Flood Basalt

Information about Flood Basalt

Moses Coulee showing multiple flood basalt flows of the Columbia River Basalt Group. The upper basalt is Roza Member, while the lower canyon exposes Frenchmen Springs Member basalt.

A flood basalt or trapp basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales (large igneous provinces) in prehistory, creating great plateaus and mountain ranges. Flood basalts have erupted at random intervals throughout history and are clear evidence that the Earth undergoes periods of enhanced activity rather than being in a uniform steady state.

One explanation for flood basalts is that they are caused by the combination of continental rifting and its associated decompression melting in conjunction with a mantle plume also undergoing decompression melting, producing vast quantities of a tholeiitic basaltic magma. These lavas have a very low viscosity, which is why they 'flood' rather than form taller volcanoes.

The Deccan Traps of central India, the Siberian Traps and the Columbia River Plateau of the western United States are three regions covered by prehistoric flood basalts. The two largest flood basalt events in historic time have been at Eldgjá and Lakagigar, both in Iceland. The maria on the Moon are additional, even more extensive, examples of flood basalts. Flood basalts on the ocean floor produce oceanic plateaus.

The surface covered by one eruption can vary from around 200,000 km² (Karoo) to 1,500,000 km² (Siberia). The thickness can vary from 2000 m (Deccan) to 12,000 m (Lake Superior). These estimates are smaller than the original volumes due to erosion.

Flood basalts originate at between 100 and 400 km depth in the asthenosphere. To obtain a partial fusion as large as that of the trapps, expelling huge quantities of lava, it is necessary to have a large heat input. Such fusion can take place near a hotspot, resulting in a mixture of magma from the depths of the hotspot with superficial magma produced by a mantle plume.

Petrography

Ethiopian Highlands basalt

Flood basalts have tholeiite and olivine compositions (according to the classification of Yoder and Tilley). The composition of the basalts from the Paraná is fairly typical of that of flood basalts; it contains phenocrysts occupying around 25% of the volume of rock, trapped in volcanic glass. These phenocrysts are pyroxenes (augite and pigeonite), plagioclases, opaque crystals such as titanomagnetite or ilmenite, and occasionally some olivine. Sometimes more differentiated volcanic products such andesites, dacites and rhyodacites have been observed, but only in small quantities at the top of former magma chambers.

Structures

Subaerial flood basalts can be of two kinds :

with a smooth or twisted surface : very compact surface; vesicles and gas bubbles are rare. Degassing was easy (magma maintained at a high temperature and more fluid in a chamber of a size such that confining pressures did not confine gases to the melt before expulsion). Such lava flows may form underground rivers; when degassing fractures and conduits are present, very large flows may reach surface.
with a chaotic surface : the basalt flood is very rich in bubbles of gas, with an irregular, fragmental surface. Degassing was difficult (less fuild magma expelled from a rift with no chance of progressive expansion in a hot chamber; the degassing took place closer to the surface where the flow forms a crust which cracks under the pressure of the gases in the flow itself and during more rapid cooling).

In the Massif Central in Auvergne, France, there is a good example of chaotic basalt floods, produced by eruptions from Puy de la Vache and Puy de Lassolas.

At depth, flows can crystallise more slowly, producing columnar jointing.

Geochemistry

Geochemical analysis of the major oxides reveals a composition close to that of mid-ocean ridge basalts (MORB) but also close to that of ocean island basalts (OIB). These are in fact tholeiites with a silicon dioxide percentage close to 50%.

Two kinds of basaltic floods basalts can be distinguished :

those poor in P₂O₅ and in TiO₂, called LPT (low phosphorus and titanium)
those rich in P₂O₅ and in TiO₂, called HPT (high phosphorus and titanium)

The isotopic ratios ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb are different from that observed in general, which shows that the basalt flood magma was contaminated as it passed through the continental crust. It is this contamination that explains the difference between the two kinds of basalt mentioned above. The LPT type has an excess of elements from the crust such as potassium and strontium.

The content in incompatible elements of basaltic floods is lower than that of ocean island basalts, but higher than that of mid-ocean ridge basalts.

Other occurrences and implications

Flood basalt volcanism has been implicated (along with the impact of large asteroids and/or comets, as well as disease and long-term climate changes) in major mass extinction events in the past.

Main article: Volcanism on Venus

Basalt floods on the planet Venus are even larger than those on earth. Their study may help understand the mechanisms responsible for these major geological events.

List of volcanic flood basalts

All major continental flood basalts (also known as traps) and oceanic plateaus, together forming a listing of large igneous provinces, which is provided below. The listing ranges from the smallest Columbia flood basalts to the largest, although not yet well characterized remnants of a possible trap in eastern Siberia^[1]:

The Columbia-Snake River flood basalts (see Columbia River Basalt Group)
The Ethiopian and Yemen traps in the Ethiopian Highlands
The Brito-Arctic province
The Deccan Traps (India) 65 million years ago (end of Cretaceous Period)
The Caribbean large igneous province
The Kerguelen Plateau
The Ontong Java–Manihiki–Hikurangi Plateau^[2]
The Paraná and Etendeka traps (Brazil-Namibia)
The Karoo and Ferrar provinces (South Africa-Antarctica)
The Central Atlantic Magmatic Province
The Siberian Traps (Russia) 251 million years ago (end of Permian)
The Emeishan (western China)
The Viluy traps
Pre-Devonian traps
The Strand Fiord Formation
The North Mountain Basalt

References

1. ^ Sur l'âge des trapps basaltiques (On the ages of flood basalt events); Vincent E. Courtillota & Paul R. Renneb; Comptes Rendus Geoscience; Vol: 335 Issue: 1, January, 2003; pp: 113-140
2. ^ Brian Taylor (31 January 2006). "The single largest oceanic plateau: Ontong Java-Manihiki-Hikurangi". Earth and Planetary Science Letters 241 (3-4): 372-380. DOI:10.1016/j.epsl.2005.11.049. Retrieved on 2007-05-22. Summary.

Volcano:
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Branch pipe
7. Layers of ash emitted by the volcano
8. Flank 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14.
..... Click the link for more information.

Basalt (IPA: /ˈbæsɒlt, bəˈsɒlt/) is a common gray to black extrusive volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth's surface.
..... Click the link for more information.

Lava is molten rock expelled by a volcano during an eruption. When first expelled from a volcanic vent, it is a liquid at temperatures from 700 °C to 1,200 °C (1,300 °F to 2,200 °F).
..... Click the link for more information.

continent is one of several large landmasses on Earth. They are generally identified by convention rather than any strict criteria, but seven areas are commonly regarded as continents – they are (from largest in size to smallest): Asia, Africa, North America, South America,
..... Click the link for more information.

Large Igneous provinces (LIPS) were originally defined by Coffin and Eldholm (1992) as areas of Earth's surface that contain very large volumes of magmatic rocks (typically basalt but including rhyolites) erupted over extremely short geological time intervals of a few million years
..... Click the link for more information.

Prehistory (Latin, præ = before Greek, ιστορία = history) is a term often used to describe the period before written history. Paul Tournal originally coined the term Pré-historique
..... Click the link for more information.

plateau, also called a high plateau or tableland, is an area of highland, usually consisting of relatively flat rural area.

Genesis

A plateau is a large and highland area of fairly level land separated from surrounding land by steep slopes (as in the Tibet),
..... Click the link for more information.

For exotic financial options, see .

A mountain range is a chain of mountains bordered by lowlands or separated from other mountain ranges by passes or rivers.
..... Click the link for more information.

rift is a place where the Earth's crust and lithosphere are being pulled apart. Typical features are a central linear downdropped fault segment, called a graben, with parallel normal faulting and rift-flank uplifts on either side forming a rift valley.
..... Click the link for more information.

Tholeiitic basalt is an igneous rock, a type of basalt. Like all basalt, the rock type is dominated by clinopyroxene plus plagioclase, with minor iron-titanium oxides. [1] Orthopyroxene or pigeonite may also be present in tholeiitic basalt, and olivine, if present, may be
..... Click the link for more information.

Magma (Plurals: magmas and magmata) is molten rock located beneath the surface of the Earth (or any other terrestrial planet) that often collects in a magma chamber. Magma may contain suspended crystals and gas bubbles.
..... Click the link for more information.

Viscosity is a measure of the resistance of a fluid to deform under either shear stress or extensional stress. It is commonly perceived as "thickness", or resistance to flow.
..... Click the link for more information.

The Deccan Traps is a large igneous province located on the Deccan Plateau of west-central India and is one of the largest volcanic features on Earth. It consists of multiple layers of solidified flood basalt that together are more than 2,000 m thick and cover an area of 500,000
..... Click the link for more information.

This page is currently protected from editing until disputes have been resolved.
Protection is not an endorsement of the current [ version] ([ protection log]).
..... Click the link for more information.

The Siberian Traps (Russian: Сибирские траппы) form a large igneous province in Siberia.
..... Click the link for more information.

Columbia River Plateau is a geologic and geographic region that lies across parts of the U.S. states of Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade and Rocky Mountains, cut through by the Columbia River.
..... Click the link for more information.

Motto
"In God We Trust" (since 1956)
"E Pluribus Unum" ("From Many, One"; Latin, traditional)
Anthem
..... Click the link for more information.

Eldgjá is a volcanic canyon in Iceland. Eldgjá and the nearby Laki craters are part of the same volcanic system as Katla in the south of the country. Eldgjá means "fire canyon" in Icelandic.
..... Click the link for more information.

Laki or Lakagígar (Craters of Laki) is a volcanic fissure situated in the south of Iceland, not far from the canyon of Eldgjá and the small town Kirkjubæjarklaustur, in Skaftafell National Park.
..... Click the link for more information.

Anthem
Lofsöngur

Location of Iceland

..... Click the link for more information.

Lunar maria (singular: mare, IPA: /ˈmɑːreɪ/) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions.
..... Click the link for more information.

Moon

The Moon as seen by an observer on Earth
Orbital characteristics
Periapsis: 363,104 km
0.0024 AU
Apoapsis: 405,696 km
0.0027 AU
Semi-major axis: 384,399 km
0.
..... Click the link for more information.

An oceanic plateau (also submarine plateau) is an undersea large igneous province, the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the Pacific Northwest of the United States.
..... Click the link for more information.

The Karoo and Farrar provinces together comprise a major flood basalt province, parts of which are found in both South Africa and Antarctica. It formed just prior to the breakup of Gondwana about 183 million years ago; this timing corresponds to the Pliensbachian-Toarcian
..... Click the link for more information.

The Siberian Traps (Russian: Сибирские траппы) form a large igneous province in Siberia.
..... Click the link for more information.

Coordinates Coordinates:
Lake type Rift lake
Primary sources Nipigon River,
St.
..... Click the link for more information.

asthenosphere (from an invented Greek ἀσθενός a + sthenos "without strength") is the region of the Earth between 100-200 km below the surface — but perhaps extending as deep as
..... Click the link for more information.

hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time. J. Tuzo Wilson came up with the idea in 1963 that volcanic chains like the Hawaiian Islands result from the slow movement of a tectonic plate across a "fixed" hot spot
..... Click the link for more information.

mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. As the heads of mantle plumes can partly melt when they reach shallow depths, they are thought to be the cause of volcanic centers known as hotspots and probably also to have caused flood basalts.
..... Click the link for more information.

This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.

Herod_Archelaus

iPedia Free Information Center