1 .Department of Geology , Northwest University , Xi'an 710069 , China ;2 .School of
Earth Sciences and Resources Management Chang'an University , Xi'an 710054 , China
South-north trending detachment structures in the basement of the western ordos block have not been documented yet though both
of the east-west trending thrust and the basement detachment structures in the western ordos block werewell studied .On the basis of distinct
reflection features in the seismic section and the relevant geological setting it is revealed that the Weizhou-Shigouyi detachment structure , as
the result of the northward decollement of the western ordos block, exhibits multi-layer reflection above the detachment surface and there is
a scarcity of chaotic reflection related to complicated deformation in the frontier of a thrust belt .This detachment structure is notably incompatible
with its neighboring areas in the regional structure and was formed in the Late Jurassic when the east-west napping led to a northwards
descending terrain .The gravity drive is interpreted as the major cause of the northerly detachment along the coal layer in the proximity of the
T9 boundary .As a result, the Weizhou-Shigouyi detachment structure is bounded on the east and west by faults and occurs as a synclinorium
comprising exotic sheeted rocks with simple deformation .Importantly , this study may help to understanding the tectonic evolution and planning
the petroleum exploration.