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Home , Deccan Traps, Large igneous province, Magmatism, Mantle plume, Ontong Java Plateau, Siberian Traps

Large Igneous Provinces: Origin and Environmental

Consequences Thousand-metre cliffs, Kivioqs Fjord, East . PHOTO IAN PARSONS Andrew D. Saunders1

pisodically, the erupts large quantities of basaltic in the main LIP, are an important part of the story, but will not be geologically short periods of time. This results in the formation of large considered in detail here. igneous provinces, which include continental provinces, E The locations and ages of the main volcanic rifted margins, and giant oceanic plateaus. These fluctuations in the LIPs are shown in FIGURE 1. This Earth’s system are still poorly understood. Do they owe their origin to selection is biased: it does not plumes, meteorite impacts, or -controlled processes? Whatever include the large silicic provinces (e.g. Chon Aike in southernmost their origin they correlate closely with major changes in oceanic and South America or the Sierra Madre atmospheric chemistry and may trigger global mass . in Mexico); the majority of the LIPs in Figure 1 are predominantly KEYWORDS: Continental flood , oceanic plateaus, mass extinctions, basaltic. It is also ageist: it does not mantle and temperature include any LIP older than 250 Ma, for example, the Emeishan INTRODUCTION Province in China () and the numerous and Archaean LIPs. It is impor- It has been nearly 15 years since the term ‘large igneous tant to stress that LIP formation has occurred throughout province’ was introduced by Mike Coffin and Olaf Eldholm Earth history and not just in the Mesozoic and Cenozoic, (1991, 1994). An umbrella term to include continental although they may occur in cycles (e.g. Ernst et al. 2005); flood basalt provinces, oceanic plateaus, volcanic rifted there is an increase in LIP formation in the (Lar- margins and aseismic ridges, it rapidly entered common son 1991), and Prokoph et al. (2004) have suggested cycles parlance even though it was, and remains, loosely defined. of LIP formation. The key aspect of large igneous provinces (LIPs) is that they represent anomalously high magmatic fluxes. The magma The information database is also strongly skewed in favour is usually basaltic, but may be rhyolitic. They are large in of the continental flood basalt provinces. Accessibility to area, covering many thousands if not millions of square the deeper parts of the dissected and faulted volcanic pile kilometres, and they testify to unusual geological processes, means that a greater range of compositions and a wider involving large amounts of thermal energy. Where this range of ages can be sampled in the continental sequences energy comes from – deep within the Earth as a mantle than in the oceanic plateaus. Some oceanic plateaus have, plume, from a meteorite impact, or from sinking of dense however, subsequently collided with a or a roots from the base of the continental or lithosphere continental margin, with the result that important infor- (‘’) – is a matter of considerable debate. As will mation can be obtained from the deeper crustal sections. be seen from the papers in this issue of Elements, there is Thus, the collision of the Caribbean Plateau with South also debate about their environmental effects. Could the America has provided a wealth of information about its pet- formation of such provinces cause the collapse of ecosys- rogenesis (Kerr et al. 1997). Similarly, the collision of the tems, either by interrupting oceanic circulation systems or with the Solomon Islands allows us to by releasing large masses of volcanic , and trigger walk through the top three kilometres of the plateau’s mass extinctions? Certainly, the timing of LIPs and mass basaltic crust. Otherwise we would be totally reliant on extinctions suggests some causality, but we do not, as yet, cored material from the top few hundred metres of crust – understand its . metaphorically, pin-pricking the elephant (Tejada et al. 2004). The basements of many other plateaus are, however, LIPS AND LIPS sampled entirely by drilling and dredging (e.g. ) or remain unsampled. No two LIPs are the same. Just as Read (1948) recognised that there are ‘Granites and Granites,’ the term LIPs encom- passes a wide range of geological structures and processes. FORMATION For the purpose of this issue, we are focusing on the conti- There are almost as many theories and models for the for- nental flood basalt provinces and their oceanic equivalents, mation of LIPs as there are individual provinces. I have the oceanic plateaus. Volcanic trails (forming aseismic attempted to summarise these models, and some of the pre- ridges across the ocean floor), which often away from dictions that arise, in TABLE 1. It is likely that no single model can account for all LIPs, and the predictions from each model are not fully understood or known. Most mod- 1. Department of Geology els agree that large amounts of thermal energy are required University of Leicester in order to produce large volumes of magma over a geolog- Leicester LE1 7RH, UK ically short period of time. Given that most LIPs are E-mail: [email protected]

E LEMENTS, VOL. 1, PP. 259–263 259 DECEMBER 2005 FIGURE 1 Map showing the distribution of the main Mesozoic and So how do we generate the high crustal thicknesses found Cenozoic large igneous provinces (continental flood in LIPs (typically 35 km for an )? There are basalts and basaltic oceanic plateaus), modified after Coffin and Eld- holm (1991). Also included are present-day hotspots (red spots), which several ways of doing this. First, we can increase the tem- may be related to individual LIPs (e.g. Réunion to the ; perature of the source. A straightforward increase in source Galapagos to the Caribbean Plateau) via plate reconstructions and potential temperature from 1300°C to 1500°C can produce volcanic chains. The are shown buried (striped ornamen- a 30+ km thick layer of melt. This is at the heart of the tation) beneath the West Siberian Basin. CAMP: Central Atlantic Mag- matic Province, located along the eastern edge of North and South plume model (White and McKenzie 1989; Campbell this America, and western edge of North Africa and southern Europe. Cre- issue), where heat energy is transferred in a mass of mantle taceous Plateaus include the Hess and Shatsky Rises, and Ontong Java ascending from a thermal boundary layer deep in the Earth and Manihiki Plateaus. (e.g. the core–mantle boundary). Second, we can increase the rate at which source material is processed through the zone of . Rather than passive upwelling (as is thought to occur at mid-ocean ridges), the mantle rock basaltic, this requires some form of energy source in the actively convects into and through the zone of partial melt- mantle. The required energy may be reduced slightly if the ing. Combined with higher temperatures, this provides a mantle source is highly fertile (see glossary). This would be potent model for large-volume melt generation, and is the case if, for example, it contains large amounts of eclog- again implicit in the plume model. Rapid fluxing may be ite (see glossary and Anderson this issue) or is volatile rich. particularly important during the start-up phase of the What is the source of this energy? And how much is (Richards et al. 1989; Campbell this issue), required? Over time, the world’s oceanic ridge system sup- when the LIP is created, but it is also a key feature of the plies a remarkably constant amount of basaltic magma. The ‘edge’ model, discussed below. The impact model (Jones thickness of the ocean crust – ignoring the sediments – is this issue) also invokes high source temperatures, induced very uniform, at about seven kilometres. There are differ- by kinetic energy following meteorite impact. And third, we ences. Very slow-spreading ridges, such as the Southwest can increase the fertility and volatile content of the source Indian Ridge, create anomalously thin crust, to the point to create more melt. None of these three factors – tempera- where it may even be absent. Similarly, ocean crust near ture, mantle ascent rates, and source composition – are major transform faults may be thin. And, conversely, in exclusive; indeed there is every reason to believe they may some areas (remarkably rare), such as , the crust is occur together. anomalously thick (perhaps as much as 35 km). But the What is the evidence for high mantle temperatures during bulk of the ocean crust is broadly uniform in thickness and LIP formation? The most direct evidence is the occurrence composition, which is remarkable given that two important of highly magnesian melts (preserved in high-Mg basalts, variables – source temperature and source composition – picrites, and ). These are found in several LIPs can have a dramatic effect on the volume and type of basalt but, importantly, not all, and this has been used as evidence produced. An increase of 100°C in the potential tempera- against an excessively hot mantle source (Anderson this ture (see glossary) of the mantle source will more than dou- issue). To counter this, it should be remembered that mag- ble the amount of melt produced, and hence double the nesian melts are more dense than normal basalt and may be thickness of the ocean crust. The source temperature of nor- trapped in magma chambers in the deep crust; in effect, mal mid-ocean ridge basalts is unlikely, therefore, to vary they are filtered out. Thus, absence of evidence for picrites, significantly. the products of crystallization of magnesian melts, is not necessarily evidence for the absence of them.

E LEMENTS 260 DECEMBER 2005 TABLE 1 PREDICTIONS ARISING FROM VARIOUS MODELS OF LIP FORMATION

Prediction Excess Regional High-T Extraterrestrial trail Currently mantle-derived uplift/doming (e.g. picrites material and leading from LIP active hotspot Model and komatiites) impact breccias Mantle plume Yes Likely Likely No Likely Possible (unless the plume (before and/or (but dense melts may impinges on the base during magmatism) not reach the surface) of thick lithosphere) Meteorite impact Likely Likely Yes Yes Possible Possible (during magmatism) (probably abundant)

Edge model, with Possible Likely Unlikely No Unlikely Unlikely enhanced mantle (if mantle can ascend (during magmatism) convection sufficiently to decompress and melt) Delamination Possible Likely Unlikely No Unlikely Unlikely (if mantle can ascend (could be substantial sufficiently to during or after decompress and melt) magmatism Melting of Possible Unlikely Unlikely No Unlikely Unlikely fertile mantle without excess heat

Arguments against very high mantle temperatures are sup- thermal energy originating from deep within the Earth. The ported by limited uplift in the vicinity of some LIPs. A hot lithosphere plays a crucial role, capping (even preventing) mantle source beneath the lithosphere would be expected melting and redirecting the hot mantle towards thin spots. to cause significant uplift, especially if it were dynamically Some LIPs may be entirely driven by lithospheric processes, emplaced by a mantle plume (Campbell this issue), but in and some may be impact generated, but the majority of some provinces the evidence for such uplift is ambiguous them appear to be plume generated. (Anderson this issue). Readers may wish to read the recent work by Burov and Guillou-Frottier (2005), however, which ENVIRONMENTAL EFFECTS suggests that the amount of uplift above a plume may be AND MASS EXTINCTIONS small, or absent, in some circumstances. There are several ways in which a LIP could affect the global If mantle plumes or impacts are not the main generators, environment. One is through the immediate, eruptive what other mechanisms may be responsible for LIP forma- release of gas and aerosols. As shown by Self et al. (this tion? King and Anderson (1995) noted that many conti- issue), a large basaltic eruption can release prodigious nental flood basalt provinces lie close to the edges of quantities of SO2, CO2 and halogens, the effects of which Archaean . They proposed that thermal insulation we are only beginning to appreciate. The initial release of by the raises the temperature of the underlying SO2 and its injection into the stratosphere could trigger a , which then flows sideways out from global volcanic , akin to the models of nuclear win- beneath the craton and under thinner lithosphere. As it ters, reducing photosynthesis through light occlusion and ascends, the mantle decompresses and melts. In this model cooling. Long-term accumulation of CO2 may lead to sub- the mantle need not be as hot as in the plume model. Fur- sequent warming – a volcanic summer – especially if the thermore, King and Anderson (1998) argued that ‘edge- biologically driven carbon-capture mechanisms are com- driven convection’, where a secondary convection cell is promised by the preceding volcanic winter. However, as established at the craton margin, could increase magma pointed out by several workers, including Self et al. (this production rates and volumes. An alternative model, but issue) and Wignall (this issue), the average flux of CO2 also involving displacement of , is the delam- released by a LIP over its entire history is not large – much ination model, in which dense lower crust and the attached less than the current annual production of anthropogenic lithospheric mantle sink into the mantle, and upper man- CO2, for example. tle flows into the ensuing space, decompressing and melt- The evidence that there is a link between LIPs and the envi- ing (Elkins-Tanton 2005; Anderson this issue). This model ronment is indicated by the close coincidence between LIPs predicts substantial uplift as the lithosphere rebounds, but and mass extinctions (FIG. 2), as noted by Vincent Cour- again does not necessarily produce high-Mg melts. It is also tillot in 1994 and subsequently developed in his book Evo- debatable whether the required volumes of magma, and lutionary Catastrophes (1999). But how does a LIP, or flood magma of the right composition, could be produced in this basalt event, trigger a mass ? What other indica- way from normal-temperature asthenospheric mantle. tors are there of ? One is a rapid shift in the My personal view is that most, if not all, LIPs can be carbon isotope record at the time of the extinctions. Such explained by mantle plumes, and that the best evidence – isotopic variations indicate massive changes in seawater picritic rocks – for the high source temperatures is often and atmospheric composition, requiring the addition of bil- hidden in the deeper crust or upper mantle. Variations in lions of tonnes of carbon to the atmosphere and ocean source composition doubtless play a role in the composi- reservoirs. This carbon, it is argued, as CO2 in the atmos- tion and amounts of liquid that are generated, but at the phere, ultimately to powerful global warming, loss of heart of the model is a mechanism for the release of habitat, and mass extinction (Kiehl and Shields 2005). But

E LEMENTS 261 DECEMBER 2005 FIGURE 2 Extinction rate versus time (continuous line, blue field) Siberian Traps, the Central Atlantic Magmatic Province (CAMP), and the (multiple-interval marine genera, modified from Sepkoski Deccan Traps, respectively. Three oceanic plateaus, the Caribbean (CP), 1996) compared with eruption ages of continental flood basalts (red Kerguelen (KP), and Ontong Java (OJP), are shown. Modified after White bands). Three of the largest mass extinctions, the Permo-, Triassic– and Saunders (2005). and the Cretaceous–Tertiary, correspond to eruptions of the where does this carbon come from? Some undoubtedly modifying gases and aerosols. 40Ar/39Ar and U/Pb comes from the basalts themselves but, given the low aver- dating offer increasingly precise methods for improving age rates of CO2 production, this is unlikely to be the entire this knowledge, but even a precision of better than 0.1% story. An alternative, mentioned by both Wignall and Kerr still leaves a lot to be desired. Mass extinction events may in this issue, is that the greenhouse effects of CO2 from the occur in periods of 100,000 years or less, which is still LIPs slowly raise the atmospheric and oceanic temperatures, outside the precision offered by the best radiometric tech- and this triggers release of previously trapped in niques for dating events that occurred during the mass permafrost and methane hydrates on the seafloor. In effect, extinctions at the Permo-Triassic, Triassic–Jurassic, and a threshold is reached, potentially leading to a runaway Cretaceous–Tertiary boundaries. greenhouse. (Intriguingly, it has recently been reported that Siberian permafrost is melting due to anthropogenically FURTHER READING driven global warming; perhaps the flood basalts offer a The International Association of Volcanology and Chem- model for current climate change.) An alternative explana- istry of the Earth’s Interior (IAVCEI) has established the LIPs tion is that near-surface intrusions that accompany LIP for- Subcommision, which maintains a webpage with up-to- mation are injected into carbon-rich sedimentary layers date information about studies on large igneous provinces. (methane- or coal-bearing) and that these then release their See http://www.largeigneousprovinces.org carbon into the ocean and atmosphere (Svensen et al. 2004; McElwain et al. 2005). For information on specific provinces, see Mahoney JJ, Coffin MF (1997) Large Igneous Provinces: Continental, The key to understanding these processes is knowing the Oceanic, and Planetary Flood . American Geo- duration and flux rates of LIP magmatism, because from physical Union Monograph 100, 438 pp. these we can calculate the flux rates of the climate- . REFERENCES Coffin MF, Eldholm O (1994) Large Elkins-Tanton LT (2005) Continental igneous provinces: crustal structure, magmatism caused by lithospheric Burov E, Guillou-Frottier L (2005) The dimensions, and external consequences. delamination. In: Foulger GR, Natland plume head-continental lithosphere Review of 32: 1-36 JH, Presnall DC, Anderson DL (eds) interaction using a tectonically realistic Plates, Plumes and Paradigms. Geological formulation for the lithosphere. Courtillot V (1994) Mass extinctions in the Society of America Special Paper 388, pp Geophysical Journal International 161: last 300 million years: one impact and 449-462 469-490 seven flood basalts? Israeli Journal of Earth Sciences 43: 255-266 Ernst RE, Buchan KL, Campbell IH (2005) Coffin MF, Eldholm O (eds) (1991) Large Frontiers in Igneous Provinces: JOI/USSAC Workshop Courtillot V (1999) Evolutionary Catastro- research. Lithos 79: 271-297 Report. The University of Texas at Austin phes: The Science of Mass Extinctions. Institute for Geophysics Technical Report Cambridge University Press, 188 pp Kerr AC, Tarney J, Marriner GF, Nivia A, 114: 79 pp Saunders AD (1997) The Caribbean- Colombian Cretaceous igneous province:

E LEMENTS 262 DECEMBER 2005 Glossary

δ13C – Carbon isotope values (and other Flow field – The total lava products of one primitive – than basalts and may be stable isotopes such as oxygen and effusive eruption, however long-lasting. indicative of a high-temperature parental hydrogen) are expressed relative to a ref- Mantle fertility – The relationship between magma. erence standard. The standard used for mantle composition and its ability to pro- Plume buoyancy flux – A measure of the carbon is a Peedee Formation belemnite duce melt. During partial melting, peri- strength of a plume, given by the differ- (PDB). The difference from the standard dotite (the main mantle rock) can pro- ence in density between the plume mantle is expressed as the delta function, which duce only so much melt before it and the surrounding mantle, multiplied may be positive (i.e. the carbon has a rel- exhausts its supply of ‘basalt producing’ by the buoyancy-driven volume flux of 13 atively higher abundance of heavy C elements, such as Ca and Al. The more of the plume. than the standard), the same, or negative these elements present in the original (a higher proportion of light 12C). Results Potential temperature – Rising, convecting rock, the more melt can be produced – it material (plastic mantle rock, or melt, or are expressed in parts per thousand. A may be said to have an increased fertility. shift or spike in the seawater isotope air) cools slightly by adiabatic decom- The presence of eclogite, which is chem- pression. This defines an adiabatic cool- curve indicates a geologically rapid ically equivalent to basalt, substantially change in the relative amounts of light ing line (or, conversely, a heating line if increases the fertility of the source. Note, the material descends) – part of the and heavy carbon. Organic carbon, espe- however, that energy, in the form of 13 Earth’s geotherm. For rock, the adiabatic cially biogenic methane, has low δ C latent heat of melting, is still required to -1 13 gradient is about 0.5°C km . The theo- values; the δ C of marine carbonate is generate melt. Increasing source fertility about zero. retical intersection of this line with the will not substantially increase the volume Earth’s surface is called the potential tem- Basalt – A basic of volcanic of melt unless that energy is also present. perature. Thus, mantle with an actual origin with between 45 and 52 wt% SiO2 Optical depth – A measure of how opaque temperature of 1400°C at 100 km depth and less than 5 wt% total alkalis. The a medium – such as air – is to the radia- will have a potential temperature of mineralogy typically comprises clinopy- tion passing through it. Solar radiation is 1400 − (0.5 × 100) = 1350°C, assuming roxene (augite) and plagioclase feldspar. partially scattered and absorbed by fine that the adiabatic gradient is linear. Olivine, and an opaque mineral such as particles in the atmosphere, and so the Potential temperature, or Tp, is a con- magnetite may also be present. The plu- amount of incident light is always greater venient shorthand to describe how hot tonic equivalent of basalt is . than the amount of transmitted light. A the mantle is regardless of depth or, put Delamination – The collapse and peeling of completely transparent medium has an another way, how much energy it con- large layers of dense material from the OD of zero. An OD of 1 results in ~40% tains. Unfortunately we can only approx- base of the lithosphere or crust. The of light reaching the ground. imate the actual Tp of the upper mantle. delamination process allows the – An ultrabasic rock, with a min- Some workers (e.g. Anderson this issue) asthenosphere to ascend into the result- eralogy dominated by olivine and with argue that the normal upper mantle has ing space, triggering decompression variable amounts of clinopyroxene (e.g. a large temperature range, varying from melting and magmatism. diopside) and orthopyroxene (e.g. ensta- place to place by ±100°C, whereas others argue that the normal mantle is much Eclogite – A high-pressure, high-density tite). Garnet or spinel may also be pres- more restricted in temperature, with a Tp metamorphic rock composed mainly of ent. It is the predominant rock in the of about 1300°C, and with localised garnet and clinopyroxene. It is the high- Earth’s mantle. Peridotite comprising hotspots (plumes) where the Tp may pressure equivalent of basalt or gabbro. mostly olivine and orthopyroxene is exceed 1500°C. Emplacement of basaltic magma into the termed harzburgite. Peridotite with lower crust may lead to the formation of olivine, orthopyroxene and clinopyrox- Viscosity – The resistance to flow within a dense eclogite, which may become ene is termed lherzolite. liquid (alternatively, a measure of the buoyantly unstable and collapse into the Picrite – A rock of volcanic origin with internal friction of a liquid, or dynamic underlying mantle (delamination). Sub- between 12 and 18 wt% MgO, less than viscosity). Kinematic viscosity is the dynamic viscosity of a liquid divided by ducted ocean crust is thought to convert 3 wt% total alkalis (K2O + Na2O), and an its density. to eclogite and be entrained in the mantle, SiO2 content between 30 and 52 wt%. eventually returning to the near-surface Picrites are more magnesian – and more by convection processes.

the internal anatomy of an oceanic Prokoph A, Ernst RE, Buchan KL (2004) the Ontong Java plateau from Pb-Sr-Hf- plateau. In: Mahoney JJ, Coffin M (eds) Time-series analysis of large igneous Nd isotopic characteristics of ODP Leg Large Igneous Provinces: Continental, provinces: 3500 Ma to present. Journal 192 basalts. In: Fitton JG, Mahoney JJ, Oceanic, and Planetary Flood Volcanism. of Geology 112: 1-22 Wallace PJ, Saunders AD (eds) Origin American Geophysical Union, Geophysi- and Evolution of the Ontong Java cal Monograph 100: 123-144 Read HH (1948) Granites and granites. Plateau. Geological Society of London In: Gilluly J (ed) Origin of Granite, Special Publication 229: 133-150 Kiehl JT, Shields CA (2005) Climate simu- Geological Society of America Memoir lation of the latest Permian: implications 28: 1-19 White R, McKenzie D (1989) Magmatism for mass extinction. Geology 33(9): at zones: the generation of volcanic 757-760 Richards MA, Duncan RA, Courtillot VE continental margins and flood basalts. (1989) Flood basalts and hot-spot tracks: Journal of Geophysical Research 94 (B6): King SD, Anderson DL (1995) An plume heads and tails. Science 246: 7685-7729 alternative mechanism of flood basalt 103-107 formation. Earth and Planetary Science White RV, Saunders AD (2005) Volcanism, Letters 136: 269-279 Sepkoski JJ (1996) Patterns of impact and mass extinctions: incredible extinction: a perspective from global data or credible coincidences? Lithos 79: 299- King SD, Anderson DL (1998) Edge-driven bases. In: Walliser OH (ed) Global Events 316 convection. Earth and Planetary Science and Event Stratigraphy, Springer, Berlin, . Letters 160: 289-296 pp 35-51 Larson RL (1991) Latest pulse of Earth: Svensen HS, Planke S, Malthe-Sørenssen A, Evidence for a mid-Cretaceous super- Jamtveit B, Myklebust R, Eidem TR, Rey plume and geological consequences of SS (2004) Release of methane from a superplumes. Geology 19: 547-550 volcanic basin as a mechanism for initial global warming. Nature 429: McElwain JC, Wade-Murphy J, Hesselbo SP 542-545 (2005) Changes in carbon dioxide during an oceanic linked to Tejada MLG, Mahoney JJ, Castillo PR, Ingle intrusion into coals. Nature SP, Sheth HC, Weis D (2004) Pin-pricking 435: 479-482 the elephant: evidence on the origin of

E LEMENTS 263 DECEMBER 2005 Adrian P. Thorvaldur (Thor) Meet the Authors Jones is reader Thordarson is a senior in petrology in researcher in volcanology the Department at the University of Iceland of Earth and University of Hawaii. Sciences at He has conducted vol- University canological research on College modern to Archean Don L. Anderson is London. With connections to Durham, successions across the globe, with emphasis Professor Emeritus in the Chicago, Caltech, and Kingston, he has on flood basalt and volcanism, Division of Geological and supervised approximately 20 graduate –climate interactions, and lava flow Planetary Sciences at students. His research group explores the emplacement mechanisms. He has written Caltech. He received a BS mineralogy, , and petrology of more than 50 articles in scientific journals in geology and geophysics carbon in the Earth’s mantle, including the and co-authored the book Iceland in the series and a DSc (Hon) from RPI, origin of diamond, and of and Classical Geology in Europe. He is a member and a PhD in geophysics melts. From 2000 to 2003 he was of the Geological Society of America, the and mathematics from Caltech. He received chairman of the ESF Eurocarb Network, which American Geophysical Union, the Interna- the Crafoord Prize at the Royal Swedish examined solid carbon reservoirs and their tional Association of Volcanology, the Geo- Academy of Sciences and the National Medal contribution to CO2 in the atmosphere logical Society of Iceland, and the Glaciologi- of Science at the White House. He is past through volcanism. He explained carbonate cal Society of Iceland. He has been appointed, president of the AGU. He is interested in the melts in the and since 2000, as of March 1, 2006, to the post of senior origin, evolution, structure, and composition has worked on large-scale impact melting. lecturer in volcanology at the University of Earth and other planets. His work inte- of Edinburgh, . grates seismological, solid state physics, geochemical, and petrological data. He was Andrew D. Saunders director of the Seismological Laboratory of is professor of geochemistry Mike Widdowson is Caltech from 1967 to 1989. See http:// at the University of lecturer in volcanology at www.gps.caltech.edu/~dla Leicester. He has studied the Open University, UK. large igneous provinces in He received his degree in , the North geology and mineralogy at Ian H. Campbell is Atlantic, and in the Pacific Oxford (1985) where, after a Senior Fellow at The and Indian Oceans, using studying the uplift history Australian National a variety of techniques, but mostly igneous of the Deccan Traps of University and is currently geochemistry. He is currently investigating , he also obtained his D Phil (1990). visiting the Institute for the role of the Siberian Traps in the end- He has over 20 years of experience studying Study of the Earth’s Permian mass extinction and asking the basic many aspects of the Deccan continental flood Interior, University of question, how does such volcanism trigger a basalt province. His broader fields of research Okayama at Misasa, Japan, worldwide ? Andy is a strong include the volcanology, geochemistry and where he is supported by the Centre of advocate for mantle plumes, but is perfectly geochronology of large igneous provinces, Excellence for the 21st Century. He is co-chair willing to accept that this amazing planet is and the wider role of volcanism upon climate of the Commission on Large Igneous Pro- sufficiently large and complex to accommo- change in the geological record. He has also vinces and was a co-convener of the Great date a variety of LIP-forming mechanisms. published papers on the evolution of passive Plume Debate held at Fort William between continental margins and the geochemistry August 28 and September 1, 2005. His of lateritization and tropical weathering principal research interests are the relation- Steve Self is professor processes. He is a fellow of the Geological ship between igneous processes and ore of volcanology and head Society of London and the Geological Society deposits, and the evolution of the Earth’s of the Volcano Dynamics of India. crust and mantle. Group at the Open University in the UK. He has studied volcanic Paul Wignall is a Andrew C. Kerr, a activity and volcanic rocks professor of palaeoenviron- native of Northern Ireland, in many parts of the world, ments at the School of grew up a few miles from concentrating on explosive eruptions, large Earth and Environment, the legendary Giants (flood) lava effusions, and the impact of University of Leeds. He Causeway columnar volcanism on the atmosphere. He has written has been interested in the basalts. He left Northern over 170 articles and reviews in the scientific origin of the end-Permian Ireland to study geochem- press, for books, and in other science mass extinction, ever since istry at the University of magazines. He is a fellow of the Geological he first visited the sections of the western US, St Andrews , followed by a PhD on the geo- Society of America and the Geological Society in 1989. In recent years he has also become chemistry of from the Isle of Mull, at of London, and a member of the American interested in other mass extinctions, notably Durham University. This was followed by two Geophysical Union, the International the end-Triassic and Early Jurassic events. His postdoctoral positions at the University of Association of Volcanology, the Mineralogical researches have taken him all over the world Leicester: one studying the accreted portions Society, and the International Association of to places such as Greenland, China, North of the Caribbean–Colombian oceanic plateau Sedimentology. He is currently head of the America and even his own backyard in and the other assessing the environmental UK’s Volcanic and Magmatic Studies Group. Yorkshire. He has published around 70 papers impact of large igneous provinces. He is cur- and two books, mostly on mass extinctions, rently a senior lecturer at Cardiff University, but also on black shales, his other main treasurer of the Commission on Solid Earth research interest. Chemistry and Evolution, and a council member of the Mineralogical Society of Great Britain.

E LEMENTS 264 DECEMBER 2005