GEOCHRONOLOGY OF CENOZOIC BASALTS IN MONGOLIA AND THEIR RELATIONSHIPS WITH NEOTECTONIC STRUCTURES

Abstract

The epiplatform (Upper Cretaceous-Paleogene) and neotectonic (Neogene-Quaternary) evolutionary stages and morphostructures are distinguished in Mongolia. The neotectonic structures are characteristic of the orogenic zone that is free of volcanics (Altay, Hentiy) and of the fore-rift (Hangay, Dariganga) and rift (Hubsugul region) volcanic zones. Seventeen distribution areas of volcanogenic rocks are outlined, and geochronological database that includes about a hundred of K-Ar and 40Ar- 39Ar dates obtained in Russia, Austria, Switzerland, the United States, and Hungary is compiled. The established geochronological reference level range from 120 to 30 Ma in the orogenic zone and correspond to 30-31, 28, 15-13, 8-5 in the fore-rift zone and to 28-25, 15-13, 5-3, and less than 1 Ma in the rift zone. The reference isotopic dates obtained for basalts enable the precise (of zone rank) dating of Cenozoic biostratigraphic (mammalian) horizons in Mongolia (Devyatkin et al., 2002). The biostratigraphic horizons and geochronological levels create a basis for remote and interregional correlations.