Water solubility in diopside [Elektronische Ressource] / vorgelegt von Polina Gavrilenko

Paulina Gavrilenko

Informations

• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2008
• Nombre de lectures: 36
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Water solubility in diopside







Von der Fakultät für Biologie, Chemie and Geowissenschaften
der Universität Bayreuth




zur Erlangung der Würde eines
Doktors der Naturwissenschaften

- Dr. rer. nat. -


genehmigte Dissertation









vorgelegt von

Polina Gavrilenko

aus Petropawlowsk-Kamtschatsky (Russland)







Bayreuth, 2008 Vollständiger Abdruck der von der Fakultät für Chemie/Biologie/Geowissenschaften der Universität
Bayreuth genehmigten Dissertation zur Erlangung des Grades eines Doktors der
Naturwissenschaften (Dr. rer. nat.).















Prüfungsausschuß:
Prof. Dr. Falko Langenhorst, Universität Bayreuth (Vorsitzender)
Prof. Dr. Hans Keppler, Universität (1. Gutachter) David Rubie, Bayreuth (2.
PD Dr. Leonid Dubrovinsky, Universität Bayreuth
Prof. Dr. Josef Breu, Universität Bayreuth




Tag der Einreichung: 05. Juni 2008 wissenschaftlichen Kolloquiums: 16. Oktober ACKNOWLEDGMENTS

I thank the Elitenetzwerk Bayern, International Graduate School program for funding the
research project that eventually became my doctoral dissertation. The administration of the
Bayerisches Geoinstitut is acknowledged with thanks for providing me with the necessary facilities
to pursue my work.
I thank my dissertation advisor Prof. Dr. Hans Keppler for his strict and patient supervision of
my work during the entire time. A lot of crystallographic and personal effort came from Dr.
Tiziana Boffa-Ballaran, whom I thank for the help with X-ray diffraction experiments and for
many suggestions according to my work.
Bayreuth has been my home for the last three years, and I thank Leonid Dubrovinsky for
introducing me to Bayerisches Geoinstitut.
Daniel Frost, Gudmundur Gudfinnsson, Shantanu Keshav, and Catherine McCammon at
Bayerisches Geoinstitut are acknowledged for their assistance with piston-cylinder and multi-anvil
experiments.
Special thanks to Hubert Schulze for displaying master craftsmanship in the preparation of my
samples, which were, more often than not, tiny. I will have to remember his comment, ‘Polina,
make bigger crystals, next time please!’. My colleagues, Uwe Dittmann, Heinz Fischer, Gerti
Göllner, Kurt Klasinski, Detlef Krauße, Sven Linhardt, Anke Pötzel, and Stefan Übelhack, are
warmly thanked for their skills and tenacity, for their assistance in the labs.
My heartfelt thanks to Petra Buchert, Lydia Kison-Herzing, and Stefan Keyssner for making it
all seem so simple and for their great organization work for every event, that involved me with the
institute.
Special thanks to my Russian colleagues Anastasia Kantor, Innokenty Kantor and Alexander
Kurnosov who were here always for me since my first days in Bayreuth. I also thank David Dolejš
for his patient answers to the bunch scientific and other questions from me all the time. I thank all
PhD students and other colleagues in Bayerisches Geoinstitut, who directly and indirectly helped
me with my dissertation and for the great time we had together at every weekend seminar and
short course, especially Olga Narygina, Micaela Longo and Deborah Schmauß-Schreiner.
And finally I would like to thank my father, Georgy Gavrilenko. He was the first person who
introduced me geology since I was little. Спасибо, папочка, за твою поддрежк у и за
уверенност ь во всем, котору ю я полу чаю от тебя! TABLE OF CONTENTS

Summary 1
Zusammenfassung 4
1. Introduction 7
1.1. Water in the mantle 7
1.2. The global water cycle 15
1.2.1. The subduction zone water cycle
1.2.2. Global sea level variations 18
1.3. Water in clinopyroxenes 20
1.3.1. Crystal chemistry of clinopyroxenes 20
1.3.2. Composition of mantle clinopyroxenes 22
1.3.3. Water solubility in clinopyroxenes 26
1.3.4. Effect of water on equation of state of clinopyroxene 29
1.4. Aims of the thesis 30

2. Experimental techniques 31
2.1. High-pressure experiments for measuring water solubility in diopside 31
2.1.1. Starting materials 31
2.1.2. Sample and capsule preparation 32
2.1.3. High-pressure apparatus 33
2.1.3.1. Piston-Cylinder press 33
2.1.3.2. Multi-Anvil 35
2.1.4. Analytical techniques for investigation of run products 38
2.1.4.1. Chemical analysis 38
2.1.4.2. Infrared spectroscopy
2.1.4.3. Powder X-ray diffraction 45
2.1.4.4. Single crystal X-ray 46
2.2. High-pressure X-ray diffraction experiments 47
2.2.1. Diamond anvil cell 47
2.2.2. Four-circle X-ray single crystal diffractometer 50 3. Results 51
3.1. Water solubility in clinopyroxene 51
3.1.1. Water solubility in pure diopside
3.1.1.1. Exploratory experiments
3.1.1.2. Effect of activities of components in the system
on infrared spectra 57
3.1.1.3. Orientation of hydroxyl group 60
3.1.1.4. Water solubility in diopside with excess silica 66
3.1.1.5. Thermodynamic model of water solubility 71
3.1.2. Effect of Al on water solubility in diopside 73
3.1.2.1. Description of run products 73
3.1.2.2. Infrared spectra 75
3.1.2.3. P-T dependence of water solubility 77
3.1.2.4. Hydrogen substitution mechanism 79
3.1.2.5. Orientation of the hydroxyl group in aluminous diopside 81
3.2. Effect of water on the equation of state of diopside 85
3.2.1. Sample description 85
3.2.2. Equation of state and compressibility 89
3.2.2.1. Theory of equation of state 89
3.2.2.2. High-pressure single-crystal X-ray diffraction 91
3.2.2.3. F -f plots and EoS parameters 95 E E
3.2.3 Discussion 98
3.3. Crystal structure refinement of hydrous diopside 100
3.3.1 Data collection and refinement 100
3.3.2 Polyhedral geometry and discussion 103
4. Geophysical and geochemical implications 110
4.1. The role of clinopyroxene in water storage in the upper mantle 110
4.2. Water in clinopyroxene and recycling of water in subduction zones 115
4.3. Remote sensing of water in the mantle 117
5. Conclusions 119
6. References 121
Apendices 134
Summary
SUMMARY

(1) Water solubility in pure diopside
Water solubility in pure diopside was measured. Water-saturated diopside crystals were
osynthesized using piston-cylinder and multi-anvil presses at 20-30 and 100 kbar and 800-1100 C
from an oxide and hydroxide starting mixture containing 10 % excess silica. The water
concentration in diopside was determined from polarized infrared measurements on doubly
polished single crystals. Water contents were calculated by integrating the absorption bands and
using published extinction coefficients for water in diopside.
All measured infrared spectra of pure diopside fall into two groups. The first group of bands
-1(Type I) occurs at higher wavenumber, at 3650 cm , the second group (Type II) at lower
–1wavenumber, at 3480-3280 cm . The appearance of Type I or Type II spectra was neither
correlated with pressure or temperature. The differences in the spectra point towards substitution
mechanisms involving different vacancies, which in turn could be the result of different oxide
activities in the starting material. Therefore, a separate series of experiments was carried out with
starting materials with an excess or deficiency of MgO or SiO . These experiments yielded 2
diopside with different absorption spectra. Starting materials with low silica activity yielded Type I
bands, which are therefore likely to be related to Si vacancies. Type II bands form at high silica
activity and may therefore be related to Mg or Ca vacancies. All spectra of both types show the
same polarization behavior with the highest absorption in β direction, almost identical but slightly
smaller absorption parallel to γ, and the lowest absorption along the α axis of the indicatrix.
Water solubility in pure diopside varies from 121 up to 568 ppm H O. Water solubility at 30 2
o o okbar increases from 700 to 1000 C and drops again above 1000 C. At 900 C, water solubility
increases to a maximum at 25 kbar and then decreases rapidly to higher pressures. The water
solubility in pure diopside may be described by the equation:

1bar solid C = A f exp(- ΔH / RT) exp(-P ΔV / RT) H2O H2O

1bar with A = 0.0185 ppm/bar, f = water fugacity, ΔH = -11117 J/mol, R = gas constant, T = H2O
solid 3temperature in K, ΔV = 14.62 cm /mol and P = pressure in bars.
Due to the low solubility of aluminum in clinopyroxene at high pressure, the data on pure
diopside are probably a good guide for the water solubility in clinopyroxenes under the conditions
of the deeper upper mantle. Since water solubility in diopside un