Large igneous province
[1] The formation of some of the LIPs in the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about causal relationships.
In 1992, Coffin and Eldholm initially defined the term "large igneous province" as representing a variety of mafic igneous provinces with areal extent greater than 100,000 km2 that represented "massive crustal emplacements of predominantly mafic (magnesium- and iron-rich) extrusive and intrusive rock, and originated via processes other than 'normal' seafloor spreading.
Some LIPs are geographically intact, such as the basaltic Deccan Traps in India, while others have been fragmented and separated by plate movements, like the Central Atlantic magmatic province—parts of which are found in Brazil, eastern North America, and northwestern Africa.
Michael Rampino and Richard Stothers cite 11 distinct flood basalt episodes—occurring in the past 250 million years—which created volcanic provinces and oceanic plateaus and coincided with mass extinctions.
[9] This theme has developed into a broad field of research, bridging geoscience disciplines such as biostratigraphy, volcanology, metamorphic petrology, and Earth System Modelling.
[12] Earth has an outer shell made of discrete, moving tectonic plates floating on a solid convective mantle above a liquid core.
In this model, tectonic plates diverge at mid-ocean ridges, where hot mantle rock flows upward to fill the space.
Hot mantle materials rising up in a plume can spread out radially beneath the tectonic plate causing regions of uplift.
The source of many or all LIPs are variously attributed to mantle plumes, to processes associated with plate tectonics or to meteorite impacts.
Others such as the Pitcairn, Samoan and Tahitian hotspots appear to originate at the top of large, transient, hot lava domes (termed superswells) in the mantle.
Images reveal continuous but convoluted vertical paths with varying quantities of hotter material, even at depths where crystallographic transformations are predicted to occur.
Molten material is postulated to have originated from this reservoir, contributing the Baffin Island flood basalt about 60 million years ago.
Basalts from the Ontong Java Plateau show similar isotopic and trace element signatures proposed for the early-Earth reservoir.
Oceanic impacts of large meteorites are expected to have high efficiency in converting energy into seismic waves.
In addition, no clear example of impact-induced volcanism, unrelated to melt sheets, has been confirmed at any known terrestrial crater.
[17] Aerally extensive dike swarms, sill provinces, and large layered ultramafic intrusions are indicators of LIPs, even when other evidence is not now observable.
Volcanic rifted margins are characterized by: a transitional crust composed of basaltic igneous rocks, including lava flows, sills, dikes, and gabbros, high volume basalt flows, seaward-dipping reflector sequences of basalt flows that were rotated during the early stages of breakup, limited passive-margin subsidence during and after breakup, and the presence of a lower crust with anomalously high seismic P-wave velocities in lower crustal bodies, indicative of lower temperature, dense media.
The early volcanic activity of major hotspots, postulated to result from deep mantle plumes, is frequently accompanied by flood basalts.
Flood basalt provinces may also occur as a consequence of the initial hot-spot activity in ocean basins as well as on continents.
[28] Large igneous provinces are associated with a handful of ore deposit types including: Enrichment in mercury relative to total organic carbon (Hg/TOC) is a common geochemical proxy used to detect massive volcanism in the geologic record, although its foolproofness has been called into question.
