Magmatic Greater Province

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Karoo Basalt , an igneous large province in South Africa

A magmatic United Province ( English large igneous province , shortly LIP ) is an area of the earth's crust , the very large amounts of igneous rocks includes (to the order 1 million km 3 on surfaces of several million km 2 ), both intrusive and extrusiv may be and formed in geologically short periods of time.

Most of the igneous major provinces are made up of basalt , but some contain large amounts of rhyolite , such as the Columbia Plateau basalt in the western United States . This rhyolite typically has only a low water content and significantly higher eruption temperatures (850 ° C to 1000 ° C) compared to the rhyolite that forms on island arcs .

Some of the magmatic large provinces are still more or less intact, such as the Deccan Traps , while others are due to plate tectonic decompose movements in parts such as the Central Atlantic Magmenprovinz ( Central Atlantic Magmatic Province , shortly CAMP ), held today in Brazil , the eastern United States, Canada, and northwest Africa .

definition

Columbia Flood Basalt , an igneous major province of the western United States

The English term Large Igneous Province goes back to MF Coffin and O. Eldholm in 1992. They referred to a number of areas that are made up of mafic rocks , have an area of ​​more than 100,000 km² (slightly larger than Portugal ), are triggered by processes that are not connected to normal plate tectonics and ocean floor spreading , and are geologically short Period, typically in a million years or less.

According to the original definition, igneous large provinces include continental flood basalts , oceanic plateaus , large swarms of dykes (most of which represent a volcanic province eroded to the roots ) and dykes, as well as passive continental margins characterized by volcanic activity . However, the definition of igneous large provinces is still in flux and is constantly being expanded and refined. In the meantime, not only mafic rocks, but all igneous rocks are included in the definition that meet the requirement for the formation of large quantities within short geological periods. In addition, the inclusion of magmatites formed by normal plate tectonic processes has been suggested if they have these characteristics. Large granite intrusions such as those of the South American Andes or western North America are also related to the igneous large provinces.

Divided, the igneous United Provinces, as suggested by Hetu C. Sheth in 2007 in the two groups by volcanism caused Volcanic United Provinces ( Large Volcanic Provinces or LVP ) and by Plutonismus incurred Plutonian United Provinces ( Large Plutonic Provinces , short LPP ).

Theories on Education

Dekkan-Trapp near Matheran east of Mumbai

The vast extent of the magmatic provinces, often several million square kilometers, and their volume of up to over a million cubic kilometers in connection with their geologically rapid formation, which is an order of magnitude greater than the basalt output of the mid-ocean ridges , is not yet fully understood. They are often linked to active hotspots by a chain of volcanic islands or volcanoes. Mantle plumes are therefore assumed to be the cause of many, if not all, magmatic large provinces that were not formed by normal plate tectonics .

According to this hypothesis, large masses of hot material rise from the earth's mantle . On the ascent they form a mushroom-shaped head, which is supplied with replenishment by a thin stem. When this hot mass hits the underside of the lithosphere , it spreads and melts, so that large amounts of basalt magma form within one to two million years. The stem, which also rises, creates a long chain of linear volcanic or volcanic island chains because the lithospheric plate moves over it, but the stem remains essentially stationary. The impact of the mantle plume on the underside of a lithospheric plate could, according to this theory, cause it to break apart and thus be responsible for the appearance of assigned magmatic large provinces on both sides of the resulting ocean. An example of this is the Paraná basalt in South America and the Etendeka basalt in Africa.

Other theories for the formation of igneous large provinces lead them back to the splitting off ( delamination ) of eclogitic lower crust, or to the side effects of powerful lithosphere. A meteor strike is also being considered .

Relationships with extinction events

The formation of igneous large provinces seems to be connected in some cases in the history of the earth to oceanic anoxic events or mass extinctions . The origin of the Deccan Trapps coincides with the mass extinction at the Cretaceous-Tertiary border , that of the Karoo basalt and the then associated Ferrar basalt of the Antarctic during the Jurassic extinction event on the Pliensbachium / Toarcium border . The emergence of the Central Atlantic Magma Province is said to be responsible for the disappearance of numerous species at the transition between the Triassic and Jurassic , and the Siberian Trapp for the largest known mass extinction at the Perm-Triassic border .

Various mechanisms have been proposed to explain the link between the formation of magmatic provinces and mass extinctions, including the release of large amounts of sulfur dioxide and the resulting sulfuric acid in the atmosphere, causing temperatures to drop. An example of this mechanism is the Laki eruption in Iceland in 1783 , which caused a drop in average temperatures in Europe. The creation of large amounts of magma in the ocean could reduce the oxygen content of seawater either by reacting directly with hydrothermal solutions or indirectly by releasing large amounts of material that causes algal blooms, which consume the oxygen.

Examples of magmatic great provinces

The following are magmatic major provinces that have been geologically explored.

Continental flood basalts

Oceanic plateaus

Volcanic passive continental margins

Gang swarms

Warehouse aisles

See also

literature

  • Don L. Anderson: Large igneous provinces, delammination, and fertile mantle . In: Elements . 1, December 2005, pp. 271-275. Retrieved February 23, 2009.
  • WRA Baragar, RE Ernst, L. Hulbert, T. Peterson: Longitudinal petrochemical variation in the Mackenzie dyke swarm, northwestern Canadian Shield . In: Journal of Petrology . 37, 1996, pp. 317-359.
  • IH Campbell: Large igneous provinces and the plume hypothesis . In: Elements . December 1, 2005. Retrieved February 23, 2009.
  • MF Coffin, O. Eldholm: Magmatism and the Causes of Continental Breakup . Volcanism and continental break-up: a global compilation of large igneous provinces. In: Storey, BC, Alabaster, T., Pankhurst, RJ (Eds.): Geological Society of London Special Publication . Geological Society of London, London 1992, p. 17-30 .
  • MF Coffin, O. Eldholm: Large igneous provinces: crustal structure, dimensions, and external consequences . In: Reviews in Geophysics . 32, 1994, pp. 1-36.
  • B. Cohen, PMD Vasconcelos, KM Knesel: Dynamic Earth: Past, Present and Future . Tertiary magmatism in Southeast Queensland. Geological Society of Australia, 2004, p. 256 .
  • International Association of Volcanology and Chemistry of the Earth's Interior. Large Igneous Provinces Commission: Large Igneous Provinces Record . Retrieved January 8, 2011.
  • AP Jones: Meteor impacts as triggers to large igneous provinces . In: Elements . 1, December 2005, pp. 277-281.
  • JS Marsh, PR Hooper, J. Rehacek, RA Duncan, AR Duncan: Large Igneous Provinces: continental, oceanic, and planetary flood volcanism . In: JJ Mahoney, MF Coffin (Eds.): Geophysical Monograph . tape 100 . American Geophysical Union, Washington, DC 1997, ISBN 0-87590-082-8 , Stratigraphy and age of Karoo basalts of Lesotho and implications for correlations within the Karoo igneous province, p. 247-272 , doi : 10.1029 / GM100p0247 .
  • DW Peate: Large Igneous Provinces: continental, oceanic, and planetary flood volcanism . In: JJ Mahoney, MF Coffin (Eds.): Geophysical Monograph . tape 100 . American Geophysical Union, Washington, DC 1997, ISBN 0-87590-082-8 , The Parana-Etendeka Province, pp. 247-272 , doi : 10.1029 / GM100p0217 .
  • K. Ratajeski: The Cretaceous Superplume. November 25, 2002, accessed January 27, 2010 .
  • J. Ritsema, HJ van Heijst and JH Woodhouse: Complex shear wave velocity structure imaged beneath Africa and Iceland . In: Science . 286, 1999, pp. 1925-1928.
  • AD Saunders: Large igneous provinces: origin and environmental consequences . In: Elements . 1, December 2005, pp. 259-263.
  • P. Wignall: The link between large igneous provinces eruptions and mass extinctions . In: Elements . 1, December 2005, pp. 293-297.
  • RE Ernst, IH Campbell and KL Buchan: Frontiers in Large Igneous Province Research . In: Lithos Special Issue . 79, 2005, pp. 271-297.

Web links

Individual evidence

  1. ↑ MF Coffin, O. Eldholm: Magmatism and the Causes of Continental Breakup . Volcanism and continental break-up: a global compilation of large igneous provinces. In: BC Storey, T. Alabaster, RJPankhurst (Eds.): Geological Society of London Special Publication . Geological Society of London, London 1992, p. 17-30 .
  2. ^ Scott Bryan, Richard Ernst: Proposed Revision to Large Igneous Province Classification. Retrieved April 9, 2018 .
  3. ↑ Hetu C. Sheth: 'Large Igneous Provinces (LIPs)': Definition, recommended terminology, and a hierarchical classification . In: Earth Science Reviews . tape 85 , 2007, p. 117–124 ( mantleplumes.org [PDF; 360 kB ]).
  4. ^ AC Kerr: Oceanic LIPS: Kiss of death . In: Elements . 1, December 2005, pp. 289-292.