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

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 Proto-Tethyan 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.