Cenozoic Tectonic Evolution Of The Fault Basin In The Northwest Margin Of Ordos Block, North China

The Cenozoic fault basins in the northwest margin of Ordos Block have undergonepoly-phase subsidence along their boundary faults, which was recorded in thekinematic characteristics of the boundary faults. On the basis of detailed measurementof slip vector from the boundary faults of the fault basins, together with the evolutionof the regional tectonics, the fault basin-fill sequence, and superimposed deformationanalysis, we proposed that the evolution of the fault basins in the northwest margin ofOrdos Block were controlled by5stages stress fields. Combined with AFTgeochronology and palaeomagnetic chronology, it is suggested in this paper that thefault basins have experienced a depression history as following:Initial depression period: the NW-SE extension results in the initial normal faultingof the boundary faults and the occurrences of the fault basins during the Eocene-lateOligocene, fault-basin was filled with reddish sediments;Slow depression stage: as a result of the NW-SE compression, the fault-basin haslow depression rate from late Oligocene to middle Miocene;Strong depression period: the NE-SW main compression led to the NW-SEsecondly extension which controlled strong depression of the fault basin. The faultbasins were filled with Pliocene sediments during late Miocene to early Pleistocenethicker than2000m;Continuous depression: sinistral strike-slip along the NNE extending boundaryfaults of the fault basin was accompanied by a continuous depression of the basinunder the NE-SW extension during late Pleistocene;Pull apart depression: since late Pleistocene, the NE-SW compression, led to thedextral slip along the boundary faults and an intensive pull-apart evolution period ofthe fault basins.