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Origin and evolution of the Ontong Java Plateau: introduction

J. GODFREY FITTON 1, JOHN J. MAHONEY 2, PAUL J. WALLACE 3 & ANDREW D. SAUNDERS 4 1School of GeoSciences, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 MW, UK (e-mail: Godfrey. [email protected]) 2School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, USA 3Departrnent of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403-1272, USA 4Department of Geology, University of Leicester, Leicester, LE1 7RH, UK

This volume summarizes the results of recent accompanying their emplacement; and the com- research on the Ontong Java Plateau (OJP) in position and temperature of their mantle the western Pacific Ocean (Fig. 1). The plateau sources. The study of continental LIPs can is the most voluminous of the world's large address these to a large extent, and considerable igneous provinces (LIPs) and represents by far progress has been made in these areas. Petro- the largest known magmatic event on Earth. logical and geochemical studies on the sources LIPs are formed through eruptions of basaltic of continental flood basalt, however, are always magma on a scale not seen on Earth at the compromised by the possibility of contami- present time (e.g. Coffin & Eldholm 1994; nation of the magma by the continental crust Mahoney & Coffin 1997). Continental flood and lithospheric mantle through which it passes. basalt provinces are the most obvious manifes- Basalt from plateaus that formed entirely in an tation of LIP magmatism, but they have oceanic oceanic environment, being free of such con- counterparts in volcanic rifted margins and tamination, offers a clear view of LIP mantle giant submarine ocean plateaus. LIPs have also sources, but is difficult and expensive to sample. been identified on the Moon, Mars and Venus, Nevertheless, the basaltic basement of several and may represent the dominant form of vol- ocean plateaus has been sampled in the course canism in the solar system (Head & Coffin of Deep Sea Drilling Project (DSDP) and Ocean 1997). The high magma production rates (i.e. Drilling Program (ODP) legs. large eruption volume and high eruption fre- quency) involved in LIP magmatism cannot be The Ontong Java Plateau accounted for by normal plate tectonic pro- cesses. Anomalously hot mantle often appears The OJP covers an area of about 2.0 • 106 km 2 to be required, and this requirement has been a (comparable in size with western Europe), and key consideration in the formulation of the OJP-related volcanism extends over a consider- currently favoured plume-head hypothesis in ably larger area into the adjacent Nauru, East which LIPs are formed through rapid decom- Mariana, and possibly the Pigafetta and Lyra, pression and melting in the head of a newly basins (Fig. 1). With a maximum thickness of ascended mantle plume (e.g. Richards et al. crust beneath the plateau of 30-35 km (e.g. 1989; Campbell & Griffiths 1990). Eruption of Gladczenko et aL 1997; Richardson et al. 2000), enormous volumes of basaltic magma over the volume of igneous rock forming the plateau short time intervals, especially in the subaerial and filling the adjacent basins could be as high as environment, may have had significant effects 6 • 107 km 3 (e.g. Coffin & Eldholm 1994). on climate and the biosphere, and LIP for- Seismic tomography experiments show a mation has been proposed as one of the causes rheologically strong, but seismically slow, upper of mass extinctions (e.g. Wignal12001). mantle root extending to about 300 km depth Several issues need to be addressed in order to beneath the OJP (e.g. Richardson et al. 2000; understand LIP formation. These include: the Klosko et al. 2001). Gomer & Okal (2003) have timing and duration of magmatism; the size, measured the shear-wave attenuation in this timing and duration of individual eruptions; the root and found it to be low, implying that the eruption environment of the magmas (subaque- slow seismic velocities must be due to a compo- ous or subaerial); the magnitude of crustal uplift sitional, rather than thermal, anomaly in the

From: FITTON,J. G., MAHONEY, J. J.,WALLACE, P. J. & SAUNDERS,A. D. (eds) 2004. Origin and Evolution of the Ontong Java Plateau. Geological Society, London, Special Publications, 229, 1-8. 0305-8719/$15.00 9The Geological Society of London 2004. Downloaded from http://sp.lyellcollection.org/ by guest on September 26, 2021

2 J.G. FITTON ETAL.

Fig. 1. Predicted bathymetry (after Smith & Sandwel11997) of the Ontong Java Plateau and surrounding areas showing the location of DSDP and ODP basement drill sites. Leg 192 drill sites are marked by black circles; open circles represent pre-Leg 192 drill sites. The edge of the plateau is defined by the -4000 m-contour, except in the SE part where it has been uplifted through collision with the Solomon arc.

mantle. The nature and origin of this composi- basement in the Solomon Islands (Fig. 1), notably tional anomaly has not yet been established. in Malaita, Santa Isabel and San Cristobal (e.g. The OJP seems to have been formed rapidly Petterson et al. 1999). In addition to these expo- at around 120 Ma (e.g. Mahoney et al. 1993; sures, the basaltic basement on the OJP and Tejada et al. 1996, 2002; Chambers et al. 2002; surrounding Nauru and East Mariana basins has Parkinson et al. 2002), and the peak magma pro- been sampled at 10 DSDP and ODP drill sites. duction rate may have exceeded that of the However, the most recent drilling leg (ODP Leg entire global mid-ocean ridge system at the time 192 in September-November 2(X)0) was the first (e.g. Tarduno et al. 1991; Mahoney et al. 1993; designed specifically to address the origin and Coffin & Eldholm 1994). Degassing from evolution of the OJP (Mahoney et al. 2001). massive eruptions during the formation of the Earlier research on the OJP has been reviewed by OJP could have increased the CO2 concen- Neal et al. (1997). The principal aim of the present tration in the atmosphere and oceans (Larson & volume is to present the results of research that Erba 1999), and led to, or at least contributed has followed from ODP Leg 192, and most of the significantly to, a world-wide oceanic anoxic papers in it were written or co-authored by event accompanied by a 90% reduction in nan- participants in this leg. The volume complements nofossil palaeoflux (Erba & Tremolada 2004). the recent thematic set of papers on the origin and Collision of the OJP with the old Solomon arc evolution of the Kerguelen Plateau, the world's has resulted in uplift of the OJP's southern second largest oceanic LIP, published in Journal margin to create on-land exposures of basaltic of Petrology (Wallace et al. 2002). Downloaded from http://sp.lyellcollection.org/ by guest on September 26, 2021

ORIGIN AND EVOLUTION OF THE ONTONG JAVA PLATEAU 3

Geological evolution and by alkaline basalt volcanism during the Eocene palaeomagnetism and by intrusion of aln6ite during the Oligocene.

Several authors (e.g. Mahoney & Spencer, 1991; Age and biostratigraphy Richards et al. 1991; Tarduno et al. 1991) have favoured the starting plume head of the The age and duration of OJP magmatism has not Louisville hot spot (now at c. 52~ as the source yet been established with any certainty. OJP of the OJP. In the first paper of the volume, basalts are difficult to date by the widely used Kroenke et al. use a new model of Pacific 4~ method because of their very low absolute plate motion, based on the fixed hot- potassium contents. Published 4~ data spot frame of reference, to track the palaeogeo- (Mahoney et al. 1993; Tejada et al. 1996, 2002) graphic positions of the OJP from its present suggest a major episode of OJP volcanism at location on the Equator back to 43~ at the time c. 122 Ma and a minor episode at c. 90 Ma. of its formation (c. 120 Ma). This inferred 4~ analysis (Chambers et al. 2002; L. M. original position is 9 ~ north of the present Chambers unpublished data) of samples from location of the Louisville hot spot, and suggests ODP Leg 192 Sites 1185, 1186 and 1187 (Fig. 1) that this hot spot was not responsible for the gives ages ranging from 105 to 122 Ma. Cham- formation of the OJP or, alternatively, that the bers et al. (2002) suggest that their younger hot spot has drifted significantly relative to the apparent ages (and, by implication, the data on Earth's spin axis (as the Hawaiian hot spot which the 90 Ma episode is based) are the result appears to have done; e.g. Tarduno et al. 2003). of argon recoil and therefore represent Kroenke et al. also note the presence of linear minimum ages. Biostratigraphic dating based on gravity highs in the western OJP, which they foraminifera and nannofossils (Sikora & speculate may indicate formation of the OJP Bergen; Bergen) contained in sediment interca- close to a recently abandoned spreading centre. lated with lava flows at ODP Sites 1183, 1185, Antretter et al. point out that the palaeomag- 1186 and 1187 suggests that magmatism on the netic palaeolatitude of the OJP (c. 25~ deter- high plateau extended from latest early Aptian mined by Riisager et al. (and Riisager et al. on the plateau crest to late Aptian on the eastern 2003) further increases the discrepancy with the edge. This corresponds to age ranges of 122-112 location of the Louisvillc hot spot. Zhao et al. 's Ma (Harland et al. 1990) or 118-112 Ma (Grad- investigation of the rock-magnetic properties of stein et al. 1995). However, Re-Os isotopic data basalt from the OJP shows that original and on basalt samples from these same four drill sites stable magnetic directions are preserved, allow- define a single isochron with an age of 121.5___1.7 ing robust estimates of palaeolatitude. The dis- Ma (Parkinson et al. 2002). crepancy between the palaeolatitudes calculated The oldest sediment overlying basement on from the palaeomagnetic data and from the the crest of the OJP occurs within the upper part fixed-hot-spot reference frame is interpreted by of the Leupoldina cabri planktonic foraminiferal Riisager et al. as evidence for movement zone and corresponds with a prominent ~13C between hot spots. Antretter et al. show that the maximum (Sikora & Bergen). This result shows Louisville hot spot may have moved southwards that eruption of basaltic lava flows continued over the past 120 Ma, and that taking account of through much of Oceanic Anoxic Event 1 a, of both hot-spot motion and true polar wander which the formation of the plateau is a postu- reduces the discrepancy and makes the for- lated cause (e.g. Larson & Erba 1999). Nanno- mation of the OJP by the Louisville hot spot fossil studies (Bergen) reveal six unconformities barely possible, if still unlikely. in the Lower Aptian-Miocene pelagic cover The thickest exposures of the OJP basement sequence recovered during Leg 192. rocks in the Solomon Islands are found on the remote island of Malaita (Fig. 1). Petterson pre- sents the results of geological surveys that reveal Petrology and geochemistry a monotonous succession of Early Cretaceous The Malaita Volcanic Group (Petterson) has tholeiitic pillow basalt, sheet flows and sills (the been divided by Tejada et al. (2002) into two Malaita Volcanic Group) 3-4 km thick. Rare and chemically and isotopically distinct stratigraphic very thin interbeds composed of laminated units: the Kwaimbaita Formation (>2.7 km pelagic chert or limestone suggest high eruption thick) and the overlying Singgalo Formation frequency and emplacement into deep water. (c. 750 m maximum exposed thickness). Basalt The Malaita Volcanic Group is conformably of the Kwaimbaita Formation was found to be overlain by a 1-2 km-thick Cretaceous-Pliocene compositionally similar to the basalt forming pelagic sedimentary cover sequence, punctuated units C-G at ODP Site 807, on the northern Downloaded from http://sp.lyellcollection.org/ by guest on September 26, 2021

4 J.G. FITTON ETAL.

flanks of the OJP (Fig. 1), whereas the Singgalo on peridotite phase equilibria. He obtains Formation is similar to the overlying unit A at values of 27 and 30% for fractional and equilib- Site 807. Thus, Kwaimbaita-type and Singgalo- rium melting, respectively. Further support for type basalt flows with the same stratigraphic large-degree melting is provided by the plat- relationship are found at two sites 1500 km apart inum-group element (PGE) concentrations on the plateau (Tejada et al. 2002). A third basalt determined by Chazey & Neal. The PGEs are type, with higher MgO and lower concentrations highly compatible in mantle phases and sul- of incompatible elements than any previously phides, so their abundance is sensitive to degree reported from the OJP, was recognized during of melting and sulphur saturation. Concentra- ODP Leg 192 at Sites 1185 and 1187 on the tions of PGEs in the OJP basalts are rather high, eastern edge of the plateau (Mahoney et al. and consistent with around 30% melting of a 2001). We propose the term Kroenke-type basalt peridotite source from which sulphide phases because it was discovered on the flanks of the had been exhausted during the melting process. submarine Kroenke Canyon at Site 1185 Some basalt samples have PGE abundances (Fig. 1). that are too high to be accounted for by a stan- Tejada et al. use radiogenic-isotope (Sr, Nd, dard model peridotite source, and an additional Pb, Hf) ratios to show that Kwaimbaita-type source of PGEs appears to be needed. Chazey basalt is found at all but one of the OJP drill sites & Neal speculate that a small amount of and therefore represents the dominant OJP material from the Earth's core may have been magma type. Singgalo-type basalt, on the other involved in the generation of OJP magmas. hand, appears to be volumetrically minor. Derivation of the dominant, evolved, Kwaim- Significantly, Kroenke-type basalt is isotopically baita magma type through fractional crystalliza- identical to Kwaimbaita-type basalt (Tejada tion of the primitive Kroenke-type magma is et al.) and may therefore represent the parental consistent with the isotopic (Tejada et al.) and magma for the bulk of the OJP. Age-corrected geochemical (Fitton & Godard) evidence, and radiogenic-isotope ratios in Kroenke- and with melting experiments carried out by Sano & Kwaimbaita-type basalts show a remarkably Yamashita. Sano & Yamashita's results show small range. Tejada et al. model the initial Sr-, that the variations in phenocryst assemblage and Nd-, Pb- and Hf-isotope ratios in these two whole-rock basalt major-element compositions basalt types as representing originally primitive can be modelled adequately by fractional crys- mantle that experienced a minor fractionation tallization in shallow (<6 km) magma reservoirs. event (e.g. the extraction of a small amount of Glass from the rims of basaltic pillows was partial melt) at about 3 Ga or earlier. recovered from most drill sites on the OJP, and The remarkable homogeneity of OJP basalts this glass preserves a record of the volatile is also seen in their major- and trace-element content of the magmas at the time of eruption. composition (Fitton & Godard). Fitton & Roberge et al. show that water contents in the Godard use geochemical data to model the glasses are uniformly low and imply water con- mantle source composition and hence to esti- tents in the mantle source that are comparable mate the degree of partial melting involved in with those in the source of mid-ocean ridge the formation of the OJP. Incompatible-element basalt. This is an important observation because abundances in the primary OJP magma can be it shows that the large degrees of melting esti- modelled by around 30% melting of a peridotitic mated for the OJP magmas cannot have been primitive mantle source from which about 1% caused by the presence of water but require high by mass of average continental crust had previ- temperatures. The sulphur contents of OJP ously been extracted. The postulated depletion glasses confirm Chazey & Neal's inference of is consistent with the isotopic modelling of sulphur undersaturation in the magmas. The Tejada et al. To produce a 30% melt requires water depth of lava emplacement controls the decompression of very hot (potential tempera- CO2 content of the glasses, and data obtained by ture >1500~ mantle beneath thin lithosphere. Roberge et al. imply depths ranging from about Thin lithosphere is consistent with the sugges- 1000 m on the crest of the OJP to about 2500 m tion by Kroenke et al. that the OJP may have on its eastern edge. The amount of CO2 released formed close to a recently abandoned spreading during formation of the OJP is difficult to deter- centre. Alternatively, lithospheric thinning mine without reliable information on primary could have resulted from thermal erosion caused magmatic CO2 contents and precise knowledge by the upwelling of hot plume material. of the duration of volcanism, but Roberge et al. An independent estimate of the degree of estimate a maximum value that is around 10 melting is provided by Herzberg, who uses a times the flux from the global mid-ocean ridge forward- and inverse-modelling approach based system. Erba & Tremolada (2004) estimate that Downloaded from http://sp.lyellcollection.org/ by guest on September 26, 2021

ORIGIN AND EVOLUTION OF THE ONTONG JAVA PLATEAU 5

the 90% reduction in nannofosil palaeofluxes in composition to the Kwaimbaita- and that they link to emplacement of the OJP Kroenke-type basalts sampled on the high requires a three- to sixfold increase in vol- plateau. Each member has a distinct glass com- canogenic CO2. position and there is no intermixing of glass The submarine emplacement of most of the compositions between them, confirming Thor- OJP resulted in low-temperature alteration of darson's conclusion that each is the result of one the basalts through contact with sea water. The eruptive phase, and that the volcaniclastic alteration ranges from slight to complete, and sequence has not been reworked. White et al.'s unaltered olivine and glass were found in some major- and trace-element data for the glass clasts of the basaltic lava flows sampled in the drill suggest that the voluminous subaerially erupted cores. A detailed study of the alteration pro- volcaniclastic rocks at Site 1184 belong to the cesses is reported by Banerjee et at, who show same magmatic event as that responsible for the that alteration started soon after emplacement construction of the main plateau. Thus, the OJP and is indistinguishable from that affecting mid- would have been responsible for volatile fluxes ocean ridge basalt. There is no evidence for into the atmosphere in addition to chemical high-temperature alteration in any of the basalt fluxes into the oceans. Both factors may have recovered from the OJP. The initial and most influenced the contemporaneous oceanic anoxic pervasive stage of alteration resulted in the event (Sikora & Bergen; Erba & Tremolada replacement of olivine and interstitial glass with 2004). celadonite and smectite. Later interaction The geochemical evidence (White et al.; between basalt and cold, oxidizing sea water Fitton & Godard) linking the phreatomagmatic caused local replacement of primary phases and eruptions recorded at Site 1184 to the formation mesostasis by smectite and iron oxyhydroxides. of the main plateau is supported by the Early Glass shards in tufts at Site 1184 show clear tex- Cretaceous age implied by the steep (-54 ~) mag- tural evidence of microbial alteration (Banerjee netic inclination preserved in the volcaniclastic & Muehlenbachs 2003). rocks (Riisager et aL). However, this evidence appears to be contradicted by the presence of rare Eocene nannofossils at several levels within Volcaniclastic rocks the succession (Bergen). In an attempt to One of the most exciting discoveries of ODP resolve this paradox, Chambers et aL applied Leg 192 was a thick succession of basaltic vol- the 4~ dating method to feldspathic caniclastic rocks at Site 1184 on the eastern material separated from two basaltic clasts, and salient of the OJP (Fig. 1). Drilling at this site to individual plagioclase crystals separated from penetrated 337.7 m of tuff and lapilli tuff, before the matrix of the volcaniclastic rocks. The clasts the site had to be abandoned through lack of gave minimum age estimates of c. 74 Ma, and the time. A detailed volcanological study by Thor- plagioclase crystals a mean value of 123.5_+1.8 darson concludes that the volcaniclastic succes- (lo-) Ma. sion was the result of large phreatomagmatic Sharer et aL analysed a suite of 14 basaltic eruptions in a subaerial setting. This setting con- clasts extracted from four of the volcaniclastic trasts strikingly with that of the lava flows units and, despite their extensive alteration, sampled on the main plateau and in the showed that the clasts were derived from a Solomons, which were all erupted under deep source similar to that of the Kroenke- and water (Roberge et ai.; Petterson). Thordarson Kwaimbaita-type basalts on the main plateau. divides the succession into six subunits or Significantly, the composition of the clasts members, each representing a single massive (Sharer et aL) varies with the bulk composition eruptive event. Fossilized or carbonized wood of their host volcaniclastic units (Fitton & fragments were found near the bottom of four of Godard), showing that they must be cognate. the eruptive members (Mahoney et al. 2001). Chambers et aL conclude that both the clasts The volcaniclastic succession at Site 1184 pro- and the plagioclase crystals that they used in vides the only evidence so far for significant their 4~ dating belong to the same mag- amounts of subaerial volcanism on the OJP. matic episode as the host volcaniclastic rocks Three of the six eruptive members at Site 1184 and are not xenoliths or xenocrysts from older contain blocky glass clasts with unaltered cores, basement. Thus, the combined 4~ geo- and these cores allow the reliable determination chemical and palaeomagnetic evidence favours of the composition of the erupted magma. White an early Cretaceous age for the volcaniclastic et al. used microbeam techniques to determine succession. Thordarson and Chambers et ai. the major- and trace-element compositions of suggest that the Eocene nannofossils were intro- samples of the glass. The glasses are very similar duced later, possibly along fractures. 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6 J.G. FITTON ETAL.

Volcaniclastic rocks (recovered during essentially non-vesicular submarine lava and the previous ODP legs) are also found in thick, absence of any basalt showing signs of subaerial reworked and redeposited successions overlying weathering show that all the other sampled por- Early Cretaceous basalt in the Nauru and East tions of the OJP were emplaced below sea level Mariana basins to the east and north of the OJP, (e.g. Neal et al. 1997; Mahoney et al. 2001). respectively. Much of the volcaniclastic material Volatile concentrations in quenched pillow-rim consists of hyaloclastite and this, together with glasses suggest eruption depths ranging from the presence of wood and shallow-water carbon- 1100 m at Site 1183 to 2570 m at Site 1187 ate fragments, suggests that both the East (Roberge et aL). Mariana Basin and the Nauru Basin volcaniclas- We have not yet been able to resolve the tic rocks were derived from once-emergent vol- paradox of apparent high mantle potential tem- canic sources or from relatively shallow water. perature coupled with predominantly sub- In the final paper in this volume, Castillo pre- marine emplacement. Widespread melting of sents chemical and isotopic data for these vol- the mantle following the impact of an asteroid caniclastic rocks and compares them with data provides a possible means of avoiding uplift (e.g. for the OJP. The Nauru Basin volcaniclastic Ingle & Coffin 2004), but the resulting magma rocks have incompatible trace-element and Nd- would be generated entirely within the upper isotope compositions typical of the Kwaimbaita- mantle and should normally be expected to have type tholeiitic lavas of the OJP, suggesting that the chemical and isotopic characteristics of these deposits were shed from the plateau itself. Pacific mid-ocean ridge basalt. OJP basalt is iso- On the other hand, the East Mariana Basin vol- topically (Tejada et aL) and chemically (Fitton caniclastic rocks have high concentrations of & Godard) distinct from Pacific mid-ocean ridge incompatible trace-elements, and Nd- and Pb- basalt. Furthermore, no mass extinction isotope ratios typical of alkalic ocean island occurred at the time of OJP formation, even basalts, and are unrelated to the OJP. though the required asteroid would have had a diameter significantly greater than that thought to have been responsible for the extinctions at A mantle plume origin for the Ontong the Cretaceous-Tertiary boundary (Ingle & Java Plateau? Coffin 2004). A more detailed case against an impact origin for the OJP is set out by Tejada et One of the principal objectives of ODP Leg 192 al. An eclogitic source does not provide an was to test the plume-head hypothesis for the alternative to the plume hypothesis because the formation of giant ocean plateaus, and many of high-Mg parental magma would require almost the results presented in this volume are con- total melting, and consequently a very high sistent with such an origin. The discovery of potential temperature would still be needed to high-MgO Kroenke-type basalt allows us to cal- provide the latent heat of fusion. We can also culate the composition of the primary magma rule out a hydrous mantle source because the and hence deduce the nature of the mantle magmas have very low H20 contents (Roberge source and the degree of melting. Isotopic et ai.). (Tejada et aL) and chemical (Fitton & Godard; The papers collected together into this Chazey & Neal) data are consistent with a mildly volume show the progress that has been made in depleted peridotite mantle source, and phase- our understanding of the origin and evolution of equilibria (Herzberg) and trace-element (Filton the Ontong Java Plateau following its successful & Godard; Chazey & Neal) modelling indepen- drilling during ODP Leg 192. We now have a dently constrain the degree of melting of this much clearer view of the range and distribution peridotite source to around 30%. Melting to this of basalt types on the plateau, and we have extent can only be achieved by decompression identified a potential parental magma composi- of hot (potential temperature >1500~ peri- tion represented by Kroenke-type basalt. The dotite beneath thin lithosphere. To achieve an age and duration of magmatism is still uncertain average of 30% melting requires that the mantle because we have still only scratched the surface is actively and rapidly fed into the melt zone, and of the 30-35 km-thick OJP crust. However, it a start-up mantle plume provides the most now seems plausible that almost the entire obvious mechanism. A plume-head impinging plateau formed in a single, widespread mag- on thin lithosphere theoretically should have matic event at c. 120 Ma. The identification of a caused uplift of a sizeable part of the plateau thick succession of volcaniclastic rocks at Site above sea level, as in Iceland, and, indeed, at 1184 shows that at least part of the plateau was least part of the eastern salient was emergent erupted in a subaerial environment. We con- (Thordarson). However, the abundance of clude that the start-up plume hypothesis appears Downloaded from http://sp.lyellcollection.org/ by guest on September 26, 2021

ORIGIN AND EVOLUTION OF THE ONTONG JAVA PLATEAU 7 to fit more of the observations than do any of the HEAt), J.W. & COFFIN, M.E 1997. Large igneous alternative hypotheses, but the lack of uplift of provinces: a planetary perspective. In: MAHONEY, the magnitude predicted by the plume hypothe- J.J. & COFFIN,M.E (eds) Large Igneous Provinces: sis and the lack of an obvious hot-spot track Continental, Oceanic, and Planetary Flood Vol- canism. American Geophysical Union, Geophys- remain to be explained. ical Monograph, 100, 411438. INGLE, S. & COFFIN, M.E 2004. Impact origin for the We thank the ODP and Transocean/Sedco-Forex staff greater Ontong Java Plateau? Earth and Plane- on board the JOIDES Resolution for their consider- tary Science Letters, 218, 123-124. able contribution to the success of ODP Leg 192. ODP KLOSKO, E.R., Russo, R.M., OKAL, E.A. & RICHARD- is sponsored by the US National Science Foundation SON,W.R 2001. Evidence for a Theologically strong (NSF) and participating countries under management chemical mantle root beneath the Ontong-Java of Joint Oceanographic Institutions (JOI), Inc. We Plateau. Earth and Planetary Science Letters, 186, also thank the many colleagues who reviewed papers 347-361. in this volume. They are acknowledged individually in LARSON, R.L. & ERBA, E. 1999. Onset of the Mid- the respective papers. Finally, we are indebted to Cretaceous greenhouse in the Barremian-Aptian: S. Oberst of the Geological Society Publishing House igneous events and the biological, sedimentary, for the care and patience with which she handled the and geochemical consequences. Paleoceanogra- production of this volume. phy, 14, 663-678. MAHONEY, J.J. & COFFIN, M.E (eds). 1997. Large Igneous Provinces: Continental, Oceanic, and References Planetary Flood Volcanism. American Geophysi- cal Union, Geophysical Monograph, 1110. BANERJEE, N.R. & MUEnLENBACHS,K. 2003. 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