Leg 192: Ontong Java Plateau

Many volcanic ocean plateaus may represent immense volumes of magma erupted on the seafloor in geologically short time periods. Emplacement rates of the largest plateaus may have approached the entire magma production rate of the global mid-ocean ridge system. The Alaska-sized Ontong Java Plateau in the western Pacific is the largest of these features, with an area of 1.8 million km2 and an average crustal thickness between 30 and 40 km. Depending on the age and duration of its emplacement, it may represent the largest igneous event of the last 200 m.y. Leg 192 is the first leg of a proposed two-leg program aimed at understanding the formation of the world's largest volcanic plateau. A transect of holes penetrating 200 m into basement across the plateau will be drilled to determine the emplacement age of different regions, the range and diversity of magmatism, the environment of eruption, its post-emplacement vertical tectonic history, the effects of rift-related tectonism, and the plateau's paleolatitude at the time of emplacement.

Most current models ascribe oceanic plateaus to mantle plumes. The Ontong Java Plateau has been proposed to be the initial product of the long-lived Louisville plume, and paleolatitude data are essential to evaluate this possibility. Information on crustal age in different sectors of the plateau will provide a test of competing plume-related hypotheses for plateau formation: (1) whether nearly all of the crust was formed in a very short period of time (plume-head impact), in two discrete episodes separated by a long period with little or no volcanism (as the few existing dates suggest), or (2) whether significant volumes erupted relatively steadily over a long interval of 30 m.y. or more. Establishing the range and diversity of magmatism is important because existing lava samples from the plateau indicate formation by large amounts of partial melting of a mantle source with very limited compositional variability, in contrast to theoretical and laboratory models that predict considerable major element, trace element, and isotopic heterogeneity in lavas erupted from different parts of a plume head, or at different times. The few previously studied sites on the plateau also indicate submarine emplacement at bathyal depths, yet data for other plateaus indicate that significant areas were originally shallow or subaerial, even though these plateaus have thinner crusts than the Ontong Java. Leg 192 will include sampling of portions of the plateau that may originally have been at shallow depths. In addition to a better understanding of plateau formation, the combined age, compositional, and paleodepth results will be important for assessing the nature and magnitude of atmospheric and environmental effects accompanying the formation of this enormous edifice.

Leg Prop # Description Site Prop Lat. Prop Long. Prop Water Depth Prop. Total Depth Prop
192 448 Ontong Java OJ-3B 1°10.6177'S 1800 1200
  Rev4   OJ-3C 2°5.3266'S 157°0.7494'E 1590 1100
      OJ-6B 7°28.224'S 161°5.9932'E 1860 790
      OJ-6C 7°13.0434'S 161°17.5313'E 1705 830
      OJ-7D 4°56.2177'S 164°16.2656'E 2003 1400
      OJ-7E 4°56.2177'S 164°9.2950'E 1635 1505
      OJ-11C 0°21.4569'S 161°40.0636'E 3915 550

Staff Scientist: Paul Wallace

Location map

Ship Schedule

Science Services

ODP home