Evolution And Mechanism Of Tectonic Geomorphology In The Central North China Block From The Mesozoic To The Cenozoic

During the Mesozoic-Cenozoic era. The central North China Block underwentcomplex tectonic transition. The original North China Craton which had been steadyfor1.7billon years was severely broken in Meso-Cenozoic. The central North ChinaBlock experienced several significant changes of tectonic regimes and tectonicfeatures, including the structural direction change from E-W-striking to NE-NNE-striking from the end of middle Jurassic to the beginning of late Jurassic, thecompressional structures were replaced by extensional structures on the east of theTaihang Mountains at the late stage of early Cretaceous, intense extension and rapidformation of the Bohai Bay Basin in the early Cenozoic. The Bohai Bay Basinchanged from a rift basin to a depression basin in the late Paleogene and tectonicactivity center jumped westward from the Bohai Bay Basin to the Shanxi GrabenSystem. In order to understand the Meso-Cenozoic tectonic geomorphology evolutionin the central North China Block in detail, this paper first discusses the regional tectonic setting, and then focus on tectonic geomorphology evolution from the latestage of Mesozoic to Cenozoic based on apatite fission track analysis andpalaeotopography recovering. We gain some insight through the study:(1) In the late Jurassic, the study area was under the super-convergent regime,overthrust structures formed in the plate margins, the main structural direction isNNE-NE-striking, indicating the study area is mainly affected by the subduction. ofthe paleo-Pacific Plate. The deformation and chronology studies of the pultons in thenorth Taihang Mountains indicated that the main overthrust structures and foldsformed before135Ma. The Taihang Mountains’ apatite fission track study shows thatthe west part of The Taihang Mountains experienced rapid uplift and exhumationduring165-135Ma, indicating this area experienced intense compression. It shouldlie in the Yanshanian North China Plateau. During the late stage of Early Cretaceous,the east part of the study area experienced a significant tectonic regime change fromcompression to extension, a lot of rift basins developed on the east of the TaihangMountains, while there was no fundamental change in the tectonic regime on the westcounterpart, and the Taihang uplift lay between them. The apatite fission track agesshow no obvious tectonic event in the area around Xinzhou City, indicating that thisrift event didn’t happen in this area.(2) The extensional structure thoroughly collapsed the Yanshanian North ChinaPlateau in the early Cenozoic, and the Bohai Bay Basin formed at the same time. Theformation of the Bohai Bay Basin consists of two stages, the Paleogene rifting stageand the Neocene depression stage. The plateau was collapsed by intense rift structuresat the early stage, and became summit surface on the mountains and basement surfacein the basin. The mountains experienced intense erosion due to relatively rapid uplift.The Cenozoic basin-mountain pattern began to form in the central and east parts ofthe north chain block. The Bohai Bay Basin experienced compression at the end ofpaleogene, devoping disconformity between the plaeogene and Neogene, and cominginto a depression stage since Miocene. The study of apatite fission track data revealstwo-stage rapid uplift events during65-55Ma and25-15Ma, respectively. The formerone exists both in the south and north parts of the Taihang Mountains, and their apatite fission track ages are the same, indicating that the north and south parts of theBohai Bay Basin formed simultaneously, and the dynamics should be derived fromthe west or east, rather than the north or south, possibly being related to thesubduction of the Pacific Plate. The latter uplift event took place earlier in the northpart of the Taihang mountains than the south part.(3) The study area met neotectonic stage from the end of Miocene to the earlyNeocene. The Shanxi Gaben System, the intermontane grabens in the TaihangMountains, and the basins on the south and north margin of the Taihang Mountainsbegan to form and migrate from southwest to northeast. There was no apparenttectonic response in the Bohai Bay Basin, indicating that the dynamics being derivedfrom the west, also the transition of tectonic activity centers from the Bohai BayBasin to the Shanxi Graben System. The present-day topography analysis shows thatthe erosion mainly happened in river areas since the Pliocene in the TaihangMountains, the strata erosion thickness is about400m and the erosion rate is about0.08km/Ma.