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23-660: The basalt samples at Paraná and Etendeka have an age of about 132 Ma, during the Valanginian stage of the Early Cretaceous . Indirectly, the rifting and extension are probably the origin of the Paraná and Etendeka traps and it could be the origin of the Gough and Tristan da Cunha Islands as well, as they are connected by the Walvis Ridge (Gough/ Tristan hotspot ). The seamounts of

46-475: A volcanic eruption ; consequently, many volcanoes are situated over magma chambers. These chambers are hard to detect deep within the Earth, and therefore most of those known are close to the surface, commonly between 1 km and 10 km down. Magma rises through cracks from beneath and across the crust because it is less dense than the surrounding rock. When the magma cannot find a path upwards it pools into

69-407: A magma chamber may result in an increase in the amount of gas within the magma near the top of the chamber, and also make this magma more viscous, potentially leading to a more explosive eruption than would be the case had the chamber not become stratified. Supervolcano eruptions are possible only when an extraordinarily large magma chamber forms at a relatively shallow level in the crust. However,

92-406: A magma chamber. These chambers are commonly built up over time, by successive horizontal or vertical magma injections. The influx of new magma causes reaction of pre-existing crystals and the pressure in the chamber to increase. The residing magma starts to cool, with the higher melting point components such as olivine crystallizing out of the solution, particularly near to the cooler walls of

115-593: A product of multiple eruptions. Moreover, units of each province are not the exact correlatives of the same eruptive event but may share the same magmatic system . In contrast, Chapecó and Palmas volcanics in Paraná are not unambiguously identified as the eastward extensions of ash-flows. Most studies have characterized Chapecó and Palmas as stacks of local lava flows and lava domes produced by effusive eruptions , and were emitted from nearby silicic conduits and feeder dikes . The extremely large volume estimations and explosive style of them, therefore, are questioned. On

138-602: A small town north of Neuchâtel in the Jura Mountains of Switzerland . The base of the Valanginian is at the first appearance of calpionellid species Calpionellites darderi in the stratigraphic column. A global reference section (a GSSP ) had in 2009 not yet been appointed. The top of the Valanginian (the base of the Hauterivian) is at the first appearance of the ammonite genus Acanthodiscus . The Valanginian

161-415: A volcano may have a deep magma chamber many kilometers down, which supplies a shallower chamber near the summit. The location of magma chambers can be mapped using seismology : seismic waves from earthquakes move more slowly through liquid rock than solid, allowing measurements to pinpoint the regions of slow movement which identify magma chambers. As a volcano erupts, surrounding rock will collapse into

184-407: Is a stub . You can help Misplaced Pages by expanding it . Magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma , in such a chamber is less dense than the surrounding country rock , which produces buoyant forces on the magma that tend to drive it upwards. If the magma finds a path to the surface, then the result will be

207-870: Is composed of eight members: Fria, Beacon, Grootberg, Wereldsend, Hoanib, Springbok, Goboboseb, and Terrace. In particular, Goboboseb consists of four eruptive units, labeled Goboboseb-I to -IV. On the basis of trans-Atlantic chemostratigraphy , the low-Ti suite in Etendeka is equivalent to Palmas volcanics in Paraná, and the high-Ti suite is equivalent to Chapecó volcanics. At a finer scale, geochemical affinities have made tentative correlations in these pairs: PAV-G of Anita Garibaldi and Beacon, PAV-B of Caxias do Sul and Springbok, PAV-A of Jacuí and Goboboseb-II, Guarapuava and Ventura, Ourinhos and Khoraseb, BRA-21 and Wereldsend, PAV-F of Caxias do Sul and Grootberg. Sarusas may correlate either to Guarapuava or Tamarana, and Fria may correlate either to Santa Maria or Clevelândia. In Etendeka,

230-448: Is composed of the three geochemical subtypes Ourinhos, Tamarana and Guarapuav. Eight major eruptive units, labeled PAV-A to -G and BRA-21, are recognized within Palmas volcanics. In Etendeka, individual eruptive units of quartz latite are grouped into high- Ti and low-Ti suites . The high-Ti suit is composed of six members : Naudé, Sarusas, Elliott, Khoraseb, and Ventura. The low-Ti suite

253-596: Is often subdivided in Lower and Upper substages. The Upper substage begins at the first appearance of ammonite species Saynoceras verrucosum and the major marine transgression Va3. In the Tethys domain , the Valanginian stage contains five ammonite biozones : The oldest fossils that can definitely be attributed to the clade Angiospermae (flowering plants) are dated to the Late Valanginian. This geochronology article

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276-456: The Rio Grande Rise (25°S to 35°S) that go eastwards from the Paraná side are part of this traps system. Interpretations of geochemistry, including isotopes , have led geologists to conclude that the magmas forming the traps and associated igneous rocks originated by melting of asthenosphic mantle due to the arrival of a mantle plume to the base of Earth's lithosphere . Then much of

299-646: The geologic timescale , the Valanginian is an age or stage of the Early or Lower Cretaceous . It spans between 139.8 ± 3.0 Ma and 132.6 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretaceous and precedes the Hauterivian Stage of the Lower Cretaceous. The Valanginian was first described and named by Édouard Desor in 1853. It is named after Valangin ,

322-406: The largest known explosive eruptions on Earth. Notably, the largest Guarapuava-Tamarana/Sarusas is estimated to have a volume of 8,600 km (2,100 cubic miles), which dwarfs other extremely large eruptions such as 30 million year old Wah Wah Springs and 28 million year old Fish Canyon Tuff . This interpretation, however, is disputed. Sarusas member is known to consist of 10 eruptive units hence

345-437: The chamber, and forming a denser conglomerate of minerals which sinks (cumulative rock). Upon cooling, new mineral phases saturate and the rock type changes (e.g. fractional crystallization ), typically forming (1) gabbro , diorite , tonalite and granite or (2) gabbro , diorite , syenite and granite . If magma resides in a chamber for a long period, then it can become stratified with lower density components rising to

368-452: The chamber. Another effect of the cooling of the chamber is that the solidifying crystals will release the gas (primarily steam ) previously dissolved when they were liquid, causing the pressure in the chamber to rise, possibly sufficiently to produce an eruption. Additionally, the removal of the lower melting point components will tend to make the magma more viscous (by increasing the concentration of silicates ). Thus, stratification of

391-420: The eruptions has been recognized. A 18 km (11 miles) diameter, circular structure, called Messum igneous complex , is identified to be the eruptive centre for Goboboseb-I to -IV and Springbok. It was postulated that Chapecó and Palmas volcanics in Paraná are the eastward extensions of Etendeka ash-flows, so each correlation represents a huge ignimbrite eruption. The volumes of these eruptions would make them

414-485: The magma was contaminated with crustal materials prior to their eruption. Some plutonic rocks related to the traps escaped crustal contamination reflecting more directly the source of the magmas in the mantle. In Paraná, the silicic rocks are divided into two compositional groups, the Palmas volcanics and Chapecó volcanics. Palmas is recognized as composed of the five geochemical subtypes Santa Maria, Caxias do Sul, Anita Garibaldi, Clevelândia and Jacuí, while Chapecó

437-467: The maximum attainable overpressure on the chamber roof, and a large magma chamber with warm walls, which has a high effective viscoelasticity , may suppress rhyolite dike formation and allow such large chambers to fill with magma. If the magma is not vented to the surface in a volcanic eruption, it will slowly cool and crystallize at depth to form an intrusive igneous body, one, for example, composed of granite or gabbro (see also pluton ). Often,

460-529: The other hand, a study has found pyroclastic -like textures in Chapecó and Palmas volcanics that are indicative of explosive eruptions. Guarapuava and Clevelândia subtypes are interpreted to be entirely of ignimbrites, while Jacuí, Anita Garibaldi, Caxias do Sul, and Santa Maria are multiple ignimbrite units intercalated with lava domes. These ignimbrites were characterzied by low-explosivity, high eruptive mass-flux, and low-column fountains . Valanginian In

483-458: The quartz latite units are interpreted to be rheomorphic ignimbrites , which are emplaced by explosive eruptions of high-temperature ash-flows . Each eruption produced voluminous and widespread pyroclastic sheet with thickness between 40–300 m (130–980 feet). Individual unit, within Etendeka, has a volume between 400–2,600 km (96–624 cubic miles) and covers an area up to 8,800 km (3,400 square miles). No air-fall layer associated with

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506-400: The rate of magma production in tectonic settings that produce supervolcanoes is quite low, around 0.002 km year , so that accumulation of sufficient magma for a supereruption takes 10 to 10 years. This raises the question of why the buoyant silicic magma does not break through to the surface more frequently in relatively small eruptions. The combination of regional extension, which lowers

529-412: The top and denser materials sinking. Rocks accumulate in layers, forming a layered intrusion . Any subsequent eruption may produce distinctly layered deposits; for example, the deposits from the 79 AD eruption of Mount Vesuvius include a thick layer of white pumice from the upper portion of the magma chamber overlaid with a similar layer of grey pumice produced from material erupted later from lower in

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