Does mantle melting due to lithospheric flexural deformation explain the rejuvenated volcanism at the Juan Fernández Ridge?

Abstract

Oceanic intraplate volcanic systems often experience a late-stage eruptive phase known as rejuvenated volcanism, characterized by small volumes of alkaline lavas with salient compositional differences from earlier shield-stage products, occurring after significant quiescence (ca. 0.5–2 Ma). Despite its ubiquity at oceanic islands, the underlying physical mechanisms driving this stage remain elusive. This study investigates the potential of lithospheric flexure to induce upward mantle advection and decompression melting as a mechanism driving the rejuvenated volcanism observed at Robinson Crusoe and Santa Clara islands (RC-SC), located along the Juan Fernández Ridge (JFR) in the SE Pacific. We applied a 2-D numerical model to simulate the flexural response of the Nazca Plate under volcanic loading during the shield stage that formed the Alejandro Selkirk Island (ca. 180 km westward), integrating geochemical constraints that reproduce mantle heterogeneity. Melting models examined two mantle end-member scenarios: (1) Primitive Mantle-dominated, and (2) Depleted Mantle-dominated, both incorporating minor contributions from pyroxenite. Our results indicate that the maximum flexural uplift and the resulting mantle decompression predict low crustal production rates that are insufficient to generate the observed magma volumes at RC-SC. Low plume potential temperatures (T_p) and the small volcanic load limit melt productivity, with pyroxenite dominating at low T_p although constrained under the modeled conditions. These findings underscore the limitation of flexural deformation alone as the primary driver for rejuvenated volcanism of JFR, calling for advanced modeling approaches that integrate time-dependent 3D lithospheric variability and plume-lithosphere interactions to better capture the complexity of intraplate plumbing systems.