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Carbon and nitrogen transfer on the early and in the deep Earth

English title Carbon and nitrogen transfer on the early and in the deep Earth
Applicant Schmidt Max Werner
Number 166153
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 Geochemistry
Start/End 01.04.2016 - 31.03.2018
Approved amount 640'000.00
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Keywords (10)

Carbon; metal melts; granitic slab melts; early atmosphere; mass partitioning; isotope fractionation; NItrogen; fluids; viscosity; solubility

Lay Summary (German)

Lead
Als die Erde vor 4.5 Milliarden Jahren unter Akkretion von Planetisimalen langsam zur heutigen Groesse wuchs, bildete sich an der Oberflaeche staendig eine neue Atmosphaere waehrend der Silikatmantel in einem globalen Magmaozean aufschmolz, aus diesem segregierte sich eine Metallschmelze, welche dann im Zentrum der Erde den Kern bildete. Jedes in die Erde krachende Planetesimal fuegte volatile Elemente, Silikate und Metall hinzu, welche unter der gewaltigen Energie des Einschlages schmolzen. Dieses Projekt untersucht die Verteilung von Kohlen- und Stickstoff zwischen der fruehesten (dichten) Atmosphaere, dem Magmaozean sowie metallischem Kernmaterial. Dazu werden experimentell bei Druecken und Temperaturen bis 350 kbar und 2200 C die Loeslichkeiten von Stickstoff und Kohlenstoff in den verschiedenen Reservoiren (Schmelzen, Fluide und Gase) untersucht, dieses Wissen erlaubt uns den Anfangszustand der Erde nach der Akkretion zu bestimmen.
Lay summary

Um obigem Ziel gerecht zu werden, wird in einem Projekt die Verteilung und Isotopenfraktionierung von Kohlenstoff uns Stickstoff zwischen einer dichten Atmosphaere (10-500 bar) einer Silikat- und einer Metallschmelze gemessen. Damit laesst sich die Ausgangssituation der Erde vor 4.5 Milliarden Jahren bestimmen sowie der bis jetzt unbekannte Kohlenstoff- und Stickstoffgehalt des Erdkerns modellieren. Um die weitere Entwicklung des Kohlenstoffkreislaufes zu verstehen, wird in einem zweiten Projekt die Kohlenstoffverteilung und Isotopenfraktionierung zwischen Mineralien (Diamant, Graphit, Karbide, Karbonate) und Schmelzen und Fluids untersucht. Dabei spielt der Oxidationszustand des Kohlenstoffs, der sich ueber die Erdgeschichte von oberflaechennah stark reduziert zu stark oxidiert veraendert hat,  eine wesentliche Rolle (von Methan bis CO2 im Fluid). In einem dritten Teilprojekt werden dann die voneinander abhaengigen Loeslichkeiten von CO2 und H2O in Schmelzen welche waehrend der Subduktion entstehen bestimmt. Letztere verbinden den Oberflaechenkohlenstoffkreislauf mit dem tiefen Kohlenstoffkreislauf und tragen entscheidend zur langfristigen Entwicklung des Inventars von Kohlenstoff an der Erdoberflaeche bei.

Um den Kohlenstoffkreislauf ueber geologisch lange Zeitraeume zu verstehen und die CO2-Entwicklung in der Atmosphaere ueber diese Zeitraeume richtig einordnen zu koennen, muss auch der Austausch mit der tiefen Erde, welcher ueber Millionen von Jahre erfolgt, verstanden werden.

Direct link to Lay Summary Last update: 20.04.2016

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
178948 Volatile Transfer in the Deep Earth 01.04.2018 Project funding (Div. I-III)
153112 Carbon and nitrogen on the early and deep Earth: isotope fractionation, carbonatites, carbides and Fe-C redox coupling - experiments from 0.01 to 35 GPa 01.04.2014 Project funding (Div. I-III)

Abstract

The redistribution of carbon and nitrogen within the early Earth and their deep cycles since Earth accretion is one of the most fascinating topics in modern petrology and geochemistry. The plate tectonics regime of our Earth is unthinkable without the deep cycling of volatiles and even if H2O is their main component, CO2/CO/CH4 and N2/NH3 play an important role, in particular where life is concerned.On the early Earth, carbon and nitrogen (and any other volatile) are repartitioned between a dense atmosphere and the metal and silicate melts of the magma ocean. Similarly, during modern magmatism N+C partition between silicate melts and a gas phase; to constrain these equilibria by high pressure experiments is the target of project B. Carbon in the oceanic lithosphere is either deeply subducted or transferred to the mantle in the subarc region (or shallower) and in part resurfaced through mantle derived arc magmatism. Project A is mainly concerned with the carbon transfer efficiency at subarc depths, investigating experimentally H2O- and CO2-solubilities in melts derived from the subducted crust. Project C constrains carbon isotope fractionation between the mobile phase (fluid or carbonatite) and residual carbon minerals by high pressure experiments. As isotopes are used to determine the provenance of carbon (primordial, mantle, surface derived), understanding the isotopic behavior during recycling will allow characterizing processes involved in the deep C-recycling and formation of e.g. diamonds. A: Volatile solubility in and viscosity of high pressure granitic melts (1-4 GPa) (postdoc, Dr. Ineke Wijbrans)This project addresses (i) CO2 + H2O solubilities in high pressure granitic melts developing from subducting slabs and (ii) their viscosity, such constraining melt migration from the slab to the mantle. (iii) These experiments should also resolve the longstanding question of (second) supercriticality between granitic melts and fluids. Solubility and viscosity data of high-pressure granitic melts are crucially lacking and will be obtained by using the unique high pressure centrifuging piston cylinder: The often unquenchable melts will be separated from the fluids by centrifuging and bulk-analyzed. As long as glasses are obtained H and C will be measured at the Swiss-SIMS, Lausanne. Separation will inform on whether two liquid phases coexist at high P and T. Falling sphere experiments (mostly in the centrifuge) will determine viscosities of high-H2O granites. All together, we will constrain the transfer of carbon from hot melting slabs to the mantle and quantify how much residual carbon may be subducted to deeper mantle domains. B: N (and C) fractionation between an early atmosphere and metal and silicate melts(PhD Iris Speelmanns)This project investigates the fractionation of N and C between a gas phase and a silicate or metal melt as well as the partitioning of N between metal and silicate melts to high pressures. The experimental results will allow modeling N and C sequestration from the atmosphere into primordial mantle and core material and to understand the related isotope fractionation. Experiments at 100-2000 bar provide sufficient quantities of N and C for mass spectrometry. The gas phase will be analyzed by gas chromatography and its speciation thermodynamically modeled as a function of fO2. The primary purpose is to understand the N (and C) redistribution at the point in time where the (reduced) Earth is fully accreted. Because of the technical similarity of the suitable experiments and analytics, this project also addresses basalt degassing at mid-ocean ridges and ocean islands (mildly oxidizing).C: High temperature isotope fractionation of carbon between C-minerals and fluids or melts (PhD Nico Küter)Recycling of carbon during subduction, its mobilization in fluids or melts and redox re-precipitation in the mantle provides ample opportunity for isotope fractionation, each time in the order of several ‰. This project investigates equilibrium fractionation between C-minerals (graphite, diamond, carbonates, carbides) and fluids or carbonatite melts. C-O-H fluids in equilibrium with graphite (or another C-mineral) with compositions from almost pure CH4 to H2O-CO2-only are extracted from the capsules by a newly constructed device operating under vacuum and including the capacity to moderately heat the sample. Fluid speciation and isotope compositions of the experimental products are subsequently determined with precisions in d13C of 0.2-0.4 ‰ (2s). Carbonatite melts equilibrated with graphite/diamond will be acid leached. This project constrains the evolution of the C-isotope composition during recycling from the slab into the mantle and allows quantifying e.g. the effects of Rayleigh fractionation during such processes.
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