Anomalous elastic thickness of the oceanic lithosphere in the south–central Pacific

Abstract

To first order the elastic thickness T_e of the oceanic lithosphere under mid-plate volcanoes increases linearly with the square root of plate age at the time of loading^1–4. A large scatter around this simple relationship is observed however, suggesting that factors other than age influence the elastic thickness and produce departure from the first-order trend⁵. To look at second-order effects, we have conducted a worldwide analysis over the Pacific, Atlantic and Indian oceans and determined T_e under sixty volcanoes, applying elastic flexure theory and using as observational constraints, geoid height data from the Seasat satellite. We find that for the three main oceans, the depth of the elastic layer under volcanoes increases with age of plate at loading time t, according to the simple relationship T_e = 2.70±0.15 t^1/2 (T_e in km, t in Myr), except under all of the volcanic chains of the south-central Pacific where this relation does not apply. The elastic layer is found to be much thinner there, and indicates a broad regional anomaly, presumably of thermal origin, well correlated with several other geophysical anomalies reported in this region^6–10.