Deformation of the Manihiki Plateau, Western Equatorial Pacific Ocean

The submarine Manihiki Plateau, an oceanic large igneous province (LIP), encompasses ∼800,000 km² of seafloor in the western equatorial Pacific Ocean. Of Early Cretaceous ( ∼120 Ma) age, the plateau stands several kilometers above the surrounding seafloor, and comprises three major structural highs. The `High' plateau to the east contains several islands, including the eponymous Manihiki atoll. To the west, the `Western' plateaus lie in slightly deeper water, and are separated from the High plateau by a long, northeast-trending, bathymetric low known as the Danger Islands troughs. North of the Western plateaus is the small, nearly separate `North' plateau that is separated from the High plateau by a deep ocean basin. In August/September 2003, we acquired ∼25,000 km² of multibeam bathymetry and reflectivity, together with magnetics and gravity, data along the Danger Islands troughs and northwestern margin of the High plateau aboard R/V Hakuho Maru. On the basis of these data, we propose a tectonic model for post-emplacement (Cretaceous?) deformation of the Manihiki Plateau involving both normal and transform faulting. The deep basin separating the High and North plateaus probably formed by seafloor spreading; the northwestern and southeastern margins of the respective plateaus appear to be conjugate rift margins, whose physical separation approximately equals the right-lateral offset between the southern flanks of High and Western plateaus. The curvilinear southwest edge of the deep basin abuts the steep northeast flank of the Western plateaus, and in our interpretation represents a fracture zone juxtaposing LIP and normal oceanic crust. The right-lateral fracture zone continues uninterrupted to the south of the deep ocean basin as the Danger Islands troughs, which in the study area comprise a series of major en echelon, right-lateral faults that step to the right, producing extensional relay zones and pull-apart basins between fault tips where displacement was transferred. Geochronology of igneous rock samples dredged from the Danger Islands troughs during the Hakuho Maru expedition may yield information on the timing of deformation, which would in turn contribute to a better understanding of regional Cretaceous plate kinematics.