Magma-Assisted Flexure of Hawaiian Lithosphere Inferred From Three-Dimensional Models of Lithospheric Flexure Constrained by Active Source Seismic Data

Abstract

Reprocessed and newly acquired seismic data provide new constraints on lithospheric flexure profiles beneath the Hawaiian Islands. We use these new observations and three-dimensional numerical models of lithospheric deformation combining elasticity, brittle failure, low-temperature plasticity (LTP) and high-temperature creep deformation mechanisms to constrain the thermal structure and rheology of the oceanic lithosphere. When simulating normal oceanic lithospheric conditions with experimentally-derived LTP flow laws, the lithosphere flexes with too little amplitude and over too large a wavelength compared to observations. This result supports prior studies which call on the need to (a) adjust the LTP flow laws or, alternatively, to (b) account for magma-assisted flexural weakening of the lithosphere. Here, models that explore reductions in the activation energy of LTP are able to explain the observations of flexure with a smaller reduction than previously suggested. Models that explore elevated temperatures attributed to hotspot magmatism localized beneath the island edifices also produce close fits to the observed flexural profiles. Although the two factors cannot be distinguished based on fits to the flexure profiles, localized magma-assisted flexural weakening is supported by recent studies of geothermobarometry of pyroxenite xenoliths from O'ahu, seismic structure and patterns of seismicity beneath the Hawaiian chain. If magma-assisted flexure is a common phenomenon at other ocean islands and seamounts, it could explain similarities in elastic plate thickness with subduction zones as well as differences with fracture zones globally.