Intrabasement reflections of the Ontong Java Plateau: Implications for plateau construction

Abstract

[1] The Early Cretaceous Ontong Java Plateau (OJP) in the western equatorial Pacific, Earth's most voluminous large igneous province (LIP), is characterized by intrabasement seismic reflections. To investigate the nature of such reflections, we have analyzed new and all older multichannel seismic (MCS) reflection data from the OJP using an instantaneous phase velocity analysis technique and synthetic seismograms. Intrabasement reflections are most prevalent on the main OJP, especially on its crest. On MCS data, the reflections (1) are semicontinuous and subparallel to the top of igneous basement; (2) in places, have the opposite phase of seafloor reflections; and (3) have an average frequency of $20 Hz. We calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at OJP scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the MCS data. Alternatively, to evaluate the possibility of sediment/sedimentary rock interbeds causing the intrabasement reflections, we use published Early Cretaceous sedimentation rates determined from OJP drill sites and published estimates for the duration of massive OJP volcanism to calculate a range of possible sedimentary interbed thicknesses. The range proves to be below the detection limit of the MCS data. Therefore, we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates, both originating from vents and fissures on the OJP, probably on its crest.

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

“…A similar seismic expression is observed in multichannel seismic profiles collected from Ontong Java Plateau (Inoue et al, 2008) and Manihiki Plateau (Pietsch and Uenzelmann-Neben, 2015).…”

“…Moreover, the high quality seismic data from Ontong Java and Manihiki plateaus display stronger and more coherent reflectors at certain depths, suggesting different phases of volcanism (Inoue et al, 2008;Pietsch and Uenzelmann-Neben, 2015). In contrast, Shatsky…”

“…Intrabasement reflectors have been imaged at a number of oceanic plateaus, including Ontong Java Plateau (Phinney et al, 1999;Inoue et al, 2008), Manihiki Plateau (Pietsch and Uenzelmann-Neben, 2015), Kerguelen Plateau (Schaming and Rotstein, 1990;Rotstein et al, 1992), Hikurangi Plateau (Davy et al, 2008), and Agulhas Plateau (Parsiegla et al, 2008). Aside from Shatsky Rise, only Ontong Java…”

“…Instead, the reflections occur from alternations of thick, massive lava flows with pillows at Ontong Java Plateau (Inoue et al, 2008) and the same in addition to thicker sediment layers at Tamu Massif . Although prior authors attributed the imaged intrabasement reflectors to lava flows, these two studies offer proof.…”

The Mozambique Ridge: a document of massive multistage magmatism

“…5a). 1999;Frey et al 2000;Inoue et al 2008;Parsiegla et al 2008;Sager et al 2013b;Pietsch & Uenzelmann-Neben 2015). We hence interpret the observed intrabasement reflections at the MozR to represent lava flow sequences.…”