关键词: 贺兰山地区, 拉张活动, 前陆盆地, 新生代, 裂谷, 拗拉槽, 碰撞谷

Abstract: The Helanshan region underwent several times of extension and showed strong characteristics of "multi-cycle" movement before the Cenozoic era.The mechanisms resulting in the extension in this area are different from each other.The so-called "Helan aulacogen" did not occur in the early Paleozoic,and there was not aulacogen there.It may be a back-arc basin of the North Qilian island arc.And later,the back-arc basin became a back-arc foreland basin.The sediments during this period showed the typical characteristics of starved peripheral foreland basins.In the later Paleozoic,due to the extension after the orogeny,there was no so-called "collision rift" in Helanshan region, while it was resulted from the postorogenic extension and collapse of North Qilianshan Orogen.The extension in this region began in the Later Devonian.In the early Mesozoic era,the extension in the northern Helanshan region was collision-induced rifting rather than frontal abyss of foreland,owing to the compression from the south.

Key words: Helanshan region, extension, foreland basin, Cenozoic, rift, aulacogen, collision rift