Th or collective redistirbution of any portion article of any by of this or collective redistirbution SPECIAL ISSUE FEATURE articleis has been published in Oceanography LARGE IGNEOUS 19, Number journal of Th 4, a quarterly , Volume PROVINCES AND permitted photocopy machine, only is reposting, means or other SCIENTIFIC OCEAN DRILLING STATUS QUO AND A LOOK AHEAD e Oceanography Society. 2006 by Th Copyright BY MILLARD F. COFFIN, ROBERT A. DUNCAN, OLAV ELDHOLM, J. GODFREY FITTON, FRED A. FREY, HANS CHRISTIAN LARSEN, JOHN J. MAHONEY, with the approval of Th ANDREW D. SAUNDERS, ROLAND SCHLICH, AND PAUL J. WALLACE A rich mosaic of disparate crustal types entifi c ocean drilling has signifi cantly Ocean, two to the Ontong Java Plateau gran is e Oceanography All rights Society. reserved. Permission characterizes the Earth beneath the sea. advanced understanding of LIPs. Herein in the western equatorial Pacifi c Ocean, or Th e Oceanography [email protected] Send Society. to: all correspondence Although “normal” oceanic crust ap- we focus on signifi cant outcomes of ten and one to the Chagos-Maldive-Laccad- proximately 7-km thick is by far the LIP-dedicated expeditions between 1985 ive Ridge and Mascarene Plateau in the most prevalent, abnormally thick oce- and 2000 and also highlight prospects Indian Ocean (Table 1). Complementary anic-type crust of large igneous prov- for future drilling efforts. The ten ex- geophysical and/or onshore geological inces (LIPs) also forms a signifi cant peditions include three to the volcanic investigations have added signifi cant component of the marine realm (e.g., margins of the North Atlantic Tertiary value to all of these expeditions. Coffi n and Eldholm, 1994; Mahoney Igneous Province, four to the Kerguelen Terrestrial LIPs are massive and rapid and Coffi n, 1997; Saunders, 2005). Sci- Plateau/Broken Ridge LIP in the Indian crustal emplacements of predominantly mafi c (Fe- and Mg-rich) rock that did ted to copy this article Repu for use copy this and research. to ted in teaching Millard F. Coffi n (mcoffi [email protected]) is Professor, Ocean Research Institute, Th e not form by seafl oor spreading or sub- University of Tokyo, Tokyo, Japan. Robert A. Duncan is Professor, College of Oceanic and duction (Coffi n and Eldholm, 1994). Atmospheric Sciences, Oregon State University, Corvallis, OR, USA. Olav Eldholm is Profes- LIPs may be the dominant type of e Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. sor, Department of Earth Science, University of Bergen, Bergen, Norway. J. Godfrey Fitton magmatism on other terrestrial plan- is Professor, School of Geosciences, University of Edinburgh, Edinburgh, UK. Fred A. Frey is ets and moons of the solar system (e.g., Professor, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Insti- Head and Coffi n, 1997). On Earth, LIP tute of Technology, Cambridge, MA, USA. Hans Christian Larsen is Vice President, IODP rocks are readily distinguishable from Management International, Sapporo, Japan. John J. Mahoney is Professor, School of Ocean mid-ocean ridge and subduction-re- and Earth Science and Technology, University of Hawaii, Honolulu, HI, USA. Andrew D. lated arc rocks on the basis of petrology, Saunders is Professor, Department of Geology, University of Leicester, Leicester, UK. Roland geochemistry, geochronology, physical blication, systemmatic reproduction, reproduction, systemmatic blication, Schlich is Professor, Institut de Physique du Globe de Strasbourg (CNRS/ULP), EOST, Stras- volcanology, and geophysical data. LIPs bourg, France. Paul J. Wallace is Associate Professor, Department of Geological Sciences, occur within continents and oceans, and University of Oregon, Eugene, OR, USA. include continental fl ood basalts in the 150 Oceanography Vol. 19, No. 4, Dec. 2006 Table 1. Large Igneous Provinces, ODP Legs, and References Large Igneous Province ODP Leg References 104 Eldholm, Thiede, Taylor, et al., 1987, 1989 Larsen, Saunders, Clift, et al., 1994; 152 North Atlantic Tertiary Saunders, Larsen, and Wise, 1998 Duncan, Larsen, Allan, et al., 1996; 163 Larsen, Duncan, Allan, and Brooks, 1999 119 Barron, Larsen, et al., 1989, 1991 Schlich, Wise, et al., 1989; 120 Wise, Schlich, et al., 1992 Kerguelen Plateau/ Peirce, Weissel, et al., 1989; 121 Broken Ridge Weissel, Peirce, Taylor, Alt, et al., 1991 Coffi n, Frey, Wallace, et al., 2000; 183 Wallace, Frey, Weis, and Coffi n, 2002; Frey, Coffi n, Wallace, and Quilty, 2003 Kroenke, Berger, Janecek, et al., 1991; 130 Berger, Kroenke, Mayer, et al., 1993 Ontong Java Plateau Mahoney, Fitton, Wallace, et al., 2001; 192 Fitton, Mahoney, Wallace, and Saunders, 2004a, 2004b Chagos-Maldive-Laccadive Ridge/ Backman, Duncan, et al., 1988; 115 Mascarene Plateau Duncan, Backman, Peterson, et al., 1990 former, and volcanic passive margins, centers (e.g., Eldholm and Coffi n, 2000). marine fl ows. Individual fl ows can ex- oceanic plateaus, submarine ridges, and LIP observations therefore suggest that tend for hundreds of kilometers, be tens ocean-basin fl ood basalts in the latter dynamic, non-steady-state circulation to hundreds of meters thick, and may (Figures 1 and 2). Transient LIPs and within Earth’s mantle has been impor- have volumes of more than 103 km3 (e.g., associated persistent, age-progressive tant for at least the last 250 million years Tolan et al., 1989). In addition to mafi c volcanic chains (“hot-spot tracks”) are and probably much longer, and there is a rock, silica-rich rock occurs in LIPs as commonly attributed to decompression strong potential for LIP emplacements to lavas, intrusive rocks, and pyroclastic de- melting of hot, buoyant mantle ascend- contribute to, and perhaps even instigate, posits, and is mostly associated with the ing from Earth’s interior (e.g., Morgan, major environmental changes. initial and late stages of LIP magmatic 1971) and thus provide a window into activity (e.g., Bryan et al., 2002). Relative mantle processes. Magmatism associ- COMPOSITION, PHYSICAL to mid-ocean ridge basalts, LIP basalts ated with LIPs currently represents VOLCANOLOGY, CRUSTAL are compositionally more diverse (e.g., ~ 10 percent of the mass and energy fl ux STRUCTURE, & MANTLE ROOTS Kerr et al., 2000), and LIP rocks form in from Earth’s deep interior to its surface The uppermost crust of LIPs is domi- both subaerial and submarine settings. (e.g., Sleep, 1992). This fl ux shows dis- nantly mafi c extrusive rock similar to The maximum crustal thickness, in- tinct episodicity over geological time, basalt originating at mid-ocean ridge cluding an extrusive upper crust, an in- in contrast to the relatively steady-state spreading centers; it most typically is trusive middle crust, and a lower crustal crustal accretion at seafl oor spreading found as gently dipping subaerial or sub- body, of an oceanic LIP can be as great Oceanography Vol. 19, No. 4, Dec. 2006 151 )#%,!.$ ² ./24( 3)"%2)! !4,!.4)# %-0%2/2 3(!43+9 #/,5-")! (%33 2)6%2 #%.42!, %-%)3(!. !4,!.4)# ² $%##!. 0)'!&%44! (!7!)) 9%-%. %!34 #!2)""%!. -!2)!.! #(!'/3 -!'%,,!. %4()/0)! .!525 ,!##!$)6% '!,!0!'/3 -!,$)6% /.4/.' ² *!6! -!3#!2%.% .).%49%!34 -!.)()+) 0!2!.! %4%.$%+! 7!,6)3 +!2// -!$!'!3#!2 3/54( ² ,/5)36),,% !4,!.4)# "2/+%. 3/54( !4,!.4)# +%2'5%,%. ()+52!.') ² ² ² ² ² &%22!2 Figure 1. Phanerozoic global LIP distribution, with transient (“plume head”) and persistent (“plume tail”) LIPs indi- cated in red and blue, respectively. LIPs are better preserved in the oceans where they are not subject to terrestrial erosional processes, off ering a prime target for scientifi c ocean drilling. Modifi ed from Coffi n and Eldholm (1994). as ~ 40 km, determined from seismic Seismic wave velocities suggest that the beneath these three LIPs apparently re- and gravity studies of Iceland (Fig- middle crust is most likely gabbroic, and fl ect residual effects, primarily chemi- ure 1) (Darbyshire et al., 2000). Nearly that the lower crust is mafi c to ultra- cal and perhaps secondarily thermal, all of our knowledge of LIPs, however, mafi c, and perhaps metamorphic (e.g., of mantle upwelling (Gomer and Okal, is derived from the most accessible la- Eldholm and Coffi n, 2000). 2003). If proven to be common, roots vas forming the uppermost portions of Low-velocity zones have been ob- extending well into the mantle beneath crust. This extrusive upper crust may served by seismic imaging of the mantle oceanic LIPs would suggest that such exceed 10 km in thickness (e.g., Cof- beneath the oceanic Ontong Java Plateau LIPs contribute to continental initiation fi n and Eldholm, 1994). On the basis of (e.g., Richardson et al., 2000), as well as well as continental growth. Instead geophysical, predominantly seismic, data as under the continental Deccan Traps of being subducted like normal oce- from LIPs, and from comparisons with (Kennett and Widiyantoro, 1999) and anic lithosphere, LIPS may be accreted normal oceanic crust, it is believed that Paraná fl ood basalts (Vandecar et al., to the edges of continents, for example, the extrusive upper crust is underlain by 1995) (Figure 1). Interpreted as litho- obduction of Ontong Java Plateau ba- an intrusive middle crust, which in turn spheric roots or keels, the zones can salts onto the Solomon Island arc (e.g., is underlain by lower crust (“lower crust- extend to at least 500–600 km into the Hughes and Turner, 1977), and terrane al body”) characterized by compressional mantle. In contrast to high-velocity roots accretion of Wrangellia (e.g., Richards seismic wave velocities of 7.0–7.6 km s-1 beneath most continental areas, and the et al., 1991) and Caribbean (e.g., Kerr (Figure 2). Dikes and sills are probably absence of lithospheric keels in most et al., 1997) LIPs to North and South common in the upper and middle crust. oceanic areas, the low-velocity zones America, respectively.