The Baikal Rift Zone is a series of

continent A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

s centered beneath

Lake Baikal Lake Baikal is a rift lake and the deepest lake in the world. It is situated in southern Siberia, Russia between the Federal subjects of Russia, federal subjects of Irkutsk Oblast, Irkutsk Oblasts of Russia, Oblast to the northwest and the Repu ...

in southeastern

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

. Current strain in the rifts tends to be extending with some shear movement. A series of

basins Basin may refer to: Geography and geology * Depression (geology) ** Back-arc basin, a submarine feature associated with island arcs and subduction zones ** Debris basin, designed to prevent damage from debris flow ** Drainage basin (hydrology), ...

form along the zone for more than , creating a

rift valley A rift valley is a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear ...

. The rifts form between the Eurasian Plate to the west and the Amur Plate to the east.

Structures

To the northwest of the rifts is the

Siberian Craton Siberia, also known as Siberian Craton, Angaraland (or simply Angara) and Angarida, is an ancient craton in the heart of Siberia. Today forming the Central Siberian Plateau, it formed an independent landmass prior to its fusion into Pangea during ...

, on the Eurasian Plate. The Sayan-Baikal and Mongolia-Okhotsk mobile belts are formations to the southeast of the rifts; beyond the Sayan-Baikal fold belt is the Amur Plate. Basins form along the rift. There are three basins in the area, the South Basin, Central Basin, and North Basin. In the North, half-grabens form smaller basins, such as the North Baikal Basin, and the Chara-Tokka Basin. The Central Basin is the deepest in the rift system. The largest fault it contains is the Morskiy Fault; however, another fault, the Primorsky is becoming the primary fault in the rift. The basins also display evidence of crustal thinning below the rift zone. The thickness of the crust beneath the rift is disputed, as the structures of the rift deep beneath the surface are unknown. The difference in thickness of the crust, between the crust under the rift and that under the surrounding areas, has been bounded to be less than . Although some seismic data is evidence for a rise in the

Lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

Asthenosphere The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...

boundary, other researchers have claimed that there are deep structures which influence seismic activity, and that the lower crust is intruded by

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

sills. They interpret the extension as a pure shear process.

Volcanism

Volcanism is generally associated with the rift.

Hot springs A hot spring, hydrothermal spring, or geothermal spring is a Spring (hydrology), spring produced by the emergence of Geothermal activity, geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow ...

are present both on land and under Lake Baikal, although thus far, no evidence of actual

volcanism Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

has been found in the immediate vicinity of the lake. Despite this,

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

volcanism has occurred nearby and is probably associated with the Baikal Rift Zone. Early volcanism has been confirmed to exist from the early

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

, although it is believed that

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Volcanism exists. The recognized volcanic centers are the Udokan Plateau, located about 400 km ENE of the northern tip of Lake Baikal, the

Oka Plateau Oka or OKA may refer to: * "Officially known as", used to introduce an official name Vehicles * Oka (automobile), a small car designed by AvtoVAZ and produced by ZMA and SeAZ * OKA (truck), a large 4-wheel-drive vehicle made in Western Australi ...

, located about 200 km WNW of the southwest tip of Lake Baikal, the Vitim Plateau, around 200 km east of the rift, and the Azas Plateau.

Geological history

The area was originally characterized by

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

and

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

northeast-southwest fold and thrust belts. The Primorsky fault zone of the central basin was present at this time also. Volcanism began in the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

in limited areas, but is mostly limited to the

. The late Cretaceous is also the age of sedimentary rocks in some basins, and the same series lasted into the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

. Rifting resumed beginning in the

, and is commonly held to have increased since the middle

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 causing the formation of basins in the form of grabens. The new rift structure may follow the Precambrian and Paleozoic faults, such as when the dormant Primorsky fault, of the Central Basin, began to extend again in the late

. Magmatic activity and rifting may also be independent events. Outside of the

graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

volcanics erupted from either end of the rift system during the uplift. The grabens mostly spread without releasing magma, except the Tunkin Depression. Most basin deposits are from the late

, except in the north where basin deposits began in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

, is the 'middle rift' unit of Pliocene coarse grained

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s and conglomerates. Finally there is the modern rift unit of fluvial, glacial, and deltaic sediments. Examining Pliocene and younger

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s reveals

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

argillite Argillite () is a fine-grained sedimentary rock composed predominantly of Friability, indurated clay particles. Argillaceous rocks are basically lithified muds and Pelagic sediment, oozes. They contain variable amounts of silt-sized particles. T ...

s, and

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

s, indicating lacustrine deposition.

Seismic monitoring

The first seismic station in the region was opened in

Irkutsk Irkutsk ( ; rus, Иркутск, p=ɪrˈkutsk; Buryat language, Buryat and , ''Erhüü'', ) is the largest city and administrative center of Irkutsk Oblast, Russia. With a population of 587,891 Irkutsk is the List of cities and towns in Russ ...

in 1901, which began instrumental observations. New instruments were put in place in 1912, and the system was expanded in the 1950s and 1960s. The monitoring network is still in operation, although the minimum spacing has been criticized for exceeding in the minimum distance between stations. Studies from foreign experiments also provide new information about the rift system.

Tectonic stress and strain

Along the boundary both normal and shear strains have occurred in the rift. Plates are diverging along the boundary at per year, although this varies along the system. In addition to divergent movement, left lateral

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

movement also occurs in the fault system, such as along the Sayan Fault. The rate of slip has been estimated at per year in the north by looking at offsets of morphological features, although this estimate does not agree with current

model A model is an informative representation of an object, person, or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin , . Models can be divided in ...

s. The total throw that has occurred has been estimated at in extension and in the vertical direction. Due to the distance from active plate boundaries, the driving forces of the rift are unknown; however, possibilities include the

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of the Pacific Plate and the

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great for ...

of the

Indian subcontinent The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...

with Eurasia. Locally, there may be a mantle up-welling driving the extension. This latter theory is held by most Russian scientists.

References