Petrology and geochronology of pelitic gneisses in the Hanhohiyn Mountains, the northwestern part of Mongolia

Abstract

Hanhohiyn Mountains is located in the northwestern part of Mongolia. The mountains are mainly composed of marble, meta-quartzite and pelitic gneisses intercalating with lenticular garnet-amphibolite, garnet-orthopyroxene gneiss and so on. Pelitic gneisses are classified into garnet-sillimanite-biotite gneiss, garnet-cordierite-biotite gneiss and garnet-biotite gneiss. These gneisses indicate the peak metamorphic condition of 600-700 degree and 5.5-6 kbar accompanied by decompression. The EPMA U-Th-Pb Monazite ages concentrate between 480-510 Ma which is interpreted as the timing of the peak metamorphism.