains. The deformation characterised by the coexistence of thin-skinned and thick-skinned tectonic, and regional buckling folding and low-angle thrusting dominated the deformation mechanisms. The contraction deformation in different directions played an important role in the formation of Taihang mountains tectonic belt at least in the middle and late Mesozoic, and resulting a significant increase of crust thickness. On the other hand, the extensional tectonic deformation characterized by the uplift of mountain block derived from the reactivation of the basement fault since Cretaceous might contribute much to the final formation of the Taihang mountains tectonic belt.