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, plateaus, and mountain ranges.[1] However, more have been recognized such as the large Ontong Java Plateau,[2] 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.[3]
Contents
1 Formation
2 Petrography
3 Structures
4 Geochemistry
5 Other occurrences
6 List of flood basalts
7 See also
8 References
Formation
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
Lava flows at Holuhraun, Iceland, September, 2014
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 state, and the biota resilience to change.[4]
One proposed 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 have a very low viscosity, which is why they 'flood' rather than form taller volcanoes. Another explanation is that they result from the release, over a short period, of melt that has accumulated in the mantle over a long period.[5]
The Deccan Traps of central India, the Siberian Traps, and the Columbia River Plateau of western North America are three regions covered by prehistoric flood basalts. The Mesoproterozoic Mackenzie Large Igneous Province in Canada contains the Coppermine River flood basalts related to the Muskox layered intrusion. The maria on the Moon are additional, even more extensive, 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 (Siberian Traps). The thickness can vary from 2000 metres (Deccan Traps) to 12,000 m[citation needed] (Lake Superior). These are smaller than the original volumes due to erosion.
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 in a fine-grained matrix. These phenocrysts are pyroxenes (augite and pigeonite), plagioclases, opaque crystals such as titanium rich magnetite or ilmenite, and occasionally some olivine. Sometimes more differentiated volcanic products such as 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 (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 the surface.
- with a chaotic surface : the basalt flood is very rich in bubbles of gas, with an irregular, fragmental surface. Degassing was difficult (less fluid 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 lava flow, produced by eruptions from Puy de la Vache and Puy de Lassolas.
Geochemistry
Multiple flood basalt flows of the Chilcotin Group, British Columbia, Canada
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 flood basalts can be distinguished :
- those poor in P2O5 and in TiO2, called low phosphorus and titanium
- those rich in P2O5 and in TiO2, called 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 low phosphorus and titanium type has an excess of elements from the crust such as potassium and strontium.
The content in incompatible elements of flood basalts is lower than that of ocean island basalts, but higher than that of mid-ocean ridge basalts.
Other occurrences
Major flood basalts, large igneous provinces and traps; click to enlarge.
Basalt floods on the planet Venus are larger than those on Earth.
List of flood basalts
Representative continental flood basalts (also known as traps) and oceanic plateaus, arranged by chronological order, together forming a listing of large igneous provinces:[6]
| Name | Initial or peak activity (Ma ago) | Surface area (in thousands of km2) | Volume (in km3) | Associated event |
|---|---|---|---|---|
Chilcotin Group | 10 | 50 | 3300 | |
Columbia River Basalt Group | 17 | 160 | 174,300 | Yellowstone Hotspot[7][8] |
Ethiopia-Yemen Continental Flood Basalts | 31 | 600 | 350,000 | |
North Atlantic Igneous Province (NAIP) | 56 (phase 2) | 1300 | 6,600,000 | Paleocene–Eocene Thermal Maximum[9] |
Deccan Traps | 66 | 1500 | 3,000,000 | Cretaceous–Paleogene extinction event |
Caribbean large igneous province | 95 (main phase) | 2000 | 4,000,000 | Cenomanian-Turonian boundary event (OAE 2)[9] |
Kerguelen Plateau | 119 | 1200 | Aptian extinction[10] | |
Ontong-Java Plateau | 120 (phase 1) | 2000 | 80,000,000 | Selli event (OAE 1a)[9] |
High Arctic Large Igneous Province (HALIP) | 120-130 | 1000 | Selli event (OAE 1a)[11] | |
Paraná and Etendeka Traps | 132 | 1500 | 2,300,000 | |
Karoo and Ferrar Provinces | 183 | 3000 | 2,500,000 | Toarcian turnover [12] |
Central Atlantic Magmatic Province | 201 | 11000 | ~2–3 × 106 | Triassic–Jurassic extinction event[13] |
Siberian Traps | 251 | 7000 | 4,000,000 | Permian–Triassic extinction event[14] |
Emeishan Traps | 265 | 250 | 300,000 | End-Capitanian extinction event[15] |
Viluy Traps | 373 | 320 | Late Devonian extinction[16] | |
Southern Oklahoma Aulacogen | 540 | 40 | 250,000 | End-Ediacaran event[17] |
Arabian-Nubian Shield | 850 | 2700 | ||
Mackenzie Large Igneous Province | 1270 | 2700 | 500,000 |
See also
Large igneous province – Huge regional accumulation of igneous rocks
Oceanic plateau – Relatively flat submarine region that rises well above the level of the ambient seabed
Supervolcano – A volcano that has erupted 1000 cubic km in a single eruption
Volcanic plateau – A plateau produced by volcanic activity
List of flood basalt provinces – Continental flood basalts and oceanic plateaus
References
 | Wikimedia Commons has media related to Flood basalts. |
^ Michael R. Rampino & Richard B. Stothers (1988). "Flood Basalt Volcanism During the Past 250 Million Years". Science. 241 (4866): 663–668. Bibcode:1988Sci...241..663R. doi:10.1126/science.241.4866.663. PMID 17839077.CS1 maint: Uses authors parameter (link) .mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
PDF via NASA[permanent dead link]
^ Neal, C.; Mahoney, J.; Kroenke, L. (1997). "The Ontong Java Plateau" (PDF). Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism, Geophysical Monograph 100. Archived from the original (PDF) on 2017-01-01.
^ Negi, J. G.; Agrawal, P. K.; Pandey, O. P.; Singh, A. P. (1993). "A possible K-T boundary bolide impact site offshore near Bombay and triggering of rapid Deccan volcanism". Physics of the Earth and Planetary Interiors. 76 (3–4): 189. Bibcode:1993PEPI...76..189N. doi:10.1016/0031-9201(93)90011-W.
^ David P.G. Bond & Paul B. Wignall (2014). "Large igneous provinces and mass extinctions: An update". GSA Special Papers: 590. doi:10.1130/2014.2505(02). Archived from the original on 2014-08-06.CS1 maint: Uses authors parameter (link)
^ Foulger, G.R. (2010). Plates vs. Plumes: A Geological Controversy. Wiley-Blackwell. ISBN 978-1-4051-6148-0.
^ 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
^ M.A. Richards, R.A. Duncan, V.E. Courtillot; Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails; SCIENCE, VOL. 246 (1989) 103–108
^ Barbara P. Nash, Michael E. Perkins, John N. Christensen, Der-Chuen Lee, & A.N. Halliday; The Yellowstone hotspot in space and time: Nd and Hf isotopes in silicic magmas; Earth and Planetary Science Letters 247 (2006) 143–156
^ abc David Bond; Paul Wignall. "Large igneous provinces and mass extinctions: An update" (PDF). p. 17. Archived from the original (PDF) on 2016-01-24.
^ Wallace, P. J.; Frey, F. A.; Weis, D.; Coffin, M. F. (2002). "Origin and Evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago: Editorial". Journal of Petrology. 43 (7): 1105–1108. Bibcode:2002JPet...43.1105W. doi:10.1093/petrology/43.7.1105.
^ Polteau, S.; Planke, S.; Faleide, J. I.; Svensen, H.; Myklebust, R. "The Cretaceous High Arctic Large Igneous Province" (PDF). Archived from the original (PDF) on 2016-01-24.
^ Pálfy, József; Smith, Paul L. (August 2000). "Synchrony between Early Jurassic extinction, oceanic anoxic event, and the Karoo-Ferrar flood basalt volcanism". Geology. 28 (8): 747–750. doi:10.1130/0091-7613(2000)28<747:SBEJEO>2.0.CO;2.
^ Blackburn, Terrence J.; Olsen, Paul E.; Bowring, Samuel A.; McLean, Noah M.; Kent, Dennis V; Puffer, John; McHone, Greg; Rasbury, Troy; Et-Touhami7, Mohammed (2013). "Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province". Science. 340 (6135): 941–945. Bibcode:2013Sci...340..941B. doi:10.1126/science.1234204. PMID 23519213.
^ Campbell, I; Czamanske, G.; Fedorenko, V.; Hill, R.; Stepanov, V. (1992). "Synchronism of the Siberian Traps and the Permian-Triassic Boundary". Science. 258 (5089): 1760–1763. Bibcode:1992Sci...258.1760C. doi:10.1126/science.258.5089.1760. PMID 17831657.
^ Zhou, MF et al., (2002). "A temporal link between the Emeishan large igneous province (SW China) and the end-Guadalupian mass extinction". Earth and Planetary Science Letters. 196: 113–122. Bibcode:2002E&PSL.196..113Z. doi:10.1016/s0012-821x(01)00608-2.
^ J, Ricci et al, (2013). "New 40Ar/39Ar and K–Ar ages of the Viluy traps (Eastern Siberia): Further evidence for a relationship with the Frasnian–Famennian mass extinction". Palaeogeography, Palaeoclimatology, Palaeoecology. doi:10.1016/j.palaeo.2013.06.020.
^ Brueseke, Matthew E.; Hobbs, Jasper M.; Bulen, Casey L.; Mertzman, Stanley A.; Puckett, Robert E.; Walker, J. Douglas; Feldman, Josh (2016-09-01). "Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)". Lithos. 260: 164–177. Bibcode:2016Litho.260..164B. doi:10.1016/j.lithos.2016.05.016.
White, R.S.; McKenzie, D.P. (1989). "Magmatism at rift zones: The generation of volcanic continental margins and flood basalts". J. Geophys. Res. 94: 7685–7729. Bibcode:1989JGR....94.7685W. doi:10.1029/jb094ib06p07685.
