Paraná and Etendeka traps

The Paraná-Etendeka traps (or Paraná and Etendeka Plateau; or Paraná and Etendeka Province) comprise a large igneous province that includes both the main Paraná traps (in Paraná Basin, a South American geological basin) as well as the smaller severed portions of the flood basalts at the Etendeka traps (in northwest Namibia and southwest Angola). The original basalt flows occurred 128 to 138 million years ago. The province had a post-flow surface area of 1.5 x 106 km² (580,000 miles²) and an original volume projected to be in excess of 2.3 x 106 km³.[1][2]

Parana traps
A cliff at the Paraná Magmatic Province. Rio do Rastro, Santa Catarina. One can see the near vertical escarpment of silicic succession from waning-stage volcanism.
World geologic provinces
The Paraná and Etendeka Traps shown as dark purple spot on the geologic map of South America

Geodynamics

The basalt samples at Paraná and Etendeka have an age of about 132 Ma, during the Valanginian stage of the Early Cretaceous.[3] 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 the Rio Grande Rise (25°S to 35°S) that go eastwards from the Paraná side[4][5] are part of this traps system.[6]

Description

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 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.[7]

A type of rock called ignimbrite is found in some parts of the traps indicating explosive volcanic activity. The Paraná Traps possibly contains the site of the single largest explosive volcanic eruption known in Earth's history.[8]

See also

References

  1. ^ Courtillot, Vincent E.; Renneb, Paul R. (January 2003). "Sur l'âge des trapps basaltiques (On the ages of flood basalt events)". Comptes Rendus Geoscience. 335 (1): 113–140. Bibcode:2003CRGeo.335..113C. CiteSeerX 10.1.1.461.3338. doi:10.1016/S1631-0713(03)00006-3.
  2. ^ Fodor, R.V.; McKee, E.H.; Roisenberg, A. (1989). "Age distribution of Serra Geral (Paraná) flood basalts, southern Brazil". Journal of South American Earth Sciences. 2 (4): 343–349. Bibcode:1989JSAES...2..343F. doi:10.1016/0895-9811(89)90012-6.
  3. ^ Stewart, Kathy; Turner, Simon; Kelley, Simon; Hawkesworth, Chris; Kirstein, Linda; Mantovani, Marta (1996). "3-D, 40Ar-39Ar geochronology in the Paraná continental flood basalt province". Earth and Planetary Science Letters. 143 (1–4): 95–109. Bibcode:1996E&PSL.143...95S. doi:10.1016/0012-821X(96)00132-X.
  4. ^ O'Neill, C.; Müller, R. D.; Steinberger, B. (2003). "Revised Indian plate rotations based on the motion of Indian Ocean hotspots" (PDF). Earth and Planetary Science Letters. 215 (1–2): 151–168. Bibcode:2003E&PSL.215..151O. CiteSeerX 10.1.1.716.4910. doi:10.1016/S0012-821X(03)00368-6. Archived from the original (PDF) on 2011-07-26.
  5. ^ O'Connor, J. M.; le Roex, A. P. (1992). "South Atlantic hot spot-plume systems. 1: Distribution of volcanism in time and space". Earth and Planetary Science Letters. 113 (3): 343–364. Bibcode:1992E&PSL.113..343O. doi:10.1016/0012-821X(92)90138-L.
  6. ^ Brazilian 'Atlantis' found - Geologists have announced the discovery of what has been dubbed the 'Brazilian Atlantis', some 900 miles from Rio., Donna Bowater, The Daily Telegraph, 7 May 2013
  7. ^ Owen-Smith, T.M.; Ashwal, L.D.; Sudo, M.; Trumbull, R.B. (2017). "Age and Petrogenesis of the Doros Complex, Namibia, and Implications for Early Plume-derived Melts in the Paraná–Etendeka LIP". Journal of Petrology. 58 (3): 423–442. Bibcode:2017JPet...58..423O. doi:10.1093/petrology/egx021.
  8. ^ Scott E. Bryan; Ingrid Ukstins Peate; David W. Peate; Stephen Self; Dougal A. Jerram; Michael R. Mawby; J.S. Marsh; Jodie A. Miller (2010). "The largest volcanic eruptions on Earth". Earth-Science Reviews. 102 (3–4): 207–229. Bibcode:2010ESRv..102..207B. doi:10.1016/j.earscirev.2010.07.001.

Further reading

  • Peate DW (1997). "The Parana-Etendeka Province" (PDF). In Mahoney JJ, Coffin MF (eds.). Large Igneous Provinces: continental, oceanic, and planetary flood volcanism. Geophysical Monograph. 100. Washington, DC: American Geophysical Union. pp. 217–245.

External links

Basalt

Basalt (US: , UK: ) is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows.

Campos Basin

The Campos Basin is one of 12 coastal sedimentary basins of Brazil. It spans both onshore and offshore parts of the South Atlantic with the onshore part located near Rio de Janeiro. The basin originated in Neocomian stage of the Cretaceous period 145–130 million years ago during the breakup of Gondwana. It has a total area of about 115,000 square kilometres (44,000 sq mi), with the onshore portion small at only 500 square kilometres (190 sq mi).

Dike swarm

A dike swarm or dyke swarm is a large geological structure consisting of a major group of parallel, linear, or radially oriented dikes intruded within continental crust. They consist of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event, and are magmatic and stratigraphic. Such dike swarms may form a large igneous province and are the roots of a volcanic province.

The occurrence of mafic dike swarms in Archean and Paleoproterozoic terrains is often cited as evidence for mantle plume activity associated with abnormally high mantle potential temperatures.

Dike swarms may extend over 400 km (250 mi) in width and length. The largest dike swarm known on Earth is the Mackenzie dike swarm in the western half of the Canadian Shield in Canada, which is more than 500 km (310 mi) wide and 3,000 km (1,900 mi) long.The number of known giant dike swarms on Earth is small, only about 25. However, the primary geometry of most giant dike swarms is poorly known due to their age and subsequent tectonic activity.

Dike swarms have also been found on Venus and Mars.

Flood basalt

A flood basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Flood basalt provinces such as the Deccan Traps of India are often called traps, after the Swedish word trappa (meaning "stairs"), due to the characteristic stairstep geomorphology of many associated landscapes. Michael R. Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in the past 250 million years, creating large volcanic provinces, lava plateaus, and mountain ranges. However, more have been recognized such as the large Ontong Java Plateau, and the Chilcotin Group, though the latter may be linked to the Columbia River Basalt Group. Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts.

Hotspot (geology)

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.

Large igneous province

A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics. The formation of some of the LIPs the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about the causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.

List of largest volcanic eruptions

In a volcanic eruption, lava, volcanic bombs and ash, and various gases are expelled from a volcanic vent and fissure. While many eruptions only pose dangers to the immediately surrounding area, Earth's largest eruptions can have a major regional or even global impact, with some affecting the climate and contributing to mass extinctions. Volcanic eruptions can generally be characterized as either explosive eruptions, sudden ejections of rock and ash, or effusive eruptions, relatively gentle outpourings of lava. A separate list is given below for each type.

There have probably been many such eruptions during Earth's history beyond those shown in these lists. However erosion and plate tectonics have taken their toll, and many eruptions have not left enough evidence for geologists to establish their size. Even for the eruptions listed here, estimates of the volume erupted can be subject to considerable uncertainty.

Mantle plume

A mantle plume is a proposed mechanism of convection of abnormally hot rock within the Earth's mantle. Because the plume head partly melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and large igneous provinces such as the Deccan and Siberian traps. Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large-volume volcanism near plate boundaries or in large igneous provinces.

The hypothesis of mantle plumes from depth is not universally accepted as explaining all such volcanism. It has required progressive hypothesis-elaboration leading to variant propositions such as mini-plumes and pulsing plumes. Another hypothesis for unusual volcanic regions is the "Plate model". This proposes shallower, passive leakage of magma from the mantle onto the Earth's surface where extension of the lithosphere permits it, attributing most volcanism to plate tectonic processes, with volcanoes far from plate boundaries resulting from intraplate extension.

Paraná Basin

The Paraná Basin (Portuguese: Bacia do Paraná, Spanish: Cuenca Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande do Sul states. The remainder area is distributed in eastern Paraguay, northeastern Argentina and northern Uruguay. The shape of the depression is roughly elliptical and covers an area of about 1,500,000 km2 (580,000 sq mi).

The Paraná River, from which the Paraná Basin derived its name, flows along the central axis of the Paraná Basin and drains it.

Pelotas Basin

The Pelotas Basin (Portuguese: Bacia de Pelotas, Spanish: Cuenca de Pelotas) is a mostly offshore sedimentary basin of approximately 346,000 square kilometres (134,000 sq mi) in the South Atlantic, administratively part of the southern states Santa Catarina and Rio Grande do Sul of Brazil and the departments Cerro Largo, Rocha and Treinta y Tres of Uruguay.

The Pelotas Basin is one of the basins that formed on the present-day South Atlantic margins of South America and Africa due to the break-up of Gondwana in the Early Cretaceous. The sedimentary succession started as the other Brazilian marginal basins with a series of basalts, younger than the Paraná and Etendeka traps exposed in the Paraná Basin to the west, followed by shallow to deeper marine carbonate and clastic sediments. Other than the northern neighbours Santos and Campos Basins, the Pelotas Basin lacks a thick layer of salt and the pre-salt layer pinches out just in the north of the Pelotas Basin stratigraphy.

Within the Brazilian Atlantic margin, the Pelotas Basin is relatively underexplored. Twenty exploration wells have been drilled in the Brazilian portion of the basin with one ultra deepwater exploration well drilled on the Uruguayan side in 2016. No hydrocarbon accumulations have been proven in the basin thus far.

Santos Basin

The Santos Basin (Portuguese: Bacia de Santos) is an approximately 352,000 square kilometres (136,000 sq mi) large mostly offshore sedimentary basin. It is located in the south Atlantic Ocean, some 300 kilometres (190 mi) southeast of Santos, Brazil. The basin is one of the Brazilian basins to have resulted from the break-up of Gondwana since the Early Cretaceous, where a sequence of rift basins formed on both sides of the South Atlantic; the Pelotas, Santos, Campos and Espírito Santo Basins in Brazil, and the Namibia, Kwanza and Congo Basins in southwestern Africa.

Santos Basin is separated from the Campos Basin to the north by the Cabo Frio High and the Pelotas Basin in the south by the Florianópolis High and the northwestern boundary onshore is formed by the Serra Do Mar coastal range. The basin is known for its thick layers of salt that have formed structures in the subsurface due to halokinesis. The basin started forming in the Early Cretaceous on top of the Congo Craton as a rift basin. The rift stage of the basin evolution combined with the arid Aptian climate of the southern latitudes resulted in the deposition of evaporites in the Late Aptian, approximately 112 million years ago. The phase of rifting was followed by a thermal sag phase and drift stage in the widening of the South Atlantic Ocean. This process led to the deposition of a more than 20 kilometres (66,000 ft) thick succession of clastic and carbonate sediments.

One of the largest Brazilian sedimentary basins, it is the site of several recently (2007 and later) discovered giant oil and gas fields, including the first large pre-salt discovery Lula (8 billion barrels), Júpiter (1.6 billion barrels and 17 tcf of gas), and Libra, with an estimated 8 to 12 billion barrels of recoverable oil. Main source rocks are the lacustrine shales and carbonates of the pre-salt Guaratiba Group and the marine shales of the post-salt Itajaí-Açu Formation. Reservoir rocks are formed by the pre-salt Guaratiba sandstones, limestones and microbialites, the Albian limestones of the Guarujá Formation and the Late Cretaceous to Paleogene turbiditic sandstones of the Itanhaém, Juréia, Itajaí-Açu, Florianópolis and Marambaia Formations. The mobile salt of the Ariri Formation forms regional seals, as well as the shales of the post-salt sedimentary infill. In 2014, the total production of only the sub-salt reservoirs accumulated to more than 250 thousand barrels per day (40×10^3 m3/d). In 2017, the Santos Basin accounted for 35% of Brazil's oil, with the northern neighbour Campos Basin at 55%.

Timeline of volcanism on Earth

This timeline of volcanism on Earth is a list of major volcanic eruptions of approximately at least magnitude 6 on the Volcanic Explosivity Index (VEI) or equivalent sulfur dioxide emission around the Quaternary period (from 2.58 Mya to the present).

Some eruptions cooled the global climate—inducing a volcanic winter—depending on the amount of sulfur dioxide emitted and the magnitude of the eruption. Before the present Holocene epoch, the criteria are less strict because of scarce data availability, partly since later eruptions have destroyed the evidence. Only some eruptions before the Neogene period (from 23 Mya to 2.58 Mya) are listed. Known large eruptions after the Paleogene period (from 66 Mya to 23 Mya) are listed, especially those relating to the Yellowstone hotspot, the Santorini caldera, and the Taupo Volcanic Zone.

Active volcanoes such as Stromboli, Mount Etna and Kilauea do not appear on this list, but some back-arc basin volcanoes that generated calderas do appear. Some dangerous volcanoes in "populated areas" appear many times: so Santorini, six times and Yellowstone hotspot, twenty-one times. The Bismarck volcanic arc, New Britain, and the Taupo Volcanic Zone, New Zealand, appear often too.

In addition to the events listed below, are many examples of eruptions in the Holocene on the Kamchatka Peninsula, which are described in a supplemental table by Peter Ward.

Trap rock

Trap rock, also known as either trapp or trap, is any dark-colored, fine-grained, non-granitic intrusive or extrusive igneous rock. Types of trap rock include basalt, peridotite, diabase, and gabbro. Trapp (trap) is also used to refer to flood (plateau) basalts, e.g. the Deccan Traps and Siberian Traps. The erosion of trap rock created by the stacking of successive lava flows often created a distinct stairstep landscape from which the term "trap" was derived from the Swedish word "trappa", which means "stairway".The slow cooling of magma either as a sill or as a thick lava flow sometimes creates systematic vertical fractures within the resulting layer of trap rock. These fractures often form rock columns that are typically hexagonal, but also four- to eight-sided.

Tristan hotspot

The Tristan hotspot is a volcanic hotspot which is responsible for the volcanic activity which forms the volcanoes in the southern Atlantic Ocean. It is thought to have formed the island of Tristan da Cunha and the Walvis Ridge on the African Plate.

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