Department of Earth Sciences, Indian Institute of Technology (IIT) Bombay, Powai, Bombay
This webpage is a condensed and modified version of the paper:Sheth, H.C., Large Igneous Provinces (LIPs): Definition, recommended terminology, and a hierarchical classification, Earth-Science Reviews 85 (2007) 117124.
Click here for Discussion of this page
Click here for a counter proposal Proposed Revision to Large Igneous Province Classification by Bryan & Ernst.
The termLarge Igneous Province(LIP) has been widely applied to large flood basalt provinces (e.g., Deccan), and the termSilicic Large Igneous Province(SLIP) to volcanic provinces of dominantly felsic composition (e.g., Whitsunday, Australia). Neither of these terms has been applied to the large granitic batholiths of the world to which both are perfectly applicable. LIP has also not been applied to broad areas of contemporaneous magmatism and sizeable layered mafic intrusions. I suggest use of the term LIP only in its broad sense and propose a minimum area of 50,000 km2for a LIP.
I present a simple hierarchical classification of LIPs that is independent of composition, tectonic setting, or emplacement mechanism. I suggest that volcanic provinces such as the Deccan Traps and Whitsunday (Australia) be calledLarge Volcanic Provinces(LVPs), and large mafic intrusions, dyke swarms, and other intrusive provinces be calledLarge Plutonic Provinces(LPPs). LVPs and LPPs together cover all large igneous provinces (LIPs), having felsic to ultramafic compositions of sub-alkalic and alkalic lineages, emplaced in continental and oceanic settings.
The intrusive equivalent of LRPs are theLarge Granitic Provinces(LGPs) (e.g., the Andean batholiths), but a corresponding term for intrusive equivalents of LBPs is not necessary or warranted. The largest LBP, and LIP, is neither the Ontong Java, the Siberian Traps, or the Central Atlantic Province, but simply the ocean floor.
What is a Large Igneous Province (LIP)?
Fig. 1. A view of the spectacular, 1-km-thick exposed section through the Deccan flood basalts at Mahabaleshwar. Photo: Hetu Sheth, December 2005.
implies a province of igneous origin that is large. Clearly, the term LIP should cover large volcanic and intrusive igneous provinces, of whatever emplacement mechanism and composition. However, the term LIP has been applied to and used only for flood basalt provinces that have been the subject of great interest and extensive research recently (
, 2005; see They represent the eruption of enormous volumes of mantle-derived magma on the Earths surface in relatively short time periods. These provinces (
,Deccan, Fig. 1, andSiberian Traps) are unquestionably LIPs in the broadest sense of the term. However, large-volume felsic provinces such as the Sierra Madre Occidental inMexicoare also LIPs, as are the huge granodioritic batholiths of the world, such as those of Tibet-Himalaya, western North America, or the Andes (Fig. 2), and the largest mafic layered intrusions such as the Bushveld Intrusion. Indeed, continental rift zones such as the Rio Grande Rift and the Cameroon Line are LIPs. None of these involve flood basalts.
Coffin & Eldholm(1992, 1993, 1994) were amongst the first to use the term LIP in the current restrictive sense. They defined LIPs as massive crustal emplacements of predominantly mafic (Mg and Fe rich) extrusive and intrusive rock which originate via processes other than normal seafloor spreading [and] include continental flood basalts, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups and ocean basin flood basalts. This cannot be a suitable definition of LIP since it excludes most types of LIPs. However, the term LIP continues to be used in this restrictive sense (Ernst et al., 2005;Saunders, 2005; I suggest that the term LIP be retained but in its broadest sense, but that new, necessary terms be introduced for various categories of LIP.
The definition of large is clearly subjective and flexible, and I suggest here 50,000 km2as the lower limit for LIPs (see below). Volume would be a better size parameter than area, but area is usually easier to measure. Most LIPs are much larger than 50,000 km2. TheDeccan, for example, covers 0.5 million km2of western-central India today and has an estimated original extent of 1.5 million km2(Wadia, 1975). The Siberian province is vastly larger (Reichow et al., 2002). The smaller of the flood basalt provinces, such as the Emeishan province (~250,000 km2;He et al., 2003) and theColumbia River province(~164,000 km2;Hooper, 1988; Ed: See also comment onColumbia River Province size), are also well above the lower size threshold I suggest.
Fig. 2 (at left). A llama overlooks the ruins of Machu Picchu, situated at 2500 m above sea level in the Peruvian batholith, a felsic large igneous province. Photo: Hetu Sheth, November 2001.
Large Volcanic Provinces (LVPs) and Large Plutonic Provinces (LPPs)
Just as there are large mafic volcanic provinces as exemplified by theDeccanand theColumbia River Basalts, there are large felsic volcanic provinces dominated by highly evolved (broadly rhyolitic) lavas. Several such provinces (the so-calledSLIPs) are described byBryan et al.(2000, 2002;SLIPs webpage) and include the early Cretaceous Whitsunday province and the Sierra Madre Occidental. There also are large volcanic provinces dominated by andesite, and others that comprise subequal volumes of basaltic and rhyolitic lavas. For all these volcanic provinces, of whatever composition, I propose the termLarge Volcanic Provinces (LVPs). Obviously, all LVPs are LIPs, but all LIPs are not LVPs.
After Pluto, the Roman god of the underworld, I suggest the termLarge Plutonic Provinces (LPPs)for all intrusive provinces meeting the size requirements, whatever their composition, emplacement depth, and internal structure. This category includes mafic-ultramafic intrusions such as the Bushveld Complex, large granite batholiths such as the Andean and Tibet-Himalayan batholiths, and giant dyke swarms such as the Mackenzie dyke swarm of Canada (Ernst et al., 1995).
Large Rhyolitic Provinces (LRPs) and Large Granitic Provinces (LGPs)
The term silicic LIP or SLIP used for rhyolite-dominated large volcanic provinces (Bryan et al., 2000, 2002;SLIPs webpage) recognizes the fact that LIPs can be of felsic composition. However, this term should strictly include the big granitic batholiths of the world but does not. I propose that large volcanic provinces dominated by broadly rhyolitic rocks (i.e., the rhyolite-rhyodacite-dacite-trachyte compositional range, both sub-alkalic and alkalic lineages) be calledLarge Rhyolitic Provinces (LRPs). Besides the Whitsunday and the Sierra Madre Occidental provinces, the NeoproterozoicMalaniprovince of northwestern India (Sharma, 2004, 2005) is a good example.
Plutonic provinces with the same compositions can similarly be calledLarge Granitic Provinces (LGPs). Granitic implies the compositional range granitegranodiorite-tonalite-trondhjemite. The Archaean-Proterozoic charnockite (hypersthenegranite) massifs of southern India (Rajesh & Santosh, 2004) are included in the LGP category. Both LRP and LGP are independent of the geodynamic origins and tectonic settings of these rocks.
I suggest that large volcanic provinces of dominantly basaltic composition be calledLarge Basaltic Provinces (LBPs). Basaltic implies the compositional range basaltic andesite-basalt-picrobasalt (and their alkalic equivalents). The rock type basaltic andesite belongs in this category because many flood basalts are in fact basaltic andesites. Examples include many Deccan lavas from the Western Ghats (see Fig. 4a on theDeccan page) and the Grande Ronde lavas of the Columbia River basalt province that constitute 85% of the volume of that province (Hooper, 1997; Ed: See also comment onColumbia River Province size).
Fig. 3 (at right). A thick pile of Palaeogene flood basalts on the Isle of Skye, Scotland. Photo: Hetu Sheth, September 2005.
Fig. 4. The Ofaerufoss in the great Eldgja (A.D. 934) fissure in southern Iceland. Photo: Hetu Sheth, September 2003.
It is to be noted that the term LBP refers not only toexclusivelybasaltic provinces that lack felsic rocks (e.g., the Columbia River province; Hooper, 1997) but equally well todominantlybasaltic provinces with subordinate amounts of more evolved rocks such as rhyolite and trachyte. Mostcontinental flood basalt(CFB) provinces are of this type. Examples of LBPs thus include theDeccanColumbia River, Rajmahal,Siberian, Emeishan, Madagascar, Karoo, Parana-Etendeka, Yemen-Ethiopia andNorth Atlantic Tertiary provinces(Fig. 3). The oceanic flood basalt provinces, the so-called oceanic plateaus (e.g.,Ontong JavaIceland, and Kerguelen; Fig. 4), are also LBPs. Large oceanic island-seamount chains such as theHawaii-Emperor (Fig. 5) and the Ninety East Ridge also belong in the LBP category, as do broad areas of diffuse basaltic volcanism on the continents (e.g.,Mongolia;Barry et al., 2003) and in the oceans (e.g., theSouth Pacific Superswell;Janney et al., 2000). The term LBP is independent of tectonic setting.
Fig. 5. Red-hot Kilauea lava in action. Photo: Hetu Sheth, July 2002.
Large Basaltic-Rhyolitic Provinces (LBRPs)
When felsic lavas and mafic lavas in an LVP each constitute nearly half of the total volume, they constitute a bimodal LVP with intermediate compositions more or less absent. These, I callLarge Basaltic-Rhyolitic Provinces (LBRPs). There are fewer members in this category than the LBPs. Examples are the Snake River Plain-OregonHigh Lava Plains provinceof the western U.S.A. (e.g.,Jordan, 2005), and the Palaeoproterozoic (2.5 2.2 Ga) Dongargarh Group in central India (Sensarma et al., 2004).
I suggest the termLarge Andesitic Province (LAP)for any andesite-dominated province that meets the LIP size requirement. No tectonic setting is implied, but it is clear that most andesites are erupted in subduction zones (Gill, 1981). This category includes as members andesitic belts along island arcs (e.g., Indonesia, Japan), active continental margins (e.g., the Ecuadorian-Colombian Andes, Peruvian-Chilean Andes, Cascades, andMexico-central America), and continental collision zones (e.g.,Iran-Turkey).
The largest LBP and LIP is not theOntong JavaSiberian Traps, or theCentral Atlantic Magmatic Province. It is, of course, the ocean floor. ThoughCoffin & Eldholm(1992, 1993, 1994) would exclude volcanic provinces formed by normal seafloor spreading from their definition of LIPs, this exclusion is not warranted. Though the formation of the ocean floor is gradual and very long-lived, the production rate is high. It takes only a 500-km-long ocean ridge segment spreading with a half-rate of 5 cm/yr to create a 100-km-long (or 50,000 km2area) expanse of new oceanic lithosphere in only 1 million years. The 50,000-km-long worldwide network of ridges, with this average half-spreading rate, creates 5 million km2of oceanic lithosphere in just 1 million years. The average thickness of the modern oceanic crust is 7 1 km (e.g., White et al., 1992), of which the basaltic part (pillow basalts and sheeted dykes) makes up ~2 km (Boudier & Nicolas, 1985;Nicolas, 1989). Thus, the lower size limit of 50,000 km2proposed here for a LIP, and the areas and volumes of most LIPs, are small in relation to the output of the mid-ocean ridge system over comparable time scales.
A hierarchical classification of large igneous provinces
The foregoing discussion shows that the term LIP is broad and vague. For this reason I suggest the hierarchical classification of LIPs described above, which is summarised in Table 1. I note the following:
The terms in boldface in Table 1, with the exception of Large Igneous Province (LIP) are proposed here for the first time. The terms in italics are either formal terms (
) currently in vogue for these provinces, or informal (
The classification proposed is independent of tectonic setting. No tectonic setting is excluded
, though most of the provinces listed belong to intraplate (continental/oceanic) or rifted continental margin. The LAP category includes members only from subduction zones.
Any LAP may include other rock types the only criterion to be satisfied by any province for inclusion in the LAP category is dominantly andesitic compositions of volcanic products and an area of at least 50,000 km
. Thus, the andesite-dominated, 1000-km-long and 50-60-km-wideMexican Volcanic Beltwith its considerable amount of alkalic, ocean-island-basalt-type magmatism (
, 2002; see alsoMexico webpages) is included in this category.
Large Basaltic Provinces (LBPs) or Large Volcanic Provinces (LVPs) in general will necessarily include, besides the lavas, their associated dyke swarms and intrusive complexes.
The category of dominantly mafic, intrusive, continental LIPs includes the layered mafic intrusions and the giant dyke swarms. Both types of features may have been feeders to flood basalt provinces now lost to erosion. The famous Skaergaard Intrusion is quite small (100 km
) and forms part of the East Greenland flood basalt province, and thus does not feature in Table 1. The Dufek and Forrestal Intrusions of Antarctica that cover ~6,600 km
, 2003) similarly belong to the Jurassic Ferrar flood basalt province. Worldwide, only the Precambrian Bushveld Complex of South Africa (60,000 km
, 2001) reaches the lower proposed size limit for a LIP. Other well-known layered mafic intrusions (Duluth, Stillwater, Muscox, Kiglapait) are well below this size.
Whereas Large Granitic Provinces (LGPs) is an apt term for broadly granitic (granite-granodiorite-tonalite) batholiths, a corresponding short and single term for dominantly mafic, intrusive, continental category (
, Large Gabbroic Provinces) does not seem possible. This is because many layered mafic intrusions have significant volumes of ultramafic rocks, and associated giant dyke swarms (
Table 1. Proposed terminology and hierarchical classification of the large igneous provinces (LIPs), with examples (Sheth,2007)
Extrusive/intrusive provinces of any composition and tectonic setting with a minimum area of 50,000 km2
(lavas: pyroclastics = 100:0 to 0:100, sub-alkalic: alkalic = 100:0 to 0:100)
LargeBasaltic-Rhyolitic Provinces (LBRPs)
Snake River Plain-Oregon High Lava Plains,
Orogenic/Anorogenic granitic batholiths:
Anorthosite massifs(size permitting)
The term Large Igneous Province (LIP) is loosely defined (Saunders, 2005), and no attempts have hitherto been made to evolve a more appropriate and accurate classification. In my opinion, LIP covers a very broad category of provinces larger than 50,000 km2in area. I suggest separate terms for each of the several categories of LIPs and define them here on the basis of dominantly extrusive or intrusive emplacement and rock compositions. Correct terminology is important as it influences the way we approach scientific problems. The classification proposed here is simple and easy to use. I hope that it will be adopted and lead to more accurate and effective communication among scientists working in this field.
I am grateful to Ian Skilling, James White, and Thor Thordarson for valuable and thought-provoking reviews, and to Ninad Bondre, Kamal Sharma, Sarajit Sensarma and Gillian Foulger for several helpful comments.
Barry, T., Saunders, A. D., Kempton, P. D., Windley, B. F., Pringle, M. S., Dorjnamjaa, D., Saandar, S., 2003. Petrogenesis of Cenozoic basalts from Mongolia: Evidence for the role of asthenospheric versus metasomatized lithospheric mantle sources.
Boudier, F., Nicolas, A., 1985. Harzburgite and lherzolite subtypes in ophiolitic and oceanic environments.
Bryan, S. E., Ewart, A., Stephens, C. J., Parianos, J., Downes, P. J., 2000. The Whitsunday volcanic province, central Queensland, Australia: lithologic and stratigraphic investigations of a silicic-dominated large igneous province.
Bryan, S. E., Riley, T. R., Jerram, D. A., Leat, P. T., Stephens, C. J., 2002. Silicic volcanism: an undervalued component of large igneous provinces and volcanic rifted margins. In: Menzies, M. A., Klemperer, S. L., Ebinger, C. J., Baker, J. (Eds.), Volcanic Rifted Margins.
Coffin, M. F., Eldholm, O., 1992. Volcanism and continental break-up: a global compilation of large igneous provinces. In: Storey, B. C., Alabaster, T., Pankhurst, R. J. (Eds.) Magmatism and the Causes of Continental Break-up.
Coffin, M. F., Eldholm, O., 1993. Scratching the surface: estimating dimensions of large igneous provinces.
Coffin, M. F., Eldholm, O., 1994. Large igneous provinces: crustal structure, dimensions, and external consequences.
Ernst, R. E., Head, J. W., Parfitt, E., Grosfils, E., Wilson, L., 1995. Giant radiating dyke swarms on Earth and Venus.
Ernst, R. E., Buchan, K. L., Campbell, I. H., 2005. Frontiers in large igneous province research.
Ferris, J. K., Storey, B. C., Vaughan, A. P. M., Kyle, P. R., Jones, P. C., 2003. The Dufek and Forrestal intrusions, Antarctica: A Centre for Ferrar large igneous province dike emplacement?
Foulger, G. R., Natland, J. H., Presnall, D. C., Anderson, D. L. (Eds.), 2005. Plates, Plumes, and Paradigms.
Gill, J. B., 1981. Orogenic Andesites and Plate Tectonics. Springer Verlag, Berlin, 358 pp.
He, B., Xu, Y.-G., Chung, S.-L., Xiao, L., Wang, Y., 2001. Sedimentary evidence for a rapid, kilometre-scale crustal doming prior to the eruption of the Emeishan flood basalts.
Hooper, P. R., 1988. The Columbia River basalt. In: Macdougall, J. D. (Ed.), Continental Flood Basalts, pp. 1-33. Kluwer Acad. Publ., Dordrecht.
Hooper, P. R., 1997. The Columbia River flood basalt province: current status. In: Mahoney, J. J., Coffin, M. F. (Eds.), Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism.
Am. Geophys. Union Geophys. Monogr.
Janney, P., Macdougall, J. D., Natland, J. H., Lynch, M. A., 2000. Geochyemical evidence from the Pukapuka volcanic ridge system for a shallow enriched mantle domain beneath the South Pacific Superswell.
Jordan, B. T., 2005. The Oregon High Lava Plains: a province of counter-tectonic age progressive volcanism. In: Foulger, G. R., Natland, J. H., Presnall, D. C., Anderson, D. L. (Eds.),Plates, Plumes, and Paradigms.
Kerr, A. C., England, R. W., Wignall, P. B. (Eds.), 2005. Mantle plumes: Physical Processes, Chemical Signatures, Biological Effects.
Macdougall, J. D. (Ed.), 1988. Continental Flood Basalts. Kluwer Acad. Publ., Dordrecht.
Mahoney, J. J., Coffin, M. F. (Eds.), 1997. Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism.
Am. Geophys. Union Geophys. Monogr.
Nicolas, A., 1989. Structures of Ophiolites and Dynamics of Oceanic Lithosphere. Kluwer, Boston.
Rajesh, H. M., Santosh, M., 2004. Charnockitic magmatism in southern India. In: Sheth, H. C., Pande, K. (Eds.) Magmatism in India through Time.
Proc. Ind. Acad. Sci. (Earth Planet. Sci.)
Reichow, M. K., Saunders, A. D., White, R. V., Pringle, M. S., AlMukhamedov, A. I., Medvedev, A., Korda, N., 2002. New
Ar data for basalts from the West Siberian Basin: extent of the Siberian flood basalt province doubled.
Saunders, A. D., 2005. Large Igneous Provinces: Origin and Environmental Consequences.
Sensarma, S., Hoernes, S., Mukhopadhyay, D., 2004. Relative contributions of crust and mantle to the origin of the Bijli Rhyolite in a Palaeoproterozoic bimodal volcanic sequence (Dongargarh Group), central India. In: Sheth, H. C., Pande, K. (Eds.) Magmatism in India through Time.
Proc. Ind. Acad. Sci. (Earth Planet. Sci.)
Sharma, K. K., 2004. The Neoproterozoic Malani magmatism of the northwestern Indian shield implications for crust-building processes. In: Sheth, H. C., Pande, K. (Eds.) Magmatism in India through Time.
Proc. Ind. Acad. Sci. (Earth Planet. Sci.)
Sharma, K. K., 2005. The Malani magmatism: an extensional lithospheric tectonic origin. In: Foulger, G. R., Natland, J. H., Presnall, D. C., Anderson, D. L. (Eds.)Plates, Plumes and Paradigms.
Sheth, H. C., Pande, K. (Eds.), 2004. Magmatism in India through Time.
Proc. Ind. Acad. Sci. (Earth Planet. Sci.)
Sheth, H. C., Torres-Alvarado, I. S., Verma, S. P., 2000. Beyond subduction and plumes: a unified tectonic-petrogenetic model for the Mexican Volcanic Belt.
Verma, S. P., 2002. Absence of Cocos plate subduction-related basic volcanism in southern Mexico: A unique case on Earth?
Wadia, D. N., 1975. The Geology of India, 4
White, R. S., McKenzie, D., ONions, R. K., 1992. Oceanic crustal thickness from seismic measurements and rare earth element inversions.
Winter, J. D., 2001. An Introduction to Igneous and Metamorphic Petrology. Prentice-Hall, New Jersey, 697 pp.
Without getting into a protracted debate, I find the new classification interesting but too broad. It seems to encompass alllarge provinces that have protracted magmatism and, technically, should also include the entire ocean floor, as Hetu says. An important feature of LIPs, and one which makes their defintion rather more restrictive, is the period of emplacement which I have always assumed to be geologically short [here, short is as fairly loosely defined as islarge].
Any useful classification scheme needs to give a least a glance towards process. Thus LIPs are produced by unusual processes (plume or not), and are thus distinct from subduction and MOR-related systems (but can overlap geographically and tectonically with these (viz Iceland and CRB).
I think Hetu has hit on an interesting topic; existing definitions are vague, as a number of us have indicated (see recent issue of Elements). Im not sure that this is necessarilya bad thing weve all tried todefine the termsplume or lithosphere – but the definition should not be too all-embracing. If it does, it becmes unwieldy and wont, I believe, help further our understanding.
Here are two relatively recent encyclopedia articles of relevance:
Coffin, M.F., and Eldholm, O., 2001. Large igneous provinces, in Steele, J.H., Thorpe, S.A., and Turekian, K.K., eds., Encyclopedia of Ocean Sciences, Academic Press, London: 1290-1298.
Coffin, M.F., and Eldholm, O., 2005. Large igneous provinces, in Selley, R.C., Cocks, R., and Plimer, I.R., eds., Encyclopedia of Geology, Elsevier, Oxford: 315-323.
I always thought that the duration and rapidity had to be controlled by the lithosphere (stress-valve) rather than mantle temperature, and that large-scale ponding prior to release was implied. I dont know if this glance toward process can be built into a definition. LIPs differ from non LIPs in that the process is finite in duration (the rates and volumes are not exceptional). This could, of course, reflect the size of the fertile blobs, or the duration of extension. The tectonic context is also necessary.
An updated definition of LIP may be in order ( and plume! ). Lavoisier said that you cannot pretend to have a science unless you have a language and definitions. Things have moved along since the Encyclopedia artiicles were published. The Elements volume is a fantastic update of the situation. But the ideas that mantle convection controls the plates rather than vice versa , and that magma volume and rate is a proxy for high T are still around. You have to decide whether volcanism, anomalous or not, and uplift and rifting, is cause or effect. The main changes in thinking are papers on melting instabilities and on the possibility that high homologous temperature, rather than high absolute temperature, is the key variable. Papers by Tackley, Stevenson, Raddick, Parmentier…on melt instabilities, and Abt, Rudnick, Kays, Cin-Ty Lee, Humphreys etc. on delamination, are important in the LIP discussion.
Although LIPs MAY require very large absolute temperature (rather than ponding, fertility, shallow recycling, delamination, homologous T, melting instabilities and lithospheric control), this should not be part of the definition. If short duration is part of the definition it should not then be stated that this is a characteristic of a plume, as Richards and Courtillot did; this is circular reasoning. Stress and fertility can change rapidly; temperature cannot.
I agree with you that process (source T or fertility, fundamental cause such as plume, EDGE convection, delamination etc) should not play a role in the definition or classification of a LIP. My initial comment was intended to mean that a definition or classification, to be useful, should bear the processes in mind. A similar approach is taken with the classification of most rocks, especially igneous (e.g, the broad division into volcanic and plutonic nods towards a recognition of emplacement style, but is not in itself dependent upon that process).
Here is my contribution to the current discussion of LIP definition. There are three points relevant to a definition of LIPs:
To these Hetu has proposed subclassifications based on magmatic composition (mafic, felsic intermediate) and whether the main magmatism is volcanic or intrusive (plutonic).
SIZE OF LIPS: See a proposal for a new classification of magmatic events (including LIPs) based on size which is extracted from the attached paper byBleeker & Ernst (2006).Note that we retain the conventional minimum size of 100,000 km2, in disagreement withHetus suggestions of50,000 km2
Bleeker & Ernst (2006) We suggest the following classification of event sizes, compatible with common usage in large igneous province terminology (e.g. Coffin & Eldholm 1994, 2001):
The first three categories (giant, major, and substantial) qualify the size of what are generally considered large igneous provinces (LIPs), with (eruptive) volume estimates on the order of one to several million cubic kilometres. When intrusive and underplated volumes are considered as well, some of the largest LIPs would classify as true giants, e.g. the Ontong Java plateau at ca. 45x106km3. The two smaller categories (moderate to small) describe sub-LIP scale events.
 Coffin & Eldholm (1994, 2001) and others (e.g. Ernst et al. 2005) have generally used a surface area of 105km2, rather than volume estimates, to define LIPs.
Some LIPs are clearlyvery short duration events, Deccan, Siberian Traps, Mackenzie (1270 Ma). However, otherevents are clearly more protracted; Keweenawan (1116-1085 Ma), probably Parana, Iapetus-margin (615-550 Ma), Matachewan (2500-2450 Ma), and many potential Archean analogues.Many of the protracted events are actually characterized by multiple pulses (e.g. the NAIP, Blekinge Dalarna (975-948 Ma; main pulse at 948 Ma), and Central Scandinavian Dolerite Group event (1270-1248; 3 pulses)). So a short duration is not a required component of the LIP definition.
Ideally, LIP definition and classification should be based on observable/measurable characteristics, not be based on interpreted origin, plume, rifting, delamination. So Hetus classification based on magmatic type (dominantly mafic, felsic intermediate, extrusive, intrusive) is interesting in that regard. I certainly agree that discussion of the LIP definition is required. Do we go toward something similar to Hetus, or do we stay with the traditional definition (e.g. Coffin & Eldholm definition) which links LIPs to process other than normal sea floor spreading, and whichimplicitly excludes normal subduction-related magmatism. I look forward to further discussion on this.
But I disagree strongly on at least two points in Hetus article:
1) It is a mistake to group the 1270 Ma Mackenzie with the Tibet-Himalayan batholiths as LPPs. There is no insight or understanding gained by grouping a classicmafic-ultramaficevent(rifting/plume related) witha classic felsicevent (collision/subduction related).
2) I think the 100,000 km2minimum size for LIPs should be retained (see my point above).
Size should not be in the definition if it is arbitrary. Is there a natural cut off? Likewise for duration and rate and thickness. If these merge into non LIPs then there may be a continuum and artificial limits would not be helpful. LIPs occur when continents are converging and diverging. They also overlap MORB, back arc basin and arc basalts in chemistry. The temperatures of the magmas or parents or source mantle would be helpful.
Clearly size, duration, rate and thickness are all a continuum from very small to very large. Maybe instead of proliferating categories we should just dump the term LIP it might be misleading us.
I am pleased to see the amount of discussion my contribution has generated. In this common Reply, I provide some clarifications on the issues raised by the readers above.
First, there seems to be complete (and fortunate) agreement that LIP is a broad and vague term. Dr. Saunders words, the definition should not be too all-embracing. If it does, it becmes unwieldy and wont help further our understanding are perfectly true of LIP. LIP IS an al