Baikal Rift Zone
The Baikal Rift Zone is a divergent plate boundary centered beneath Lake Baikal in southeastern Russia. Along it form a series of basins more than 2,000 kilometres (1,200 mi) long. To its west is the Eurasian Plate and the Siberian platform and to its east is the Amur Plate which is moving away from the rift toward Japan at about 4 mm per year.
As in all divergent plate boundary zones, the crust in the Baikal Rift Zone is thinning and magma is very close to the surface. Hot springs are present both on land and under Lake Baikal, although thus far, no evidence of actual volcanism has been found in the immediate vicinity of the lake. However, geologically-recent volcanic activity has occurred nearby and is probably associated with the Baikal Rift Zone. These volcanic centers are the Udokan Plateau, located about 400 km ENE of the northern tip of Lake Baikal, the Oka Plateau, located about 200 km WNW of the southwest tip of Lake Baikal, and the Vitim Plateau, around 200 km east of the rift.
The driving forces of the rift are unknown; however, possibilities include the subduction of the Pacific Plate and the collision of the Indian subcontinent with Eurasia. Locally, there may be a mantle up-welling driving the extension.
The area was originally characterized by Precambrian and Paleozoic northeast-southwest fold and thrust belts. Volcanism began in the late Cretaceous in limited areas, but is mostly limited to the Miocene. It is also the age of sedimentary rocks in some basins, and the same series lasted into the Eocene. Rifting resumed beginning in the Oligocene, and is commonly held to have increased since the middle Pliocene, causing the formation of basins in the form of grabens. The new rift structure may follow the Precambrian and Paleozoic faults. Magmatic activity and rifting may also be independent events. Outside of the grabens basalt volcanics erupted from either end of the rift system during the uplift. The grabens mostly spread without releasing magma, except the Tunka depression.
Most basin deposits are from the late Oligocene, except in the north where basin deposits began in the Pliocene. Three series of sediment are present; the 'proto-rift', the 'middle rift', and the 'modern rift'. The proto-rift unit is made of shallow-water deposits and is often folded and faulted. Examining Pliocene and younger sediments reveals sands, argillites, and silts, indicating lacustrine deposition. The basins also display evidence of crustal thinning below the rift zone.
The deepest basin in the system is the Central Basin. The largest fault it contains is the Morskiy Fault; however, another fault, the Primorsky is becoming larger. The Primorsky fault zone is an early Paleozoic fault system, which began extending again in the Cenozoic.
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