Heat advection during exhumation can explain high temperatures along the subduction plate interface

The pressure-temperature (P-T) evolution of subduction‐zone plate interfaces controls metamorphism, fluid flow, deformation, and seismicity. However, temperature estimates derived from exhumed rocks frequently exceed those predicted by subduction models, particularly at pressures below ~2.5 GPa. There are two main types of numerical subduction models: models that simulate subduction only without exhumation and models that simulate subduction and simultaneously ongoing exhumation. To investigate the discrepancy between modelled and rock-based temperature estimates, published numerical models that simulate both subduction and rock exhumation are re-examined. The analysis demonstrates that, at equivalent pressure, subduction plate interface temperatures are substantially lower during pure subduction (without exhumation) than during later stages when subduction and exhumation occur simultaneously. This increase in temperature results from advective heat transport, whereby exhuming rocks transfer heat from deeper, hotter regions to shallower levels of the subduction interface. Clockwise P-T paths recorded by exhumed rocks are consistent with this mechanism. Accounting for exhumation-related heat advection significantly improves agreement between modeled interface temperatures and rock-based P-T estimates. This heat advection effect is illustrated using as representative example the two-dimensional petrological-thermo-mechanical model of Vaughan-Hammon et al. (2022), which successfully reproduces P-T paths and metamorphic facies distributions in the Western Alps. Comparisons between interface P-T profiles during pure subduction and during combined subduction-exhumation stages show that interface temperatures at a given pressure can be elevated by more than 200 °C once exhumation initiates. A scaling analysis based on the Péclet number (Pe) combined with systematic two-dimensional numerical simulations of heat advection and diffusion along a channel generalize these results and provide a criterion for assessing the thermal impact of exhumation. Where exhumation occurs along the subduction interface and Pe > 1, advective heat transport can substantially raise interface temperatures. This framework applies to both oceanic and continental subduction zones and offers a potential explanation for the long-standing mismatch between subduction model temperature predictions and rock-based P-T data, particularly those associated with clockwise P-T paths.

Reference

Vaughan‐Hammon, J. D., Candioti, L. G., Duretz, T., & Schmalholz, S. M. (2022). Metamorphic facies distribution in the Western Alps predicted by petrological‐thermomechanical models of syn‐convergent exhumation. Geochemistry, Geophysics, Geosystems, 23(8), e2021GC009898, https://doi.org/10.1029/2021GC009898.