Subsidence and growth of Pacific Cretaceous plateaus

Abstract

The Ontong Java, Manihiki, and Shatsky oceanic plateaus are among the Earth's largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes. We investigate this hypothesis by using sediment descriptions of Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) drill cores to constrain plateau subsidence histories which reflect mantle thermal and crustal accretionary processes. We find that total plateau subsidence is comparable to that expected of normal seafloor but less than predictions of thermal models of hotspot-affected lithosphere. If crustal emplacement was rapid, then uncertainties in paleo-water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes, comparable to the sources of modern-day hotspots such as Hawaii and Iceland. Rapid emplacement over a plume head of high temperature and volume, however, is difficult to reconcile with the subsidence reconstructions. An alternative possibility that reconciles low subsidence over a high-temperature, high-volume plume source is a scenario in which plateau subsidence is the superposition of (1) subsidence due to the cooling of the plume source, and (2) uplift due to prolonged crustal growth in the form of magmatic underplating. This prolonged crustal growth and uplift scenario may explain the low and thus submarine relief during plume initiation, the late stage eruptions found on Ontong Java (90 Ma) and Manihiki (~70 Ma), a large portion of the high-seismic-velocity lower crust, and the widespread normal faults observed throughout and along the margins of the three plateaus. Such late stage underplating may have occurred continuously or in discrete stages over ~30 m.y. and implies lower magmatic fluxes than previously estimated.