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Speaker: Dr. Paolo A. Sossi (ETH Zürich)

Talk title: Vaporising Earth: An Experimental Approach

Abstract: With respect to the composition of the Sun, rocky bodies of the inner Solar system are variably depleted in volatile metals. The patterns of elemental loss in basaltic rocks from these bodies, including the Earth, are distinct from those observed in chondrites, their potential building blocks. Heating of rocky material by radioactive decay and impacts among planetary bodies may induce melting and vaporisation of their silicate mantles, thereby creating scope for elemental fractionation via atmospheric escape; processes not experienced during the formation of chondrites.
Here we aim to quantify element volatilities under a range of relevant planet-forming conditions. Vaporisation experiments on basaltic liquids doped with 20 trace elements were performed under controlled temperature (T), time (t) and oxygen fugacity (fO2) in 1-atm, CO-CO2 gas-mixing furnaces. We find that fO2 controls relative elemental volatilities, by reactions of the generalised form: M(x+n)O(x+n)/2(l) = MxOx/2(g) + n/4O2(g). In cases where n is negative (as in most cases), lower fO2 promotes vaporisation. We develop a framework, by integrating these vaporisation stoichiometries with Hertz-Knudsen-Langmuir theory, to quantify elemental loss as a function of T, t, and fO2.
We show that specific T-fO2 conditions of vaporisation leave distinct chemical imprints upon the composition of the residual magma that are readily identifiable in the meteorite record. Evaporation in a single event strongly discriminates between elemental abundances, producing a step-like abundance pattern in the residuum, similar to that observed in the Moon or Vesta. Contrastingly, the gradual depletion of elements according to their volatility in the Earth instead likely reflects accretion from many smaller bodies that had each experienced different degrees of volatilisation.

Office: G6, 004

Host: Kaustubh Hakim (kaustubh.hakim"at"


Thursday, November 14, 2019
10.15–11.15: Special Seminar, Alessandro Morbidelli, ExWi 119
12.15–13.00: CSH Seminar, Kamber Schwarz, G6 -108
13.00–14.00: Lunch at Grosse Schanze
14.15–15:00: Special Seminar, Paolo Sossi, G6 -105
15.15–16.00: Kaustubh Hakim, G6 111
16.00–17.00: Dan Bower, G6 111
17.00–18.00: Meng Tian, G6 105

Lunch plans: Grosse Schanze 13:00-14:00 (participants: Paolo Sossi, Kaustubh Hakim, Dan Bower, Holly Capelo, Tobias Meier, …)