Geologic structure, relief, and neotectonics of the Chulyshman Upland (Gorny Altai)

The Chulyshman Upland is a big mountain structure at the boundary between the Altai and West Sayan mountain ranges. It is composed mostly of metamorphic rocks of the greenschist, epidote-amphibolite, and amphibolite facies as well as several large granitoid massifs. The upland stretches for 150 km to the northwest and is < 50 km in width. The main divides are flattened and are almost 3000 m (or, seldom, slightly more) in height. The southwestern and northeastern boundaries of the upland are formed by recent dextral strike-slip faults, and the northwestern and southeastern boundaries, by reverse faults. Neotectonic structures of lower rank divide the upland into four mountain massifs similar in morphology and size; the mountain massifs, in turn, are divided into altitude stages. Recent E-W trending faults are reverse, whereas N-S trending faults are normal. Horizontal displacements along the dextral strike-slip faults are > 2000 m, while vertical displacements along the reverse and normal faults are within 150-500 m. There is no contemporary glaciation on the upland. In the Pleistocene, the upper stage of the relief was occupied by ice sheets, which left numerous traces of exaration. The middle stage was a transit zone for the outlet tongues of ice sheets; here, moraine deposits cover the bottoms and slopes of valleys. The lower stage was a zone of moraine accumulation in the Pleistocene. In the Holocene, neotectonic activity in the area was expressed as numerous earthquakes, which have left traces in the form of rock slides at the base of 20% of the extension of the sides of glacial valleys and seismogenic trenches 80 to 2300 m in length. Studies have revealed a pleistoseist zone (50°37'10" N; 88°51'08" E) from a recent (about 200-300 years ago) catastrophic earthquake.