Jurassic Deformation in and Around the Ordos Basin, North China

The Jurassic era was an important period for tectonic development of the East Asia continent in general, and can be divided into two different deformation stages around the Ordos basin in particular. It was under weak extension during the Early to Middle Jurassic, with the stretching direction in N-S to NNE-SSW, and the stretching deformation mainly occurred in zones surrounding the Ordos basin. This extension was possibly associated with intra-continental stress adjustment following the Late Triassic collision between North and South China Blocks along the Qinling ranges. During the Middle to Late Jurassic, the tectonic regime changed in the Ordos basin to multi-directed compressions, with the maximum stress axes oriented in W-E, NW-SE, and NE-SW; the boundary compressional belts with different trends and structural styles were formed around the Ordos basin. The formation of the N-S trending thrust and nappe belt developed along the western margin of the Ordos basin, resulted from the eastward extrusion of the Alashan and Longxi blocks; and the eastern boundary belt is characterized by W-dipping back-thrust reverse faults and associated folds, which is inferred to occur on the frontal hinging wall ramp (HWR) of a westward propagated decollement system beneath the Shanxi faulted uplift. Large-scale thrust and nappe structures and inversion tectonics of the Early to Middle Jurassic grabens along the Daqingshan in the north of the Ordos basin indicate strong N-S crustal shortening and rejuvenation of the Yinshan Range. The boundary structural belts around the Ordos basin well record multi-directed compressions and continental crust thickening during the Middle to Late Jurassic, which were dynamically associated with far-field effects produced by synchronous convergences toward the East Asia continent of three different plates (Siberia, Paleo-Pacific, and Tethys). This multi-directed compressional deformation accelerated hydrocarbon generation and had profound impact on the accumulation and localization of the multi-energy mineral deposits in the Ordos basin.