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2 Local Geology and the Sample 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 Doktors der Naturwissens ch aften genehmigte Dissertation vorge legt von M.Sc . Zs olt Schléd er aus Sárbogárd, Ungarn Berichter: Univ.-Prof. Dr. János L. Urai Prof. Dr. Christopher J. Spiers Univ.-Prof. Dr. 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 zahlreiche Subkörner auf, die vermutlich durch Versetzungsklettern im Kristallgitter der Salzkristalle noch vor dem Salzaustritt an die Erdoberfläche entstanden. Orientierungsmessungen (EBSD) zeigen, dass in diesen Proben Korngrößen-Reduktion durch Subkornrotationsrekristallisation und vermutlich durch Kristallneuwachstum während der Aufwärtsbewegung des Salzes stattfand. Anhand von Paleo-Piezometriemessungen an Subkörnern ergibt sich eine Differenzialspannung von < 2 MPa für fast alle untersuchten Proben, ausgenommen den Salz-Extrusiva aus dem Iran. In diesen Proben wurde eine Differenzialspannung von ca. 3 MPa gemessen, welche sehr wahrscheinlich die Bedingungen im Diapirbereich eines Salzstockes widerspiegelt. Table of contents Chapter 1: Introduction, definition of problems and aims ............................. 15 1 Introduction........................................................................................................................... 15 2 Scope......................................................................................................................................
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