Дөч голын дүүргийн онон формацын тунамал чулуулгийн геологи, геохронологийн судалгааны үр дүн

Abstract

In this paper, we have U-Pb geochronological and zircon geochemical studies of sandstones from Duchgol and Onon formation with the aim of constraining the depositional age, and the implication for tectonic setting. CL imaging reveal that most of grains exhibit oscillatory growth zoning and they have intermediate Th/U ratios (0.10-0.29), which suggests a magmatic origin. The zircons have highly concordant ages ranging between 240±2 and 2078±21 Ma with major age peaks clustering 251±2 and 240±2 Ma for the sample DG-11. Youngest eight igneous zircon grains yield a weighted age of 250.6±1.8 Ma (MSWD=0.17) which constrains the youngest depositional age of sandstone. CL imaging reveal that most of grains exhibit oscillatory growth zoning and they have intermediate Th/U ratios (0.25-1.0), which suggests a magmatic origin. The zircons have highly concordant ages ranging between 236±6 and 1253±43 Ma with major age peaks clustering 252 and 240.7±2.9 Ma ба for the sample DG-08. Youngest eight igneous zircon grains yield a weighted mean age of 240.7±2.9 Ma (MSWD=0.25) which constrains the youngest depositional age of sandstone. New geochronological data is indicating that depositional age of Duchgol and Onon formation must be younger than, ~ 240-250 Ma, age of formation that reasonable a lower Triassic.