Abstract: The Central Asian Orogenic Belt (CAOB) is a region characterized by the superimposition of multiple tectonic systems. Although extensive research has been conducted on the CAOB, there is still considerable debate regarding the correlation between different blocks with Precambrian crystalline basements in the eastern segment of the CAOB, as well as the history of the southward subduction of the Mongol–Okhotsk Ocean. This study compares and analyzes the basement composition, Late Paleozoic magmatism, and sedimentation of the Ereendavaa Block in Eastern Mongolia, the Erguna Block in Northeastern China, and the Mamyn Block in the Russian Far East, all of which are located in the eastern segment of the CAOB. The study suggests that the Erguna Block should be spatially correlated with the Ereendavaa and Mamyn Blocks, forming the Ereendavaa–Erguna–Mamyn Block chain (EEMB). By systematically summarizing and analyzing the geochronological and geochemical data of Late Paleozoic arc-related magmatic rocks from these tectonic units and the ophiolites within the Mongol–Okhotsk suture zone, the study proposes that the southward subduction of the Mongol–Okhotsk Ocean initiated during the Late Carboniferous.