Estimating core-mantle boundary temperature from seismic shear velocity and attenuation

Abstract

The temperature at Earth’s core-mantle boundary (CMB) is a key parameter to understand the dynamics of our planet’s interior. However, it remains poorly known, with current estimate ranging from about 3000 K to 4500 K and more. Here, we introduce a new approach based on joint measurements of seismic shear-wave velocity, VS, and quality factor, QS, in the lowermost mantle. Lateral changes in both VS and QS above the CMB provide constraints on lateral temperature anomalies with respect to a reference temperature, Tref, defined as the average temperature in the layer immediately above the CMB. The request that, at a given location, temperature anomalies inferred independently from VS and QS should be equal gives a constraint on Tref. Correcting Tref for radial adiabatic and super-adiabatic increases in temperature gives an estimate of the CMB temperature, TCMB. This approach further relies on the fact that VS-anomalies are affected by the distribution of post-perovskite (pPv) phase. As a result, the inferred Tref is linked to the temperature TpPv at which the transition from bridgmanite to pPv occurs close to the CMB. A preliminary application to VS and QS measured beneath Central America and the Northern Pacific suggest that for TpPv = 3500 K, TCMB lies in the range 3,470–3880 K with a 95% likelihood. Additional measurements in various regions, together with a better knowledge of TpPv, are however needed to determine a precise value of TCMB with our method.

The sensitivity of lowermost mantle anisotropy to past mantle convection

“…The CMB boundary is also isothermal (3000 K) and is free-slip. The CMB boundary temperature is lower than current seismological and mineral physics estimates for CMB temperature (Kim et al, 2020;Lobanov et al, 2021;Deschamps and Cobden, 2022) due to the incompressible equation of state that we use. A theoretical adiabat is added to account for compressibility when using the temperature field to calculate post-perovskite stability.…”

The Distribution of Impactor Core Material During Large Impacts on Earth-like Planets

“…In our main simulation suite, our surface temperature of 293 K, lithospheric thickness of 1 × 10 5 m, and thermal gradient of 1 × 10 −3 K m −1 lead to a base-of-lithosphere temperature of T l = 1293 K and a mantle-side CMB temperature of T CMB ∼ 2700 K. This depicts a relatively cold mantle, even by presentday observations, e.g., =  -+ T 1318 C l 32 44 determined by midocean ridge basalts (Matthews et al 2016) and T CMB up to 4000 K (Deschamps & Cobden 2022). Earth's mantle during the Hadean was likely hotter than the present day due to remnant heat from formation, with evidence for this in the geological record and inferred models (e.g., Korenaga 2008Korenaga , 2021Davies 2009;Herzberg et al 2010;Ganne & Feng 2017).…”

A Giant Impact Origin for the First Subduction on Earth

“…Most model runs include an intrinsically dense layer of Theia mantle materials above the CMB. Current estimates of the present-day CMB temperature that account for a lower boundary layer range from ∼3473 to 4573 K (Deschamps & Cobden, 2022), but because of Earth's secular cooling, the Hadean CMB temperature should have been higher. Moreover, a hot CMB is anticipated after the MGI due to the deposition of Theia's iron core, as shown in previous MGI simulations (Canup, 2004).…”