探讨黔中古隆起形成机制及演化

Discussion on Forming Mechanism and Evolution of the Central Guizhou Palaeouplift

黔中地区未出露中元古代褶皱基底。上覆新元古代沉积盖层厚度、沉积相及地层接触关系反馈出南华纪之前古隆起区已处于基底古地形的高部位。新元古代裂谷盆地演化及地球物理方面证据表明古隆起区与南北两侧边缘区基底存在一定差异。由此推测古隆起区沉积盖层之下可能有与四堡群相当的中元古代褶皱基底,并处于古地形的高部位。褶皱基底南北向的挤压背景,决定了黔中古隆起形成时为东西方向展布。震旦纪—寒武纪,古隆起区褶皱基底处于沉积盖层之下,构造较为稳定。奥陶纪初黔中古隆起雏形形成,此时其边缘地区仍为沉积区。奥陶纪—志留纪都匀运动的显著隆升造成暴露区扩大,对古隆起影响明显,但基底形态及构造走向的控制才是古隆起形成的原因。

Mesoproterozoic folded basement was unexposed in central Guizhou province.The thickness and facies of the regional Neoproterozoic sedimentary cover and stratigraphic contact relationship reveal that the Central Guizhou palaeouplift was on the high position of the folded basement before Nanhuaian.South and north margins were still receiving deposits within relative low position of the basement.Neoproterozoic rifting history and geophysical proof also indicate that the basement might have some differences between the palaeouplift area and the marginal area.Thus,we could speculate that there has Mesoproterozoic folded basement under the sedimentary cover in correspondence with Sibao Group.Central Guizhou palaeouplift was lying on the high position of the folded basement.Compressive stress of south-north direction of the folded basement determines the palaeouplift＇s distribution in the east-west direction after uplifted above the seawater level.During the period of Sinian and Cambrian,the folded basement of the palaeouplift was under the sedimentary strata.The strata in this area are continuous deposits with a relatively stable structure.Honghuayuan Formation＇s offlap and Meitan Formation＇s overlap shows that the folded basement and sedimentary strata above were uplifted and became a palaeouplift at the beginning of Ordovician.Periphery area,however,was still receiving deposits.The palaeouplift＇s obvious uplift by the influence of Duyun Movement between the Ordovician and Silurian had made the periphery area exposure,resulting in karst and offlap-overlap of the strata.Within the process of uplift,the sedimentary system of the south and north margins was separated with certain degrees.In Mid-Late Silurian,the last episode of Caledonian Movement occurred strongly.During this movement period,seawater regressed from the Middle and Upper Yangtze block,and the Central Guizhou Palaeouplift became one part of the land.Duyun Movement had great impact on this palaeouplift,but the effect of basement forms and structural trend was its forming mechanism.