北祁连造山带东段上奥陶统-下、中泥盆统砂岩碎屑组分与物源分析

Detrital Composition and Provenance of Sandstones from the Upper Ordovician to Lower-Middle Devonian,the Eastern Part of North Qilian Orogenic Belt

北祁连造山带东部武威斜豪-古浪石城子-靖远水泉一带上奥陶统-下、中泥盆统砂岩碎屑组分源区大地构造背景的判别结果表明,上奥陶统砂岩中的沉积物主要来自弧造山带内的过渡岛弧源区,并且早期可能含有较多的来自未分割岛弧源区的物质,下志留统砂岩中的沉积物主要来自碰撞造山带,而下、中泥盆统砂岩中的沉积物主要来自卷入碰撞造山带内的分割岛弧、俯冲杂岩和隆起的大陆块体。上奥陶统-下、中泥盆统砂岩中岛弧物源区的属性经历了未分割岛弧-过渡岛弧-分割岛弧的连续变化,暗示晚奥陶世北祁连岛弧已经开始隆起并遭受剥蚀,北祁连造山带东部的初始碰撞发生在晚奥陶世,并形成上奥陶统与中奥陶统之间的角度不整合面——古浪运动。这次碰撞型式是在"斜向碰撞、不规则边缘碰撞"型式下的"点碰撞"。

The tectonic settings of sandstone sources from the Upper Ordovician to Lower-Middle Devonian were discriminated by the detrital model.The sediments in the Upper Ordovician were derived from the transitional arc,with the earlier undissected arc.The detrital grains in the Lower Silurian mainly came from the collisional orogen.The sediments in the Lower-Middle Devonian were mainly derived from the dissected arc,subducted complex and continent engulfed in the orogen.The nature of the arc,as the source,developed from undissected arc to transitional arc,to dissected arc during the Late Ordovician-Early-Middle Devonian.This suggests that the North Qilian Arc began to uplift in the Early Ordovician.Thus the original collision should have happened in the Early Ordovician and resulted in the angular unconformity named Gulang movement between the Early Ordovician and Middle Ordovician.The collision was just ＂point collision＂ controlled by the diachronous collision.