大兴安岭地区古生代构造格架重建:来自俯冲增生杂岩研究进展

Research progress on the subduction-accretion complex:Reconstruction of the tectonic framework of the Great Xing’an Range

大兴安岭地区古生代处于古亚洲洋闭合阶段,其间发育众多的弧盆系和蛇绿岩带,笔者等在大兴安岭地区1∶1 000 000地质编图和野外地质调研基础上,应用“洋板块地质”学术思想在大兴安岭地区元古宙、古生代地质体中划分出一系列“俯冲增生杂岩”、地块基底残块、岛弧、弧前盆地、弧后盆地等构造单元,结合陆(地)块和岩浆弧、弧前盆地、弧后盆地和“俯冲增生杂岩”的时空展布,划分出9条俯冲增生杂岩带,其中新识别出3条俯冲增生杂岩带。俯冲增生杂岩带主要分布于兴蒙造山带内部各地块之间和地块与大型岛弧带之间,相当于地块间及地块与岛弧带间的缝合带。依据俯冲增生杂岩带两侧对应的陆(地)块、岛弧带等构造级别,归并出5条结合带。俯冲增生杂岩带的展布方向以北东向为主,时代自北向南依次变新,从早奥陶世演化到中—晚二叠世,暗示古亚洲洋洋盆向大兴安岭地区陆(地)块俯冲作用最早发生在北部额尔古纳一带,逐渐向南后撤,不断形成新的洋壳和产生俯冲增生作用,相应的活动陆缘从北部额尔古纳地块向南逐渐增生,配套弧盆系时代也逐渐向南变新。早—中三叠世至西拉木伦一带发生陆-陆拼贴,完成华北板块与西伯利亚板块的对接。通过对大兴安岭地区古生代“俯冲增生杂岩”的研究,重建了大兴安岭地区古生代构造格架,提高了古亚洲洋东段洋-陆转换的研究程度。

The Great Xing’an Range region, which experienced the closure of the Paleo-Asian Ocean during the Paleozoic, has developed numerous arc-basin systems and ophiolite belts. In this contribution, based on the concept of “ocean plate geology”, various tectonic units including subduction-accretion complexes, ancient block relicts, island arcs, forearc basins and back-arc basins were identified based on 1∶1 000 000 scale geological mapping and geological survey of the region. Among the tectonic units, there are 9 subduction-accretion complex belts, of which 3 were identified for the first time. The subduction-accretion complex belts, structurally equivalent to 5 suture zones, divide the tectonic blocks and magmatic arcs of the region. These suture zones mainly orient in the northeast direction, and their formation age becomes younger southward, from Early Ordovician to Middle and Late Permian, indicating the subduction initiates in the northern Erguna region then retreats southward in a prolonged subduction-accretion process. Plenty of new continental crust are formed, followed by southward accretion. Not until the Early to Middle Triassic, the Central Asian Orogenic Belt and North China Craton are amalgamated along the Xar Moron suture zone. By reconstructing the Paleozoic tectonic framework of the Great Xing’an Range region, this study helps to advance our understanding of the oceanic-continental transition in the eastern Paleo-Asian Ocean.