Late Paleozoic Tectonic Evolution of the Northern Great Xing’an Range, Northeast China: Constraints from Carboniferous Magmatic Rocks in the Wunuer Area

Abstract

Northeast China composes the main part of the Central Asian Orogenic Belt. Traditionally, Northeast China has been considered a collage of several microcontinental blocks. However, the tectonic evolution of these blocks remains uncertain. Igneous rocks can be used to infer the magmatic histories of the blocks and thus help reconstruct their evolution. In this study, we present new zircon U–Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing’an Range, Northeast China, to constrain the Carboniferous amalgamation of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs. On the basis of zircon U–Pb dating results, we identify two main stages of magmatism, i.e., early Carboniferous (332–329 Ma) and late Carboniferous (312–310 Ma). The early Carboniferous igneous rocks include diorites and granodiorites, with the former being classified as calc-alkaline to tholeiitic and the latter as tholeiitic. Both rock types are enriched in Th and U and depleted in Nb and Ti. The rocks display slightly fractionated rare earth element (REE) patterns, with an enrichment in light REEs and a depletion in heavy (H)REEs. The geochemical characteristics of the early Carboniferous rocks indicate that they formed in a subduction-related continental-arc setting. The late Carboniferous igneous rocks include monzogranites and syenogranites, both of which are classified as high-K calc-alkaline rocks and show enrichment in Th, U, and Rb and depletion in Nb and Ti. The rocks display strongly fractionated REE patterns, with an enrichment in light REEs and a depletion in HREEs. The geochemical characteristics of the late Carboniferous rocks indicate that they formed in a syn-collisional tectonic setting. Combining the new geochronological and geochemical results and inferred tectonic settings with regional magmatic data, we propose a new three-stage model to interpret the late Paleozoic tectonic evolution of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs of Northeast China: (1) early Carboniferous (360–340 Ma) subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and formation of the Wunuer oceanic basin in the Yakeshi area; (2) early to late Carboniferous (340–310 Ma) sustained subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and initiation of subduction of the Wunuer oceanic basin; and (3) late Carboniferous–early Permian (310–275 Ma) syn-collisional to post-collisional tectonic transition between the united Xing’an–Erguna Massif and the Songnen–Zhangguangcai Range Massif.