Early Mesozoic Alkaline Magmatism in the Western Framing of the Mongol–Okhotsk Belt: Age and Structural Position

Abstract

A zonal igneous areal appeared at the western end of the Mongol–Okhotsk Belt in the Early Mesozoic. Its central part is comprised of the Khentei–Daurian giant batholith, which is framed on its north and west by riftlike structures with manifestations of bimodal and alkaline granite magmatism. Geochronological studies of the Choyr and Gal-Shara massifs of peralkaline granites, belonging to the North Gobi (southern) border of the batholith, are carried out. The ages of the former and latter are 215 and 213 Ma, respectively. It is shown that associations involving alkaline igneous rocks are fairly well developed in the North Gobi zone and controlled by NE-trending faults and grabens. Thus, it is established that the zonal magmatic area was formed under a specific regime. In its central part, which corresponds to the zone of the Mongol–Okhotsk suture, anatexis and batholith-formation processes took place, while the periphery was involved in rifting. The data obtained indicate the closure of the western part of the Mongol–Okhotsk trough before the formation of the zonal magmatic areal. The structure of the magmatic areal was determined by the mechanisms of the plume–lithosphere interaction between the collisional suture (anatectic melting zone) and its less tectonically strained framing (rifting zones).