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Volatile Transfer in the Deep Earth

English title Volatile Transfer in the Deep Earth
Applicant Schmidt Max Werner
Number 178948
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Mineralogy
Start/End 01.04.2018 - 31.03.2022
Approved amount 1'280'000.00
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All Disciplines (2)

Discipline
Mineralogy
Geochemistry

Keywords (7)

early magma ocean and atmosphere; redox (mantle) melting; second critical end point to the solidus; carbon isotope fractionation; volatiles C-N-H-S; carbonatites; CO2- and H2O-solubility in slab melts

Lay Summary (German)

Lead
Eine Vielzahl von geologischen Prozessen sowohl in der tiefen als auch der oberflächennahen Erde wird durch sogennante volatile, d.h. leicht flüchtige Elemente angetrieben oder ermöglicht. Zu diesen Elementen gehören Wasserstoff, Kohlenstoff und Stickstoff, die in ihren Verbindungen die Erdkernzusammensetzung, Aufschmelzprozesse in der Erde und mehr generell (mit Sauerstoff zusammen) für Transportprozesse im Erdinneren sorgen.
Lay summary

In ersten Teil des Projektes soll erforscht werden, wie sich Kohlenstoff und Stickstoff während der Bildung der Erde zwischen dem metallischen und silikatischem Teil sowie der Atmosphäre verteilt haben. Dies erlaubt uns, die früheste Atmosphäre der Erde zu verstehen. Im tiefen Mantel reichern sich diese Elemente nicht in den >99% Silikaten an, sondern in der kleinen Fe-Metallfraktion die vorhanden ist. Dieser Anreicherungsprozess sowie der Aufschmelzungsprozess der reduzierten Legierungen und Verbindungen sind das zweite Thema dieses Projektes, unsere Vermutung ist, dass das tiefste Aufschmelzen im Erdmantel und damit der Ursprung vieler Magmen die die Oberfläche erreichen, mit der Oxidation der reduzierten Phasen beginnt. Der dabei entstehende Intraplatten-Magmatismus ist relativ CO2-reich und bringt Karbonatschmelzen hervor. Die Entwicklung dieser Karbonatschmelzen durch Unmischbarkeit mit Silikatschmelzen und Fluiden (d.h. H2O-CO2-Lösungen) ist das Thema des dritten Teilprojekts, es geht vor allem darum, aus den im Feld gefundenen Karbonatit-Gesteinen die ursprüngliche Schmelzzusammensetzung zu rekonstruieren. Im letzten Teil geht es um die Unmischbarkeit zwischen Fluiden und krustalen Teilschmelzen die in Subduktionszonen entstehen. In diesen werden volatile Elemente wieder ins Erdinnere verfrachtet und durch Schmelzen oder Lösungen umverteilt. Dabei wird ein Teil rasch, d.h. in Millionen Jahren, durch Subduktionszonenvukanismus wieder an die Oberfläche gebracht, während der andere Teil in den tiefen Mantel versenkt wird. Die chemischen Signale die dabei entstehen sind das Ziel dieses Projektes.

Direct link to Lay Summary Last update: 25.04.2018

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
166153 Carbon and nitrogen transfer on the early and in the deep Earth 01.04.2016 Project funding (Div. I-III)

Abstract

The redistribution of H, C, N and S within the early Earth and their deep cycles are one of the most fascinating topics in modern Earth sciences. Magmatism, plate tectonics (and climate) on Earth would be very different without these volatiles, yet many key questions remain open. This project addresses (A) how volatiles distributed between the early atmosphere and magma ocean, a process that controlled the deep Earth volatile inventory; (B) the mineral hosts of C, S and metal in the deep reduced mantle and their redox melting, which most likely leads to the deepest (and CO2-rich) mantle melts; (C) the geochemistry of carbonatites unmixing from CO2-rich silicate alkaline magmas at subvolcanic conditions; and (D) replenishment of the mantle in H and C during subduction. This 4 year project draws on >5 years of experimental and analytical developments in centrifuging, high-temperature gas pressure experiments and carbon isotope analysis of experimental products.A: Carbon and Nitrogen fractionation between early atmosphere and magma ocean (PhD P. Petschnig) This project targets mass and isotope fractionation of C and N between a reducing gas phase and silicate or metal melt. The experimental results will allow modeling C and N sequestration from the atmosphere into the magma ocean, where metal/silicate melt partitioning will redistribute the volatiles between primordial mantle and core material. The final goal is to understand the C and N distribution at the point in time where the (reduced) Earth is fully accreted. The gas phase will be analyzed by gas chromatography and its speciation thermodynamically modeled as a function of fO2. The same experiments but at mildly oxidizing conditions will address basalt degassing at mid-ocean ridges and ocean islands.B: The rest - hosts of the silicate-incompatible elements and their melting in the deep mantle (PhD NN)The deep, reduced mantle is made up by silicates which host most but not all of the chemical inventory of the Earth mantle. Reduced C, S, and Fe will form their own phases, which then scavenge sidero- and chalcophile elements from the silicates. Such sulfides, carbides and metal phases are only studied in simple systems, and this project will establish (i) which minor minerals will be present in the chemically complex Earth mantle, (ii) their chemical composition in terms of trace elements and (iii) their melting behavior. Existing data suggest that such interstitial minor phases may melt before the silicates and hence contribute over-proportionally to the first melts forming in mantle upwellings.C: Carbonatites - immiscibility and element+isotope fractionation at subvolcanic conditions (PhD NN)Arguably, carbonatites are the most fascinating mode of magmatic C-resurfacing, the related amount of publications being completely disproportional to their minuscule volume. Nevertheless, they are the ultimate manifestation of C-degassing during intraplate magmatism and carbonatite-silicate liquid immiscibility has neither been studied for the compositions that make >99% of all known carbonatite-silicate melt pairs, the role of H2O remains unknown, and isotopic fractionation (of C) has not yet been investigated. Exactly theses topics are at the heart of this project, which will address major, trace and C-isotope fractionation between carbonatites, alkaline silicate melts and a gas phase. This information is crucially lacking to understand what can be deduced from carbonatite magmas.D: Volatile solubilities and critical endpoints of siliceous high pressure melts (1.5-4 GPa) (postdoc, Dr. F. Cafagna) Using the unique high-pressure centrifuge we will determine (i) CO2-H2O-solubilities and -fluid-melt partitioning for siliceous melts typical for slab melting, (ii) the second critical end point between siliceous melts and H2O-CO2-fluids, and (iii) viscosities of volatile-rich granites at high pressure. Centrifuging pressures will be extended from presently 1.7 to 4 GPa and a high-g pressure regulation system constructed. The unquenchable melts and fluids will be separated in-situ by centrifuging and each bulk-analyzed. Whether separation occurs informs on the one- (i.e. supercritical) or two-phase state of the system. Falling sphere experiments at high g will determine viscosities of high-H2O-CO2 granites. These data are of fundamental value and will constrain the fraction of carbon released at subarc pressures vs. subducted into the deep mantle.
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