Ontong Java plateau
The Ontong Java Plateau (OJP) is a huge oceanic plateau located in the south-west Pacific Ocean, north of the Solomon Islands. The OJP was emplaced c. 120 Ma with a much smaller volcanic event c. 90 Ma. Two other south-west Pacific plateaus, Manihiki and Hikurangi, now separated from the OJP by Cretaceous ocean basins, are of similar age and composition and probably formed as a single plateau and a contiguous large igneous province together with the OJP. When emplaced this Ontong Java-Manihiki-Hikurangi plateau covered 1% of Earth's surface and represented a volume of 1,000,000 km3 (240,000 cu mi) of basaltic magma. This "Onotong Java event", first proposed in 1991, represents the largest volcanic event of the past 200 million years, with a magma emplacement rate estimated at up to 22 km3 (5.3 cu mi)/year over three million years, several times larger than the Deccan Traps. The smooth surface of the OJP is punctuated by seamounts such as the Ontong Java Atoll, the largest atoll in the world.
The OJP covers 1,500,000 km2 (580,000 sq mi), roughly the size of Alaska. It reaches up to 1,700 m (5,600 ft) below sea level but has an average depth closer to 2–3 km (1.2–1.9 mi). It is bounded by Lyra Basin to the north-west, East Mariana Basin to the north, Nauru Basin to the north-east, and the Ellice Basin to the south-east. The OJP has collided with the Solomon Islands island arc and now lies on the inactive Vitiaz Trench and the Pacific-Australian plate boundary.
The high plateau, with a crustal thickness estimated to at least 25 km (16 mi) but probably closer to 36 km (22 mi), has a volume of more than 5,000,000 km3 (1,200,000 cu mi). The maximum extent of the event can, however, be much larger since lavas in several surrounding basins are closely related to the OJP event and probably represent dike swarms associated with the emplacement of the OJP.
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