Variable conductivity: Effects on the thermal structure of subducting slabs

Understanding the thermal structure of the lithosphere in subduction zone environments is a key element in the realization of the source of deep focus earthquakes and other geodynamic processes. Model predictions of the thermal structure of subducting slabs are dependent upon a priori knowledge of how thermal conductivity varies within the slab. Using recent results for the variation of thermal conductivity as a function of temperature, pressure, and gross mineralogy, we investigate how models that utilize a realistic model for variable conductivity compare with canonical models for constant conductivity. Results suggest that jumps in thermal conductivity across the phase boundaries that arise due to transformations to beta and gamma-spinel phases lead to old, fast, steeply dipping slabs being considerably warmer than previously thought. Although these results do not rule out the possibility of a metastable wedge source of deep focus earthquakes, they do imply the likelihood of metastable olivine being found at depth is less than once thought.