Amudzhikan volcano-plutonic association of the eastern part of the West-Stanovoy superterrane (Central Asian orogenic belt): age, sources, and tectonic setting

Abstract

Geochronological (U-Pb on zircons, ID-TIMS), isotope-geochemical (Nd, Sr, Pb), and geochemical studies of rocks of the Amanan and Amudzhikan intrusive complexes and volcanic rocks of the Ukurey Suite in the eastern part of the West Stanovoy superterrane of the Central Asian Fold Belt were performed. The belonging of granitoids of these complexes to high-potassium C-type adakites is substantiated. The cogeneticity of the studied rocks has been established, which makes it possible to unite them into one Amudzhikan volcano-plutonic association formed in the age range of 133±1–128±1 Ma. The igneous complexes of this association are part of the Stanovoy volcano-plutonic belt, which extends in the sublatitudinal direction from the Pacific Ocean deep into the North Asian continent for more than 1000 km subparallel to the Mongol-Okhotsk suture zone and stitches the tectonic structures of the Dzhugdzhur-Stanovoy and West-Stanovoy superterranes. The formation of the Stanovoy Belt is connected with the closure of the Mongolo-Okhotsk Ocean and the collision of the continental masses of the North Asian and Sino-Korean continents at the turn of ~140 Ma. The subsequent collapse of the collisional orogen, accompanied by large-scale lithospheric extension and delamination of the lower part of the continental lithosphere, led to upwelling of the asthenospheric mantle. This caused the melting of the lithospheric mantle and continental crust and, as a consequence, the formation of both mafic melts of the shoshonite type and anatectic crustal melts of the adakite type. The mixing of these melts led to the formation of the parent magmas of the Amudzhikan magmatic association. The crustal component in the source was of a heterogeneous nature and was finally formed as a result of the Early Cretaceous collision event. It is characterized by upper-crustal isotopic parameters: an increased Rb/Sr and U/Pb ratio and a decreased Sm/Nd ratio in the source. The mantle component is represented by the material of the enriched lithospheric mantle of the Central Asian fold belt, the formation of which is associated with subduction processes at the stage of closure of the Mongol-Okhotsk paleoocean. Metasomatic transformation of the mantle with the introduction of melts and fluids with isotopic parameters of an EMII-type source or upper crust occurred at this stage.