东昆仑南缘晚古生代地层组合、大地构造相及大地构造意义

现代大陆边缘盆地研究结果显示,仅根据蛇绿岩分布划分大地构造单元、分析构造演化可能得出误导性结果.而详细的沉积建造分析、结合其他地质资料可以得到更可靠的结论.东昆仑南缘西段1∶25万区域地质调查显示,该区晚古生代地层为一套不含火山岩的碎屑岩-碳酸盐岩组合,从石炭系到三叠系,由北往南沉积建造由陆缘碎屑岩逐步转化为深海浊积岩,显示典型被动陆缘构造环境.这种特点表明,东昆仑南缘蛇绿岩并不代表成熟大洋地壳残片,而是发育于夭折裂谷环境的初始洋盆;其代表位于研究区以南地区的金沙江古特提斯洋盆的北部被动陆缘(现代地理方位).研究区内不整合覆盖在晚古生代地层之上的侏罗系磨拉石建造代表碰撞造山晚期的上叠前陆盆地,表明印支期造山旋回的结束.

Late Paleozoic Strata and Tectonic Facies in the Northern Margin of the Eastern Kunlun Orogen and their Tectonic Implications

Detail studies on modern continental margins have demonstrated that tectonic divisions and evolutions only based on ophiolite suits are always elusive. In contrast, analyses of sedimentary buildups may provide positive constrains for identification of tectonic units and then help deduce reasonable tectonic evolutions. Detailed geological mapping with scale of 1∶250000 on the west segment of the southern Kunlun suture demonstrated that the southern Kunlun ophiolite suit represents in fact an infant rather than a mature oceanic crustal slice. The associated sedimentary rocks are mainly continental clastics or carbonates. From the Permian to Triassic and from the north to the south, the stratigraphic buildups are gradually variable from continental clastics to turbidite without any volcanic rocks, suggesting they deposited in a rifted passive continental marginal basin. Its abyssal oceanic basin (the Jinshajiang ocean) was located in south of the Kunlun suture. The Jurassic piggyback foreland basin developing upon the folded Permian to Triassic strata indicated the termination of the Indosinian tectonic event.