From seismic models to mantle temperatures: Uncertainties related to mineralogical complexities and limited tomographic resolution

Robl, Gabriel ; Schuberth, Bernhard S. A. ; Papanagnou, Isabel; Thomas, Christine (2025): From seismic models to mantle temperatures: Uncertainties related to mineralogical complexities and limited tomographic resolution. Geophysical Journal International, 241 (3). pp. 2002-2026. ISSN 0956-540X

Abstract

Many geophysical studies require knowledge on the present-day temperature distribution in Earth’s mantle. One example is geodynamic inverse models, which utilize data assimilation techniques to reconstruct mantle flow back in time. The thermal state of the mantle can be estimated from seismic velocity perturbations imaged by tomography with the help of thermodynamic models of mantle mineralogy. Unique interpretations of the tomographically imaged seismic heterogeneity can either be obtained by incorporating additional data sets or requires assumptions on the chemical composition of the mantle. However, even in the case of (assumed) known chemical composition, both the seismic and the mineralogical information are significantly affected by inherent limitations and different sources of uncertainty.Here, we investigate the theoretical ability to estimate the thermal state of the mantle from tomographic models in a synthetic closed-loop experiment. The ‘true’ temperature distribution of the mantle is taken from a 3-D mantle circulation model with Earth-like convective vigour. We aim to recover this reference model after: (1) mineralogical mapping from the ‘true’ temperatures to seismic velocities, (2) application of a tomographic filter to mimic the effect of limited seismic resolution, and (3) mapping of the ‘imaged’ seismic velocities back to temperatures. We test and quantify the interplay of tomographically damped and blurred seismic heterogeneity in combination with different approximations for the mineralogical ‘inverse’ conversion from seismic velocities to temperature. Owing to imperfect knowledge of the parameters governing mineral anelasticity, we additionally investigate the effects of over- or underestimating the corresponding correction to the underlying mineralogical model. Our results highlight that, given the current limitations of seismic tomography and the incomplete knowledge of mantle mineralogy, magnitudes and spatial scales of a temperature field obtained from global seismic models deviate significantly from the true state, even in the idealized case of known bulk chemical composition. The average deviations from the reference model are on the order of 50–100 K in the upper mantle and depending on the resolving capabilities of the respective tomography—can increase with depth throughout the lower mantle to values of up to 200 K close to the core–mantle boundary. Furthermore, large systematic errors exist in the vicinity of phase transitions due to the associated mineralogical complexities. When used to constrain buoyancy forces in time-dependent geodynamic simulations, errors in the temperature field might grow nonlinearly due to the chaotic nature of mantle flow. This could be particularly problematic in combination with advanced implementations of compressibility, in which densities are extracted from thermodynamic mineralogical models with temperature-dependent phase assemblages. Erroneous temperatures in this case might activate ‘wrong’ phase transitions and potentially flip the sign of the associated Clapeyron slopes, thereby considerably altering the model evolution. Additional testing is required to evaluate the behaviour of different compressibility formulations in geodynamic inverse problems. Overall, the strategy to estimate the present-day thermodynamic state of the mantle must be selected carefully to minimize the influence of the collective set of uncertainties.

• Dokumententyp: Artikel (LMU)
• Organisationseinheit (Fakultäten): 20 Geowissenschaften > Department für Geo- und Umweltwissenschaften > Geophysik
• DFG-Fachsystematik der Wissenschaftsbereiche: Naturwissenschaften
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 491502892
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 456788150
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 521548190