再论贺兰山地区新生代之前拉张活动的性质

贺兰山地区在新生代之前经历了几次区域性的伸展活动,表现出显着的“多旋回”构造特点。而导致这些伸展活动的机制并不一样,更不是简单的重复。分析结果表明,该地区在早古生代不是拗拉槽,而更可能是北祁连岛弧靠大陆一侧的弧后盆地,在晚期演变为弧后前陆盆地。在此期间,其沉积表现出较典型的非补偿型前陆盆地的特征。在晚古生代,由于伸展的时间晚于造山期,因此该地区也不是所谓的碰撞谷,而是北祁连造山带及临近地区后期伸展跨塌的结果,伸展开始的时间发生在晚泥盆世晚期;在中生代早期,贺兰山地区北段由于受南侧的挤压发生伸展,因此不是前陆前渊而是碰撞谷。

Re-discussion on natures of extension in Helanshan region before Cenozoic era

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.