| Abstract: | The Hercynian mobile belts in Central Asia comprise the Hercynian proper and the Late Hercynian (Indosinian) belts separated
by the South Gobi microcontinent, the origin of which is related to the evolution of the South Mongolian and Inner Mongolian
basins with the oceanic crust. Crystalline complexes within these belts occur as tectonic sheets of a variety of sizes. At
the early stages, the metamorphic grade of these complexes reached conditions of high-temperature subfacies of amphibolite
and locally developed granulite facies. In tectonic terms, the Hercynian belt of metamorphic rocks is situated at the margin
of the North Asian Caledonian continent and extends from the southeast to the northwest along the southern slope of the Gobi,
Mongolian, and Chinese Altai to East Kazakhstan, where metamorphic rocks are localized in the Irtysh Shear Zone. All these
rocks are combined into the South Altai metamorphic belt of more than 1500 km in extent. Another belt of isolated outcrops
of crystalline rocks conventionally combined into the Indosinian South Gobi metamorphic belt is traced along the junction
of the Hercynides with the South Gobi microcontinent. The high-grade metamorphic rocks within both belts are not fragments
of an ensialic Caledonian or older basement. These rocks were formed 390–360 and 230–220 Ma ago as a result of the closure
of the Tethian South Mongolian and Inner Mongolian oceanic basins (Paleotethys I and Paleotethys II). The spatial position
of the South Altai and South Gobi metamorphic belts is caused by the asymmetric structure of the Tethian basins, where active
continental margins are expressed most distinctly along their northern parts, while passive margins extend along the southern
parts (in present-day coordinates). |
