华北板块西南缘早古生代构造演化与沉积响应——以段家峡剖面为例

TECTONIC EVOLUTION OF SOUTHWEST MARGIN OF NORTH CHINA IN EARLY PALAEOZOIC AND ITS'SEDIMENTARY RESPONSE:A CASE STUDY OF THE DUANJIAXIA PROFILE

通过分析陇县地区下古生界的沉积物特征,认为其物质响应很好地反映了该地区对构造转型所带来的环境变迁。华北板块西南缘的盆地演化先后经历了震旦纪—中奥陶世的被动大陆边缘和晚奥陶纪—志留纪的活动大陆边缘两个构造期次;前者相应形成走廊被动陆缘盆地和贺兰盆地,该时期发育从碎屑岩潮坪到浅水碳酸盐陆棚的沉积环境;后者形成走廊弧后盆地,中奥陶世晚期至晚奥陶世之间该地区开始发生强烈的凹陷,使得该海域沉积一套深水斜坡相滑塌沉积以及浊积岩。直到晚奥陶世晚期开始,由于受加里东运动的影响,随着海平面逐步下降,华北板块西南缘的沉积环境再次由深水相过渡至以一套碳酸盐岩为主的浅水环境。

According to the depositional characteristics of the early Paleozoic in the southwest margin of North China, we believe that the sedimentary response could well reflect the environment changes caused by tectonic transformation in this region. Basin evolution of the region has gone through two tectonic peri- ods. a passive continental margin in Sinian-Middle Ordovician and an active continental margin in Late Or- dovician-Silurian. The Zoulang passive continental marginal basin and the HeLan basin were formed in the former period under clastic flat and Shallow carbonate shelf environments, and the Zoulang back-arc basin was formed in the later period. The area began to strongly subside when the Zoulang back-arc basin was formed in Late Ordovician-Silurian. Slumping and turbidite deposits have been found on the deep-water slope.. Owing to the influence of the Caledonian Movement, the deep water environment changed into the shallow carbonate environment again when the sea level dropped in Later Ordovician.