New experimental data for a re-calibration of the Fe-Ti oxide thermo-oxybarometers [Elektronische Ressource] / vorgelegt von Ursula Sauerzapf

Sujets

• Physik

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2006
• Nombre de lectures: 26
• Langue: English
• Poids de l'ouvrage: 90 Mo

Extrait

NewExperimentalDatafora
Re CalibrationoftheFe TiOxide
Thermo Oxybarometers.
INAUGURAL DISSERTATION
zur
ErlangungderDoktorwürde
der
Naturwissenschaftlich MathematischenGesamtfakultät
derRuprecht Karls Universität
Heidelberg
vorgelegtvon
Diplom MineraloginUrsulaSauerzapf
ausHeidelbergNewExperimentalDataforaRe Calibrationof
theFe TiOxideThermo Oxybarometers.
Gutachter:
Prof. Dr. DominiqueLattard
HochschuldozentinDr. AgnesKontny
TagdermündlichenPrüfung: 29.05.2006Contents
Abstract v
Kurzfassung ix
1 Introduction 1
1.1 AshortpresentationofFe Tioxidemineralsandtheirsignificance . 1
1.2 Stateoftheart: crystallinephasesinthesystemFe Ti O . . . . . . 5
1.2.1 A general introduction to relevant Fe Ti oxide phases:
chemistry,structureandstability . . . . . . . . . . . . . . . 5
1.2.2 Wüstite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.3 Titanomagnetite . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.4 Titanomaghemite . . . . . . . . . . . . . . . . . . . . . . . 18
1.2.5 Ilmenite . . . . . . . . . . . . . . . . . . . . . . . . . . . 20ss
1.2.6 Pseudobrookite . . . . . . . . . . . . . . . . . . . . . . . 21ss
1.3 Thermo oxybarometry . . . . . . . . . . . . . . . . . . . . . . . . 23
1.4 Aimsofthepresentstudy . . . . . . . . . . . . . . . . . . . . . . . 34
2 Experimentalandanalyticalmethods 35
2.1 Generalapproach . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.2 High temperatureexperiments . . . . . . . . . . . . . . . . . . . . 36
2.2.1 Preparationofstartingmixtures . . . . . . . . . . . . . . . 36
2.2.2 High temperaturetechniques . . . . . . . . . . . . . . . . . 38
2.2.3 Synthesisexperiments . . . . . . . . . . . . . . . . . . . . 39
2.2.4 Re equilibrationexperiments . . . . . . . . . . . . . . . . . 41
2.2.5 Annealingexperiments . . . . . . . . . . . . . . . . . . . . 42
2.2.6 Quenchingprocedures . . . . . . . . . . . . . . . . . . . . 42
2.3 Characterisationandanalysisoftherunproducts . . . . . . . . . . 43
2.3.1 Opticalexamination(eye,binocular) . . . . . . . . . . . . . 43
2.3.2 X raypowderdiffraction . . . . . . . . . . . . . . . . . . . 43
2.3.3 Scanningelectronmicroscopy . . . . . . . . . . . . . . . . 44
2.3.4 Electronmicroprobe(EMP)analysis . . . . . . . . . . . . . 45
2.3.5energy lossspectroscopy . . . . . . . . . . . . . . 47
i3 Textures of synthetic sub solidus Fe Ti oxide assemblages in the sys
temFe Ti±Al±Mg O 49
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.2 Generalremarksonexperimentalconditionsandprocedures . . . . 50
3.3descriptionofcommontexturalfeatures . . . . . . . . . . . 51
3.3.1 Crystalshapes,sizesanddistribution . . . . . . . . . . . . 51
3.3.2 Porosityandcracks . . . . . . . . . . . . . . . . . . . . . . 51
3.4 Formationofconcentrictextures-correlationtothestartingmaterial 54
3.4.1 Generalremarks . . . . . . . . . . . . . . . . . . . . . . . 54
3.4.2 ExperimentswithFe O +TiO startingmixturesfrompre 2 3 2
annealedreagents . . . . . . . . . . . . . . . . . . . . . . . 55
3.4.3withFe O +TiO startingmixtures . . . . . . 562 3 2
◦3.4.4 ExperimentswithFe +TiO starting . . . . . . . 642
◦3.4.5withFe O +Fe +TiO startingmixtures . . 662 3 2
3.4.6 Time dependentexperiments . . . . . . . . . . . . . . . . . 67
3.4.7 Interpretationandconclusion . . . . . . . . . . . . . . . . . 68
3.5 Oxy exsolutiontextures . . . . . . . . . . . . . . . . . . . . . . . . 71
3.5.1 SEMobservationsandEMPanalysis . . . . . . . . . . . . 71
3.5.2 Interpretationandconclusion . . . . . . . . . . . . . . . . . 73
3.6 Chemicalinhomogeneitiesofphasesinproductsofsynthesisruns . 75
3.7 Summaryandconclusion . . . . . . . . . . . . . . . . . . . . . . . 77
4 PhaserelationsandphasecompositionsinthesystemFe Ti O 81
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.2 Generalexperimentalapproach . . . . . . . . . . . . . . . . . . . . 82
4.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.3.1 Indicationsfortheattainmentofequilibrium . . . . . . . . 82
4.3.2 Re equilibrationexperiments . . . . . . . . . . . . . . . . . 84
4.3.3 Phaseboundariesandcompositions . . . . . . . . . . . . . 90
4.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.1 TheTmt Ilm assemblage: phasecompositionsandbound ss
aries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.2 TheTmt Ilm Comparisontothermodynamicss
models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.4.3 TheIlm Psb assemblage . . . . . . . . . . . . . . . . . 100ss ss
4.4.4 Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . 1025 High Tnon stoichiometryinmagnetite ulvöspinelsolidsolution 103
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.2 Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.3 Theannealingmethod. . . . . . . . . . . . . . . . . . . . . . . . . 105
5.3.1 Principlesoftheannealingmethod . . . . . . . . . . . . . . 105
5.3.2 Uncertaintiesofthemethods . . . . . . . . . . . . . . . . . 112
5.3.3 Actualandallegedpitfalls . . . . . . . . . . . . . . . . . . 114
5.3.4 Presentationanddiscussionoftheresults . . . . . . . . . . 120
5.4 Non stoichiometryfromcelldimensions . . . . . . . . . . . . . . . 126
5.4.1 Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
5.4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
5.4.3 Summaryandinterpretation . . . . . . . . . . . . . . . . . 129
5.5 Non stoichiometryfromEELS . . . . . . . . . . . . . . . . . . . . 132
5.5.1 Principlesandmeasurement . . . . . . . . . . . . . . . . . 132
5.5.2 Sampleselectionandpreparation . . . . . . . . . . . . . . 133
5.5.3 Pitfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
5.5.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
5.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
5.6.1 Summary of annealing method results, lattice parameter
dataandEELSdatafromthepresentstudy . . . . . . . . . 138
5.6.2 Comparisonwithliterature . . . . . . . . . . . . . . . . . . 139
5.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
6 InfluenceofminorelementcontentsofMgandAl 143
6.1 Introduction: minorelementcontentsinFe Tioxides . . . . . . . . 143
6.2 Experimentalandanalyticalapproach . . . . . . . . . . . . . . . . 145
6.3 Phaserelations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
6.4 PhasecompositionsinthesystemFe Ti Mg Al O . . . . . . . . . . 148
6.4.1 Mg andAl contentsoftheFe Tioxidephases . . . . . . . 148
6.4.2 Projection of Mg Al bearing compositions into the Ilm
HemandMag Uspbinaries . . . . . . . . . . . . . . . . . 153
6.4.3 Comparisonoftheprojectionschemes . . . . . . . . . . . . 156
6.4.4 of X’ and X’ derived with equations 6.5Usp Ilm
and 6.6, with the data from the simple system Fe Ti O
andwiththeexistingthermodynamicthermo oxybarometer
models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
6.5 Non stoichiometry in Mg Al bearing Tmt - results from annealing
experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
6.6 Discussionandconclusion . . . . . . . . . . . . . . . . . . . . . . 1667 Outlook 171
Bibliography 175
A Appendix 187
A.1 Tableofabbreviations . . . . . . . . . . . . . . . . . . . . . . . . . 187
A.2 Startingmixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
A.3 Tablesofexperimentalconditionsandanalysisresults . . . . . . . . 192
A.4 Conversionofwt%andvol%intomol% . . . . . . . . . . . . . . . 222
A.5 Tmtprojection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
B Author’spublicationsrelatedtothisthesis 227
B.1 Paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
B.2 Abstractsandconferenceparticipations . . . . . . . . . . . . . . . 227
Acknowledgements 229
Erklärung 231Abstract
Despite their modest modal abundances, the Fe Ti oxide minerals are important
accessory minerals in igneous rocks. They are major carriers of rock magnetism
andpetrologicindicatorsoftemperatureandredoxconditionsduringthemagmatic
stage(Buddington&Lindsley,1964).
The titanomagnetite ilmenite (Tmt Ilm ) thermo oxybarometer has beenss ss
widely used to retrieve information on redox states in the Earth’s mantle, pro
cesses in magma chambers, the crystallisation conditions of lunar or martian
basalts,redoxconditionsduringmetamorphicevolution,orfluid rockinteractions.
However, the current thermodynamic formulations of the Tmt Ilm thermo ss
oxybarometer (Andersen & Lindsley, 1988; Ghiorso & Sack, 1991) fail to repro
duce experimental results, in particular at the high temperatures that are relevant
for basaltic assemblages. This is shown in chapter 1 (section 1.3) by applying the
formulationstoexperimentalliteraturedata. Theshortcomingsoftheexistingmod
els are partly due to the limited T-fO range of experiments used for the original2
calibrations. Further, theeffectofsmallcontentsofMg, Al, etc. typicalfornatural
Tmt and Ilm was only partly evaluated, and the non stoichiometry of the phasesss
(inparticularTmt)wasnotconsideredatall.
To support a revised version of the Tm