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Subduction derived carbonatites, related mantle metasomatism, and redox coupling of Fe and C - experiments from 2 to 35 GPa

Applicant Schmidt Max Werner
Number 140541
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 01.04.2012 - 31.03.2014
Approved amount 596'647.00
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All Disciplines (2)

Discipline
Geochemistry
Mineralogy

Keywords (8)

kimberlites; metasomatised mantle; iron carbides; deep carbon cycle ; carbonatites; physical melt properties; carbon transfer; banded iron formation

Lay Summary (English)

Lead
Lay summary

Beside the "Surface Carbon Cycle" there is a "Deep Carbon Cycle" which involves subduction and thus burial of carbon into the deep mantle. The re-fertilized mantle gives then rise to certain CO2-rich types of volcanism, which complete the deep carbon cycle. This subducted carbon was either precipitated in the igneous oceanic crust through seawater circulation or deposited in form of oceanic sediments.

The main tool of this research project are high-pressure (to 350 kbar), high-temperature (to 2200 ºC) experiments through which we investigate mineral and melting reactions, chemical compositions and physical properties of melts working on natural rock compositions or simplified chemical model systems.

In one part of this research project we investigate the melting of one type of carbonate bearing sediments, the so called Banded Iron Formation (BIF), which was a major carbon-containing chemical sediment in Archean times and which constitutes one of the primary iron resources worldwide. We investigate the conditions and chemical signature of melts in BIF's forming upon subduction and thus clarify the fate of this unique extremely dense material before disappearing into the deepest parts of the silicate Earth. A second part of this research project  investigates the reaction of carbonatite melts derived from melting of carbonate bearing clay sediments (which constitute the most important modern carbonate burial flux) with the mantle. Such reactions of oxidized melts (from previous surface sediments) with the reducing mantle leads among others to the formation of diamonds and forms chemically modified mantle domains which upon reheating give rise to e.g. kimberlite magmatism (kimberlites contain the gross of today's diamond production). In this second part we investigate the mineralogy and geochemistry and redox state of the source regions of such magmas. The third part deals with mineralogical modifications of the reduced mantle due to carbon influx, in particular the formation of carbides and carbide-melts, i.e. their stability and composition. At the same time we investigate the at present almost unknown densities of carbonatite melts at high pressure through an in-situ method: we observe the floating or sinking of suited mineral spheres of known density in the carbonatite melt and thus can indirectly determine the density of these melts. Possibly, these melts are very compressible such that they might gravitationally migrate downwards at very high pressures instead of upwards (as silicate melts generally do).

The bulk of the results will constrain an important part of the Deep Carbon Cycle and will ultimately lead to a better understanding of the larger carbon (and thus CO2) cycles and their variability over geological time. The removal and re-introduction of carbon from the Earth's surface over geological time has certainly contributed to the secular evolution of the Earth's atmosphere over billions of years,which is still poorly understood.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Melting of phase D in the lower mantle and implications for recycling and storage of H2O in the deep mantle.
Ghosh S, Schmidt MW (2014), Melting of phase D in the lower mantle and implications for recycling and storage of H2O in the deep mantle., in Geochim. Cosmochim. Acta, online, GCA8881-1.
Phase relations and melting of carbonated peridotite between 10 and 20 GPa: a proxy for alkali- and CO2-rich silicate melts in the deep mantle.
Ghosh S, Litasov K, Ohtani E (2014), Phase relations and melting of carbonated peridotite between 10 and 20 GPa: a proxy for alkali- and CO2-rich silicate melts in the deep mantle., in Contrib. Min. Pet., 167 (2), 1-23.
The stability of Fe-Ni carbides in the Earth's mantle: evidence for a low Fe-Ni-C melt fraction in the deep mantle.
Rohrbach A, Ghosh G, Schmidt MW, Wijbrans CH, Klemme S (2014), The stability of Fe-Ni carbides in the Earth's mantle: evidence for a low Fe-Ni-C melt fraction in the deep mantle., in Earth Planet Sci Lett, 388, 211-221.
Effect of water in depleted mantle on post-spinel transition and implication for 660 km seismic discontinuity at the Earth's mantle.
Ghosh Sujoy (2013), Effect of water in depleted mantle on post-spinel transition and implication for 660 km seismic discontinuity at the Earth's mantle., in Earth and Planetary Science Letters, 371-372, 103-111.
Single-crystal equation of state of phase D to lower mantle pressures and the effect of hydration on the buoyancy of deep subducted slabs.
Rosa AD, Mezouar M, Gabarino G, Bouvier P, Ghosh S, Rohrbach A, Sanchez-Valle C (2013), Single-crystal equation of state of phase D to lower mantle pressures and the effect of hydration on the buoyancy of deep subducted slabs., in J. Geophy. Res. - Solid Earth, 118, 6124-6133.
The U/Pb ratio of the Earth's mantle - a signature of late volatile addition.
Ballhaus C, Laurenz V, Muenker C, Raul OC, Fonseca ROC, Albarede F, Rohrbach A, Lagos M, Schmidt MW, Jochum K, Stoll B, Weis U, Helmy H (2013), The U/Pb ratio of the Earth's mantle - a signature of late volatile addition., in Earth Planet. Sci. Lett., 362, 237-245.
Elasticity of phase D and implication for the degree of hydration of deep suducted slabs.
Rosa AD, Sanchez-Valle C, Ghosh S (2012), Elasticity of phase D and implication for the degree of hydration of deep suducted slabs., in Geophys.Res.Lett., 39, L06304.
Element partitioning during pelite melting at 8, 13, and 22 GPa and the sediment signature in the EM mantle component.
Grassi D, Schmidt MW, Günther D (2012), Element partitioning during pelite melting at 8, 13, and 22 GPa and the sediment signature in the EM mantle component., in Earth Planet. Sci. Lett., 327-328, 177-190.
Single-crystal equation of state of dense hydrous magnesium silicate phase D to lower mantle pressures.
Ghosh Sujoy, Single-crystal equation of state of dense hydrous magnesium silicate phase D to lower mantle pressures., in Journal of Geophysical Research, 1.

Collaboration

Group / person Country
Types of collaboration
Università degli Studi di Milano Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Awards

Title Year
Dana Medal American Mineralogical Society 2013

Associated projects

Number Title Start Funding scheme
130100 Fe and C rich melting and redox equilibria in the deep Earth - from Fe(II)-disproportionation to banded iron formation recycling, experiments from 3 to 40 GPa 01.04.2010 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)
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 deep carbon cycle essentially consists of three steps: burial of carbon contained in the subducting lithosphere, transfer of carbon from the lithosphere into the mantle, and mantle derived magmatism bringing carbon back to the surface. This project is mainly concerned with the carbon transfer step, an almost unstudied process, that we will investigate through high pressure experiments from 2-35 GPa, at temperatures of 1000-2500 oC and controlled oxygen fugacities. At deeper mantle depths, carbon is most likely transferred in the form of carbonate melts and we will experimentally investigate how these form in banded iron formations, an ancient sediment type which fate in the mantle remains unknown. Defining the melting conditions and melt compositions of this lithology will allow to understand what geochemical signal might be derived from them, and whether these lithologies could subduct deeply without major chemical modification. Secondly, we will determine the mineralogy and geochemistry of mantle reservoirs resulting from the infiltration of alkali-rich carbonatites derived from pelitic sediments (these were investigated in a previous PhD). Such reservoirs are most likely at the origin of many kimberlites and ultrapotassic melts and the quantification of their geochemistry and mineralogy will allow to model the formation of such ultrapotassic melts. Third, when oxidized carbonate melts migrate into the deep reduced mantle (likely to be metal saturated), iron-nickel carbides or Fe-Ni-C melts should result during redox freezing of these carbonate melts. We will determine subsolidus and minimum melting relations in the Fe-Ni-C system with the aim to define the hitherto unknown role of iron carbides in the mantle. Finally, we will investigate two fundamental physical properties of deep carbonate liquids, both necessary for physical melt migration models. We will determine high pressure densities of carbonate melts by floating/sinking experiments and the wetting properties by measuring the contact angles between carbonatite and mantle minerals. The total of the results should constitute a crucial step forwards in our understanding of the deep carbon transfer (and cycle).
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