造山带中古海山残片的识别——以拉脊山缝合带青沙山和东沟地质填图为例

Identification of the relics of paleo-seamount in orogens:A case study from the geological mapping in Qingshashan and Donggou areas within the Lajishan suture zone

造山带内海山/洋岛残片的识别是确定古缝合带和古洋盆存在的直接地质证据。祁连造山带被普遍认为是原特提斯洋盆俯冲和闭合的产物,然而南祁连地区是否存在古洋盆长期存在争议。通过对拉脊山关键地段早古生代岩石开展大比例尺地质填图和室内综合研究,在青沙山和东沟地区识别出连续的由洋岛型枕状玄武岩、火山碎屑岩、泥岩、凝灰岩和灰岩组成的火山-沉积组合序列,它们分别呈构造窗和构造残片产出,是拉脊山增生杂岩的重要组成部分,代表中寒武世—早奥陶世原特提斯洋内海山残片。这些海山残片的识别不仅表明拉脊山地区存在早古生代洋盆和缝合带,同时为造山带古洋盆构造演化研究提供了新思路。

Identification of the relics of seamount/oceanic island in orogens can provide critical geological evidence for the presence of the suture zone and paleo-ocean basin.The Qilian Orogen is widely considered as the product of subduction and closure of the ProtoTethyan Ocean.However,whether there exists a paleo-ocean basin in the South Qilian is still hotly debated.Based on large-scale geological mapping and comprehensive study on the Early Paleozoic rocks in the key area of Lajishan,a successive volcanic-sedimentary sequence composed of OIB-type pillow basalt,pyroclastic rock,mudstone,tuff,and limestone was recognized in the Qingshashan and Donggou areas.The rocks are outcropped as the tectonic slice and tectonic window respectively.The volcanic-sedimentary sequence is the major components of the accretionary complex within Lajishan,and represents the relics of Middle Cambrian to Early Ordovician seamounts within the Proto-Tethyan Ocean.The identification of these relics of seamount not only indicates that there exist Early Paleozoic ocean basin and suture zone in the Lajishan area but also provides a new idea for the study of tectonic evolution of the paleo-ocean basin in orogens.