Time-Dependent Flexural Deformation Beneath the Emperor Seamounts

Abstract:

The Hawaii-Emperor seamount chain stretches over 6000 km from the Big Island of Hawaii to the subduction cusp off Kamchatka and represents a near-continuous record of hotspot volcanism since the Late Cretaceous. The load of these seamounts and islands has caused the underlying lithosphere to deform, developing a flexural flanking moat that is now largely filled with volcanoclastic sediments. Because the age differences between the seafloor and the seamounts vary by an order of magnitude or more along the chain, the Hawaii-Emperor chain and surrounding area is considered a natural laboratory for lithospheric flexure and has been studied extensively in order to infer the rheology of the oceanic lithosphere. While most investigations have focused on the Hawaiian Islands and proximal seamounts (where data sets are more complete, including seismic reflection and refraction, swath bathymetry and even mapping and dating of drowned reef terraces), far fewer studies have examined the flexural deformation beneath the remote Emperor chain. Preliminary analysis of satellite altimetry data shows the flexural moats to be associated with very large negative gravity anomalies relative to the magnitudes of the positive anomalies over the loads, suggesting considerable viscous or viscoelastic relaxation since the loads were emplaced 50-80 Myr ago. In our study, we will attempt to model the Emperor seamount chain load as a superposition of individual elliptical Gaussian seamounts with separate loading histories. We use Optimal Robust Separation (ORS) techniques to extract the seamount load from the regional background bathymetry and partition the residual load into a set of individual volcanoes. The crustal age grid and available seamount dates are used to construct a temporal loading model and evaluate the flexural response of the lithosphere beneath the Emperor seamounts. We explore a variety of rheological models and loading scenarios that are compatible with the inferred load sizes and observed gravity anomalies, with emphasis on the temporal-spatial variation in vertical deformation along the hotspot chain, and examine their implications for the tilting history of the loads and the stratigraphic “architecture” of their flanking flexural moats.