1. Leg 192 Synthesis: Origin and Evolution of the Ontong Java Plateau1

J.G. Fitton,2 J.J. Mahoney,3 P.J. Wallace,4 and A.D. Saunders5

INTRODUCTION

This paper summarizes the results of recent research into the composition and origin of the Ontong Java Plateau (OJP) in the western Pacific Ocean (Fig. F1) following its successful drilling during Ocean Drilling Program (ODP) Leg 192. The plateau is the most voluminous of the world's large igneous provinces (LIPs) and represents by far the largest known magmatic event on Earth. LIPs are formed through eruptions of basaltic magma on a scale not seen on Earth at the present time (e.g., Coffin and Eldholm, 1994; Mahoney and Coffin, 1997). Continental flood basalt provinces are the most obvious manifestation of LIP magmatism, but they have oceanic counterparts in volcanic rifted margins and giant submarine ocean plateaus. LIPs have also been identified on the moon, Mars, and Venus and may represent the dominant form of volcanism in the solar system (Head and Coffin, 1997). The high magma production rates (i.e., large eruption volume and high eruption frequency) involved in LIP magmatism cannot be accounted for by normal plate tectonic processes. Anomalously hot mantle often appears to be required, and this requirement has been a key consideration in the formulation of the currently favored plume-head hypothesis in which LIPs are formed through rapid decompression and melting in the head of a newly ascended mantle plume (e.g., Richards et al., 1989; Campbell and Griffiths, 1990). Eruption of enormous volumes of basaltic magma over short time intervals, especially in the subaerial environment, may have had significant effects on climate and the biosphere, and LIP formation has been proposed as one of the causes of mass extinctions (e.g., Wignall, 2001).

Several issues need to be addressed in order to understand LIP formation. These include

  1. Timing and duration of magmatism;
  2. Size, timing, and duration of individual eruptions;
  3. Eruption environment of the magmas (subaqueous or subaerial);
  4. Magnitude of crustal uplift accompanying their emplacement; and
  5. Composition and temperature of their mantle sources.

The study of continental LIPs can address these issues to a large extent, and considerable progress has been made in these areas. Petrological and geochemical studies on the sources of continental flood basalt, however, are always compromised by the possibility of contamination of the magma by the continental crust and lithospheric mantle through which it passes. Basalt from plateaus that formed entirely in an oceanic environment is free of such contamination and therefore offers a clear view of LIP mantle sources, but is difficult and expensive to sample. Nevertheless, the basaltic basement of several ocean plateaus has been sampled during the course of Deep Sea Drilling Project (DSDP) and ODP cruises. ODP Leg 192 was the latest of these.

1Fitton, J.G., Mahoney, J.J., Wallace, P.J., and Saunders, A.D., 2004. Leg 192 synthesis: origin and evolution of the Ontong Java Plateau. In Fitton, J.G., Mahoney, J.J., Wallace, P.J., and Saunders, A.D. (Eds.), Proc. ODP, Sci. Results, 192 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/192_SR/synth/synth.htm>. [Cited YYYY-MM-DD]

2School of GeoSciences, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 3JW, United Kingdom. Godfrey.Fitton@ed.ac.uk

3Department of Geology and Geophysics/School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, 49/10 East-West Road, Honolulu HI 96822, USA.

4Department of Geological Sciences, 1272 University of Oregon, Eugene OR 97403-1272, USA.

5Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom.

Initial receipt: 28 May 2004
Acceptance: 21 July 2004
Web publication: 3 September 2004
Ms 192SR-101

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