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Numerous large igneous provinces formed in the Pacific Ocean during Early Cretaceous time, but their origins and relations are poorly understood. We present new geochronological and geochemical data on rocks from the Manihiki Plateau and compare these results to those for other Cretaceous Pacific plateaus. A dredged Manihiki basalt gives an 40Ar-39Ar age of 117.9 ± 3.5 Ma (2σ), essentially contemporaneous with the Ontong Java Plateau ∼2500 km to the west, and the possibly related Hikurangi Plateau ∼3000 km to the south. Drilled Manihiki lavas are tholeiitic with incompatible trace element abundances similar to those of Ontong Java basalts. These lavas may result from high degrees of partial melting during the main eruptive phase of plateau formation. There are two categories of dredged lavas from the Danger Islands Troughs, which bisect the plateau. The first is alkalic lavas having strong enrichments in light rare earth and largeion lithophile elements; these lavas may represent late-stage activity, as one sample yields an 40Ar-39Ar age of 99.5 ± 0.7 Ma. The second category consists of tholeiitic basalts with U-shaped incompatible element patterns and unusually low abundances of several elements; these basalts record a mantle component not previously observed in Manihiki, Ontong Java, or Hikurangi lavas. Their trace element characteristics may result from extensive melting of depleted mantle wedge material mixed with small amounts of volcaniclastic sediment. We are unaware of comparable basalts elsewhere. [ABSTRACT FROM AUTHOR]

The ∼120 Ma Ontong Java Plateau and neighboring, contemporaneous Nauru, East Mariana, and (probably) Pigafetta basin flood basalts in the western equatorial Pacific Ocean comprise the Earth’s largest flood basalt province. Geophysical, geochemical, and geodynamic evidence from the province are difficult to reconcile with mantle plume models; absence of an obvious hotspot source or track, minor crustal uplift associated with emplacement, minor total subsidence compared with normal oceanic crust or other oceanic plateaus and submarine ridges, high degrees of melting at shallow, upper mantle depths, low water contents of basalts, enrichment of platinum group elements in basalts, and a ∼300 km deep, seismically slow mantle root are more consistent with the consequences of an impacting bolide. An object ∼20 km in diameter impacting relatively young (∼20 Myr) Pacific lithosphere and penetrating into the uppermost asthenosphere would have initiated massive decompression melting in the upper mantle, and may have resulted in emplacement of the greater Ontong Java Plateau. [Copyright &y& Elsevier]