DISCOVERY OF KULUN COMPLEX IN THE EAST PART OF THE NORTHERN MARGIN OF NORTH CHINA PLATE: Tectonic Implication

The Kulun complex, mainly composed of Late Paleozoic meta-volcanic rocks, has been newly discovered in Kulun Qi area on the border between Liaoning and Inner Mongolia in the east part of the northern margin of North China Plate. The profile survey confirms the rock association of Kulun complex including tuff, andesite and metasedimentary rock. The zircon LA-ICP-MS U-Pb isotope test for the tuff shows 391.0±3.7 Ma, indicating the formation age of Middle Devonian. The geochemical characteristics show that the complex was formed in later island arc environment. The tectonic evolution process of the Paleozoic accretionary orogenic belt in the east part of the northern margin of North China Plate is established through the study of the newly discovered Middle Devonian Kulun complex and related Paleozoic sedimentary events, magmatic events and deformation, combined with the research results of the Paleozoic complex, magmatic rocks and volcanic sedimentary strata in the area. The orogenic belt has experienced the Silurian active continental margin stage, Devonian arc-continental collision stage, Carboniferous-Middle Permian active continental margin stage and Late Permian collision orogenic stage. The Silurian Fangjiatun and Xibiehe rock formations were formed in the back-arc basin environment, indicating the study area was in the active continental margin environment during the Ordovician-Silurian. The volcano-sedimentation of the Devonian Kulun complex is the result of arc-continent collision, accompanied by magmatic activity under extensional background. The study area underwent pull-apart again under the post-collision extension background, and received the deposits of Baijiadian rock formation and Jiujuzi rock formation in the Carboniferous-Middle Permian, leading to the formation of the volcanic island arc of Tongjiatun rock formation. In the Late Permian, continent-continent collision occurred with the closure of Paleo-Asian Ocean, and the post-orogeny continued to the Triassic.