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1 Department of Geological Sciences, 1272 University of Oregon, Eugene, Oregon 97403-1272, USA
2 Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK
3 Ocean Research Institute, University of Tokyo, Tokyo 164-8639, Japan
The Ontong Java Plateau in the western Pacific is anomalous compared to other oceanic large igneous provinces in that it appears to have never formed a large subaerial plateau. Paleoeruption depths (at 122 Ma) estimated from dissolved H2O and CO2 in submarine basaltic glass pillow rims vary from
1100 m below sea level (mbsl) on the central part of the plateau to 22003000 mbsl on the northeastern edge. Our results suggest maximum initial uplift for the plateau of 25003600 m above the surrounding seafloor and 1500 ± 400 m of postemplacement subsidence since 122 Ma. Our estimates of uplift and subsidence for the plateau are significantly less than predictions from thermal models of oceanic lithosphere, and thus our results are inconsistent with formation of the plateau by a high-temperature mantle plume. Two controversial possibilities to explain the anomalous uplift and subsidence are that the plateau (1) formed as a result of a giant bolide impact, or (2) formed from a mantle plume but has a lower crust of dense garnet granulite and/or eclogite; neither of these possibilities is fully consistent with all available geological, geophysical, and geochemical data. The origin of the largest magmatic event on Earth in the past 200 m.y. thus remains an enigma.
Key Words: large igneous province basalt volatiles mantle plume meteorite impact
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