Verkhoyansk-Chukotka folded region
VERKHOYANSK-CHUKOTKA FOLDED REGION (RU: Верхояно-Чукотская складчатая область) is the region of the Mesozoic folding at the junction between the Pacific ocean geosynclinal belt and the Arctic geosynclinal belt. This region includes the territories of the Eastern Siberia to the east of the Lena and Aldan rivers, to the Koryak Highland and the coast of the Sea of Okhotsk. This region is separated from the Siberian craton by the deep pre-Verkhoyansk foredeep, and by the system of the faults along the western slope of the Sette-Daban ridge. The eastern boundary of the region is the system of the deep faults, which is expressed on the surface as the stripe of the Cretaceous effusives and granitic massifs of the Okhotsk-Chukotka peripheral volcanic belt.
The large part of the territory is characterized by the mountainous relief. At the west, the Verkhoyansk, Sette-Daban, Chersky, Moma, Tas-Kystabyt, and other ridges have the sub-meridional or north-western strike, while at the north-east, the Southern Anuysky, Northern Anuysky, Oloy, Chukchi, and other ridges have the sub-latitudinal strike. The central and northern parts of the territory are occupied by the Indigirka-Kolyma and Yana-Indigirka lowlands. Within the geological cross section of the Verkhoyansk-Chukotka folded region, there are distinguished several structural complexes of the different ages: the Archean - Lower Proterozoic metamorphic complex, which is forming the protrusions of the basement of the pre-Riphean massifs (Okhotsk, Omolon, Chukchi, and others); the Riphean - Lower Paleozoic sedimentary complex, which is forming the covers of the massifs, and is emerging onto the surface within the cores of the large horst-anticlinoria (Sette-Daban, Tas-Hayakhtakh, Omulevsky, periphery of Kolyma, and others); the Middle Carboniferous - Permian, Triassic, Lower to Middle Jurassic complex, which is the main geosynclinal complex, the Verkhoyansk complex proper.
There form the lower parts of the cross section the anticlinoria (Verkhoyansk, Chukchi, Anuysky), and there form the upper parts the synclinoria (Inyali-Debinsky, and others). The molasse strata of the Upper Jurassic - Lower Cretaceous fill the depressions of the orogenic stage, namely, the foredeep, the intermountain depressions, and the rift structures; within the internal zones, there are distributed the neutral and acidic volcanic rocks. There are associated with these rocks the deposits of the mineral coals. The Cenozoic depositions near the northern coast form the cratonic cover, which is lining also the bottom of the coastal shelf seas of the Arctic ocean. The western part of the Verkhoyansk-Chukotka folded region is characterized by the exclusively terrigenous composition of the geosynclinal formations, while at the east, there are well developed the cherty and siliceous-volcanogenic strata. The granitic magmatism is associated with the orogenic stage (the Late Jurassic - Early Cretaceous), and with the stage of the forming of the peripheral volcanic belt (the Late Cretaceous). There associate with these stages the deposits of the ores of tin, gold, mercury, and polymetals. The folded structures have been formed mostly during the Early Cretaceous time, and the modern mountainous relief has been formed during the Neogene-Quaternary time.
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