Mathematics – Logic
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.v12b0575i&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #V12B-0575
Mathematics
Logic
1212 Earth'S Interior: Composition And State (8105), 3640 Igneous Petrology, 6022 Impact Phenomena, 8450 Planetary Volcanism (5480)
Scientific paper
Voluminous basaltic magmatism at ˜120 Ma created Earth's biggest large igneous province (LIP), the Greater Ontong Java Plateau (OJP) in the west Pacific Ocean. This volcanic event has been generally attributed to a large mantle plume. However several important lines of geochemical and petrologic evidence are at odds with a plume origin. High concentrations of heavy rare earth elements (HREE) indicate melting at shallow mantle depths, and major and trace element systematics for OJP basalts are consistent with >30% batch melting. These conditions and extents of melting are typical at mid-ocean ridges influenced by hot or wet mantle plumes, but pelagic sediments overlie mostly vesicle-free basalts, implying a deep-water environment of emplacement away from a spreading center. H2O contents of these basalts are very low indicating that melting was not facilitated by a wet plume. Radiogenic isotopes vary little considering the large size of OJP. Platinum group elements (PGE) are enriched relative to predicted values assuming a primitive mantle source, but OJP basalts are also sulfide-free, leaving PGE levels difficult to explain. An extraterrestrial impact model for OJP seems more consistent with existing data. A bolide ˜20 km in diameter would remove >60 km of overburden, and instigate extensive decompression melting. High extents of melting in the shallow mantle would explain the geochemical homogeneity of the basalts, high HREE contents and low H2O%. Magmas might also entrain residual bolide which would create basalts with relative PGE enrichment. In the impact scenario, OJP was not heated from below by a mantle plume, so neither uplift nor subsidence would have been extensive, thus explaining the submarine emplacement of the lavas. A major bolide impact could have also caused or contributed to some unexplained phenomena coincident with the timing of OJP emplacement including: onset of the Cretaceous normal magnetic polarity superchron, the Selli oceanic anoxic event, marine faunal extinctions and worldwide radiogenic isotopic excursions that suggest a rapid change from terrigenous-dominated values to mantle-dominated values in marine sediments (Sr and Hf).
Coffin Millard F.
Ingle Stephanie
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