Geological Structure and Tectonics of the Chuy Valley

The Chui Valley (depression) and the Kyrgyz Ridge framing it from the south are located within the Caledonian Ulu-Tau-North Tien Shan structural-facial zone, which serves as a peculiar structural axis of the Tien Shan.

Within the territory of the Chui Valley, two structural-geological parts are distinguished: the mountainous framing, composed mainly of Precambrian-Paleozoic rocks, and the valley itself, which has a two-part structure: a Precambrian-Paleozoic basement and a Meso-Cenozoic cover.

The Kyrgyz Ridge is mainly composed of Precambrian and Paleozoic rocks, both of sedimentary and effusive origin. A significant role is played by a thick suite of metamorphic schists, phyllites, chlorite, siliceous rocks, with interlayers of sandstones and slaty conglomerates. The slopes of the Kyrgyz Ridge, the upper reaches of the Aspara River, and the interfluve of the Kegety and Issyk-Ata rivers are composed of the Maralayskaya and Tyukskiy suites: carbonaceous quartz schists, carbonate-chlorite, and mica gneisses. The Aktyuz suite is represented by rocks of eclogite and granulite facies, i.e., thick (5000-6000 m) biotite and biotite-amphibole paragneisses, aplite-like orthogneisses, migmatites, eclogites of the oldest - Lower Proterozoic and Archean age. The suite is intensely displaced in the Caledonian era and pierced by huge batholiths of arkosic granites and small veins of porphyries. Most of the Caledonian-age granites are predominant in the Kyrgyz Ridge. There are also Hercynian intrusions.

The Paleozoic in the Kyrgyz Ala-Too is represented by all rock types. Outcrops of Cambrian rocks are noted west of the Tyo-Ashuu pass along the axis of the ridge. Here, terrigenous rocks - porphyries, sandstones, and shales are developed.

The Ordovician in the mountainous framing is marked by two areas of outcrops: the interfluve of the Shamshe and Aspara rivers to the upper reaches of the Kuragaty River. The Middle Ordovician in the eastern part is volcanogenic-carbonate. In the central part of the ridge, terrigenous materials are already present: sandstones, aleurolites, shales with interlayers of marbled limestones (Karabalta suite). The thickness of the suite is significant.

Ordovician-Silurian granitoids formed the Sokuluk, Ala-Archa, and Issyk-Ata massifs. Diorites and quartz diorites intruded in the upper reaches of Merke and Aspara (Ashmara). Crystalline schists and granites compose the axial part of the Kyrgyz Ridge.

Silurian deposits have not been found in the area, although some researchers consider it possible to relate the Jartash fine-grained suite of clayey, phyllitic shales, aleurolites, etc. to it.

Devonian rocks are found in all sections, mainly in the central part of the Kyrgyz Ridge. Here, the Devonian rock complex is represented from bottom to top by several suites (Sugandinskaya, Kastekskaya, etc.), consisting of conglomerates, gravelites, sandstones, and argillites.

Carbon is widely developed in this area. The composition of the Lower Carbon deposits is terrigenous: gray conglomerates, sandstones, aleurolites - their thickness is 700 m (Ibragimov et al., 1985). The most complete section of Visean rocks is established in the valleys of the Kegety, Ak-Suu, Kara-Balta rivers, where it consists of gray-green sandstones, tuffs, limestones (100-600 m). Namurian rocks - red-colored sandstones, aleurolites, etc., are described in detail in the basin of the Kegety River (Kegetin suite, thickness 300 m). The Middle and Upper sections are represented by the outcrop of the Orthok suite in the valley of the Shamshe River.

Permian deposits in the Kyrgyz Ridge are rare. This is understandable: in the Permian, the Northern Tien Shan experienced a geoanticlinal regime, and sediment accumulation occurred only in certain late Hercynian superimposed depressions. One of these depressions was located in the eastern part of the Kyrgyz Ridge (the valleys of the Shamshe, Konorchok, Kokjar-Suu, Ashukolter rivers), where a thickness of volcanogenic-territorial rocks was formed, with a thickness of 600-1700 m (Knauf, Korolev et al., 1972).

Mesozoic system deposits - a Triassic-Jurassic coal-bearing thickness have been found on the southwestern slope of the Chu-Ili mountains, 10 km from the village of Blagoveshchenka.