Joint mineral physics and seismic wave traveltime analysis of upper mantle temperature

• Main Authors: Ritsema, J, Cupillard, P, Tauzin, B, Xu, WB, Stixrude, L, Lithgow-Bertelloni, C
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: GEOLOGICAL SOC AMER, INC 2009
• Subjects: TRANSITION ZONE; RECEIVER FUNCTIONS; CONVECTING MANTLE; DISCONTINUITIES; VELOCITY; CONSTRAINTS; ICELAND; MODELS; ORIGIN; PHASES; Iceland
• Online Access: http://discovery.ucl.ac.uk/126543/

We employ a new thermodynamic method for self-consistent computation of compositional and thermal effects on phase transition depths, density, and seismic velocities. Using these profiles, we compare theoretical and observed differential traveltimes between P410s and P (T-410) and between P600s and P410s (T660-410) that are affected only by seismic structure in the upper mantle. The anticorrelation between T-410 and T660-410 suggests that variations in T-410 and T660-410 of similar to 8 s are due to lateral temperature variations in the upper mantle transition zone of similar to 400 K. If the mantle is a mechanical mixture of basaltic and harzburgitic components, our traveltime data suggest that the mantle has an average temperature of 1600 +/- 50 K, in agreement with temperature estimates from magma compositions of mid-ocean ridge basalts. We infer a 100 K hotter mantle if we assume the mantle to have a homogeneous pyrolitic composition. The transition-zone temperature beneath hotspots and within subduction zones is relatively high and low, respectively. However, the largest variability in T-410 and T660-410 is recorded by global stations far from subduction zones and hotspots. This indicates that the 400 K variation in upper mantle temperature is complicated by tilted upwellings, slab flattening and accumulation, ancient subduction, and processes unrelated to present-day subduction and plume ascent.