Abstract:

Since the plate tectonic theory was introduced into China in 1970’s, aulacogen has been considered in the area of Helan Mountain in Ordos Basin by some geologists. It is believed that Helan Mountain, Qinling and northern Qilian area were at the stage of rifting development fromMid-Neoproterozoic to Early-Mid Cambrian, and that Qinling, northern Qilian, Helan Mountain formed a trifurcate rift valley system. This viewpoint was quickly accepted and quoted by many geologists in China. The concept of aulacogen was extended and developed by some scholars. This paper raises the queries about the aulacogen in Helan Mountain. Through consulting a large amount of documents and data about aulacogen both at home and abroad, researching the shapes and sedimentary features of Qinling-Qilian- Helan Mountain area, and carefully verifying seismic, gravity, magnetic and electric profiles of the so-called aulacogens that cross the Mid-Lower Proterozoic, the authors think that the evidence of aulacogen in Helan Mountain is insufficient, and it is quite different from the aulacogen defined at home and abroad in the aspects of sedimentation and structure. So it is believed that aulacogen does not exist in Helan Mountain area.

Key words: rift period, rift-depression period, depression period, structural-sedimentary evolution, Paleogene;LiaoheDepression