Editing Flood basalt

{{Short description|Very large volume eruption of basalt lava}}
[[Image:3-Devils-grade-Moses-Coulee-Cattle-Feed-Lot-PB110016.JPG|thumb|[[Moses Coulee]] in the US 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 '''plateau basalt'''<ref name=Jackson1997fb>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0922152349 |edition=Fourth |chapter=flood basalt}}</ref>) is the result of a giant [[volcanic eruption]] or series of [[eruption]]s that covers large stretches of land or the [[ocean]] floor with [[basalt]] [[lava]]. Many flood basalts have been attributed to the onset of a [[hotspot (geology)|hotspot]] reaching the surface of the Earth via a [[mantle plume]].<ref name="RichardsDucan1989">{{Cite journal |author=Mark A. Richards |author2=Robert A. Duncan |author3=Vincent E. Courtillot |year=1989 |title=Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails |journal=Science Magazine |volume=246 |issue=4926 |pages=103–107 |bibcode=1989Sci...246..103R |doi=10.1126/science.246.4926.103 |pmid=17837768 |s2cid=9147772}}</ref> [[List of flood basalt provinces|Flood basalt provinces]] such as the [[Deccan Traps]] of India are often called ''[[Trap rock|traps]]'', after the Swedish word ''trappa'' (meaning "staircase"), 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 igneous province]]s, [[lava plateau]]s, and [[mountain range]]s.<ref>{{cite journal |author=Michael R. Rampino |author2=Richard B. Stothers|title=Flood Basalt Volcanism During the Past 250 Million Years|doi=10.1126/science.241.4866.663|year=1988|journal=Science|volume=241|issue=4866|pages=663–668|pmid=17839077|bibcode=1988Sci...241..663R|s2cid=33327812|url=https://zenodo.org/record/1230982}} [http://pubs.giss.nasa.gov/docs/1988/1988_Rampino_Stothers_1.pdf PDF via NASA]{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}}</ref> However, more have been recognized such as the large [[Ontong Java Plateau]],<ref>{{cite journal|title=The Ontong Java Plateau|author1=Neal, C.|author2=Mahoney, J.|author3=Kroenke, L.|url=http://www3.nd.edu/~icpmslab/pdfs/OJP_Paper.pdf|year=1997|journal=Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism, Geophysical Monograph 100|url-status=dead|archive-url=https://web.archive.org/web/20170101204714/http://www3.nd.edu/~icpmslab/pdfs/OJP_Paper.pdf|archive-date=2017-01-01}}</ref> 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,<ref name="VolumeRateCO2">{{cite journal |last1=Jiang |first1=Qiang |last2=Jourdan |first2=Fred |last3=Olierook |first3=Hugo K. H. |last4=Merle |first4=Renaud E. |last5=Bourdet |first5=Julien |last6=Fougerouse |first6=Denis |last7=Godel |first7=Belinda |last8=Walker |first8=Alex T. |date=25 July 2022 |title=Volume and rate of volcanic {{CO2}} emissions governed the severity of past environmental crises |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=119 |issue=31 |pages=e2202039119 |doi=10.1073/pnas.2202039119 |doi-access=free |pmid=35878029 |pmc=9351498 |bibcode=2022PNAS..11902039J }}</ref> and may be associated with [[bolide]] impacts.<ref>{{Cite journal | doi = 10.1016/0031-9201(93)90011-W| title = A possible K-T boundary bolide impact site offshore near Bombay and triggering of rapid Deccan volcanism| journal = Physics of the Earth and Planetary Interiors| volume = 76| issue = 3–4| pages = 189| year = 1993| last1 = Negi | first1 = J. G. | last2 = Agrawal | first2 = P. K. | last3 = Pandey | first3 = O. P. | last4 = Singh | first4 = A. P. |bibcode = 1993PEPI...76..189N }}</ref>

==Description==
[[Image:Ethiopian highlands 01 mod.jpg|thumb|[[Ethiopian Highlands]] basalt]]
[[File:Ages of flood basalt events 1.png|thumb|Ages of flood basalt events and oceanic plateaus.<ref>[[Vincent Courtillot]], [[Paul Renne]]: ''[https://www.sciencedirect.com/science/article/pii/S1631071303000063?via%3Dihub On the ages of flood basalt events]''</ref>]]

Flood basalts are the most voluminous of all [[Extrusive rock|extrusive igneous rocks]],<ref>{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521880060 |edition=2nd |page=52}}</ref> forming enormous deposits of [[basaltic]] rock<ref name=Jackson1997>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0922152349 |edition=Fourth |chapter=plateau basalt}}</ref><ref name=Allaby2013>{{cite book |last1=Allaby |first1=Michael |title=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=9780199653065 |edition=Fourth |chapter=flood basalt}}</ref> found throughout the geologic record.<ref name=Jackson1997/>{{sfn|Philpotts|Ague|2009|p=380}} They are a highly distinctive form of [[intraplate volcanism]],<ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=978-3-540-43650-8 |page=107}}</ref> set apart from all other forms of volcanism by the huge volumes of lava erupted in geologically short time intervals. A single flood basalt province may contain hundreds of thousands of cubic kilometers of basalt erupted over less than a million years, with individual events each erupting hundreds of cubic kilometers of basalt.{{sfn|Philpotts|Ague|2009|p=380}} This highly fluid basalt lava can spread laterally for hundreds of kilometers from its source vents,{{sfn|Philpotts|Ague|2009|p=53}} covering areas of tens of thousands of square kilometers.{{sfn|Schmincke|2003|p=107}} Successive eruptions form thick accumulations of nearly horizontal flows, erupted in rapid succession over vast areas, flooding the Earth's surface with lava on a regional scale.<ref name=Jackson1997/>{{sfn|Philpotts|Ague|2009|p=52}}

These vast accumulations of flood basalt constitute [[large igneous province]]s. These are characterized by plateau landforms, so that flood basalts are also described as ''plateau basalts''. Canyons cut into the flood basalts by erosion display stair-like slopes, with the lower parts of flows forming cliffs and the upper part of flows or [[interbedded]] layers of sediments forming slopes. These are known in Dutch as ''trap'' or in Swedish as ''trappa'', which has come into English as ''trap rock'', a term particularly used in the quarry industry.{{sfn|Philpotts|Ague|2009|p=52}}{{sfn|Schmincke|2003|p=108}}

The great thickness of the basalt accumulations, often in excess of {{convert|1000|m|sigfig=1|sp=us}},{{sfn|Schmincke|2003|p=108}} usually reflects a very large number of thin flows, varying in thickness from meters to tens of meters, or more rarely to {{convert|100|m||sp=us}}. There are occasionally very thick individual flows. The world's thickest basalt flow may be the Greenstone flow of the [[Keweenaw Peninsula]] of [[Michigan]], US, which is {{convert|600|m||sp=us}} thick. This flow may have been part of a lava lake the size of [[Lake Superior]].{{sfn|Philpotts|Ague|2009|p=53}}

Deep erosion of flood basalts exposes vast numbers of parallel dikes that fed the eruptions.{{sfn|Philpotts|Ague|2009|p=57}} Some individual dikes in the [[Columbia River Plateau]] are over {{convert|100|km|sigfig=1|sp=us}} long.{{sfn|Schmincke|2003|p=108}} In some cases, erosion exposes radial sets of dikes with diameters of several thousand kilometers.{{sfn|Philpotts|Ague|2009|p=380}} Sills may also be present beneath flood basalts, such as the [[Palisades Sill]] of [[New Jersey]], US. The sheet intrusions (dikes and sills) beneath flood basalts are typically [[diabase]] that closely matches the composition of the overlying flood basalts. In some cases, the chemical signature allows individual dikes to be connected with individual flows.{{sfn|Philpotts|Ague|2009|pp=381-382}}

===Smaller-scale features===
Flood basalt commonly displays [[columnar jointing]], formed as the rock cooled and contracted after solidifying from the lava. The rock fractures into columns, typically with five to six sides, parallel to the direction of heat flow out of the rock. This is generally perpendicular to the upper and lower surfaces, but rainwater infiltrating the rock unevenly can produce "cold fingers" of distorted columns. Because heat flow out of the base of the flow is slower than from its upper surface, the columns are more regular and larger in the bottom third of the flow. The greater hydrostatic pressure, due to the weight of overlying rock, also contributes to making the lower columns larger. By analogy with Greek temple architecture, the more regular lower columns are described as the ''colonnade'' and the more irregular upper fractures as the ''entablature'' of the individual flow. Columns tend to be larger in thicker flows, with columns of the very thick Greenstone flow, mentioned earlier, being around {{convert|10|m|sigfig=1|sp=us}} thick.{{sfn|Philpotts|Ague|2009|p=55}}

Another common small-scale feature of flood basalts is ''pipe-stem vesicles''. Flood basalt lava cools quite slowly, so that dissolved gases in the lava have time to come out of solution as bubbles (vesicles) that float to the top of the flow. Most of the rest of the flow is massive and free of vesicles. However, the more rapidly cooling lava close to the base of the flow forms a thin [[chilled margin]] of glassy rock, and the more rapidly crystallized rock just above the glassy margin contains vesicles trapped as the rock was rapidly crystallizing. These have a distinctive appearance likened to a clay [[tobacco pipe]] stem, particularly as the vesicle is usually subsequently filled with [[calcite]] or other light-colored minerals that contrast with the surrounding dark basalt.{{sfn|Philpotts|Ague|2009|p=58}}

=== Petrology ===
At still smaller scales, the [[Texture (geology)|texture]] of flood basalts is [[aphanitic]], consisting of tiny interlocking crystals. These interlocking crystals give trap rock its tremendous toughness and durability.{{sfn|Philpotts|Ague|2009|p=55}} Crystals of [[plagioclase]] are embedded in or wrapped around crystals of [[pyroxene]] and are randomly oriented. This indicates rapid emplacement so that the lava is no longer flowing rapidly when it begins to crystallize.{{sfn|Philpotts|Ague|2009|p=53}} Flood basalts are almost devoid of large [[phenocrysts]], larger crystals present in the lava prior to its being erupted to the surface, which are often present in other extrusive igneous rocks. Phenocrysts are more abundant in the [[Dike (geology)|dikes]] that fed lava to the surface.{{sfn|Philpotts|Ague|2009|p=383}}

Flood basalts are most often [[quartz]] [[tholeiite]]s. [[Olivine]] tholeiite (the characteristic rock of [[mid-ocean ridges]]{{sfn|Philpotts|Ague|2009|p=366}}) occurs less commonly, and there are rare cases of [[alkali basalt]]s. Regardless of composition, the flows are very homogeneous and rarely contain [[xenoliths]], fragments of the surrounding rock ([[country rock (geology)|country rock]]) that have been entrained in the lava. Because the lavas are low in dissolved gases, [[pyroclastic rock]] is extremely rare. Except where the flows entered lakes and became [[pillow lava]], the flows are massive (featureless). Occasionally, flood basalts are associated with very small volumes of [[dacite]] or [[rhyolite]] (much more silica-rich volcanic rock), which forms late in the development of a large igneous province and marks a shift to more centralized volcanism.{{sfn|Philpotts|Ague|2009|p=381}}

=== Geochemistry ===
[[File:Parana traps.JPG|thumb|Parana traps]]
Flood basalts show a considerable degree of chemical uniformity across geologic time,{{sfn|Philpotts|Ague|2009|p=380}} being mostly iron-rich tholeiitic basalts. Their major element chemistry is similar to mid-ocean ridge basalts (MORBs), while their trace element chemistry, particularly of the [[rare earth elements]], resembles that of [[ocean island basalt]].<ref name=Wilson2007>{{cite book |last1=Wilson |first1=Marjorie |title=Igneous Petrogenesis |chapter=Continental tholeiitic flood basalt provinces |date=2007 |pages=287–323 |doi=10.1007/978-94-010-9388-0_10|isbn=978-0-412-75080-9 }}</ref> They typically have a silica content of around 52%. The magnesium number (the [[mol%]] of magnesium out of the total iron and magnesium content) is around 55,{{sfn|Philpotts|Ague|2009|p=383}} versus 60 for a typical MORB.{{sfn|Philpotts|Ague|2009|p=367}} The [[rare earth elements]] show abundance patterns suggesting that the original (primitive) magma formed from rock of the [[Earth's mantle]] that was nearly ''undepleted''; that is, it was mantle rock rich in [[garnet]] and from which little magma had previously been extracted. The chemistry of plagioclase and olivine in flood basalts suggests that the magma was only slightly contaminated with melted rock of the [[Earth's crust]], but some high-temperature minerals had already crystallized out of the rock before it reached the surface.{{sfn|Philpotts|Ague|2009|p=382}} In other words, the flood basalt is moderately [[Magma differentiation|evolved]].<ref name=Wilson2007/> However, only small amounts of plagioclase appear to have crystallized out of the melt.{{sfn|Philpotts|Ague|2009|p=382}}

Though regarded as forming a chemically homogeneous group, flood basalts sometimes show significant chemical diversity even with in a single province. For example, the flood basalts of the [[Parana Basin]] can be divided into a low phosphorus and titanium group (LPT) and a high phosphorus and titanium group (HPT). The difference has been attributed to inhomogeneity in the upper mantle,<ref>{{cite journal |last1=Hawkesworth |first1=C. J. |last2=Mantovani |first2=M. S. M. |last3=Taylor |first3=P. N. |last4=Palacz |first4=Z. |title=Evidence from the Parana of south Brazil for a continental contribution to Dupal basalts |journal=Nature |date=July 1986 |volume=322 |issue=6077 |pages=356–359 |doi=10.1038/322356a0|bibcode=1986Natur.322..356H |s2cid=4261508 }}</ref> but [[strontium isotope]] ratios suggest the difference may arise from the LPT magma being contaminated with a greater amount of melted crust.<ref>{{cite journal |last1=Mantovani |first1=M. S. M. |last2=Marques |first2=L. S. |last3=De Sousa |first3=M. A. |last4=Civetta |first4=L. |last5=Atalla |first5=L. |last6=Innocenti |first6=F. |title=Trace Element and Strontium Isotope Constraints on the Origin and Evolution of Paran Continental Flood Basalts of Santa Catarina State (Southern Brazil) |journal=Journal of Petrology |date=1 February 1985 |volume=26 |issue=1 |pages=187–209 |doi=10.1093/petrology/26.1.187}}</ref>

==Formation==
[[File:Plume 2.jpg|thumb|Plume model of flood basalt eruption]]
Theories of the formation of flood basalts must explain how such vast amounts of magma could be generated and erupted as lava in such short intervals of time. They must also explain the similar compositions and tectonic settings of flood basalts erupted across geologic time and the ability of flood basalt lava to travel such great distances from the eruptive fissures before solidifying.

===Generation of melt===
A tremendous amount of heat is required for so much magma to be generated in so short a time.{{sfn|Philpotts|Ague|2009|p=380}} This is widely believed to have been supplied by a [[mantle plume]] impinging on the base of the Earth's [[lithosphere]], its rigid outermost shell.<ref>{{cite journal |last1=White |first1=Robert |last2=McKenzie |first2=Dan |title=Magmatism at rift zones: The generation of volcanic continental margins and flood basalts |journal=Journal of Geophysical Research |date=1989 |volume=94 |issue=B6 |pages=7685 |doi=10.1029/JB094iB06p07685|bibcode=1989JGR....94.7685W }}</ref><ref name="Saunders2005">{{cite journal |last1=Saunders |first1=A. D. |title=Large Igneous Provinces: Origin and Environmental Consequences |journal=Elements |date=1 December 2005 |volume=1 |issue=5 |pages=259–263 |doi=10.2113/gselements.1.5.259|bibcode=2005Eleme...1..259S }}</ref>{{sfn|Philpotts|Ague|2009|p=52}} The plume consists of unusually hot mantle rock of the [[asthenosphere]], the ductile layer just below the lithosphere, that creeps upwards from deeper in the Earth's interior.{{sfn|Schmincke|2003|p=111}} The hot asthenosphere [[Rifting|rifts]] the lithosphere above the plume, allowing magma produced by decompressional melting of the plume head to find pathways to the surface.{{sfn|Schmincke|2003|pp=110-111}}{{sfn|Philpotts|Ague|2009|p=57}}

The swarms of parallel dikes exposed by deep erosion of flood basalts show that considerable [[crustal extension]] has taken place. The dike swarms of west Scotland and Iceland show extension of up to 5%. Many flood basalts are associated with rift valleys, are located on passive continental plate margins, or extend into [[aulacogen]]s (failed arms of [[triple junction]]s where continental rifting begins.) Flood basalts on continents are often aligned with [[hotspot (geology)|hotspot]] volcanism in ocean basins.{{sfn|Philpotts|Ague|2009|pp=57, 380}} The [[Paraná and Etendeka traps]], located in South America and Africa on opposite sides of the Atlantic Ocean, formed around 125 million years ago as the South Atlantic opened, while a second set of smaller flood basalts formed near the Triassic-Jurassic boundary in eastern North America as the North Atlantic opened.{{sfn|Philpotts|Ague|2009|p=52}}{{sfn|Schmincke|2003|p=108}} However, the North Atlantic flood basalts are not connected with any hot spot traces, but seem to have been evenly distributed along the entire divergent boundary.{{sfn|Philpotts|Ague|2009|p=381}}

Flood basalts are often interbedded with sediments, typically [[red beds]]. The deposition of sediments begins before the first flood basalt eruptions, so that subsidence and crustal thinning are precursors to flood basalt activity.{{sfn|Philpotts|Ague|2009|p=380}} The surface continues to subside as basalt erupt, so that the older beds are often found below sea level.{{sfn|Philpotts|Ague|2009|p=57}} Basalt strata at depth (''dipping reflectors'') have been found by [[reflection seismology]] along passive continental margins.{{sfn|Schmincke|2003|p=111}}

=== Ascent to the surface ===
The composition of flood basalts may reflect the mechanisms by which the magma reaches the surface. The original melt formed in the upper mantle (the ''primitive melt'') cannot have the composition of quartz tholeiite, the most common and typically least evolved volcanic rock of flood basalts, because quartz tholeiites are too rich in iron relative to magnesium to have formed in equilibrium with typical mantle rock. The primitive melt may have had the composition of [[picrite basalt]], but picrite basalt is uncommon in flood basalt provinces. One possibility is that a primitive melt ''stagnates'' when it reaches the mantle-crust boundary, where it is not buoyant enough to penetrate the lower-density crust rock. As a tholeiitic magma differentiates (changes in composition as high-temperature minerals crystallize and settle out of the magma) its density reaches a minimum at a magnesium number of about 60, similar to that of flood basalts. This restores buoyancy and permits the magma to complete its journey to the surface, and also explains why flood basalts are predominantly quartz tholeiites. Over half the original magma remains in the lower crust as [[cumulates]] in a system of dikes and sills.<ref name=Cox1980>{{cite journal |last1=Cox |first1=K. G. |title=A Model for Flood Basalt Vulcanism |journal=Journal of Petrology |date=1 November 1980 |volume=21 |issue=4 |pages=629–650 |doi=10.1093/petrology/21.4.629}}</ref>{{sfn|Philpotts|Ague|2009|p=383}}

As the magma rises, the drop in pressure also lowers the [[liquidus]], the temperature at which the magma is fully liquid. This likely explains the lack of phenocrysts in erupted flood basalt. The ''resorption'' (dissolution back into the melt) of a mixture of solid olivine, augite, and plagioclase—the high-temperature minerals likely to form as phenocrysts—may also tend to drive the composition closer to quartz tholeiite and help maintain buoyancy.{{sfn|Philpotts|Ague|2009|p=382}}{{sfn|Philpotts|Ague|2009|p=383}}

=== Eruption ===
Once the magma reaches the surface, it flows rapidly across the landscape, literally flooding the local topography. This is possible in part because of the rapid rate of extrusion (over a cubic km per day per km of fissure length{{sfn|Schmincke|2003|p=108}}) and the relatively low viscosity of basaltic lava. However, the lateral extent of individual flood basalt flows is astonishing even for so fluid a lava in such quantities.{{sfn|Philpotts|Ague|2009|pp=52-53}} It is likely that the lava spreads by a process of ''inflation'' in which the lava moves beneath a solid insulating crust, which keeps it hot and mobile.<ref name="SelfEtal1996">{{cite journal |last1=Self |first1=S. |last2=Thordarson |first2=Th. |last3=Keszthelyi |first3=L. |last4=Walker |first4=G. P. L. |last5=Hon |first5=K. |last6=Murphy |first6=M. T. |last7=Long |first7=P. |last8=Finnemore |first8=S. |title=A new model for the emplacement of Columbia River basalts as large, inflated Pahoehoe Lava Flow Fields |journal=Geophysical Research Letters |date=15 September 1996 |volume=23 |issue=19 |pages=2689–2692 |doi=10.1029/96GL02450|bibcode=1996GeoRL..23.2689S }}</ref> Studies of the Ginkgo flow of the Columbia River Plateau, which is {{convert|30 to 70|m||sp=us}} thick, show that the temperature of the lava dropped by just {{convert|20|C||sp=us}} over a distance of {{convert|500|km||sp=us}}. This demonstrates that the lava must have been insulated by a surface crust and that the flow was [[laminar flow|laminar]], reducing heat exchange with the upper crust and base of the flow.<ref name="HoCashman1997">{{cite journal |last1=Ho |first1=Anita M. |last2=Cashman |first2=Katharine V. |title=Temperature constraints on the Ginkgo flow of the Columbia River Basalt Group |journal=Geology |date=1 May 1997 |volume=25 |issue=5 |pages=403–406 |doi=10.1130/0091-7613(1997)025<0403:TCOTGF>2.3.CO;2|bibcode=1997Geo....25..403H }}</ref>{{sfn|Philpotts|Ague|2009|pp=53-54}} It has been estimated that the Ginkgo flow advanced 500&nbsp;km in six days (a rate of advance of about 3.5&nbsp;km per hour).<ref name="HoCashman1997"/>

The lateral extent of a flood basalt flow is roughly proportional to the cube of the thickness of the flow near its source. Thus, a flow that is double in thickness at its source can travel roughly eight times as far.{{sfn|Philpotts|Ague|2009|p=53}}

Flood basalt flows are predominantly [[pāhoehoe]] flows, with [[ʻaʻā]] flows much less common.<ref>{{cite book |last1=Self |first1=S. |last2=Thordarson |first2=T. |last3=Keszthelyi |first3=L. |title=Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism |chapter=Emplacement of Continental Flood Basalt Lava Flows |year=1997 |series=Geophysical Monograph Series |volume=100 |pages=381–410 |doi=10.1029/GM100p0381 |bibcode=1997GMS...100..381S |isbn=9781118664346 |chapter-url=https://books.google.com/books?id=5H8vobp2x3AC&dq=flood+basalt+aa&pg=PA381 |access-date=17 January 2022}}</ref>

Eruption in flood basalt provinces is episodic, and each episode has its own chemical signature. There is some tendency for lava within a single eruptive episode to become more silica-rich with time, but there is no consistent trend across episodes.{{sfn|Philpotts|Ague|2009|p=382}}

==Large igneous provinces==
{{Main|Large igneous province}}
Large Igneous Provinces (LIPs) were originally defined as voluminous outpourings, predominantly of basalt, over geologically very short durations. This definition did not specify minimum size, duration, petrogenesis, or setting. A new attempt to refine classification focuses on size and setting. LIPs characteristically cover large areas, and the great bulk of the magmatism occurs in less than 1 Ma. Principal LIPs in the ocean basins include ''Oceanic Volcanic Plateaus'' (OPs) and ''Volcanic Passive Continental Margins''. ''Oceanic flood basalts'' are LIPs distinguished from [[oceanic plateau]]s by some investigators because they do not form morphologic plateaus, being neither flat-topped nor elevated more than 200 m above the seafloor. Examples include the Caribbean, Nauru, East Mariana, and Pigafetta provinces. Continental flood basalts (CFBs) or plateau basalts are the continental expressions of large igneous provinces.<ref>{{cite book |last1=Winter |first1=John |title=Principles of Igneous and Metamorphic Petrology |date=2010 |publisher=Prentice Hall |location=New York |isbn=9780321592576 |pages=301–302 |edition=2nd}}</ref>

==Impact==
Flood basalts contribute significantly to the growth of continental crust. They are also catastrophic events, which likely contributed to many [[mass extinctions]] in the geologic record.

===Crust formation===
The extrusion of flood basalts, averaged over time, is comparable with the rate of extrusion of lava at mid-ocean ridges and much higher than the rate of extrusion by hotspots.{{sfn|Schmincke|2003|pp=107-108}} However, extrusion at mid-ocean ridges is relatively steady, while extrusion of flood basalts is highly episodic. Flood basalts create new continental crust at a rate of {{convert|0.1 to 8|km3|sigfig=1|sp=us}} per year, while the eruptions that form oceanic plateaus produce {{convert|2 to 20 |km3|sigfig=1|sp=us}} of crust per year.{{sfn|Schmincke|2003|p=108}}

Much of the new crust formed during flood basalt episodes takes the form of [[underplating]], with over half the original magma crystallizing out as cumulates in sills at the base of the crust.<ref name=Cox1980/>

===Mass extinctions===
[[File:Redstoneslake.jpg|thumb|Siberian Traps at Red Stones Lake]]
The eruption of flood basalts has been linked with mass extinctions. For example, the [[Deccan Traps]], erupted at the [[Cretaceous-Paleogene boundary]], may have contributed to the extinction of the non-avian dinosaurs.<ref name="Wignall2005">{{cite journal |last1=Wignall |first1=P. |title=The Link between Large Igneous Province Eruptions and Mass Extinctions |journal=Elements |date=1 December 2005 |volume=1 |issue=5 |pages=293–297 |doi=10.2113/gselements.1.5.293|bibcode=2005Eleme...1..293W }}</ref> Likewise, mass extinctions at the [[Permian-Triassic]] boundary, the [[Triassic-Jurassic event|Triassic-Jurassic]] boundary, and in the [[Toarcian]] [[Age (geology)|Age]] of the [[Jurassic]] correspond to the ages of large igneous provinces in Siberia, the Central Atlantic Magmatic Province, and the [[Karoo-Ferrar]] flood basalt.{{sfn|Philpotts|Ague|2009|p=52}}

Some idea of the impact of flood basalts can be given by comparison with historical large eruptions. The [[1783 eruption of Laki|1783 eruption of Lakagígar]] was the largest in the historical record, killing 75% of the livestock and a quarter of the population of Iceland. However, the eruption produced just {{convert|14|km3||sp=us}} of lava,<ref name=GuilbaudEtal2005>{{cite journal |last1=Guilbaud |first1=M.N. |last2=Self |first2=S. |last3=Thordarson |first3=T. |last4=Blake |first4=S. |year=2005 |title=Morphology, surface structures, and emplacement of lavas produced by Laki, AD 1783–1784 |journal=Geological Society of America Special Papers |volume=396 |pages=81–102 |isbn=9780813723969 |url=https://books.google.com/books?id=efqyc-fh82YC&dq=guilbaud+2005+morphology&pg=PA81 |access-date=12 January 2022}}</ref>{{sfn|Philpotts|Ague|2009|p=52}} which is tiny compared with the Roza Member of the Columbia River Plateau, erupted in the mid-[[Miocene]], which contained at least {{convert|1500|km3||sp=us}} of lava.<ref name=Allaby2013/>

During the eruption of the [[Siberian Traps]], some {{convert|5 to 16|e6km3|e6mi3|abbr=off|sp=us}} of magma penetrated the crust, covering an area of {{convert|5|e6km2|e6mi2|abbr=off}}, equal to 62% of the area of the contiguous states of the United States. The hot magma contained vast quantities of [[carbon dioxide]] and [[sulfur oxides]], and released additional carbon dioxide and [[methane]] from deep [[petroleum reservoir]]s and younger [[coal]] beds in the region. The released gases created over 6400 [[diatreme]]-like ''pipes'',<ref name="SaundersReichow2009">{{cite journal | title=The Siberian Traps and the End-Permian mass extinction: a critical review | first1=A. | last1=Saunders | first2=M. | last2=Reichow | journal=Chinese Science Bulletin | year=2009 | volume=54 | issue=1 | pages=20–37 | doi=10.1007/s11434-008-0543-7| bibcode=2009ChSBu..54...20S | s2cid=1736350 | url=https://figshare.com/articles/journal_contribution/10119755 | hdl=2381/27540 | hdl-access=free }}</ref> each typically over {{convert|1.6|km|mi|0}} in diameter. The pipes emitted up to 160 trillion tons of carbon dioxide and 46 trillion tons of methane. Coal ash from burning coal beds spread toxic [[chromium]], [[arsenic]], [[Mercury (element)|mercury]], and [[lead]] across northern Canada. [[Evaporite]] beds heated by the magma released [[hydrochloric acid]], [[methyl chloride]], [[methyl bromide]], which damaged the [[ozone layer]] and reduced ultraviolet shielding by as much as 85%. Over 5 trillion tons of [[sulfur dioxide]] was also released. The carbon dioxide produced extreme greenhouse conditions, with global average sea water temperatures peaking at {{convert|38|C|F}}, the highest ever seen in the geologic record. Temperatures did not drop to {{convert|32|C|F}} for another 5.1 million years. Temperatures this high are lethal to most marine organisms, and land plants have difficulty continuing to photosynthesize at temperatures above {{convert|35|C|F}}. The Earth's equatorial zone became a dead zone.<ref>{{cite book |last1=McGhee |first1=George R. |title=Carboniferous Giants and Mass Extinction: The Late Paleozoic Ice Age World |date=2018 |publisher=Columbia University Press |location=New York |isbn=9780231180979 |pages=190–240}}</ref>

However, not all large igneous provinces are connected with extinction events.{{sfn|Philpotts|Ague|2009|p=384}} The formation and effects of a flood basalt depend on a range of factors, such as continental configuration, latitude, volume, rate, duration of eruption, style and setting (continental vs. oceanic), the preexisting [[climate]], and the [[Biota (ecology)|biota]] resilience to change.<ref>{{Cite journal|first1=David P.G. |last1=Bond |first2=Paul B. |last2=Wignall|title=Large igneous provinces and mass extinctions: An update|journal=GSA Special Papers |volume=505 |year=2014 |pages=29–55 |doi=10.1130/2014.2505(02)|isbn=9780813725055 |url=https://hull-repository.worktribe.com/373637/1/10877%20Bond.pdf}}</ref>

[[Image:Chasm Provincial Park trees and flood basalts.jpg|thumb|Multiple flood basalt flows of the [[Chilcotin Group]], [[British Columbia]], Canada]]
[[Image:Flood_Basalt_Map.jpg|thumb|Major flood basalts, [[large igneous province]]s and [[trap rock|traps]]; click to enlarge.]]

==List of flood basalts==
{{See also|List of flood basalt provinces|World's largest eruptions}}

Representative continental flood basalts and oceanic plateaus, arranged by chronological order, together forming a listing of [[large igneous province]]s:<ref>{{cite journal |last1=Courtillot |first1=Vincent E. |last2=Renne |first2=Paul R. |title=Sur l'âge des trapps basaltiques |journal=Comptes Rendus Geoscience |date=1 January 2003 |volume=335 |issue=1 |pages=113–140 |doi=10.1016/S1631-0713(03)00006-3 |url=https://ui.adsabs.harvard.edu/abs/2003CRGeo.335..113C/abstract |access-date=23 October 2021 |trans-title=On the ages of flood basalt events |issn=1631-0713 |bibcode=2003CRGeo.335..113C}}</ref>

{| class="wikitable sortable"

!Name

!Initial or peak activity<br>([[megaannum|Ma]] ago)

!Surface area<br>(in thousands of km<sup>2</sup>)

!Volume<br>(in km<sup>3</sup>)

!Associated event

|-

|[[Chilcotin Group]]

|{{sort|.0010|10}}

|{{sort|.00050|50}}

|{{sort|3.3|3300}}

|
|-

|[[Columbia River Basalt Group]]

|{{sort|.0017|17}}

|{{sort|.00160|160}}

|{{sort|174.3|174,300}}

|[[Yellowstone Hotspot]]<ref name="RichardsDucan1989" /><ref>{{cite journal |last1=Nash |first1=Barbara P. |last2=Perkins |first2=Michael E. |last3=Christensen |first3=John N. |last4=Lee |first4=Der-Chuen |last5=Halliday |first5=A. N. |title=The Yellowstone hotspot in space and time: Nd and Hf isotopes in silicic magmas |journal=Earth and Planetary Science Letters |date=15 July 2006 |volume=247 |issue=1 |pages=143–156 |doi=10.1016/j.epsl.2006.04.030 |url=https://www.research-collection.ethz.ch/handle/20.500.11850/24040 |access-date=23 October 2021 |language=en |issn=0012-821X |bibcode=2006E&PSL.247..143N|url-access=subscription }}</ref>

|-

|[[Ethiopia-Yemen Continental Flood Basalts]]

|{{sort|.0031|31}}

|{{sort|.00600|600}}

|{{sort|350|350,000}}

|
|-

|[[North Atlantic Igneous Province]] (NAIP)

|{{sort|.0056|56 (phase 2)}}

|{{sort|.01300|1300}}

|{{sort|6600|6,600,000}}

|[[Paleocene–Eocene Thermal Maximum]]<ref name="bondwig">{{harvnb|Bond|Wignall|2014|p=17}}</ref>

|-

|[[Deccan Traps]]

|{{sort|.0066|66}}

|{{sort|.01500|1500}}

|{{sort|3000|3,000,000{{citation needed|date=June 2021}}}}

|[[Cretaceous–Paleogene extinction event]]

|-

|[[Caribbean large igneous province]]

|{{sort|.0095|95 (main phase)}}

|{{sort|.02000|2000}}

|{{sort|4000|4,000,000}}

|[[Cenomanian-Turonian boundary event]] (OAE 2)<ref name="bondwig"/>

|-

|[[Kerguelen Plateau]]

|{{sort|.0119|119}}

|{{sort|.01200|1200}}

|
|[[Aptian extinction]]<ref>{{Cite journal 
 | last1 = Wallace | first1 = P. J.
 | last2 = Frey | first2 = F. A.
 | last3 = Weis | first3 = D.
 | last4 = Coffin | first4 = M. F.
 | year = 2002 | journal = Journal of Petrology | volume = 43 | issue =7 | pages = 1105–1108
 | title = Origin and Evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago: Editorial
 | doi = 10.1093/petrology/43.7.1105 | bibcode = 2002JPet...43.1105W| doi-access = free }}</ref>

|-

|[[Ontong-Java Plateau]]

|{{sort|.0120|120 (phase 1)}}

|{{sort|.02000|2000}}

|{{sort|80000|80,000,000}}

|[[Anoxic event#Cretaceous|Selli event]] (OAE 1a)<ref name="bondwig"/>

|-

|[[High Arctic Large Igneous Province]] (HALIP)

|{{sort|.0125|120-130}}

|{{sort|.01000|1000}}

|
|[[Anoxic event#Cretaceous|Selli event]] (OAE 1a) <ref>{{cite journal |last1=Polteau |first1=Stéphane |last2=Planke |first2=Sverre |last3=Faleide |first3=Jan Inge |last4=Svensen |first4=Henrik |last5=Myklebust |first5=Reidun |title=The Cretaceous High Arctic Large Igneous Province |date=1 May 2010 |journal=EGU General Assembly 2010 |page=13216 | bibcode = 2010EGUGA..1213216P |url=https://ui.adsabs.harvard.edu/abs/2010EGUGA..1213216P/abstract}}</ref>

|-

|[[Paraná and Etendeka traps|Paraná and Etendeka Traps]]

|{{sort|.0132|132}}

|{{sort|.01500|1500}}

|{{sort|2300|2,300,000}}

|
|-

|[[Karoo-Ferrar|Karoo and Ferrar Provinces]]

|{{sort|.0183|183}}

|{{sort|.03000|3000}}

|{{sort|2500|2,500,000}}

|[[Toarcian Oceanic Anoxic Event|Toarcian extinction event]]<ref>{{cite journal |last1=Pálfy |first1=József |last2=Smith |first2=Paul L. |date=August 2000 |title=Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism |journal=Geology |volume=28 |issue=8 |pages=747–750 |doi=10.1130/0091-7613(2000)28<747:SBEJEO>2.0.CO;2|bibcode=2000Geo....28..747P |url=http://real.mtak.hu/34435/1/Palfy_Smith_2000_Geology.pdf }}</ref>

|-

|[[Central Atlantic magmatic province|Central Atlantic Magmatic Province]]

|{{sort|.0201|201}}

|{{sort|.11000|11000}}

|{{sort|2000|~2,000,000 – 3,000,000}}

|[[Triassic–Jurassic extinction event]]<ref>{{cite journal |doi=10.1126/science.1234204|last1= Blackburn |first1=Terrence J.|last2= Olsen |first2= Paul E. |last3= Bowring |first3= Samuel A. |last4= McLean |first4= Noah M.|last5= Kent |first5= Dennis V. |last6= Puffer |first6= John |last7= McHone |first7= Greg |last8= Rasbury |first8= Troy |last9= Et-Touhami7|first9= Mohammed |year=2013|title= Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province |journal= Science |volume=340|pages=941–945 |bibcode= 2013Sci...340..941B|issue=6135|pmid=23519213|s2cid= 15895416 |url= http://academiccommons.columbia.edu/download/fedora_content/download/ac%3A170114/CONTENT/Blackburn_2013.pdf }}</ref>

|-

|[[Siberian Traps]]

|{{sort|.0251|251}}

|{{sort|.07000|7000}}

|{{sort|4000|4,000,000}}

|[[Permian–Triassic extinction event]]<ref>{{cite journal
 | author = Campbell, I.|author2=Czamanske, G. |author3=Fedorenko, V. |author4=Hill, R. |author5=Stepanov, V. 
 | year = 1992
 | title = Synchronism of the Siberian Traps and the Permian-Triassic Boundary
 | journal = Science
 | volume = 258
 | issue = 5089
 | pages = 1760–1763
 | doi = 10.1126/science.258.5089.1760
 | pmid=17831657
|bibcode=1992Sci...258.1760C|s2cid=41194645 }}</ref>

|-

|[[Emeishan Traps]]

|{{sort|.0265|265}}

|{{sort|.00250|250}}

|{{sort|300|300,000}}

|[[Capitanian mass extinction event|End-Capitanian extinction event]]<ref>{{Cite journal|title = A temporal link between the Emeishan large igneous province (SW China) and the end-Guadalupian mass extinction|author-link1=Mei-Fu Zhou|last = Zhou|first = MF |display-authors=etal |date = 2002|journal = Earth and Planetary Science Letters|doi = 10.1016/s0012-821x(01)00608-2|volume=196|issue = 3–4|pages=113–122|bibcode =2002E&PSL.196..113Z}}</ref>

|-

|[[Vilyuy Traps]]

|{{sort|.0373|373}}

|{{sort|.00320|320}}

|
|[[Late Devonian extinction#Magmatism|Late Devonian extinction]]<ref>{{Cite journal|doi = 10.1016/j.palaeo.2013.06.020|title = New 40Ar/39Ar and K–Ar ages of the Viluy traps (Eastern Siberia): Further evidence for a relationship with the Frasnian–Famennian mass extinction|last = J|first = Ricci |display-authors=etal |date = 2013|journal = Palaeogeography, Palaeoclimatology, Palaeoecology|volume = 386|pages = 531–540| bibcode=2013PPP...386..531R }}</ref>
|-
|[[Southern Oklahoma Aulacogen]]
|{{sort|.0540|540}}
|{{sort|.00040|40}}
|250,000
|End-[[Ediacaran]] event<ref>{{Cite journal|last1=Brueseke|first1=Matthew E.|last2=Hobbs|first2=Jasper M.|last3=Bulen|first3=Casey L.|last4=Mertzman|first4=Stanley A.|last5=Puckett|first5=Robert E.|last6=Walker|first6=J. Douglas|last7=Feldman|first7=Josh|date=2016-09-01|title=Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)|journal=[[Lithos (journal)|Lithos]] |volume=260|pages=164–177|doi=10.1016/j.lithos.2016.05.016|bibcode=2016Litho.260..164B|doi-access=free}}</ref>
|-

|[[Arabian-Nubian Shield]]{{citation needed|date=June 2021}}

|{{sort|.0870|850}}

|{{sort|.02700|2700}}

|
|
|-

|[[Mackenzie Large Igneous Province]]

|{{sort|.1270|1270}}

|{{sort|.02700|2700}}

|{{sort|500|500,000<ref name="QIE">{{cite book|last=Lambert|first=Maurice B.|title=Volcanoes|year=1978|publisher=[[Energy, Mines and Resources Canada]]|location=[[North Vancouver (district municipality)|North Vancouver]], [[British Columbia]]|isbn=978-0-88894-227-2|url-access=registration|url=https://archive.org/details/volcanoes0000lamb}}</ref>}}

|Contains the [[Coppermine River Group|Coppermine River flood basalt]]s related to the [[Muskox intrusion|Muskox layered intrusion]]<ref name="AS">{{cite book|last=Ernst|first=Richard E.|author2=Buchan, Kenneth L.|title=Mantle plumes: their identification through time|publisher=[[Geological Society of America]]|year=2001|pages=143, 145, 146, 147, 148, 259|isbn=978-0-8137-2352-5}}</ref>
|}

===Elsewhere in the Solar System===
Flood basalts are the dominant form of magmatism on the other planets and moons of the Solar System.<ref>{{cite journal |last1=Self |first1=Stephen |last2=Coffin |first2=Millard F. |last3=Rampino |first3=Michael R. |last4=Wolff |first4=John A. |title=Large Igneous Provinces and Flood Basalt Volcanism |journal=The Encyclopedia of Volcanoes |date=2015 |pages=441–455 |doi=10.1016/B978-0-12-385938-9.00024-9|isbn=9780123859389 }}</ref>

The [[lunar mare|maria]] on the [[Moon]] have been described as flood basalts<ref name=Benes1979>{{cite journal |last1=Benes |first1=K. |year=1979 |title=Flood basalt volcanism on the Moon and Mars |journal=Geologie en Mijnbouw |volume=58 |number=2 |pages=209–212}}</ref> composed of picritic basalt.<ref>{{cite journal |last1=O’Hara |first1=M. J. |title=Flood Basalts and Lunar Petrogenesis |journal=Journal of Petrology |date=1 July 2000 |volume=41 |issue=7 |pages=1121–1125 |doi=10.1093/petrology/41.7.1121|doi-access=free }}</ref> Individual eruptive episodes were likely similar in volume to flood basalts of Earth, but were separated by much longer quiescent intervals and were likely produced by different mechanisms.<ref>{{cite journal |last1=Oshigami |first1=Shoko |last2=Watanabe |first2=Shiho |last3=Yamaguchi |first3=Yasushi |last4=Yamaji |first4=Atsushi |last5=Kobayashi |first5=Takao |last6=Kumamoto |first6=Atsushi |last7=Ishiyama |first7=Ken |last8=Ono |first8=Takayuki |title=Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder data: MARE VOLCANISM BASED ON KAGUYA LRS DATA |journal=Journal of Geophysical Research: Planets |date=May 2014 |volume=119 |issue=5 |pages=1037–1045 |doi=10.1002/2013JE004568|s2cid=130489146 |doi-access=free }}</ref>
[[File:G19 025499 1789 XI 01S200W.jpg|thumb|Flood Basalt on Mars]]
Extensive flood basalts are present on Mars.<ref>{{cite journal |last1=Jaeger |first1=W.L. |last2=Keszthelyi |first2=L.P. |last3=Skinner |first3=J.A. |last4=Milazzo |first4=M.P. |last5=McEwen |first5=A.S. |last6=Titus |first6=T.N. |last7=Rosiek |first7=M.R. |last8=Galuszka |first8=D.M. |last9=Howington-Kraus |first9=E. |last10=Kirk |first10=R.L. |title=Emplacement of the youngest flood lava on Mars: A short, turbulent story |journal=Icarus |date=January 2010 |volume=205 |issue=1 |pages=230–243 |doi=10.1016/j.icarus.2009.09.011|bibcode=2010Icar..205..230J }}</ref>

== Uses ==
Trap rock is the most durable [[construction aggregate]] of all rock types, because the interlocking crystals are oriented at random.{{sfn|Philpotts|Ague|2009|p=52}}

==See also==
{{commons category|Flood basalts}}
{{Portal|Geology}}
*{{annotated link|Supervolcano}}
*{{annotated link|Volcanic plateau}}

==References==
{{Reflist}}

==External links==
* {{YouTube|st_2C_Wrw4A|Flood Volcanism Explained}}

{{basalt}}
{{Doomsday}}
{{Authority control}}

{{DEFAULTSORT:Flood Basalt}}
[[Category:Basalt]]
[[Category:Flood basalts| ]]
[[Category:Volcanic landforms]]
[[Category:Orogeny]]
[[Category:Volcanism]]
[[Category:Geological hazards]]
[[Category:Future problems]]
[[Category:Doomsday scenarios]]

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