Carbon in the earth's mantle [Elektronische Ressource] : solubility and speciation in major nominally volatile-free mantle minerals / vorgelegt von Svyatoslav Shcheka

Shcheka.Svyatoslav

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2006
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Carbon in the Earth’s Mantle:

Solubility and speciation in major nominally
volatile-free mantle minerals





Dissertation
zur Erlangung des Grades eines Doktors der Naturwissenschaften





der Geowissenschaftlichen Fakultät
der Eberhard-Karls-Universität Tübingen









vorgelegt von
SVYATOSLAV SHCHEKA
aus Wladiwostok (Russland)




2006









































Tag der mündlichen Prüfung: 08.02.2006

Dekan: Prof. Klaus G. Nickel, Ph.D.

1. Berichterstatter: Prof. Dr. Hans Keppler

2. Berichterstatter: Prof. Dr. Dr. h.c. Muharrem Satir Acknowledgement
_____________________________________________________________________

Acknowledgements


I want to thank all people who contributed and helped me to make possible
this research at Institute for Geosciences, University of Tübingen. I have really
enjoyed working here.
First of all, I would like to express my deepest gratitude to Prof. Dr. H.
Keppler, for being an outstanding advisor. Thank him for giving me the opportunity to
deal with interesting subjects and valuable discussions during this work, for his
fruitful assistance and patience, without which composing the current dissertation
would not have been possible. His very critical but very true and constructive reviews
of earlier versions substantially improved the text of this thesis. Thanks also for
allowing me to participate at several conferences and workshops and supporting any
kind of travel. His generous support allowed me to concentrate on the research.
I am very grateful to Dr. Michael Wiedenbeck (GFZ Potsdam) for his
comprehensive help with SIMS measurements and for his incurable optimism in
solving the problems seemed to be unsolvable.
I would like to express my immense gratitude to Dr. Dan Frost (BGI,
Bayreuth) and Dr. Paul Balog (Max Planck Institute for Solid State Research,
Stuttgart) for introducing me into the multianvil world and for their assistance with
preparation and conducting the experiments.
Many thanks are given to my office companion Katrin Mierdel who was
helping me every day not only with a routine work, but also with many aspects of my
private life, especially during my first months in Germany.
Special appreciation goes to Dr. Cristoph Berthold for hours he spent with me
to perform X-ray powder diffraction analyses and to interpret the obtained data. His
philosophical and sometimes provoking questions helped me to broaden my general
understanding the science.
I am thankful to Dr. Catherine McCammon (BGI, Bayreuth) for critical
reading of the manuscript and very productive discussions of its basic points.
I want to thank Bernd Binder and Michael Dorn for their assistance with
Raman spectroscopy and Dr. Thomas Wenzel for his thoughtful approach to electron
microprobe analyses of my samples. Acknowledgement
_____________________________________________________________________
I am grateful to all of my colleagues, who have constructed a very friendly
atmosphere for working. This work would not be successful without technical support
of our mechanical workshop, particularly, of Norbert Walker and Barbara Maier.
Valuable tips of Hubert Schulze (BGI, Bayreuth) on sample preparation saved weeks
of my time.
Lastly but not least, I am indebted to my family for their multilateral support,
sympathy and prominent encouragement they have always expressed. Above all, I
thank my wife, Galina for her love and patience and for taking the burden of the day-
to-day activities and responsibilities of our children, when I was occupied with the
study. Without her understanding and support it would be impossible to complete this
work. Table of contents
_____________________________________________________________________

Table of contents

Abstract ..................................................................................... 1
Zusammenfassung .................................................................... 3
1. Introduction.......................................................................... 5
1.1 Geochemical significance of carbon.........................................5
1.2 Estimates of bulk carbon content of the mantle and carbon
global cycle ...............................................................................6
1.3 Mantle oxidation state and carbon phases in the mantle ........10
1.3.1 Redox state of the mantle.........................................................10
1.3.2 Oxidized carbon...............................................13
1.3.3 Neutral carbon..........................................................................15
1.3.4 Reduced carbon........................................................................17
1.4 Carbon in nominally volatile-free mantle minerals................17
2. Experimental procedure .....................................................21
2.1 Sample synthesis.....................................................................21
2.1.1 Starting materials.....................................................................21
2.1.2 High-pressure experiments......................................................23
2.1.2.1 Piston-cylinder apparatus...................23
2.1.2.2 Multianvil press........................................................26
2.2 Synthesis of reference materials .............................................30
2.3 Sample characterization..............................34
3. Secondary ion mass spectrometry (SIMS) ........................37
3.1 Principles of SIMS..................................................................37
3.2 Sample preparation ...................39
3.3 Calibration ..............................................................................39
3.4 Analytical conditions ..............................................................41
3.5 Calculations ............................................................................43 Table of contents
_____________________________________________________________________
4. Results ..................................................................................48
4.1 Run products...........................................................................48
4.2 Carbon solubility in minerals of the upper mantle .................52
4.2.1. Olivine......................................................................................52
4.2.2. Enstatite............................................................56
4.2.3. Diopside...................................................................................59
4.2.4. Pyrope and MgAl O -spinel ....................................................60 2 4
4.3 Carbon solubility in minerals of the transition zone and lower
mantle......................................................................................61
5. Discussion and geological implications..............................64
5.1 Carbon speciation in silicates .................................................64
5.2 Implications for carbon storage in the mantle and global
carbon cycle ............................................................................68
5.3 Flood basalt eruptions and mass extinctions ..........................71
6. References ............................................................................75
Erklärung .................................................................................92 Abstract 1
_____________________________________________________________________
Abstract


(1) Carbon solubility in upper mantle minerals

The solubility of carbon in forsterite, enstatite, diopside, pyrope and MgAl O 2 4
spinel has been quantified. Previously reported problems of contamination and slow
diffusion of carbon in minerals have been overcome by (1) growing carbon-saturated
crystals from carbonatite melts in piston-cylinder (T=900-1100 °C; P=1.5 GPa) and
multianvil (T=900-1400 °C; P=6-11 GPa) experiments in the presence of ~1 wt.%
water and by (2) using starting materials, isotopically enriched to contain ~99 wt.% of
13C. Secondary ion mass spectrometry (SIMS) was employed to measure the carbon
contents of the synthesized minerals.
Carbon solubility in silicates at uppermost mantle conditions is exceedingly
low, in the order of a few hundred parts per billion by weight. Solubility increases
exponentially as a function of pressure to a maximum of ~12 ppm by weight in
forsterite at 11 GPa and 1200 °C. No clear dependence of carbon solubility on
temperature, oxygen fugacity and iron content was observed. Carbon solubility in
MgAl O spinel is below the limit of detection of the analytical technique used (i.e., 2 4
below 30 ppb by weight).

(2) Carbon solubility in minerals of the transition zone and lower mantle

A similar technique was used to obtain the first exp