Origin and evolution of magmas on the Ontong Java Plateau

Abstract

Abstract:The Early Cretaceous Ontong Java Plateau (OJP) represents by far the largest igneous event on Earth in the last 200 Ma and yet, despite its size, the OJP's basaltic crust appears to be remarkably homogeneous in composition. The most abundant rock type is a uniform low-K tholeiite, represented by the Kwaimbaita Formation on Malaita and found at all but one of the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) drill sites on the plateau and in the adjacent basins. This is capped by a thin and geographically restricted veneer of a slightly more incompatible-element-rich tholeiite (the Singgalo Formation on Malaita and the upper flow unit at ODP Site 807), distinguished from Kwaimbaita-type basalt by small but significant differences in Sr-, Nd-and Pb-isotope ratios. A third magma type is represented by high-Mg (Kroenke-type) basalt found in thick (>100 m) successions of lava flows at two drill sites (ODP Sites 1185 and 1187) 146 km apart on the eastern flank of the plateau. The high-Mg basalt is isotopically indistinguishable from Kwaimbaita-type basalt and may therefore represent the parental magma for the bulk of the OJP. Low-pressure fractional crystallization of olivine followed by olivine+augite+plagioclase can explain the compositional range from high-Mg Kroenketype to Kwaimbaita-type basalt. The Singgalo-type basalt probably represents slightly smaller-degree, late-stage melting of an isotopically distinct component in the mantle source. Primary magma compositions, calculated by incremental addition of equilibrium olivine to aphyric Kroenke-type basalt glass, contain between 15.6% (in equilibrium with Fo90 ) and 20.4% (Fo92) MgO. Incompatible-element abundances in the primary OJP magma can be modelled by around 30% melting of a peridotitic primitive-mantle source from which about 1% by mass of average continental crust had previously been extracted. This large degree of melting implies decompression of very hot (potential temperature >1500~ mantle beneath very thin lithosphere. The initiation of an exceptionally large and hot plume head close to a mid-ocean ridge provides the best explanation for the size, homogeneity and composition of the OJP, but is difficult to reconcile with the submarine eruption of virtually all of the basalt so far sampled.

Formation and evolution of Shatsky Rise oceanic plateau: Insights from IODP Expedition 324 and recent geophysical cruises

“…Although coring at Site U1348 did not penetrate deeply (~120 m into basement), they suggest that the large cone-like feature at whose summit the site penetrated (Expedition 324 Scientists, 2010d) may thus be a A C C E P T E D M A N U S C R I P T (Thordarson, 2004) whereas the recovered lava flows from other sites were emplaced in deep water (Neal et al, 1997;Fitton and Godard, 2004). Basal volcaniclastic sediments were cored at Manihiki Plateau and interpreted as phreatomagmatic products of shallow water eruptions (Jackson and Schlanger, 1976).…”

IODP Expedition 324: Ocean Drilling at Shatsky Rise Gives Clues about Oceanic Plateau Formation

“…Site 1213 data are from Mahoney et al (2005). OJP = Ontong Java Plateau (data of Tejada et al, 1996Tejada et al, , 2002Fitton and Godard, 2004), EPR = East Pacific Rise (data of Sinton et al, 1991;Bach et al, 1994;Mahoney et al, 1994). high content of zeolite and volcaniclastics; they display cross-bedding and intense bioturbation and contain a neritic (<200 m water depth) assemblage of benthic foraminifera.…”

Site U1373

“…Shown for comparison are data for dredge samples from the length of the Louisville Seamount Trail (only data for dredge samples with LOI < 6 wt% are included; data of Hawkins et al, 1987;Vanderkluysen et al, 2007;Beier et al, 2011). Also shown are fields for the southern East Pacific Rise (EPR; data of Sinton et al, 1991;Bach et al, 1994;Mahoney et al, 1994), and Ontong Java Plateau (OJP; data of Tejada et al, 1996Tejada et al, , 2002Fitton and Godard, 2004). Figure F41.…”

“…"Hawaii postshield" fields include Lapahoehoe and Hamakua lavas (data of Frey et al, 1990;West et al, 1988). Also shown are fields for the southern East Pacific Rise (EPR; data of Sinton et al, 1991;Bach et al, 1994;Mahoney et al, 1994), and Ontong Java Plateau (OJP; data of Tejada et al, 1996Tejada et al, , 2002Fitton and Godard, 2004). Figure F46.…”