Study Of Tectonic Evolution Of Wenfeng Region, Chongqing

South Daba Mountains foreland fold belt is located at the transition part betweenSichuan basin and Qinling orogenic belt, which is connected with Micangshan upliftbelt to the west, ended at Huangling uplift to the east and separated by Chengkoufracture and north Daba Mountains thrust belt to the north. In general, it looks like asouth convex arcuate tectonic belt. Taking Tiexi-Wuxi concealed fault as a boundary,it was separated by the north part of Sichuan basin and they together form the studyarea, the Daba Mountains foreland basin.Taking Tiexi-Wuxi buried fault as a boundary, the study area is separated asthrust-fracture fold belt (North Belt) and low fold zone (South Belt). A series ofparallel distribution of the inverse (thrust) fault (F1-F3faults, Tiexi-Wuxi concealedfault) and the Jura-type-like folds (Z01-Z18) are the main features of North Belt, itsstrata strongly deformed. The main fold form is closed with sameramp-rewind-recumbent fold, and the main tectonic modes are overthrust basedsystems and fault-propagation folds. The north-northwest-south-southeast paralleldistribution of arc fold belt (F4fault, Z19-Z27folds) is the main feature of South Belt,its strata weakly deformed. And the fold form is upright-relief fold and the maintectonic modes are recoil structures and fault-slip folds.Each of the two belts have a different slip tectonic system. The North Belt takestwo slip layers, which was formed by the bottom of Silurian and Sinian, as sliptectonic system. The stratas gradually become younger from north to south. This is theresult that thrust sheets push layer by layer along with the two slip layers.During the Indo-china movement period, the study area was affected by theextrusion pressure of north Dabashan overthrust body combined with force fromBamianshan arcuate structure belt and then formed a “joint double arc” stress mode.And study area lies just at the interchange of the double arc, which the track of itsstructure line stretches from east to west and it coincides with the track of minimumprincipal stress. Since Yanshan Movement period, with the start of the North Chinablock southward sub-thrusting, the study area got into a second peak time ofoverthrust. Early structure formations in the study area had been re-activated, so that the formations of a series of thrust faults had thrusted again and made deformedinclined-folds turn into the overturned folds. Meanwhile, during this period,northward subduction of the South China Block began the process of the role ofclockwise rotation. This relative rotation superimposed on the thrust faults of SouthBelt of the study area. Thus, it horned faults with sinistral-right lateral slip type andthe track of fold axis turned into north-northwest, and even northwest. All thesephenomena belong to the structural transformation of the role of the superposition.Tectonic evolution of the study area can be divided into three stages.①Passivecontinental edge period: Paleozoic to Middle Triassic, study area had been a passivecontinental edge south of the Tethys Qinling Mountains Ocean, accepted stabletransgressive-regressive type sedimentary cycles.②Foreland basin conformationperiod: Late in the middle Triassic to late Jurassic, with the start of Indo-Chinamovement orogenic period, the impact of Dabashan Mountains overthrust movement,the study area strata had been gradually rised and involved in deformation, along theslippage belt of Sinian bottom formed Tiexi-Wuxi concealed fault and the F1-F3inverse (thrust) fault, the study area had been uplifted as deep zone of DabashanMountains foreland basin and accepted continental sedimentary of foreland basin.③Fold orogenic period: Since the late of late Jurassic, Yanshan-Himalayan orogenyperiod, based on the uplift, the study area continued orogenic uplift. North Belt ofstudy area formed a new thrust F0(presumably concealed) and caused stronglydeformation and folding of strata. Inclined folds gradually turned into overturnedfolds. And at the same time, a recoil fault, F4, of South Belt had been formed andgradually formed a structure pattern today.