Tunkin Depression is a volcanic field in Russia .
29-775: The Tunkin Depression itself is a 200 kilometres (120 mi) tectonic depression, part of the Baikal Rift Zone , between Lake Baikal and Khövsgöl Nuur . The depression consists of a number of basins and is covered by alluvial sediments of the Irkut River . The basin is bordered by the Tunka Range to the north and by the Khamar-Daban mountains to the south. The history of the Baikal Rift begins in
58-527: Is a planet's "original" crust. It forms from solidification of a magma ocean. Toward the end of planetary accretion , the terrestrial planets likely had surfaces that were magma oceans. As these cooled, they solidified into crust. This crust was likely destroyed by large impacts and re-formed many times as the Era of Heavy Bombardment drew to a close. The nature of primary crust is still debated: its chemical, mineralogic, and physical properties are unknown, as are
87-495: Is debated. The anorthosite highlands of the Moon are primary crust, formed as plagioclase crystallized out of the Moon's initial magma ocean and floated to the top; however, it is unlikely that Earth followed a similar pattern, as the Moon was a water-less system and Earth had water. The Martian meteorite ALH84001 might represent primary crust of Mars; however, again, this is debated. Like Earth, Venus lacks primary crust, as
116-453: Is made of shallow-water deposits and is often folded and faulted. Overlying this unit, separated by a small unconformity , is the 'middle rift' unit of Pliocene coarse grained sandstones and conglomerates . Finally there is the modern rift unit of fluvial, glacial, and deltaic sediments. Examining Pliocene and younger sediments reveals sands , argillites , and silts , indicating lacustrine deposition. The first seismic station in
145-496: Is needed to create tertiary crust, and Earth is the only planet in the Solar System with plate tectonics. Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere , a division of Earth's layers that includes the crust and the upper part of the mantle . The lithosphere is broken into tectonic plates that move, allowing heat to escape from
174-596: The Mesozoic , when intracontinental extension took place at the rift. In the Cenozoic , rifting proper commenced generating basins that were filled by sediments and basaltic volcanism. The causes of the rifting are unclear and may involve either tectonic effects of the India-Asia collision , mantle plumes and asthenospheric processes. The volcanic field consists of numerous cinder cones and lava flows west of
203-506: The Pleistocene and Holocene ; potassium-argon dating of some cones has yielded several ages, including 1.58 ± 0.14 million years ago and 700,000 ± 400,000 years before present. Baikal Rift Zone The Baikal Rift Zone is a series of continental rifts centered beneath Lake Baikal in southeastern Russia . Current strain in the rifts tends to be extending with some shear movement. A series of basins form along
232-473: The adiabatic rise of mantle causes partial melting. Tertiary crust is more chemically-modified than either primary or secondary. It can form in several ways: The only known example of tertiary crust is the continental crust of the Earth. It is unknown whether other terrestrial planets can be said to have tertiary crust, though the evidence so far suggests that they do not. This is likely because plate tectonics
261-925: The crust is the outermost solid shell of a planet , dwarf planet , or natural satellite . It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase (solid crust vs. liquid mantle). The crusts of Earth , Mercury , Venus , Mars , Io , the Moon and other planetary bodies formed via igneous processes and were later modified by erosion , impact cratering , volcanism, and sedimentation. Most terrestrial planets have fairly uniform crusts. Earth, however, has two distinct types: continental crust and oceanic crust . These two types have different chemical compositions and physical properties and were formed by different geological processes. Planetary geologists divide crust into three categories based on how and when it formed. This
290-537: The grabens basalt 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 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
319-662: The Baikal Rift Zone. Early volcanism has been confirmed to exist from the early Miocene , although it is believed that Oligocene 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 , located about 200 km WNW of the southwest tip of Lake Baikal, the Vitim Plateau, around 200 km east of
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#1732779820654348-596: The Tunkin Depression with about 500 metres (1,600 ft) of volcanic products, which range from Miocene to Quaternary and include basaltic lava flows and tuffs . Subsidence is still occurring, and the volcanic cones are consequently lowering; one of the cones now rises only about 6 metres (20 ft) above terrain. The field has produced basalt , which in this field contains carbonatite , olivine or palagonite . The basalts range from alkali basalts to tholeiites . Volcanism may have protracted through
377-423: The crust ranges between about 20 and 120 km. Crust on the far side of the Moon averages about 12 km thicker than that on the near side . Estimates of average thickness fall in the range from about 50 to 60 km. Most of this plagioclase-rich crust formed shortly after formation of the Moon, between about 4.5 and 4.3 billion years ago. Perhaps 10% or less of the crust consists of igneous rock added after
406-453: The entire planet has been repeatedly resurfaced and modified. Secondary crust is formed by partial melting of mostly silicate materials in the mantle, and so is usually basaltic in composition. This is the most common type of crust in the Solar System. Most of the surfaces of Mercury, Venus, Earth, and Mars comprise secondary crust, as do the lunar maria . On Earth secondary crust forms primarily at mid-ocean spreading centers , where
435-463: The formation of the initial plagioclase-rich material. The best-characterized and most voluminous of these later additions are the mare basalts formed between about 3.9 and 3.2 billion years ago. Minor volcanism continued after 3.2 billion years, perhaps as recently as 1 billion years ago. There is no evidence of plate tectonics . Study of the Moon has established that a crust can form on a rocky planetary body significantly smaller than Earth. Although
464-491: The igneous mechanisms that formed them. This is because it is difficult to study: none of Earth's primary crust has survived to today. Earth's high rates of erosion and crustal recycling from plate tectonics has destroyed all rocks older than about 4 billion years , including whatever primary crust Earth once had. However, geologists can glean information about primary crust by studying it on other terrestrial planets. Mercury's highlands might represent primary crust, though this
493-416: The interior of Earth into space. A theoretical protoplanet named " Theia " is thought to have collided with the forming Earth, and part of the material ejected into space by the collision accreted to form the Moon. As the Moon formed, the outer part of it is thought to have been molten, a " lunar magma ocean ". Plagioclase feldspar crystallized in large amounts from this magma ocean and floated toward
522-414: The lower crust is intruded by mafic sills . They interpret the extension as a pure shear process. Volcanism is generally associated with the rift. 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. Despite this, Cenozoic volcanism has occurred nearby and is probably associated with
551-418: The north by looking at offsets of morphological features, although this estimate does not agree with current models . The total throw that has occurred has been estimated at 7 ± 0.5 kilometres (4.35 ± 0.31 mi) in extension and 12 ± 1 kilometre (7.46 ± 0.62 mi) in the vertical direction. Due to the distance from active plate boundaries , the driving forces of
580-481: The region was opened in Irkutsk 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 100 kilometres (62 mi) in the minimum distance between stations. Studies from foreign experiments also provide new information about
609-531: 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. This latter theory is held by most Russian scientists. 53°30′N 108°00′E / 53.5°N 108.0°E / 53.5; 108.0 Crust (geology) In geology ,
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#1732779820654638-547: The rift system. Along the boundary both normal and shear strains have occurred in the rift. Plates are diverging along the boundary at 3 to 4 millimetres (0.12 to 0.16 in) per year, although this varies along the system. In addition to divergent movement, left lateral strike-slip movement also occurs in the fault system, such as along the Sayan Fault. The rate of slip has been estimated at 3.2 ± 0.5 millimetres (0.126 ± 0.020 in) per year in
667-582: 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 10 kilometres (6.2 mi). Although some seismic data is evidence for a rise in the Lithosphere - Asthenosphere boundary, other researchers have claimed that there are deep structures which influence seismic activity, and that
696-522: The rift, and the Azas Plateau . The area was originally characterized by Precambrian and Paleozoic 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 in limited areas, but is mostly limited to the Miocene . The late Cretaceous is also the age of sedimentary rocks in some basins, and
725-823: 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
754-702: 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, such as when the dormant Primorsky fault, of the Central Basin, began to extend again in the late Cenozoic . Magmatic activity and rifting may also be independent events. Outside of
783-444: The surface. The cumulate rocks form much of the crust. The upper part of the crust probably averages about 88% plagioclase (near the lower limit of 90% defined for anorthosite ): the lower part of the crust may contain a higher percentage of ferromagnesian minerals such as the pyroxenes and olivine , but even that lower part probably averages about 78% plagioclase. The underlying mantle is denser and olivine-rich. The thickness of
812-489: The western tip of Lake Baikal . The largest number of individual volcanoes is found close to the town of Tunka and is named the Khobok group. The highest of these volcanoes is Khara-Boldok or Ulyborskiy, which is 125–120 metres (410–394 ft) high. This cone further features a 90–85 metres (295–279 ft) wide crater . Four other groups of volcanoes are found in the Tunkin Depression. The Tunkin volcanic field has filled
841-795: The zone for more than 2,000 kilometres (1,200 mi), creating a rift valley . The rifts form between the Eurasian Plate to the west and the Amur Plate to the east. To the northwest of the rifts is the Siberian Craton , 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
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