The grain-scale distribution and behaviour of melt and fluid in crystalline analogue systems [Elektronische Ressource] / Nicolas Peter Walte

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2005
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 18 Mo

Extrait

The grain-scale distribution and behaviour of melt and
fluid in crystalline analogue systems
Dissertation zur Erlangung des Grades
„Doktor der Naturwissenschaften“
am Fachbereich Geowissenschaften
der Johannes Gutenberg–Universität Mainz
Nicolas Peter Walte
geboren in Bremen
Mainz, Oktober 2004Erklärung
Ich versichere hiermit, die vorliegende Arbeit selbständig und nur unter Verwendung
der angegebenen Quellen und Hilfsmittel verfasst zu haben.
Mainz, Oktober 2004
Dekanin: Prof. Dr. B. M. W. Ratter
1. Gutachter:
2. Gutachter:
Tag der mündlichen Prüfung:„Hier sei nur kurz vorausbemerkt: (...) Je besser und feiner eine geologische Struktur
bekannt ist, desto vollständiger stimmt sie nach meinen Erfahrungen mit dem
sachgemäß ausgeführten Experiment überein, welches der Natur nicht nur durch die
Sichtbarkeit seiner Entwicklung, sondern auch durch die Vollkommenheit seiner
Aufschlüsse überlegen ist.”
Hans CloosAbstract
Abstract
The production, segregation and migration of melt and aqueous fluids (henceforth called
liquid) plays an important role for the transport of mass and energy within the mantle and the
crust of the Earth. Many properties of large-scale liquid migration processes such as the
permeability of a rock matrix or the initial segregation of newly formed liquid from the host-
rock depends on the grain-scale distribution and behaviour of liquid. Although the general
mechanisms of liquid distribution at the grain-scale are well understood, the influence of
possibly important modifying processes such as static recrystallization, deformation, and
chemical disequilibrium on the liquid distribution is not well constrained. For this thesis
analogue experiments were used that allowed to investigate the interplay of these different
mechanisms in-situ.
In high-temperature environments where melts are produced, the grain-scale distribution
in “equilibrium” is fully determined by the liquid fraction and the ratio between the solid-
solid and the solid-liquid surface energy. The latter is commonly expressed as the dihedral or
wetting angle between two grains and the liquid phase (Chapter 2). The interplay of this
“equilibrium” liquid distribution with ongoing surface energy driven recrystallization is
investigated in Chapter 4 and 5 with experiments using norcamphor plus ethanol liquid.
Ethanol in contact with norcamphor forms a wetting angle of about 25°, which is similar to
reported angles of rock-forming minerals in contact with silicate melt. The experiments in
Chapter 4 show that previously reported disequilibrium features such as trapped liquid lenses,
fully-wetted grain boundaries, and large liquid pockets can be explained by the interplay of
the liquid with ongoing recrystallization. Closer inspection of dihedral angles in Chapter 5
reveals that the wetting angles are themselves modified by grain coarsening. Ongoing
recrystallization constantly moves liquid-filled triple junctions, thereby altering the wetting
angles dynamically as a function of the triple junction velocity. A polycrystalline aggregate
will therefore always display a range of equilibrium and dynamic wetting angles at raised
temperature, rather than a single wetting angle as previously thought.
For the deformation experiments partially molten KNO –LiNO experiments were used3 3
in addition to norcamphor–ethanol experiments (Chapter 6). Three deformation regimes were
observed. At a high bulk liquid fraction >10 vol.% the aggregate deformed by compaction
and granular flow. At a “moderate” liquid fraction, the mainly by grain
boundary sliding (GBS) that was localized into conjugate shear zones. At a low liquid
fraction, the grains of the aggregate formed a supporting framework that deformed internally
by crystal plastic deformation or diffusion creep. Liquid segregation was most efficient during
framework deformation, while GBS lead to slow liquid or even liquid dispersion
in the deforming areas.Contents
Contents
Abstract ................................................................................................................5
Contents................................................................................................................7
1. Introduction ................................................................................................11
1.1 Melting the Earth...............................................................................12
1.2 Melt segregation, migration, and accumulation..................................13
1.3 Problems of investigating the geology of liquid .................................14
1.4 Experiments with partially-molten systems........................................16
1.5 The importance of the small-scale liquid geometry for the large-scale
liquid behaviour ................................................................................16
1.6 Aims and structure of this study.........................................................17
1.7 Published parts ..................................................................................19
2. The liquid distribution in ideal solid-liquid systems in textural
equilibrium..................................................................................................21
2.1 The wetting angle concept .................................................................21
2.2 The role of interfacial curvature.........................................................23
2.3 Liquid distribution in two and three dimensions ................................27
2.4 Recrystallization and Ostwald ripening..............................................33
3. Sample preparation and experimental setup.............................................39
3.1 Norcamphor experiments...................................................................39
3.2 Nitrate experiments ...........................................................................42
4. Disequilibrium melt distribution during static recrystallization ..............45
Abstract........................................................................................................45
4.1 Introduction.......................................................................................45
4.2 Experiments ......................................................................................47
4.3 Results ..............................................................................................48Contents
4.4 Discussion.........................................................................................51
4.5 Conclusion ........................................................................................53
5. Evolution and significance of dynamic wetting angles in a
polycrystalline solid–liquid system.............................................................55
Abstract........................................................................................................55
5.1 Introduction.......................................................................................55
5.2 Experiments and Methods .................................................................60
5.3 Results ..............................................................................................65
5.4 Discussion.........................................................................................70
5.5 Conclusion ........................................................................................74
6. Deformation of melt-bearing systems – insight from in situ
grain-scale analogue experiments ..............................................................77
Abstract........................................................................................................77
6.1 Introduction.......................................................................................77
6.2 Experiments ......................................................................................79
6.3 Results ..............................................................................................81
6.4 Discussion.........................................................................................90
6.5 Conclusions.....................................................................................101
7. The grain-scale behaviour of liquid in crystalline aggregates:
A summary and outlook ...........................................................................103
7.1 Response of a liquid to a change of the dynamic or the equilibrium
wetting angle...................................................................................105
7.2 Driving forces for the change of Q or Q .....................................106inst eq
7.3 Surface energy driven static recrystallization...................................107
7.4 Gravity and liquid overpressure.......................................................107
7.5 Chemical disequilibrium between the liquid and the grains..............110
7.6 Deformation ....................................................................................111
Appendix A: Notation ......................................................................................117Contents
Appendix B: Movie captions............................................................................119
Static norcamphor– ethanol experiments.....................................................119
Overview mo