Superposition of Paleo-Asian and West-Pacific Tectonic Domains in the Eastern Section of the Solonker Suture Zone: Insights from Petrology, Geochemistry and Geochronology of Deformed Diorite in Xar Moron Fault Zone, Inner Mongolia

Some diorite stocks developed in the Xar Moron fault belt in Linxi county, Inner Mongolia. They intruded into the Shuangjing schist and display variable degrees of deformation. This study presents the petrology, geochemistry, a LA-ICPMS U-Pb zircon age and a hornblende ⁴⁰Ar-³⁹Ar age of the diorite. The diorite was emplaced in the Early Permian, as reflected by a LA-ICPMS U-Pb zircon age of 286±1 Ma. The magma is derived from enriched mantle metasomatized by slab-derived fluids or melts. The diorites were subject to epidote-amphibolite facies metamorphism during the Early Jurassic, resulting in a hornblende ⁴⁰Ar-³⁹Ar age of 188.7±1.4 Ma. Combining the new data with the latest published results from the study area and the region, we conclude that the Early Paleozoic and younger mafic rocks in the Solonker suture zone are derived from mantle that was metasomatized by subducted sediments, and that metasomatism increased with time. A stage of collision occurred before the Late Carboniferous (~310 Ma) and the Solonker suture zone underwent post-orogenic extension during the Late Carboniferous to Early Permian (~310 to 276 Ma). The diorite studied is part of a widespread diorite-granodiorite suite that formed during this period of extension in the suture zone. In the Late Permian oceanic basins occurred locally in the suture zone. The closure of these basins induced the final collision of the Solonker suture during the Late Permian to Middle Triassic (~272 to 230 Ma). Spatial variation in the timing of final collision led to the coeval formation of syn-collisional and post-collisional granites in the suture zone. Closure of the Solonker suture zone resulted in the amalgamation of the North China Craton with some microcontinents to its north. North of the accreted microcontinents, the Mongol-Okhotsk Ocean, a branch of the Paleo-Pacific Ocean, formed the remaining NE-striking oceanic domain between the Siberia Craton to the north and the North China Craton to the south. The closure of the Mongol-Okhotsk Ocean in NE Mongolia in the Early Jurassic induced the continent-continent collision recorded by the hornblende ⁴⁰Ar-³⁹Ar age from the Solonker diorite. The research area then entered post-orogenic extension, while further east the Paleo-Pacific plate subducted beneath the North China Craton. The combination of regional post-orogenic extension and distant subduction led to alternating compression and extension in the Jurassic in what is now northeastern China. After the change in the subduction direction of the Paleo-Pacific plate in the Late Jurassic, the tectonic environment in northeastern China finally became extensional and the region entered the West-Pacific tectonic domain.