Structure, Age, and Evolution of the Late Mesozoic Eastern Mongolian Volcanic Belt

Abstract

Geochronological studies of volcanic rocks ascribed to the Late Mesozoic Eastern Mongolian Volcanic Belt (EMVB) allowed the recognition of several groups, which differ in age and composition of igneous associations, as well as their occurrence. The youngest group (~215 Ma) includes the rocks of bimodal association abundant in the western part of the EMVB. The next group (170–150 Ma) mostly consists of felsic lavas of the shoshonite–latite association composing the large volcanic fields in the eastern part of the EMVB. The rocks with the age of 140–105 Ma form a cover of the EMVB and mostly include basaltic trachyandesite, the fields of which are accompanied by small volcanoes of trachydacite and trachyrhyolite. Separated extrusions of alkaline basaltoids formed in age range of 105–80 Ma. The rock associations of various ages have different geological links with ambient igneous complexes. By age and composition, the Late Triassic bimodal complex is compared with similar associations that occur in Central Mongolia and West Transbaikalia along the frame of the Khentei–Dauria batholith. Their origination is related to the formation of the Early Mesozoic Khentei–Dauria zoned igneous area. The Middle to Late Jurassic igneous complexes are mostly localized in the eastern part of the EMVB. Their fields occur within the area of Late Jurassic volcanic fields of the Great Xing’an Volcanic Belt (GXVB), which are similar both in the age of the formation and in the composition of volcanic associations. The Cretaceous magmatism was responsible for the main evolution of the EMVB, which was accompanied by rifting and formation of numerous troughs and grabens, as well as regular evolution of its mantle sources directed toward the increasing amount of an intraplate component. The sizes, boundaries, and characteristics of the EMVB magmatism are refined. Its western boundary is shifted to the east and is determined by a frontal NW-trending fault system, which controls a chain of Early Cretaceous granitic plutons, as well as rocks of the Late Mesozoic extrusive complex. The eastern boundary of the area is shifted to the west, where it coincides with a field of the Early Cretaceous extrusive complex. Taking into account data on the alien setting of the Late Triassic and Middle to Late Jurassic complexes in the EMVB structure, it is established that the EMVB igneous products mainly include mafic volcanic rocks. This is in agreement with similarity of the EMVB and other Late Mesozoic volcanic areas of the intracontinental part of East Asia, with a subordinate role of felsic igneous rocks.