SUBSIDENCE AND GROWTH OF PACIFIC CRETACEOUS PLATEAUS

The Ontong Java, Manihiki, and Shatsky oceanic plateaus are among the Earth's largest igneous provinces and are commonly believed to have er upted 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 ma ntle thermal and crustal accretionary processes. Fire find that total plateau subsidence is comparable to that expected of normal seafloor b ut less than predictions of thermal models of hotspot-affected lithosp here. if crustal emplacement was rapid, then uncertainties in paleo-wa ter depths allow for the anomalous subsidence predicted for plumes wit h only moderate temperature anomalies and volumes, comparable to the s ources of modem-day hotspots such as Hawaii and Iceland. Rapid emplace ment over a plume head of high temperature and volume, however, is dif ficult to reconcile with the subsidence reconstructions. An alternativ e possibility that reconciles low subsidence over a high-temperature, high-volume plume source is a scenario in which plateau subsidence is the superposition of (I) subsidence due to the cooling of the plume so urce, and (2) uplift due to prolonged crustal growth in the form of ma gmatic 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 ( similar to 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 ha ve occurred continuously or in discrete stages over similar to 30 m.y. and implies lower magmatic fluxes than previously estimated. (C) 1998 Elsevier Science B.V. All rights reserved.