Modeling Slab Temperature: a Reevaluation of the Thermal Parameter

Abstract

We re‐evaluate the effects of slab age, speed and dip on slab temperature with numerical models. The Thermal Parameter Φ =t v sin θ, where t is age, v is speed, and θ is angle, is traditionally used as an indicator of slab temperature. However, we find that an empirically derived quantity, in which slab temperature T ∝ log (t−av−b) , is more accurate at depths <120 km, with the constants a and b depending on position within the slab. Shallower than the decoupling depth (~70‐80 km), a~1; b~0, i.e. temperature is dependent on slab age alone. This has important implications for the early devolatisation of slabs in the hottest (youngest) cases and for shallow slab seismicity. At sub‐arc depths (~100 km), within the slab mantle, a~1; b~0 again. However, for the slab crust, now a~0.5; b~1 i.e. speed has the dominant effect. This is important when considering the generation of arc magmatism, and in particular, slab melting and the generation of slab‐derived melange diapirs. Moving deeper into the Earth, the original thermal parameter performs well as a temperature indicator, initially in the core of the slab (the region of interest for deep water cycling). Finally, varying the decoupling depth between 40 – 100 km has a dominant effect on slab temperatures down to 140 km depth, but only within the slab crust. Slab mantle temperature remains primarily dependent on age.