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Origin and Evolution of the Ontong Java Plateau: Introduction Downloaded from http://sp.lyellcollection.org/ by guest on September 26, 2021 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.
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