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89-744: The P436 regional road connecting Ulan-Ude and Chita passes through Romanovka across the plateau. The Vitim Plateau lies along the headwaters of the Vitim River , a tributary of the Lena between the Southern Muya Range to the north, the Ikat Range to the west, the Yablonoi Mountains to the south, and in the east with the lower reaches of the Kalakan River to the right bank of the lower reaches of

178-525: A dike , a sill , a laccolith , a pluton , or a batholith . While the study of magma has relied on observing magma after its transition into a lava flow , magma has been encountered in situ three times during geothermal drilling projects , twice in Iceland (see Use in energy production ) and once in Hawaii. Magma consists of liquid rock that usually contains suspended solid crystals. As magma approaches

267-453: A subarctic climate ( Dwc ). The climate is characterised by long, dry, bitterly cold winters and short but very warm summers. Precipitation is low and heavily concentrated in the warmer months. The record high is 40.6 °C (105.1 °F) on 8 July 2016. The record low is −54.4 °C (−65.9 °F) on 6 January 1931. Temperatures have never risen above freezing from 31 December to 1 February, inclusive. The Ulan-Ude Aviation Plant

356-452: A combination of these processes. Other mechanisms, such as melting from a meteorite impact , are less important today, but impacts during the accretion of the Earth led to extensive melting, and the outer several hundred kilometers of the early Earth was probably a magma ocean . Impacts of large meteorites in the last few hundred million years have been proposed as one mechanism responsible for

445-420: A depth of 2,488 m (8,163 ft). The temperature of this magma was estimated at 1,050 °C (1,920 °F). Temperatures of deeper magmas must be inferred from theoretical computations and the geothermal gradient. Most magmas contain some solid crystals suspended in the liquid phase. This indicates that the temperature of the magma lies between the solidus , which is defined as the temperature at which

534-427: A dissolved water content in excess of 10%. Water is somewhat less soluble in low-silica magma than high-silica magma, so that at 1,100 °C and 0.5 GPa , a basaltic magma can dissolve 8% H 2 O while a granite pegmatite magma can dissolve 11% H 2 O . However, magmas are not necessarily saturated under typical conditions. Carbon dioxide is much less soluble in magmas than water, and frequently separates into

623-406: A distinct fluid phase even at great depth. This explains the presence of carbon dioxide fluid inclusions in crystals formed in magmas at great depth. Viscosity is a key melt property in understanding the behaviour of magmas. Whereas temperatures in common silicate lavas range from about 800 °C (1,470 °F) for felsic lavas to 1,200 °C (2,190 °F) for mafic lavas, the viscosity of

712-435: A high charge (the high-field-strength elements, or HSFEs), which include such elements as zirconium , niobium , hafnium , tantalum , the rare-earth elements , and the actinides . Potassium can become so enriched in melt produced by a very low degree of partial melting that, when the magma subsequently cools and solidifies, it forms unusual potassic rock such as lamprophyre , lamproite , or kimberlite . When enough rock

801-546: A hypothetical magma formed entirely from melted silica, NBO/T would be 0, while in a hypothetical magma so low in network formers that no polymerization takes place, NBO/T would be 4. Neither extreme is common in nature, but basalt magmas typically have NBO/T between 0.6 and 0.9, andesitic magmas have NBO/T of 0.3 to 0.5, and rhyolitic magmas have NBO/T of 0.02 to 0.2. Water acts as a network modifier, and dissolved water drastically reduces melt viscosity. Carbon dioxide neutralizes network modifiers, so dissolved carbon dioxide increases

890-474: A layer that appears to contain silicate melt and that stretches for at least 1,000 kilometers within the middle crust along the southern margin of the Tibetan Plateau. Granite and rhyolite are types of igneous rock commonly interpreted as products of the melting of continental crust because of increases in temperature. Temperature increases also may contribute to the melting of lithosphere dragged down in

979-420: A magma. In practice, it is difficult to unambiguously identify primary magmas, though it has been suggested that boninite is a variety of andesite crystallized from a primary magma. The Great Dyke of Zimbabwe has also been interpreted as rock crystallized from a primary magma. The interpretation of leucosomes of migmatites as primary magmas is contradicted by zircon data, which suggests leucosomes are

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1068-425: A rock type commonly enriched in incompatible elements. Bowen's reaction series is important for understanding the idealised sequence of fractional crystallisation of a magma. Magma composition can be determined by processes other than partial melting and fractional crystallization. For instance, magmas commonly interact with rocks they intrude, both by melting those rocks and by reacting with them. Assimilation near

1157-567: A solidified crust. Most basalt lavas are of ʻAʻā or pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas , which are rather similar to entrail-type pahoehoe lavas on land. Ultramafic magmas, such as picritic basalt, komatiite , and highly magnesian magmas that form boninite , take the composition and temperatures to the extreme. All have a silica content under 45%. Komatiites contain over 18% magnesium oxide, and are thought to have erupted at temperatures of 1,600 °C (2,910 °F). At this temperature there

1246-407: A subduction zone. When rocks melt, they do so over a range of temperature, because most rocks are made of several minerals , which all have different melting points. The temperature at which the first melt appears (the solidus) is lower than the melting temperature of any one of the pure minerals. This is similar to the lowering of the melting point of ice when it is mixed with salt. The first melt

1335-459: A surface area of 10,000 square kilometres (3,900 sq mi). In it smooth, low mountain ranges such as the Bolshoy Khapton , with average heights between 1,200 metres (3,900 ft) and 1,600 metres (5,200 ft), alternate with intermontane basins . The Vitim Plateau is covered by larch taiga and forest steppe , as well as thickets of shrubby birches , meadows, and swampy areas in

1424-515: A tendency towards alkaline compositions. The melts that give rise to Vitim Plateau magmas appear to originate in the lithospheric mantle , starting from garnet pyroxenite and peridotite and leaving phlogopite as residual phase when starting from pyroxenite. Petrology indicates that a complex magma production process takes place beneath the Vitim Plateau, including remelting and crystallization. Two volcanic phases have been identified in

1513-439: A tetrahedral arrangement around the much smaller silicon ion. This is called a silica tetrahedron . In a magma that is low in silicon, these silica tetrahedra are isolated, but as the silicon content increases, silica tetrahedra begin to partially polymerize, forming chains, sheets, and clumps of silica tetrahedra linked by bridging oxygen ions. These greatly increase the viscosity of the magma. The tendency towards polymerization

1602-638: A typical viscosity of 3.5 × 10 cP (3,500 Pa⋅s) at 1,200 °C (2,190 °F). This is slightly greater than the viscosity of smooth peanut butter . Intermediate magmas show a greater tendency to form phenocrysts . Higher iron and magnesium tends to manifest as a darker groundmass , including amphibole or pyroxene phenocrysts. Mafic or basaltic magmas have a silica content of 52% to 45%. They are typified by their high ferromagnesian content, and generally erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F). Viscosities can be relatively low, around 10 to 10 cP (10 to 100 Pa⋅s), although this

1691-633: A viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines , lava domes or "coulees" (which are thick, short lava flows). The lavas typically fragment as they extrude, producing block lava flows . These often contain obsidian . Felsic lavas can erupt at temperatures as low as 800 °C (1,470 °F). Unusually hot (>950 °C; >1,740 °F) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in

1780-409: Is added to the rock, the temperature remains at 1274 °C until either the anorthite or diopside is fully melted. The temperature then rises as the remaining mineral continues to melt, which shifts the melt composition away from the eutectic. For example, if the content of anorthite is greater than 43%, the entire supply of diopside will melt at 1274 °C., along with enough of the anorthite to keep

1869-518: Is based in Ulan-Ude. Ulan-Ude serves as the endpoint for the Mongol Rally . Ulan-Ude is twinned with: Magma Magma (from Ancient Greek μάγμα ( mágma )  'thick unguent ') is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as lava ) is found beneath the surface of

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1958-444: Is called the eutectic and has a composition that depends on the combination of minerals present. For example, a mixture of anorthite and diopside , which are two of the predominant minerals in basalt , begins to melt at about 1274 °C. This is well below the melting temperatures of 1392 °C for pure diopside and 1553 °C for pure anorthite. The resulting melt is composed of about 43 wt% anorthite. As additional heat

2047-410: Is concentrated in a thin layer in the toothpaste next to the tube, and only here does the toothpaste behave as a fluid. Thixotropic behavior also hinders crystals from settling out of the magma. Once the crystal content reaches about 60%, the magma ceases to behave like a fluid and begins to behave like a solid. Such a mixture of crystals with melted rock is sometimes described as crystal mush . Magma

2136-456: Is driven out of the oceanic lithosphere in subduction zones , and it causes melting in the overlying mantle. Hydrous magmas with the composition of basalt or andesite are produced directly and indirectly as results of dehydration during the subduction process. Such magmas, and those derived from them, build up island arcs such as those in the Pacific Ring of Fire . These magmas form rocks of

2225-417: Is expressed as NBO/T, where NBO is the number of non-bridging oxygen ions and T is the number of network-forming ions. Silicon is the main network-forming ion, but in magmas high in sodium, aluminium also acts as a network former, and ferric iron can act as a network former when other network formers are lacking. Most other metallic ions reduce the tendency to polymerize and are described as network modifiers. In

2314-417: Is magma extruded onto the surface, are almost all in the range 700 to 1,400 °C (1,300 to 2,600 °F), but very rare carbonatite magmas may be as cool as 490 °C (910 °F), and komatiite magmas may have been as hot as 1,600 °C (2,900 °F). Magma has occasionally been encountered during drilling in geothermal fields, including drilling in Hawaii that penetrated a dacitic magma body at

2403-647: Is melted before the heat supply is exhausted. Pegmatite may be produced by low degrees of partial melting of the crust. Some granite -composition magmas are eutectic (or cotectic) melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization . Most magmas are fully melted only for small parts of their histories. More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve. As magma cools, minerals typically crystallize from

2492-416: Is melted, the small globules of melt (generally occurring between mineral grains) link up and soften the rock. Under pressure within the earth, as little as a fraction of a percent of partial melting may be sufficient to cause melt to be squeezed from its source. Melt rapidly separates from its source rock once the degree of partial melting exceeds 30%. However, usually much less than 30% of a magma source rock

2581-615: Is practically no polymerization of the mineral compounds, creating a highly mobile liquid. Viscosities of komatiite magmas are thought to have been as low as 100 to 1000 cP (0.1 to 1 Pa⋅s), similar to that of light motor oil. Most ultramafic lavas are no younger than the Proterozoic , with a few ultramafic magmas known from the Phanerozoic in Central America that are attributed to a hot mantle plume . No modern komatiite lavas are known, as

2670-650: Is reported at Divizionnaya, within the Vagzhanovo microdistrict of Ulan Ude. The first occupants of the area where Ulan-Ude now stands were the Evenks and, later, the Buryat Mongols . Ulan-Ude was settled in 1666 by the Russian Cossacks as the fortress of Udinskoye. Due to its favorable geographical position, it grew rapidly and became a large trade center which connected Russia with China and Mongolia and, from 1690,

2759-448: Is still many orders of magnitude higher than water. This viscosity is similar to that of ketchup . Basalt lavas tend to produce low-profile shield volcanoes or flood basalts , because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath

Vitim Plateau - Misplaced Pages Continue

2848-622: Is the capital city of Buryatia , Russia , located about 100 kilometers (62 mi) southeast of Lake Baikal on the Uda River at its confluence with the Selenga . According to the 2021 Census , 437,565 people lived in Ulan-Ude; up from 404,426 recorded in the 2010 Census , making the city the third-largest in the Russian Far East by population. Ulan-Ude was first called Udinskoye ( Удинское , [ˈudʲɪnskəjə] ) for its location on

2937-514: Is the right inflow of the Selenga river. The length of the watercourse is 467 kilometers (290 miles). The largest known Russian military equipment storage base is located in Vagzhanovo, northwest of Ulan-Ude. Prior to the invasion of Ukraine in 2022 , approximately 3840 units of armored vehicles were stored there under open skies. Since the advent of the war, more than 40% of the units have been removed. A Central Tank Reserve Base, Military Unit 44286,

3026-474: Is traversed by two rivers, the Selenga and Uda. The Selenga provides the greatest inflow to Baikal Lake , supplying 50% of all rivers in its basin. The Selenga brings about 30 cubic kilometers (7 cubic miles) of water into the lake per year, exerting a major influence on the lakewater's renewal and its sanitary condition. Selenga is the habitat of the most valuable fish species such as Omul , Siberian sturgeon , Siberian taimen , Thymallus and Coregonus . Uda

3115-413: Is typically also viscoelastic , meaning it flows like a liquid under low stresses, but once the applied stress exceeds a critical value, the melt cannot dissipate the stress fast enough through relaxation alone, resulting in transient fracture propagation. Once stresses are reduced below the critical threshold, the melt viscously relaxes once more and heals the fracture. Temperatures of molten lava, which

3204-408: Is typically the most abundant magmatic gas, followed by carbon dioxide and sulfur dioxide . Other principal magmatic gases include hydrogen sulfide , hydrogen chloride , and hydrogen fluoride . The solubility of magmatic gases in magma depends on pressure, magma composition, and temperature. Magma that is extruded as lava is extremely dry, but magma at depth and under great pressure can contain

3293-506: The Earth , and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites . Besides molten rock, magma may also contain suspended crystals and gas bubbles . Magma is produced by melting of the mantle or the crust in various tectonic settings, which on Earth include subduction zones , continental rift zones , mid-ocean ridges and hotspots . Mantle and crustal melts migrate upwards through

3382-620: The Karenga River (both Vitim tributaries) and the latter's right tributary, the Bugarikta . The Vitim River begins at the confluence of the China and Vitimkan rivers on the plateau and makes a wide bend around the volcanic zone before flowing northwards. Rivers Tsipa , Tsipikan and Amalat cut across the plateau and the Baunt Depression is located in the northwestern corner. The plateau has

3471-666: The Snake River Plain of the northwestern United States. Intermediate or andesitic magmas contain 52% to 63% silica, and are lower in aluminium and usually somewhat richer in magnesium and iron than felsic magmas. Intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes , such as in the Andes . They are also commonly hotter, in the range of 850 to 1,100 °C (1,560 to 2,010 °F)). Because of their lower silica content and higher eruptive temperatures, they tend to be much less viscous, with

3560-417: The Uda River . It was founded as a small fort in 1666. From around 1735, the settlement was called Udinsk ( Удинск , [ʊˈdʲinsk] ) and was granted town status under that name in 1775. It was renamed Verkhneudinsk ( Верхнеудинск , [vʲɪrxnʲɪˈudʲɪnsk] ; "Upper Udinsk") in 1783, to differentiate it from Nizhneudinsk ("Lower Udinsk") lying on a different Uda River near Irkutsk which

3649-458: The calc-alkaline series, an important part of the continental crust . With low density and viscosity, hydrous magmas are highly buoyant and will move upwards in Earth's mantle. The addition of carbon dioxide is relatively a much less important cause of magma formation than the addition of water, but genesis of some silica-undersaturated magmas has been attributed to the dominance of carbon dioxide over water in their mantle source regions. In

Vitim Plateau - Misplaced Pages Continue

3738-529: The city of republic significance of Ulan-Ude — an administrative unit with the status equal to that of the districts . As a municipal division , the city of Ulan-Ude is incorporated as Ulan-Ude Urban Okrug. According to the 2021 Census , 437,565 people lived in Ulan-Ude; up from 404,426 recorded in the 2010 Census . In terms of population, it is the third-largest city in eastern Siberia . It ranks 45th among all cities in Russia . Roughly 600,000 people live in

3827-453: The convection of solid mantle, it will cool slightly as it expands in an adiabatic process , but the cooling is only about 0.3 °C per kilometer. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3 °C to 4 °C per kilometer. If the rock rises far enough, it will begin to melt. Melt droplets can coalesce into larger volumes and be intruded upwards. This process of melting from

3916-687: The ideology of the Communist Party of the Soviet Union . Ulan-Ude lies 5,640 kilometers (3,500 mi) east of Moscow and 100 kilometers (62 mi) southeast of Lake Baikal . It is 600 meters (2,000 ft) above sea level at the foot of the Khamar-Daban and Ulan-Burgas mountain ranges, next to the confluence of the Selenga River and its tributary , the Uda , which divides the city. Ulan-Ude

4005-563: The Buryat, was the first stone building in the city and is a Siberian baroque architectural monument. The cathedral is considered unique because it is built in a zone of high seismic activity in the heart of the city on the banks of the River Uda River where it flows into the Selenga. One of the attractions of Ulan-Ude is a monument in the town square — the square of the Soviets ;— in

4094-472: The Earth's mantle has cooled too much to produce highly magnesian magmas. Some silicic magmas have an elevated content of alkali metal oxides (sodium and potassium), particularly in regions of continental rifting , areas overlying deeply subducted plates , or at intraplate hotspots . Their silica content can range from ultramafic ( nephelinites , basanites and tephrites ) to felsic ( trachytes ). They are more likely to be generated at greater depths in

4183-465: The Earth's upper crust, but this varies widely by region, from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km along mid-ocean ridges or near mantle plumes . The gradient becomes less steep with depth, dropping to just 0.25 to 0.3 °C/km in the mantle, where slow convection efficiently transports heat. The average geothermal gradient is not normally steep enough to bring rocks to their melting point anywhere in

4272-674: The M55 section of the Baikal Highway (part of the Trans-Siberian Highway ), the main federal road to Vladivostok . Air traffic is served by the Ulan-Ude Airport (Baikal), as well as the smaller Ulan-Ude Vostochny Airport . Intracity transport includes tram , bus , and marshrutka ( share taxi ) lines. Until 1991, Ulan-Ude was closed to foreigners . There are old merchants' mansions richly decorated with wood and stone carving in

4361-684: The Vitim Plateau. The first took place during the Miocene ; potassium-argon dating has yielded ages of 10.65 - 6.6 million years ago. The second occurred during the Pleistocene with the most recent eruption dated 810,000 years ago. Later volcanic activity was concentrated in river valleys and cones on the surface of the plateau. Ulan-Ude Ulan-Ude ( / ʊ ˈ l ɑː n ʊ ˈ d ɛ / ; Russian : Улан-Удэ , Russian pronunciation: [ʊˈlan ʊˈdɛ] ; Buryat : Улаан-Үдэ , romanized:  Ulaan-Üde , IPA [ʊˌlaːɴ‿ˈʉdə] )

4450-476: The anorthite is melted. If the anorthite content of the mixture is less than 43%, then all the anorthite will melt at the eutectic temperature, along with part of the diopside, and the remaining diopside will then gradually melt as the temperature continues to rise. Because of eutectic melting, the composition of the melt can be quite different from the source rock. For example, a mixture of 10% anorthite with diopside could experience about 23% partial melting before

4539-458: The crust or upper mantle, so magma is produced only where the geothermal gradient is unusually steep or the melting point of the rock is unusually low. However, the ascent of magma towards the surface in such settings is the most important process for transporting heat through the crust of the Earth. Rocks may melt in response to a decrease in pressure, to a change in composition (such as an addition of water), to an increase in temperature, or to

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4628-432: The crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During magma's storage in the crust, its composition may be modified by fractional crystallization , contamination with crustal melts, magma mixing, and degassing. Following its ascent through the crust, magma may feed a volcano and be extruded as lava, or it may solidify underground to form an intrusion , such as

4717-455: The crystallization process would not change the overall composition of the melt plus solid minerals. This situation is described as equillibrium crystallization . However, in a series of experiments culminating in his 1915 paper, Crystallization-differentiation in silicate liquids , Norman L. Bowen demonstrated that crystals of olivine and diopside that crystallized out of a cooling melt of forsterite , diopside, and silica would sink through

4806-399: The eutectic temperature of 1274 °C. This shifts the remaining melt towards its eutectic composition of 43% diopside. The eutectic is reached at 1274 °C, the temperature at which diopside and anorthite begin crystallizing together. If the melt was 90% diopside, the diopside would begin crystallizing first until the eutectic was reached. If the crystals remained suspended in the melt,

4895-512: The extensive basalt magmatism of several large igneous provinces. Decompression melting occurs because of a decrease in pressure. It is the most important mechanism for producing magma from the upper mantle. The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. Peridotite at depth in the Earth's mantle may be hotter than its solidus temperature at some shallower level. If such rock rises during

4984-407: The form of the head of Lenin (sculptors G.V. Neroda, J.G. Neroda, architects Dushkin, P.G. Zilberman). The monument, weighing 42 tons and with a height of 7.7 meters (25 ft), was opened in 1971 in honor of the centenary of Lenin's birth. Ulan-Ude can be described as possessing a humid steppe climate ( Köppen climate classification BSk ), bordering on a humid continental climate ( Dwb ) and

5073-442: The historical center of Ulan-Ude, along the river banks which are exceptional examples of Russian classicism. The city has a large ethnographic museum which recalls the history of the peoples of the region. There is a large and highly unusual statue of the head of Vladimir Lenin in the central square: the largest in the world. Built in 1970 for the centennial of Lenin's birth and weighing 42 tons, as of 2018 it continued to tower over

5162-420: The importance of each mechanism being a topic of continuing research. The change of rock composition most responsible for the creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800 °C in the presence of excess water, but near 1,500 °C in the absence of water. Water

5251-476: The magma completely solidifies, and the liquidus , defined as the temperature at which the magma is completely liquid. Calculations of solidus temperatures at likely depths suggests that magma generated beneath areas of rifting starts at a temperature of about 1,300 to 1,500 °C (2,400 to 2,700 °F). Magma generated from mantle plumes may be as hot as 1,600 °C (2,900 °F). The temperature of magma generated in subduction zones, where water vapor lowers

5340-408: The magma. Gabbro may have a liquidus temperature near 1,200 °C, and the derivative granite-composition melt may have a liquidus temperature as low as about 700 °C. Incompatible elements are concentrated in the last residues of magma during fractional crystallization and in the first melts produced during partial melting: either process can form the magma that crystallizes to pegmatite ,

5429-528: The main plaza at 7.7 meters (25 ft). The Ethnographic Museum of the peoples of Transbaikal is one of Russia's largest open-air museums. The museum contains historical finds from the era of the Slab Grave Culture and the Xiongnu until the mid 20th century, including a unique collection of samples of wooden architecture of Siberia . Odigitrievsky Cathedral – Eastern Orthodox Church Diocese of

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5518-419: The mantle than subalkaline magmas. Olivine nephelinite magmas are both ultramafic and highly alkaline, and are thought to have come from much deeper in the mantle of the Earth than other magmas. Tholeiitic basalt magma Rhyolite magma Some lavas of unusual composition have erupted onto the surface of the Earth. These include: The concentrations of different gases can vary considerably. Water vapor

5607-424: The melt at different temperatures. This resembles the original melting process in reverse. However, because the melt has usually separated from its original source rock and moved to a shallower depth, the reverse process of crystallization is not precisely identical. For example, if a melt was 50% each of diopside and anorthite, then anorthite would begin crystallizing from the melt at a temperature somewhat higher than

5696-438: The melt at the eutectic composition. Further heating causes the temperature to slowly rise as the remaining anorthite gradually melts and the melt becomes increasingly rich in anorthite liquid. If the mixture has only a slight excess of anorthite, this will melt before the temperature rises much above 1274 °C. If the mixture is almost all anorthite, the temperature will reach nearly the melting point of pure anorthite before all

5785-449: The melt deviated from the eutectic, which has the composition of about 43% anorthite. This effect of partial melting is reflected in the compositions of different magmas. A low degree of partial melting of the upper mantle (2% to 4%) can produce highly alkaline magmas such as melilitites , while a greater degree of partial melting (8% to 11%) can produce alkali olivine basalt. Oceanic magmas likely result from partial melting of 3% to 15% of

5874-402: The melt on geologically relevant time scales. Geologists subsequently found considerable field evidence of such fractional crystallization . When crystals separate from a magma, then the residual magma will differ in composition from the parent magma. For instance, a magma of gabbroic composition can produce a residual melt of granitic composition if early formed crystals are separated from

5963-429: The melting temperature, may be as low as 1,060 °C (1,940 °F). Magma densities depend mostly on composition, iron content being the most important parameter. Magma expands slightly at lower pressure or higher temperature. When magma approaches the surface, its dissolved gases begin to bubble out of the liquid. These bubbles had significantly reduced the density of the magma at depth and helped drive it toward

6052-481: The more abundant elements in the source rock. The ions of these elements fit rather poorly in the structure of the minerals making up the source rock, and readily leave the solid minerals to become highly concentrated in melts produced by a low degree of partial melting. Incompatible elements commonly include potassium , barium , caesium , and rubidium , which are large and weakly charged (the large-ion lithophile elements, or LILEs), as well as elements whose ions carry

6141-415: The most abundant chemical elements in the Earth's crust, with smaller quantities of aluminium , calcium , magnesium , iron , sodium , and potassium , and minor amounts of many other elements. Petrologists routinely express the composition of a silicate magma in terms of the weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the magma. Because many of

6230-545: The neighbourhood of the rift zone, and this volcanism has produced about 5,000 cubic kilometres (1,200 cu mi) of volcanic rock in several volcanic fields, including the Udokan Plateau and the Vitim Plateau which are the largest volcanic fields of the Baikal Rift. The reasons for the rifting process aren't well known. One theory holds that the collision between India and Asia and other tectonic processes triggered

6319-439: The presence of carbon dioxide, experiments document that the peridotite solidus temperature decreases by about 200 °C in a narrow pressure interval at pressures corresponding to a depth of about 70 km. At greater depths, carbon dioxide can have more effect: at depths to about 200 km, the temperatures of initial melting of a carbonated peridotite composition were determined to be 450 °C to 600 °C lower than for

6408-630: The properties of a magma (such as its viscosity and temperature) are observed to correlate with silica content, silicate magmas are divided into four chemical types based on silica content: felsic , intermediate , mafic , and ultramafic . Felsic or silicic magmas have a silica content greater than 63%. They include rhyolite and dacite magmas. With such a high silica content, these magmas are extremely viscous, ranging from 10 cP (10 Pa⋅s) for hot rhyolite magma at 1,200 °C (2,190 °F) to 10 cP (10 Pa⋅s) for cool rhyolite magma at 800 °C (1,470 °F). For comparison, water has

6497-618: The pull-apart in the Baikal Rift. Another one postulates the existence of thermal anomalies such as a mantle plume beneath the Baikal Rift as the driving force of the rifting. The basement beneath the Baikal Rift is granitic and up to 20 kilometres (12 mi) thick. It may be of Paleozoic age. Other rocks in the region are sediments close to river valleys and Mesozoic volcanic rocks. Vitim Plateau volcanic rocks are mainly alkaline to subalkaline basalts , nephelinites and melanephelinites , with phenocryst phases containing clinopyroxene , olivine and plagioclase . Younger rocks have

6586-411: The rate of flow is proportional to the shear stress . Instead, a typical magma is a Bingham fluid , which shows considerable resistance to flow until a stress threshold, called the yield stress, is crossed. This results in plug flow of partially crystalline magma. A familiar example of plug flow is toothpaste squeezed out of a toothpaste tube. The toothpaste comes out as a semisolid plug, because shear

6675-451: The river basins. The volcanic field in its southwestern part has an area of 4,500 square kilometres (1,700 sq mi). There are a number of lakes, such as Baunt , Busani , Kapylyushi , Telemba , Arakhley , Bolshoy and Maly Yeravna . The area is marked by permafrost . About five circular groups of volcanoes occur in the field, which is in turn subdivided into two major provinces. Both central volcanoes and cinder cones occur in

6764-405: The roof of a magma chamber and fractional crystallization near its base can even take place simultaneously. Magmas of different compositions can mix with one another. In rare cases, melts can separate into two immiscible melts of contrasting compositions. When rock melts, the liquid is a primary magma . Primary magmas have not undergone any differentiation and represent the starting composition of

6853-405: The same composition with no carbon dioxide. Magmas of rock types such as nephelinite , carbonatite , and kimberlite are among those that may be generated following an influx of carbon dioxide into mantle at depths greater than about 70 km. Increase in temperature is the most typical mechanism for formation of magma within continental crust. Such temperature increases can occur because of

6942-442: The same lavas ranges over seven orders of magnitude, from 10 cP (10 Pa⋅s) for mafic lava to 10 cP (10 Pa⋅s) for felsic magmas. The viscosity is mostly determined by composition but is also dependent on temperature. The tendency of felsic lava to be cooler than mafic lava increases the viscosity difference. The silicon ion is small and highly charged, and so it has a strong tendency to coordinate with four oxygen ions, which form

7031-404: The source rock. Some calk-alkaline granitoids may be produced by a high degree of partial melting, as much as 15% to 30%. High-magnesium magmas, such as komatiite and picrite , may also be the products of a high degree of partial melting of mantle rock. Certain chemical elements, called incompatible elements , have a combination of ionic radius and ionic charge that is unlike that of

7120-468: The surface and the overburden pressure drops, dissolved gases bubble out of the liquid, so that magma near the surface consists of materials in solid, liquid, and gas phases . Most magma is rich in silica . Rare nonsilicate magma can form by local melting of nonsilicate mineral deposits or by separation of a magma into separate immiscible silicate and nonsilicate liquid phases. Silicate magmas are molten mixtures dominated by oxygen and silicon ,

7209-401: The surface in the first place. The temperature within the interior of the earth is described by the geothermal gradient , which is the rate of temperature change with depth. The geothermal gradient is established by the balance between heating through radioactive decay in the Earth's interior and heat loss from the surface of the earth. The geothermal gradient averages about 25 °C/km in

7298-613: The upward intrusion of magma from the mantle. Temperatures can also exceed the solidus of a crustal rock in continental crust thickened by compression at a plate boundary . The plate boundary between the Indian and Asian continental masses provides a well-studied example, as the Tibetan Plateau just north of the boundary has crust about 80 kilometers thick, roughly twice the thickness of normal continental crust. Studies of electrical resistivity deduced from magnetotelluric data have detected

7387-462: The upward movement of solid mantle is critical in the evolution of the Earth. Decompression melting creates the ocean crust at mid-ocean ridges , making it by far the most important source of magma on Earth. It also causes volcanism in intraplate regions, such as Europe, Africa and the Pacific sea floor. Intraplate volcanism is attributed to the rise of mantle plumes or to intraplate extension, with

7476-715: The urban agglomeration. The ethnic makeup of Ulan-Ude in 2021 was: The city is the center of Tibetan Buddhism in Russia and the important Ivolginsky datsan is located 23 km (14 mi) from the city. Ulan-Ude is located on the main line (Trans-Siberian line) of the Trans-Siberian Railway between Irkutsk and Chita at the junction of the Trans-Mongolian line (the Trans-Mongolian Railway ) which begins at Ulan Ude and continues south through Mongolia to Beijing in China. The city also lies on

7565-467: The viscosity. Higher-temperature melts are less viscous, since more thermal energy is available to break bonds between oxygen and network formers. Most magmas contain solid crystals of various minerals, fragments of exotic rocks known as xenoliths and fragments of previously solidified magma. The crystal content of most magmas gives them thixotropic and shear thinning properties. In other words, most magmas do not behave like Newtonian fluids, in which

7654-682: The volcanic field, with the largest volcanoes reaching heights of 150 metres (490 ft) and diameters of 1.5 kilometres (0.93 mi). Since the Oligocene and especially the Pliocene , the Asian Plate has been rifting apart in the Baikal Rift where the Siberian craton and a Paleozoic assembly of terranes (ancient microcontinents) form a contact zone. This rifting process is associated with volcanism in

7743-454: Was granted town status that year. The descriptors "upper" and "lower" refer to the positions of the two cities relative to each other, rather than the location of the cities on their respective Uda rivers. Verkhneudinsk lies at the mouth of its river, while Nizhneudinsk is along the middle stretch. The current name was given to the city on 27 July 1934 and means " red Uda " in Buryat , reflecting

7832-481: Was the administrative center of the Transbaikal region. By 1775, it was known as Udinsk, and in 1783 it was granted city status and renamed Verkhneudinsk. After a large fire in 1878, the city was almost completely rebuilt. The Trans-Siberian Railway reached the city in 1900 causing an explosion in growth. The population, which was 3,500 in 1880, reached 126,000 in 1939. From 6 April to October 1920, Verkhneudinsk

7921-589: Was the capital of the Far Eastern Republic (Дальневосточная Республика) , also known as the Chita Republic. It was a nominally independent state that existed from April 1920 to November 1922 in the easternmost part of the Russian Far East. On 27 July 1934, the city was renamed Ulan-Ude. Ulan-Ude is the capital of the republic. Within the framework of administrative divisions , it is incorporated as

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