1 10 2 https://theses.otagogeology.org.nz/files/original/68a46294e55cb886bd88475e18d74f51.pdf 07c784ae8768a4815d20675e91886b19 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Author last name Last name of the Author Vaughan Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? PhD Advisers Who supervised/advised this student Prior, D.J. Abstract The Abstract for this thesis Ice is ubiquitous on Earth and on the outer planets and satellites of the solar system. Ice is an important geologic material, and is a critical contributor to global climate and sea-level models. Understanding and modelling the dynamic behaviour of the glaciated regions on earth and in the outer solar systems requires an intimate knowledge of the mechanisms that control the mechanical behaviour of ice polycrystals. During dynamic events, such as rapid heating or ice-shelve collapse, much of the response of ice sheets is governed by its internal deformation, that is, the ductile flow behaviour of the ice. Ductile flow in ice is primarily controlled by temperature and the arrangement of ice crystals into crystallographic preferred orientations (CPO), which both have a dramatic effect on flow rates and mechanical anisotropy. Seismic field surveys provide a window into the regional characteristics of ice sheet flow, via the relationship between CPO and polycrystal elastic anisotropy. That is, CPO effects the velocity of elastic waves travelling at different directions through a textured polycrystal. CPO geometry in ice evolves as a function of deformation conditions such as temperature and the stress field. Thus, elastic anisotropy can be used to interpret mechanical anisotropy, an important parameter for predicting long-term ice sheet behaviour. Here, we present the results of several un-confined uniaxial compression experiments on cylinders of isotropic polycrystalline ice under controlled temperature and displacement-rate conditions. The deformed material was characterised in real-time by measuring ultrasonic time-of-flight in-situ during ductile creep, and post-deformation using cryo electron backscatter diffraction to characterise the final microstructure. Resonant ultrasound spectroscopy measurements were made on cylinders of synthetic isotropic ice polycrystals, to determine the relationship between temperature and the elastic and anelastic characteristics that govern wave propagation in ice. At high homologous temperatures (-5°C), uniaxial shortening gives rise to a CPO cone girdle, where the c-axes of the individual crystals become aligned into an orientation 30-50° from the shortening direction. The evolution of this CPO is controlled primarily by strain-energy driven grain boundary migration, where grains in orientation favourable for slip on the basal planes grow at the expense of those in hard slip orientations. Grains in hard basal slip orientations deform by non-basal slip on pyramidal planes. Rapid weakening occurs in the samples around 3% strain, and corresponds to the formation of a network of grains well oriented for basal slip. Through in-situ measurements of elastic wave velocity evolution, we observe that changes in ultrasonic velocity anisotropy can be used as a continuous proxy for CPO evolution, quantifying the relationship between velocity anisotropy and fabric strength. Resonant ultrasound measurements show that elastic wave velocity is strongly sensitive to temperature in ice polycrystals, as are the components of the elasticity tensor. These measurements reveal that compressional wave speeds and intrinsic attenuation are most sensitive to temperature, which we attribute to liquid phases on ice grain boundaries associated with pre-melting conditions. OURArchive handle The handle from the Otago University Research Archive (OURArchive) <a href="http://hdl.handle.net/10523/7159">http://hdl.handle.net/10523/7159 </a> OURArchvive access level Open Access Department The department where the student is studying primarily. Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2017Vaughan Creator An entity primarily responsible for making the resource Vaughan, Matthew James Hatfield (Matt) Date A point or period of time associated with an event in the lifecycle of the resource 2017 Title A name given to the resource The creep behaviour, and elastic and anelastic properties of polycrystalline ice Subject The topic of the resource Rock Deformation Anelasticity anisotropy CPO creep deformation Ductile EBSD Elasticity Fabric MIcrostructure Polycrystalline slip-systems Velocity https://theses.otagogeology.org.nz/files/original/ee4fb14489bb8461a0639585c821ef32.pdf a2d949a9270c7bbc194579edee663238 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Geology theses OU Geology thesis Thesis or dissertation completed by University of Otago Geology students Author last name Last name of the Author Crookbain Project type Is it an MSc, PhD, BSc(Hons) or PGDipSci? MSc Advisers Who supervised/advised this student Smith, S.A.F. Abstract The Abstract for this thesis Understanding the dynamics of shallow earthquake rupture and coseismic slip in carbonate-dominated fault zones is exceptionally important in many areas worldwide. Although constraints are available from rock mechanics experiments and paleoseismological investigations of surface breaks, little is currently known about the dynamic processes that occur in narrow fault slipping zones in the near-surface (<3 km) environment. The Tre Monti Fault, central Italy (exhumed from depths <2 km) is an active carbonate-dominated fault zone that has probably hosted large (Mw >6) earthquakes. In previous studies of the principal slip zone (PSZ) of the Tre Monti Fault, peculiar aggregate- type grains were recognised and termed “Clast-Cortex Aggregates” (CCAs). Such grains contain a central clast (often angular) of host rock or reworked cataclasite surrounded by an outer, often laminated cortex containing much finergrained material. CCAs were only identified in the high-strain PSZ of the Tre Monti Fault (i.e. they are restricted to an ultracataclastic layer <2 cm thick) and as such they potentially record the effects of localized dynamic slip processes during the seismic cycle. However, because of their monomineralic composition, fine grain size and extremely low porosity, previous attempts to image CCAs using standard SEM-based techniques were not successful. Using high-resolution Electron Backscatter Diffraction (EBSD) analysis of a single CCA, this thesis presents new observations regarding the microstructure and evolution of CCAs in carbonate-dominated fault zones. Results indicate that: 1) the diameter of individual grains comprising the CCA outer cortex and surrounding matrix of the PSZ is on the order of 1-5 ?m; 2) mean grain size decreases progressively from the inner laminations towards the outer laminations; 3) in all locations around the CCA, and in the surrounding matrix of the PSZ, individual grains are markedly elongate (mean aspect ratio between 1.5 and 2.1) and are aligned at c. 70°-90° to the principal slip surface, and; 4) there is no significant crystallographic preferred ordinations of grains within the laminations of the outer cortex. These new results support a model in which CCAs form by accretion of grains on to the outside of a central clast rotating clast within the cataclastic PSZ at shallow depths (<2 km). The PSZ is progressively crushed during slip events decreasing the grain size and resulting in grain size grading within the laminations of the CCAs. The formation of CCAs may be related to coseismic slip, however the data does not allow tight constraints on slip rates during formation. Following the formation of the CCAs, compaction within the fault zone, perhaps accommodated by pressure solution processes, results in individual grains within the CCA and surrounding matrix developing a systematic elongate shape. such distributed compaction may correspond to the shallow interseismic creep that has been observed at shallow depths following major recent earthquakes in carbonate-dominated fault zones. OURArchive handle The handle from the Otago University Research Archive (OURArchive) <a href="http://hdl.handle.net/10523/7437">http://hdl.handle.net/10523/7437</a> OURArchvive access level Open Access Department The department where the student is studying primarily. Geology Thesis description Number of pages, maps, CDs, etc. 154 pages A4 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Identifier An unambiguous reference to the resource within a given context 2017Crookbain Creator An entity primarily responsible for making the resource Crookbain, Kieran Date A point or period of time associated with an event in the lifecycle of the resource 2017 Title A name given to the resource Granular Dynamics in Shallow Earthquake Slip Zones: Insights from Microstructural Analysis of Clast-Cortex Aggregate Grains Subject The topic of the resource Structural Geology Rock Deformation Cataclasite CCA Clast Cortex Aggregate Grains Principal Slip Zone PSZ Slip Dynamics Tre Monti Fault