DEFINITION OF ONTONG-JAVA PLATEAU, PACIFIC OCEAN

The Ontong-Java plateau is the largest igneous province in the world not associated

with the oceanic ridge spreading center network, covering

an area roughly the size of Alaska (9,300,000 square

miles, or 15,000 km2). The plateau is located northeast of

Papua New Guinea and the Solomon Islands in the southwest

Pacific Ocean, centered on the equator at 160°E longitude.

Most of the plateau formed about 120 million years ago in

the Cretaceous period, probably as a result of a mantle plume

rising to the surface and causing massive amounts of volcanism

over a geologically short interval likely lasting only about

a million years. Smaller amounts of volcanic material were

erupted later, at about 90 million years ago. Together, these

events formed a lava plateau that is 20 miles (32 km) thick.

The amount of volcanic material produced to form the

plateau is estimated to be approximately the same as that

erupted from the entire global ocean ridge spreading center

system in the same period. Such massive amounts of volcanism

cause worldwide changes in climate and ocean temperatures

and typically have great impacts on the biosphere. Sea

levels rose by more than 30 feet (9 m) in response to this volcanic

outpouring. The gases released during these eruptions

are estimated to have raised average global temperatures by

23°F (13°C). Perhaps more remarkably, the Ontong-Java

plateau is but one of many Cretaceous oceanic plateaus in the

Pacific, suggesting that the Cretaceous was characterized by

long-standing eruption of massive amounts of deeply derived

magma. Some geologists have suggested that events like this

may be related to major mantle overturn events, when heat

loss from the Earth is dominated by plumes instead of oceanic

ridge spreading as occurs in the present plate mosaic.

The plateau is thought to be composed largely of basalt,

based on limited sampling, deep-sea drilling, and seismic

velocities. Great difficulties are encountered trying to sample

the plateau because it is covered by a thick veneer of sediments

exceeding thousands of feet (a kilometer or more) in

most places. The plateau is colliding with the Solomon

trench, but thick oceanic plateaus like the Ontong-Java are

generally unsubductable. When oceanic plateaus confront

subduction, they typically get accreted to the continents, leading

to continental growth.

See also FLOOD BASALT.

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