Deformation mechanisms of naurally deformed rocksalt [Elektronische Ressource] / vorgelegt von Zsolt Schléder

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2006
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 12 Mo

Extrait

Deformation mechanisms of naturally deformed
rocksalt



Von der Fakultät für Georessourcen und Materialtechnik
der Rheinisch -Westfälischen Technischen Hochschule Aachen






zur Erlangung des akademischen Grades eines
D oktors d er Naturwissens c h aften
genehmigte Dissertation








vorg e l egt von M. Sc . Zs olt Sc hl éd er
aus Sárbogárd, Ungarn










Beric hter: U niv. -Prof. D r. Ján os L. U rai
Prof. Dr. Christop her J. Sp iers
Univ. -Prof. D r. Peter A. Kukla

Tag der mündlichen Prüfung: 02 Juni 2006

Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar








Dedicated to
my parents
and
Windhoffer Gábor


Acknowledgements
I would like to sincerely thank the various people who, during the three years in which this
work lasted, provided me with useful and helpful assistance.
János Urai is sincerely thanked for supervising of this thesis and for finding time in his rather
busy schedule to provide me with an insightful introduction at the beginning of the project
and a thorough review during the whole work. Without his care and consideration, this work
would not have matured.
I would like to thank all the colleagues at Aachen for their dedication, interest and
enthusiasm. To Sofie Nollet, Katerina Scholz, Oliver Schenk, Johannes Schoenherr and Marc
Holland who were always ready for discussing any kinds of problems and for carefully
reading and correcting many parts of this thesis. Thanks to all the HiWis at GED; Joyce
Schmatz, Manuel Bumenthal, Ansgar Heimann and Frank Strozyk for the countless
immediate help in sample preparation, photocopying and other monotonous tasks. GED
secretary, Bettina Dulle, is heartily thanked for her patience and professionalism in
explaining the official ways in German bureaucracy. Werner Kraus preparator provided me
feedback and invaluable insights in rocksalt sample preparation, which is greatly
acknowledged. Kai Jasper, Danilo Cifola and Heijn van Gent, who worked at the neighbor
department or joined the GED group for some period, were always ready for a small chat
and their presence made the GED atmosphere even more colourful.
Chris Hilgers demonstrated interest in this work early on, provided assistance throughout
some important questions, and has been an enthusiastic supporter and partner. Wim Paar
provided rocksalt samples from Hengelo and provided me with all the desired detail
information during the work. Stanislaw Burliga is thanked for organizing a fieldwork in
Poland, for the hospitality, and for the discussions on salt tectonics. Chris Talbot provided
me the opportunity to join him in the 2005 field season in central Iran. His introduction into
the salt tectonic processes in Iran and his guidance is kindly acknowledged. Abbas Bahroudi
and his colleagues at GSI are heartily thanked for the hospitality while staying in Iran. The
fieldwork in Neuhof salt mine would have not been possible without the help of Reiner Stax
at K+S. Both the samples and the discussion on salt tectonics-related features of the mine are
thanked. I would like to commend the interest, supervision and great job done by Manfred
Thomé at the Jülich Forschungszentrum throughout the overall gamma-irradiation process.
Friends at Budapest, especially Bodó Péter and Windhoffer Gábor, are thanked for their –
very likely unconscious – encouragement and support. Most important, thanks to Nóra, who
put up with a string of lost weekends and odd working hours.


Abstract
This thesis presents an analysis of deformation and recrystallization processes in a variety of
naturally deformed rocksalt. Tools used for the analysis involve simple microtectonic
methods: transmitted and reflected light microscopy of gamma-irradiated thin sections and
orientation measurements with EBSD. Case studies were chosen to represent different
tectonic settings. Slightly deformed bedded Lower Triassic Röt rocksalt from Hengelo, The
Netherlands; horizontal, though locally folded Z1 Zechstein salt from Neuhof-Ellers salt
mine, Germany; highly strained Z4 Zechstein domal salt from Klodawa salt mine, Poland
and highly deformed extrusive salt from Qum Kuh and Gramsar Hills (central Iran) were
studied.
The Hengelo and Neuhof-Ellers samples show abundant primary structures such as fluid-
inclusion-outlined chevron or hopper crystals. The microstructures suggest that the
sedimentary environment was ephemeral salt-pan for the Hengelo samples and perennial salt
lake for the Neuhof-Ellers samples. The main deformation mechanisms are dislocation
processes and solution-precipitation in the Hengelo samples, while the samples from
Neuhof-Ellers deform solely by solution-precipitation creep due to its very fine grain size (~1
mm). In both set of samples, widespread evidence for grain boundary migration
recrystallization (GBM) is present. The GBM swept out the primary fluid inclusions and
transferred them to grain boundary fluid.
The Klodawa samples show no primary microstructures, suggesting that it is completely
recrystallized by process of GBM. The main deformation mechanism was dislocation creep
as evidenced by the widespread presence of subgrains. Presence of static recrystallization
related euhedral grains in some samples suggest that mine-wall convergence induced static
recrystallization may alter the natural deformation-related microstructures.
The highly deformed extrusive salt samples from Iran contain thin shear zones. In the shear
zones, the deformation mechanism is solution-precipitation creep. The preserved
porphyroclasts are rich in subgrain, indicating climb controlled dislocation creep in the
subsurface. Orientation measurements demonstrate that the grain size reduction involves
subgrain rotation and perhaps nucleation during the upward transport of the salt.
Based on subgrain size piezometry the differential stress was less than 2 MPa for all the
samples studied except that for the extrusive Iran samples, where the differential stress of ~3
MPa was calculated. This high stress value very likely represents the conditions during the
upward transport of the salt.

Zusammenfassung
Die vorliegende Doktorarbeit präsentiert zahlreiche Untersuchungen zu Deformations- und
Rekristallisationsprozessen natürlich deformierter Salzgesteine. Zur Analyse wurden die in
der Halit-Mikrotektonik üblichen Methoden angewandt: Durchlicht- und
Auflichtmikroskopie von Gamma-bestrahlten Salzdünnschliffen sowie
Orientierungsmessungen mit EBSD.
Zur Untersuchung von unterschiedlichen tektonischen Szenarien wurden entsprechende
Fallstudien gewählt: Schwach deformiertes geschichtetes Röt Steinsalz (Untere Trias) aus
Hengelo (Niederlande), horizontal bis lokal gefaltetes Werra Zechsteinsalz (Z1) aus dem
Neuhof-Ellers Salzbergwerk (Deutschland), hoch verformtes Aller (Z4) Steinsalz aus einem
Salzstock Bergwerk in Klodawa (Polen) und hoch deformierte Salz-Extrusiva aus Qum Kuh
and Gramsar Hills (Zentral-Iran).
Proben aus Hengelo und Neuhof enthalten eine Vielzahl von Primärstrukturen, wie zum
Beispiel Fluideinschlüsse – in der Literatur als „chevron“- oder „hopper“-Kristalle
bezeichnet. Mikrostrukturelle Beobachtungen deuten darauf hin, dass Proben aus Hengelo
einem kurzzeitig vorhandenen (ephemeralen) Salz-Becken entstammen und Salzgesteine aus
Neuhof sich in einem langlebigen Salzsee bildeten.
Die Hauptdeformationsmechanismen in den Hengelo-Proben sind Versetzungskriechen
sowie Drucklösung. Das extrem feinkörnige Gefüge der Salzproben aus Neuhof deutet
dagegen ausschließlich auf Drucklösungs-Prozesse hin. Gleichzeitig verweisen die
Mikrostrukturen der Hengelo- und Neuhof-Proben auf Korngrenzmigrationsprozesse.
Während der Korngrenzmigration (KGM) werden die im Salzkristall primär enthaltenen
Fluideinschlüsse entlang von Korngrenzen freigesetzt.
Salzgesteine aus Klodawa weisen keine primären Mikrostrukturen (z.B. „hopper“-Kristalle)
auf, was auf eine komplette Rekrisatllisation des Salzgefüges durch KGM hindeutet. Das weit
verbreitete Auftreten von Subkörnern in den Klodawa-Proben lässt eindeutig auf
Versetzungskriechen als vorwiegend aktiven Hauptdeformationsmechanismus schließen.
Idiomorph gewachsene statisch rekristallisierte Körner in einigen der Proben aus Klodawa,
weisen höchst wahrscheinlich auf Rekristallisationsprozesse hin, die durch
Konvergenzbewegungen von Bergbauwänden in der Salzmine hervorgerufen wurden und
dadurch die natürlich deformierten Mirkostukturen überprägen.
Hoch deformierte extrusive Salzgesteine aus Iran beinhalten gering-mächtige Scherzonen.
Die Mikrostrukturen in diesen Proben sind im Wesentlichen durch Drucklösungsprozesse
entstanden. In diesem Gefüge vorhandene Porphyroklasten weisen zahlreich