Melting conditions and mantle source composition from probabilistic joint inversion of major and rare earth element concentrations

The chemical composition of erupted basalts provides a record of the thermo-chemical state of their source region and the melting conditions that lead to their formation. Here we present the first probabilistic inversion framework capable of inverting both trace and major element data of mafic volcanic rocks to constrain mantle potential temperature, depth of melting, and major and trace element source composition. The inversion strategy is based on the combination of i) a two-phase multi-component reactive transport model, ii) a thermodynamic solver for the evolution of major elements and mineral/liquid phases, (iii) a disequilibrium model of trace element partitioning and iv) an adaptive Markov chain Monte Carlo algorithm. The mechanical and chemical evolution of melt and solid residue are therefore modelled in an internally- and thermodynamically-consistent manner. We illustrate the inversion approach and its sensitivity to relevant model parameters with a series of numerical experiments with increasing level of complexity. We show the benefits and limitations of using major and trace element compositions separately before demonstrating the advantages of a joint inversion. We show that such joint inversion has great sensitivity to mantle temperature, pressure range of melting and composition of the source, even when realistic uncertainties are assigned to both data and predictions. We further test the reliability of the approach on a real dataset from a well-characterised region: the Rio Grande Rift in western North America. We obtain estimates of mantle potential temperature ($\sim$ 1340 $^o$C), lithospheric thickness ($\sim$ 60 km) and source composition that are in excellent agreement with numerous independent geochemical and geophysical estimates. In particular, this study suggests that the basalts in this region originated from a moderately hot upwelling and include the contribution from a slightly depleted source that experienced a small degree of melt or fluid metasomatism. This component is likely associated with partial melting of the lower portions of the lithosphere. The flexibility of both the melting model and inversion scheme developed here makes the approach widely applicable to assessing the thermo-chemical structure and evolution of the lithosphere-asthenosphere system and paves the way for truly joint geochemical-geophysical inversions.

Research of the degree of compression and stability of liquid metal in a high&frequency magnetic field

The influence of a high-frequency magnetic field on liquid metal under melting conditions, the choice of technological parameters and the control of the melting process are considered. On the example of galinstan, the factors are established and the parameters are determined that cause the unstable movement of the metal. Keywords: high-frequency magnetic field, high-frequency inductors, galinstan, skin effect depth. [email protected], [email protected]

Investigating mantle melting temperatures on Earth, Mars and the Moon using Al-in-olivine thermometry

<p>Al-in-olivine thermometry, based upon the temperature-dependent solubility of Al in the olivine crystal structure [1], has become a widely adopted method to investigate the crystallisation temperatures of primitive mantle melts on Earth [2]. The thermometer is calibrated using the Al contents of co-existing olivine and spinel: these phases are on or near the liquidus of primitive magmas, so the thermometer should access liquidus temperatures of mantle melts, thereby constraining the minimum mantle melting temperature. CFB-associated primitive melts have average olivine crystallisation temperatures well in excess of MORB, and back-calculation to the potential temperature of their mantle source regions suggests mantle thermal anomalies of several hundred degrees [3].</p><p>Whilst mantle thermal anomalies are moderately well-understood on Earth, relatively little is known about the melting conditions in the mantles of the Moon and Mars that led to the production of Maria basalts and Martian surface basalts and associated volcanic activity. Several samples returned from the Moon and basaltic meteorites from Mars (shergottites) are primitive and rich in both olivine and spinel, so would appear ideal samples for the application of Al-in-olivine thermometry to unravel their respective mantle melting conditions and, more generally, the thermal structures of those planetary interiors. In this study, we present preliminary investigations into a) five Apollo 12 primitive lunar basalts, and b) two olivine-phyric shergottites. We find that pervasive shock features make the trace Al concentrations of shergottitic olivines difficult to use, because high Al concentrations are associated with a fine micron to sub-micron network of K-rich melt veins, suggestive of fluid-mediated melt transport. On the other hand, olivine phenocrysts in all five lunar samples yield clear trends in Al contents and are excellent targets for Al-in-olivine studies. We present preliminary thermal results, as well as a newly-calibrated set of relevant thermodynamic parameters needed for back-calculating lunar melting temperatures. A fully quantitative assessment of lunar maria liquidus temperatures is, however, currently hampered by the limited calibration range of the Al-in-olivine thermometer and the unconstrained effect of high spinel TiO<sub>2</sub> contents on the results.</p><p>[1] Coogan, L. A., Saunders, A. D. & Wilson, R. N. Chem. Geol. <strong>368</strong>, 1–10 (2014).</p><p>[2] Trela, J. et al. Nat. Geosci. <strong>10</strong>, 451–456 (2017).</p><p>[3] Jennings, E. S., Gibson, S. A. & Maclennan, J. Chem. Geol. <strong>529</strong>, 119287 (2019).</p>