Pseudosecondary clastic rocks of the Dzuramtai massif (Southern Mongolia)

Specific rocks (tectonomixtites) developed in the framing of Mongolian granite massifs (Dzuramtai and some others) at the Mesozoic section bottom are studied. It is shown that the tectonomixtites are tectonic rocks rather than eluvial or sedimentary rocks, as was considered previously. They formed in the Cenozoic in the process of granite protrusion beneath a thick sedimentary cover owing to the crushing of granites and abrasion of granite fragments with the subsequent transformation of clastic rocks by groundwaters (suffosion). In this process, clastic rocks yielded fine products of the destruction of feldspars and quartz was concentrated. The rocks formed at relatively low temperatures (no more than 200–300°C) under stress strains.