Water in coesite and wadsleyite: quantification,
incorporation mechanism and effect on the phase stability
vorgelegt von
Diplom-Geologin Fiorenza Deon
aus Rom
Fakultät VI - Planen Bauen Umwelt
der Technischen Universität Berlin
zur Erlangung des akademischen Grades
Doktorin der Naturwissenschaften
-Dr.rer.nat-
genehmigte Dissertation
Promotionsausschuss:
Vorsitzender: Prof. Dr. Wilhelm Heinrich
Berichterin: Prof. Dr. Monika Koch-Müller
Berichter: Prof. Dr. Gerhard Franz
Berichter: Prof. Dr. Eugen Libowitzky
Tag der Wissenschaftlichen Aussprache: 26.03.10
Berlin 2010
D-83
Table of contents
I
Table of contents
Summary……………………………………………………………………………………….1
Zusammenfassung……………………………………………………………………….…….3
Introduction……………………………………………………………………………………4
References…………………………………………………………………………….16
Chapter 1……………………………………………………………………………………...24
“Coupled boron and hydrogen incorporation in coesite”
Abstract……………………………………………………………………………………….25
Introduction…………………………………………………………………………………...26
Experimental methods……………………………………………………………………......27
Syntheses……………………………………………………………………………...27
FTIR spectroscopy……………………………………………………………………27
Secondary Ion Mass Spectrometry………………….……………………….…….….29
Results………………………………………………………………………………………...30
Syntheses……………………………………………………………………………...30
Hydrogen and Boron incorporation…………………………………………...……...31
Discussion…………………………………………………………………………………….36
Conclusion……………………………………………………………………………………39
Acknowledgements…………………………………………………………………………...40
References…………………………………………………………………………………….41
Chapter 2……………………………………………………………………………………...44
“Location and quantification of hydroxyl in wadsleyite: new insights”
Abstract……………………………………………………………………………………….45
Introduction…………………………………………………………………………………...46
Experimental methods………………………………………………………………………..49
Syntheses……………………………………………………………………………...49
Electron Microprobe………………………………………………………………….50
Raman spectroscopy………………………………………………………………….51
FTIR spectroscopy……………………………………………………………………52
Secondary Ion Mass Spectrometry……………………………………………………53
X-ray diffraction single crystal X-ray diffraction (SC-XRD).......................................54
Powder X-ray diffraction…………………………………………………..…………55
Table of contents
II
Transmission Electron Microscopy…………………………………………………...56
Results………………………………………………………………………………………...57
Syntheses……………………………………………………………………………...57
Qualitative and quantitative intrinsic OH analyses…………………………………...59
TEM – EMPA………………………………………………………………………...59
Water Quantification by SIMS and Raman Spectroscopy……………………………60
FTIR spectroscopy……………………………………………………………………62
OH location in the wadsleyite structure………………………………………………63
High pressure FTIR Spectroscopy…………...……………………………………….63
SC-XRD………………………………………………………………………………64
Discussion…………………………………………………………………………………….67
Saturation and first direct IR calibration for OH in wad……………………………...67
High-pressure behavior of the OH-bands………..…………………………………...68
OH incorporation and localization in the structure…………………………………...69
Acknowledgements…………………………………………………………………………...73
References…………………………………………………………………………………….74
Chapter 3………………………………………………………………..………………….....84
In which extent does water affect the P-T-x coordinates of the 410-km discontinuity in
the Earth upper mantle?”
Abstract……………………………………………………………………………………….85
Introduction…………………………………………………………………………………...87
Experimental methods…………………………………….………………………………….88
Multi-anvil syntheses…………………………………………………………………88
Electron Microprobe………………………………………………………………….93
Secondary Ion Mass Spectrometry……………………………………………...……94
Raman spectroscopy…………………..…………………..….........................…...….94
FTIR spectroscopy……………………………………………………………………95
Transmission Electron Microscopy……………………………………….…………..96
Results……………………………………………………………………………………….. 96
Syntheses…………………………………………………………………………...…96
Secondary Ion Mass Spectrometry-Raman spectroscopy-FTIR spectroscopy.……..103
TEM………………………………………………………………………………… 104
Table of contents
III
Water concentration………………………………………………………………………….105
Water in the system MgO-SiO
2
-H
2
O……………………………………………..…105
MgO-FeO-SiO
2
-H
2
O system………………………………………………….…......105
Evidence of equilibrium…………………………………………………………….…....….106
Influence of water on the phase stability…………………………………….……….……...107
System MgO-SiO
2
-H
2
O...………………………………………………..….………107
System FeO-MgO-SiO
2
-H
2
O……...…….………………………...…………...........108
Conclusion...............................................................................................................................110
Acknowledgments...................................................................................................................111
References...............................................................................................................................112
Many thanks to........................................................................................................................117
Curriculum Vitae.....................................................................................................................118
Eidesstattliche Erklärung.........................................................................................................121
Summary
1
Summary
The current PhD thesis focuses on the incorporation of hydrogen in three important
constituents of the Earth upper mantle: coesite (cs), olivine (ol) and wadsleyite (wad). They
belong to the category of Nominally Anhydrous Minerals (NAMs), however they may
incorporate water as hydrogen in their structure via point defects. Major aim of this work is to
provide a reliable and proper quantification of hydrogen (expressed as water) of these
minerals and to study the influence of water on their P-T stabilities. Coesite is a common
constituent of high pressure metamorphic rocks. Due to the olivine-wadsleyite phase
transition an important seismic-petrologic discontinuity in the Earth upper mantle occurs: the
410-km discontinuity.
I will approach the topic by: 1) studying the coupled boron and hydrogen substitution in
coesite and compare it with the hydrogarnet substitution; 2) analyzing the water storage
capacity of Mg2SiO4 wadsleyite and the H incorporation mechanisms; 3) determining how
water affects the phase transition of olivine to wadsleyite in the system MgO-SiO2-H2O and,
to approach the nature, in the system MgO-FeO-SiO2-H2O.
1) Coesite can incorporate H via the hydrogarnet substitution, i.e. a vacant Si site with four
coordinating OH groups instead of four oxygens for charge balancing and via Al or B based
defects. In the latter substitution B3+ (or Al3+) enters the Si site and one of the tetrahedral
oxygens forms a hydroxyl group for charge balancing. In this study coesite that stores H only
via B based defects were synthesized for the first time at 9-12 GPa and 1000-2000°C with
water in excess. The experimental methods used provide important information on the amount
of B and H incorporated in the structure and on B location. All the results lead to the
conclusion that the relatively high pressures and temperatures that were chosen for the
experiments tend to favour the B based defect, instead of the hydrogarnet substitution, as the
B-based defect is accompanied by a general decrease of the size of the tetrahedral site
compared to the hydrogarnet substitution (approximately 20%). Thus, coesite with the B-
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