Angara Shield,large, geologically stable area of Precambrian rocks, N Asia, comprising much of Siberia, Russia. It is bounded, in general, on the west by the Yenisei River, on the east by the Lena River, on the north by the Arctic Ocean, and on the south by the general latitude of Lake Baykal. Most of the region is covered by strata of lower Paleozoic sediments and it is thought that since the early Paleozoic era it has remained above the level of invading seas that flooded most continental land masses. Tundra and taiga cover the region, which also has a rich variety of minerals.
one of the large, ancient (pre-Riphe-an) platforms, located in the central part of northern Asia. The platform’s western boundary coincides with the Enisei River valley; its northern boundary, with the southern edge of the Byrranga Mountains; and its eastern boundary, with the lower reaches of the Lena River (Verkhoiansk Foredeep). In the southeast the platform’s boundary comes close to the southern edge of the Dzhugdzhur Range. In the south it runs along the faults on the southern edge of the Stanovoi and lablonovyi ranges; then, skirting Transbaikalia and the Baikal Region on the north along a complex system of faults, it descends to the southern tip of Lake Baikal. The southwestern boundary stretches along the Vostochnyi Saian Main Fault.
The Siberian Platform has an Archean-Proterozoic folded crystalline basement conformably covered by a sedimentary Riphean-Phanerozoic mantle. The basement emerges on the surface in the north (Anabar Massif, Olenek Uplift), in the southeast (Aldan Shield), and in the southwest (Baikal and Vostochnyi Saian marginal uplifts, Kan prominence). On the platform’s remaining territory, the basement, covered by a mantle of sedimentary deposits up to 10–12 km thick, is broken into blocks that have subsided to varying depths. The thickness of the earth’s crust (down to the Mohorovičić discontinuity) varies from 25–30 km in the Viliui and Tungus syneclises to 40–45 km on the Aldan Shield and in the basement’s marginal uplifts in the south.
The Aldan Shield and the Anabar Massif, separated below the sedimentary mantle by the Urik-Viliui Late Precambrian Aulakogene (intracratonal mobile belt), form the eastern mega-block of the basement. The western megablock lies between the eastern megablock and the southwestern marginal uplifts (Baikal, Vostochnyi Saian, and Kan prominences). A system of submeridional and sublatitudinal faults divides the western megablock into smaller blocks. Along the sublatitudinal Angara faults, east of the Baikalides of the Enisei Ridge, the western megablock is divided by the Irkineeva-Chadobets Riphean Aulakogene into the northern Tungus and the southern Kan-Angara parts, which differ in terms of the age of the basement rock.
The basement includes folded, highly metamorphosed Ar-chean and Proterozoic crystalline rocks (gneisses, schists, amphibolites, charnockites, marbles) whose absolute ages range from 2.3 billion years (Anabar Massif) to 3.7 billion years (Kan prominence). The sedimentary mantle is composed of deposits dating from the Upper Precambrian to the Quaternary. The most widely found are Riphean, Cambrian, and Ordovi-cian rocks, represented by detrital, calcareous, and salt-bearing strata. These rocks make up the Anabar and Aldan anteclises, the Angara-Lena Trough, the Kan-Angara Depression, and other platform structures.
The platform’s broadest syneclise, the Tungus, is filled with terrigenous coal-bearing Carboniferous and Permian deposits and with Upper Permian and Triassic tufogenic rocks. Basic igneous rock, trap, is represented abundantly, particularly along the edge of the syneclise. The trap forms sills, dykes, veins (dolerites and gabbrodolerites), and mantles (plateau basalts). Jurassic deposits fill the Irkutsk (Cheremkhovo) Trough and a number of other depressions, and Jurassic and Cretaceous deposits are associated with the Enisei-Khatanga and Lena troughs and the Viliui syneclise. The latter also contains Ceno-zoic deposits. Characteristic of the northeastern part of the platform are intrusive ultrabasic rocks (chiefly meymacites) and kimberlites, which form diamond-bearing pipes.
The rocks of the mantle, lying relatively conformably, have in places been dislocated to a varying degree and broken by faults. The fold-fracture dislocations normally become stronger toward the margins of the platform, particularly in the Angara-Lena Trough in the southeast.
The rocks of the basement contain deposits of iron ore, mica (phlogopite), piezoquartz, and apatite. The sedimentary mantle is rich in petroleum, oil and bituminous shales, gas, coal (Lena, Tungus, and Irkutsk coal basins), rock salt, gypsum, iron ore, phosphorites, manganese, and placers. The rocks of the trap formations contain deposits of magnetite ores (Angara-Ilim deposits, Kamyshevskii Baikitik, Tynokit), nickel and copper ores (Noril’sk Ore Region), precious metals, graphite, and Iceland spar. Deposits of rare metals and diamonds are associated with the kimberlites.
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N. S. ZAITSEV