Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
The 100s: Significant Exposures of the World (No. 4-5)
Ontong - Java Plateau, the World's largest Oceanic Plateau, Has Been Subducted 50%, with the Remaining 50% on the Surface, and with a < 1% Accretion on the Hanging Wall of the Solomon Islands
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2011 Volume 120 Issue 6 Pages 1035-1044


 The Ontong - Java plateau (OJP) , which is ca. 2000 km across, was formed at ca. 122 Ma and 90 Ma directly above the Pacific Superplume region in the central Pacific. It migrated westward after being formed, and has subducted southward due to the rapid northward movement of the Australian plate since 65 Ma. Subduction of OJP started at 20-25 Ma under the Solomon Islands to form an accretionary complex that is at least 1500 km in length along the trench, and about half of it has been taken deep into the lower mantle, with the remaining 1% on the hanging wall of the overriding plate as fragments.
 The Solomon Islands, an EW-trending narrow chain of accretionary complexes, are composed mainly of a pile of massive lava flows, auto-brecciated lavas with minor dikes and dominant pillowed basalts, which are a few kilometers thick, overlain by calcareous pelagic sediments, all derived from the subducted Ontong - Java plateau. The representative outcrops of those effusive rocks are introduced here in detail.
 CA volcano-plutonism is recorded to have stopped in the overlying cover sediments on the Solomon Islands at 25-20 Ma, indicating the arrival of a buoyant OJP mass to change the tectonic regime of the hanging wall plate together with extensive tectonic erosion of the frontal portion of Solomon-Australia plate.
 Subduction of most of the OJP together with Pacific slab into the deep mantle, with the remaining minor fragments accounting for < 1% volume seems to be consistent with Jurassic-Cretaceous examples in Japan and other orogenic belts around the world.

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© 2011 Tokyo Geographical Society
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