Ordos Block

[1] The block is currently stable and large earthquakes are restricted to the bordering fault zones.

It has been suggested that the block is currently undergoing anti-clockwise rotation with respect to the Eurasian Plate, as a result of the ongoing eastward spreading of the Tibetan Plateau,[2] although this view has been challenged.

It covers an area of about 250,000 km2 and has a thick lithosphere of more than 200 km, suggesting that, unlike other parts of the NCB, it retains a fully cratonic character.

Following a regional unconformity associated with the Caledonian orogeny, sedimentation resumed during the Carboniferous and continued through the Permian with a sequence of clastic sedimentary rocks, including significant thicknesses of coal.

The youngest unit preserved in the basin is of Lower Cretaceous age, with any younger parts of the sequence having been eroded following uplift during the Neogene.

On the basis of this dataset, the block appears to be divided into a northern and southern part with contrasting histories.

[2][8] This belt of NNW–SSE trending thrusting and reverse faulting runs for about 180 km and forms the southwestern margin of the Ordos Block.

It has had a long tectonic history, starting with a phase of northwest–southeast directed extension from the Oligocene to the middle Miocene.

From the Late Pleistocene to the present day, the basin has been in an overall transtensional regime affected by a combination of NE–SW compression and NW–SE extension.

It shares the early history of the Yinchuan and Jilintai basins, but the recent tectonics in this case appear to be approximately north–south extension.

[2] This group of rift basins forms the SSW–NNE trending eastern margin of the Ordos Block, over a distance of >900 km.

However, it has been suggested that is currently rotating anticlockwise due to interactions with neighbouring blocks, particularly the continuing eastward spread of the Tibetan Plateau.