The relationship between plate curvature and elastic plate thickness: a study of the Peru-Chile Trench

Abstract

The age of the Nazca plate where it enters the Peru and northern Chile trenches varies from 30 Ma in the north to 45 Ma in the south as its dip beneath the South American continent steepens from 13° to 30°. If the elastic thickness Te of oceanic lithosphere depends only on its age, and therefore thermal state, we would expect that Te determined from fitting the flexure of the lithosphere over the outer rise would increase from the Peru Trench in the north to the northern Chile Trench further south. We find that the opposite is true: the lithosphere appears stiffer outboard of the Peru Trench than it does offshore Chile. To explain deflections of the lithosphere seaward of Peru, the isotherm controlling the elastic/ductile transition must be near 800°C, providing the thermal structure of the plate is that predicted by the standard thermal plate model. Because the decrease in plate stiffness to the south is correlated with an increase of plate curvature over the outer rise and outer trench wall, we interpret our result in terms of inelastic yielding of the oceanic lithosphere when bent to high strains. -from Authors