Early mesozoic alkaline magmatism of the western framing of the Mongol-Okhotsk belt: age and structural position

A zonal igneous area appeared at the western end of the Mongol-Okhotsk belt in the early Mesozoic. Its central part forms a giant Khentey-Dauria batholith, which from the north and west is framed by rift-like structures with bimodal and alkaline granite magmatism. The geochronological studies of the peralkaline granites of the Choyr and Gal-Shara massifs were carried out. These massifs belong to the North Gobi (southern) border of the batholith. The age of the first was 215 million years, the age of the second was 213 million years. It is shown that associations involving alkaline igneous rocks are fairly well developed in the North Gobi zone. They are controlled by faults and grabens of the northeast strike. Thus, it was established that the formation of the zonal magmatic area was characterized by a specific mode. In its central part, which corresponds to the zone of the Mongol-Okhotsk suture, anatexis and batholite formation processes took place, and the periphery was involved in the processes of rifting. The data obtained indicate the closure of the western part of the Mongol-Okhotsk trough before the formation of the zonal magmatic area. The structure of the magmatic area was determined by the mechanisms of the plume-lithospheric interaction in the region characterized by a collision suture (anatectic melting zone) and its less tektonic tense framing (rifting zones).