Closure of the Paleo-Asian Ocean and amalgamation of the northern part of the East Asian continent in the latest Paleozoic: Evidence from the Xingshuwa ophiolitic mélange in southeastern Inner Mongolia

The location and timing of the development of the suture zone between the Siberian and North China paleoplates in the northern part of the East Asian continent are controversial. This work involved petrological, geochronological, and geochemical analyses of the Xingshuwa ophiolitic mélange to determine the tectonic affinity of the Xar Moron River ophiolite belt and place further constraints on the late Paleozoic tectonic evolution of the northern part of the East Asian continent. Geological mapping and petrological analyses revealed various sizes of serpentinite, gabbro, basalt, chert, and oceanic-island/seamount and sandstone blocks, which represent a dismembered ophiolite and oceanic plate stratigraphy (OPS) above the ophiolite, in the matrix of deformed sandstones and siltstones. Geochemical analysis revealed multiple types of ophiolites and chert blocks in the mélange. The diversity of ophiolite and OPS components suggests that they represent fragments of a broad oceanic basin like today’s Pacific Ocean. Zircon U-Pb dating revealed that some ophiolite blocks formed in the Early Permian, and the youngest zircons in the matrix formed in the middle‒Late Permian. Based on zircon U-Pb dating and regional geological data, the emplacement of the Xingshuwa ophiolitic mélange occurred in the Late Permian‒Early Triassic. Compared with the other ophiolite belts in the southeastern Central Asian Orogenic Belt (CAOB), the Xar Moron River ophiolite belt has the youngest formation age, which is similar to that of the Solonker ophiolite belt. The Solonker‒Xar Moron River ophiolite belt is suggested to represent the final suture zone between the Siberian and North China paleoplates, and indicates that the Paleo-Asian Ocean closed in the Late Permian‒Early Triassic.