Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.t13a1121s&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #T13A-1121
Other
1500 Geomagnetism And Paleomagnetism, 4900 Paleoceanography (0473, 3344), 8157 Plate Motions: Past (3040), 9355 Pacific Ocean, 9609 Mesozoic
Scientific paper
The Ontong Java Plateau (OJP) in the southwest Pacific represents the world's largest Large Igneous Province and represents an enigma in terms of its origin and evolution. Origins through plume(s), meteorite impact, or perisphere/upper mantle models all fail to explain all the features observed on this Greenland-size LIP (e.g., Tejada et al., 2004, Geol Soc. London Spec. Pub. 229, 133). Over the last 25-30 years, more information on the OJP has been obtained, yet the observations and interpretations have brought us more questions than answers. Therefore, it is time to look at what we know about the OJP and evaluate what other information is needed, and where we need to go to get this, in order to better understand how this LIP formed and evolved, as well as its impact on the environment. So what do we know? The first and most noticeable feature of the OJP is its immense size, which could be even larger if the Manihiki and Hikurangi plateaus represent rifted portions of the OJP (Taylor, 2006, EPSL 241, 372). The OJP has a seismically distinct mantle root extending up to 300 km into the mantle that appears to be attached to the OJP and moving with it (Richardson et al., 2000, PEPI 118, 29; Klosko et al., 2001, EPSL 186, 347). Fieldwork on the obducted portions of the OJP outcropping in the Solomon Islands and two Ocean Drilling Program legs have demonstrated that the OJP is remarkable in its monotony, with the Kwaimbaita Basalt (Tejada et al., 2001, J. Pet. 43, 449) dominating the interior of the plateau. What little variability there is in lava composition is found at the plateau margins (Singgalo and Kroenke type basalts: Tejada et al. ibid.; Fitton and Goddard, 2004, Geol Soc. London Spec. Pub. 229, 151). In addition, the majority of lava flows erupted in ~5 m.y. around 122 Ma. However, there is evidence at the plateau margins (Site 803 of ODP Leg 130; the islands of Malaita, Santa Isabel, San Cristobal) of a minor eruptions at ~90 Ma; remarkably, these younger basalts are compositionally indistinct from the ~122 Ma Kwaimbaita type. The topography of the OJP is also enigmatic: plume theory predicts that much of the plateau would have been erupted subaerially, yet evidence suggests the eruption environment was predominantly deep marine. Volcaniclastic debris cored at Site 1184 on the Eastern Salient of the OJP is the only evidence for shallow water/subaerial eruptions. Likewise, the OJP has not subsided as far as is predicted from oceanic crust relaxation models. Rapid and massive eruptions must have occurred during the formation of the OJP yet very few extinctions are coincident with its ~122 Ma age. However, the eruption of the OJP is approximately coincident with the Selli oceanic anoxic event (OAE-1a). Given the information we now have, focused ocean drilling is needed to understand the origin and evolution of the OJP and the consequences its formation had for the environment. This presentation will present a rationale for a new ocean drilling expedition in order to probe further the enigma that is the Ontong Java Plateau.
Neal Chris R.
Shafer John T.
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