The effective elastic thickness along the Emperor Seamount Chain and its tectonic implications

SUMMARY The Hawaiian–Emperor Seamount Chain, a pre-eminent example of a hotspot-generated intraplate seamount chain, provides key constraints not only on the kinematics of plates but also on their rigidity. Previous studies have shown that the effective elastic thickness, Te, a proxy for the long-term strength of the lithosphere, changes abruptly at the Hawaiian–Emperor ‘bend’ from low values (∼16 km) at the Emperor Seamounts to high values (∼27 km) at the Hawaiian Ridge. To better constrain Te along the poorly explored Emperor Seamounts we have used a free-air gravity anomaly and bathymetry gridded data set, together with fully 3-D elastic plate (flexure) models, to estimate the continuity of Te and volcano load and infill densities along 1000 profiles spaced 2 km apart of the chain. Results show that Te generally decreases northwards along the chain. The decrease is most systematic between Ojin and Jimmu guyots where Te depends on the age of the lithosphere at the time of volcano loading and is controlled by the 340 and 400 °C oceanic isotherms. The largest variation from these isotherms occurs at the northern and southern ends of the chain where Te is smaller than expected suggesting the influence of pre-existing, older, loads. We use these results to constrain the subsidence, flexural tilt, rheological properties and tectonic setting along the seamount chain. We found an excess subsidence in the range 1.2–2.4 km, a tilt as large as 2–3°, oceanic lithosphere that is weaker than it is seawards of the weak zone at subduction zones, and a tectonic setting at Detroit and Koko seamounts that, despite their forming an integral part of the hotspot generated seamount chain, retains a memory of their proximity to earlier loads associated with plume influenced mid-oceanic ridges.