Pin-pricking the elephant; evidence on the origin of the Ontong Java Plateau from Pb-Sr-Hf-Nd isotopic characteristics of ODP Leg 192 basalts

Author(s): Tejada, M. L. G.; Mahoney, John J.; Castillo, Paterno R.; Ingle, S. P.; Sheth, H. C.; Weis, D.
Author Affiliation(s): Primary:
University of the Philippines, National Institute of Geological Sciences, Quezon City, Philippines
Other:
University of Hawaii, United States
University of Oregon, United States
University of Leicester, United Kingdom
University of California at San Diego, United States
Université Libre de Bruxelles, Belgium
Volume Title: Origin and evolution of the Ontong Java Plateau
Volume Author(s): Fitton, J. Godfrey, editor; Mahoney, John J.; Wallace, Paul J.; Saunders, Andrew D.
Source: Origin and evolution of the Ontong Java Plateau, edited by J. Godfrey Fitton, John J. Mahoney, Paul J. Wallace and Andrew D. Saunders. Geological Society Special Publications, Vol.229, p.133-150. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719. ISBN: 1-86239-157-2 CODEN: GSLSBW
Note: In English. 86 refs.; illus., incl. 3 tables, sketch map
Summary: Age-corrected Pb, Sr and Nd isotope ratios for early Aptian basalt from four widely separated sites on the Ontong Java Plateau that were sampled during Ocean Drilling Program Leg 192 cluster within the small range reported for three earlier drill sites, for outcrops in the Solomon Islands, and for the Nauru and East Mariana basins. Hf isotope ratios also display only a small spread of values. A vitric tuff with εND(t) = +4.5 that lies immediately above basement at Site 1183 represents the only probable example from Leg 192 of the Singgalo magma type, flows of which comprise the upper 46-750 m of sections in the Solomon Islands and at Leg 130 Site 807 on the northern flank of the plateau. All of the Leg 192 lavas, including the high-MgO (8-10 wt%) Kroenke-type basalts found at Sites 1185 and 1187, have εNd(t) between +5.8 and +6.5. They are isotopically indistinguishable from the abundant Kwaimbaita basalt type in the Solomon Islands, and at previous plateau, Nauru Basin and East Mariana Basin drill sites. The little-fractionated Kroenke-type flows thus indicate that the uniform isotopic signature of the more evolved Kwaimbaita-type basalt (with 5-8 wt% MgO) is not simply a result of homogenization of isotopically variable magmas in extensive magma chambers, but instead must reflect the signature of an inherently rather homogeneous (relative to the scale of melting) mantle source. In the context of a plume-head model, the Kwaimbaita-type magmas previously have been inferred to represent mantle derived largely from the plume source region. Our isotopic modelling suggests that such mantle could correspond to originally primitive mantle that experienced a rather minor fractionation event (e.g. a small amount of partial melting) approximately 3 Ga or earlier, and subsequently evolved in nearly closed-system fashion until being tapped by plateau magmatism in the early Aptian. These results are consistent with current models of a compositionally distinct lower mantle and a plume-head origin for the plateau. However, several other key aspects of the plateau are not easily explained by the plume-head model. The plateau also poses significant challenges for asteroid impact, Icelandic-type and plate separation (perisphere) models. At present, no simple model appears to account satisfactorily for all of the observed first-order features of the Ontong Java Plateau.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 03 Geochronology; 18 Geophysics, Solid-Earth; Absolute age; Aptian; Basalts; Cretaceous; Dates; East Mariana Basin; Hot spots; Igneous rocks; Isotopes; Jurassic; Leg 192; Lower Cretaceous; Mantle; Mantle plumes; Melanesia; Mesozoic; Nauru Basin; Nd/Nd; North Pacific; Northwest Pacific; ODP Site 1183; ODP Site 1184; ODP Site 1185; Ocean Drilling Program; Oceania; Ontong Java Plateau; Pacific Ocean; Paleomagnetism; Pb/Pb; Plate tectonics; Sampling; Solomon Islands; Volcanic rocks; West Pacific
Coordinates: S050000 N050000 E1650000 E1550000
S011100 S011100 E1570100 E1570100
S002100 S002100 E1614000 E1614000
Record ID: 2006012375
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