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1
Bretan, P. G. "Deformation processes within mylonite zones associated with some fundamental faults." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37954.
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Maurel, Olivier. "L'exhumation de la zone axiale des Pyrénées-Orientales une approche thermo-chronologique multi-méthodes du rôle des failles /." Montpellier : Institut des sciences de la terre, de l'environnement et de l'espace de Montpellier, 2003. http://catalogue.bnf.fr/ark:/12148/cb401527828.
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Point, Raymond. "La lame cratonique et les unités supracrustales de la chaîne calédonienne scandinave méridionale orientale : un exemple d'évolution polycyclique de mylonites précambriennes." Paris 7, 1990. http://www.theses.fr/1990PA077217.
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Dans les caledonides orientales scandinaves, l'etude des roches impliquees dans les deux nappes situees a la base de la grande nappe de seve, permet de definir deux grandes unites formees de mylonites heterogenes et polycycliques: 1) a la base, la lame cratonique, unite formee de lames de socle cristallin mylonitique a lithologie variee parmi lesquelles les orthogneiss de tannas representent une part importante en volume; 2) au-dessus, la nappe de sarv-humelfjell, unite de roches supracrustales formee de lames de tectonites ultramylonitiques et protomylonitiques a facies de pseudo-metaquartzite. Ces nappes contiennent en intercalation et en faible quantite, des marbres et des sediments periglaciaires d'age inconnu. L'analyse petrographique et structurale, les relations avec les filons basiques secants, permettent de separer une evolution crustale cisaillante et heterogene, catazonale a epizonale, datant de la fin de l'orogenese svecofennienne, d'une evolution crustale cisaillante et heterogene, strictement epizonale, rapportee a l'orogenese caledonienne. La diversite des facies des mylonites est expliquee a partir de l'etude de la mineralogie des roches structurees ou mises en place dans les zones profondes et, l'heterogeneite des deformations, par la distribution spatiale des zones de cisaillement qui se relaient dans le temps et dans l'espace au cours de l'evolution retrograde datant du premier episode. L'origine des roche-meres des mylonites cristallines et para-derivees les plus typiques est precisee. Une etude comparative entre les roches supracrustales et les sediments varegiens est abordee. Les resultats geochimiques rendent compte de la structuration en zone profonde. Ils permettent aussi de mettre en evidence des migrations metasomatiques d'elements majeurs lies a l'orogenese caledonienne. Ces nappes sont considerees comme des nappes de socle. Ce sont des nappes polycy
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Papa, Simone. "The pseudotachylyte-mylonite association: an insight into the mechanics of deep earthquakes." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3425421.
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The aim of this thesis is to investigate the association of fault rocks formed by seismic deformation with coeval ductile deformation. The only recognised geological record of these two concurrent deformation mechanisms is represented by the relationship between coeval pseudotachylytes (quenched melts produced during seismic slip) and mylonites (high-‐strain rocks deformed in high-temperature ductile flow). The scientific importance of this association of rocks lies in the fact that their existence in rocks exhumed from below the long-‐term brittle/ductile transition is a compelling evidence that rheology of the deep crust cannot be treated simply in terms of brittle and ductile models. By investigating associations of coeval pseudotachylytes and mylonites we aim at giving an original and meaningful contribution to the understanding of the mechanisms involved in the interplay in space and time between seismic deformation and ductile flow.
A model proposed to explain such association of fault rocks is “self-‐localising thermal runaway”, assuming a spontaneous acceleration of localized slip in a ductile shear zone eventually leading to seismic slip and melting. This model is supported by numerical modelling, but its application to nature is disputed and speculative. We analyse a pseudotachylyte-ultramylonite association in exhumed lower crustal, quartz-‐rich metapelites from the Mont Mary nappe of the Western Italian Alps, representing a possible candidate for thermal runaway instability, to find evidence in support or against this process.
• We document by detailed electron backscatter diffraction (EBSD) analysis of quartz-‐rich layers, the progressive microstructural evolution, at nearly constant temperature conditions (550 °C), to high differential stresses (> 200 MPa) and high strain rates (10-‐9 s-‐1) within the most strongly deformed portions of the ultramylonite hosting the pseudotachylyte. This microstructural evolution is associated with a switch in deformation mechanism from grain-size-insensitive to grain-size-sensitive creep assisted by grain boundary sliding and creep cavitation. These latest recorded stages of deformation were still aseismic, as the rate-controlling process was precipitation of oriented biotite in cavitation pores.
• We calculate, by calibrated numerical models, the critical conditions for thermal runaway instability in quartz for a wide range of temperature/strain-‐rate combinations, and determine that deformation in the studied ultramylonite occurred close to the conditions for the instability to occur. At the same time, we estimate that deformation occurred proximal to brittle-ductile transition for such high strain rates.
• We conclude that the observed pseudotachylyte-mylonite association is best explained by transient downward propagation of seismic rupture from the nearby, overlying base of the seismogenic crust; or by earthquake nucleation below the long-term brittle/ductile transition permitted by the downward deflection of the transition after a large seismic event in the upper crust.
Based on the study of wall-rock garnet coseismic fragmentation in the Mont Mary pseudotachylyte-ultramylonite and on garnet preferential melting within the pseudotachylyte, we suggest a general process for garnet disappearance due to thermal shock fragmentation during co-seismic frictional heating. We show that garnet has the lowest thermal shock resistance between the host rock minerals (garnet, plagioclase, quartz, and sillimanite, in an increasing sequence of resistance), and thus underwent extreme comminution leading to total melting within the frictional melt. Our
analysis highlights the critical role of thermal shock as a general process in mineral comminution during the initial stages of co-seismic slip preceding (and promoting) extensive frictional melting.
We also present the preliminary results (mechanical and microstructural) of rotary shear experiments designed to reproduce the formation of Mont Mary pseudotachylytes in the lab.
We extend the study of deep crustal pseudotachylytes and pseudotachylyte-mylonite associations to the Calabrian lower crust (Southern Italy) in a preliminary study that aims at paving the way to a further in-depth analysis of Calabrian pseudotachylytes, which represent a unique information source about the rheology of the granulitic continental lower crust. We present microstructural
evidence for cyclic pseudotachylyte and mylonite development in the dry lower crust and document the first finding of low-‐p/high T, cordierite-bearing, peraluminous pseudotachylytes featuring sillimanite microlites.
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Stewart, Martyn. "Kinematic evolution of the Great Glen Fault Zone, Scotland." Thesis, Oxford Brookes University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364096.
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Parsons, Martha Mary. "Field and Microstructural Constraints on Deformation Conditions and Shear Zone Kinematics in the Burlington Mylonite Zone, Massachusetts:." Thesis, Boston College, 2017. http://hdl.handle.net/2345/bc-ir:107375.
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Thesis advisor: Seth C. Kruckenberg<br>The Burlington Mylonite Zone (BMZ) is a northeast-trending, greenschist- to amphibolite-facies shear zone located entirely within the Boston Avalon terrane in Eastern Massachusetts along the tectonic boundary with the Nashoba terrane (the trailing marginal terrane of Ganderia). The juxtaposition of these terranes, and the development of the BMZ, is hypothesized to represent the amalgamation of Avalon and Laurentia during the late Silurian-early Devonian Acadian orogeny, but the timing of its formation and its structural evolution remain largely unconstrained. Field observations and microstructural analysis using electron backscatter diffraction (EBSD) of 24 samples from 16 field sites throughout the BMZ provide new constraints on the kinematics and conditions of deformation that facilitated the development of this large-scale crustal shear zone. The BMZ samples comprise a heterogeneous mix of quartzofeldspathic +/- hornblende-bearing gneisses and quartzites with varying microstructures. Nearly all samples contain abundant mixed, but predominantly sinistral, kinematic indicators (e.g., asymmetric porphyroclasts, tiled feldspars) and a strong crystallographic preferred orientation (CPO). Quartz – the dominant mineral by mode in all of the samples analyzed – is known from experimental deformation studies to develop distinct patterns of CPO which vary as a function of deformation kinematics, temperature, and strain geometry. Patterns of CPO in quartz are used to determine the dominant intracrystalline deformation mechanisms that accommodated the formation of the BMZ. Quartz CPO patterns in the BMZ samples are characterized by variably developed c- and a-axis distributions, broadly consistent with patterns expected for mixed to prism slip at intermediate temperatures of deformation. Corresponding intragranular misorientation axis plots are more diagnostic and indicate dominant prism slip in all of the shear zone samples analyzed, consistent with microstructures observed in thin section (e.g., undulose extinction, subgrain development, grain boundary migration, dynamic recrystallization) and metamorphic conditions inferred from shear zone mineral parageneses. Application of the quartz recrystallized grain size piezometer places additional constraints on deformation conditions, indicating that the BMZ rocks record differential stresses ranging from ~44 to 92 MPa. Field and microstructural observations of shear sense indicators are combined with two analytical methods for determining aspects of kinematic vorticity and deformation geometry in the BMZ. This study applies a new analytical method - crystallographic vorticity axis (CVA) analysis - that leverages rotational statistics on crystallographic orientations within the interiors of grains to constrain the dominant axis of material rotation in deformed samples. This dominant axis provides a uniquely objective proxy for the vorticity normal reference frame required for further quantitative kinematic vorticity analyses. The rotational axis of kinematic vorticity, and its relationship to structural fabrics (i.e. foliation and lineation), provides an important constraint on the geometry of the deforming zone (e.g., monoclinic versus triclinic shear zones). The results of the CVA analysis are invariable across the entire length of the BMZ; the kinematic vorticity axis lies within the plane of mylonitic foliation perpendicular to lineation – the pattern expected for monoclinic deformation geometries. The mean kinematic vorticity number (Wm: a measure of the relative contribution of pure and simple shear) is calculated using Rigid Grain Net (RGN) analysis for the BMZ mylonites and ranges from 0.4-0.5, indicating general shear. Combined field, microstructural, and vorticity analyses are interpreted to suggest that crustal strain localization along the Avalon-Nashoba boundary, as recorded in the BMZ mylonites, involved the combined effects of pure and simple shear in a predominantly sinistral, monoclinic transpressional shear zone. Rock microstructures, patterns of crystallographic preferred orientation, and paleostress estimates suggest that mylonitization occurred at or near the brittle-ductile transition under relatively high stress conditions. This study demonstrates the power of new microstructural methods, such as CVA analysis of electron backscatter diffraction data, to augment traditional field-based methods of kinematics and deformation analysis in enigmatic, large-scale crustal shear zones
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Loehn, Clayton William. "Monazite Geochronology of the Madison Mylonite Zone and Environs, Southwestern Montana: With Implications for Precambrian Thermotectonic Evolution of the Northern Wyoming Province." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/31692.
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Neoarchean thermotectonism at in the northern Wyoming province is preserved in metamorphic zircon rims and monazite growth throughout the Snowy shear zone (SSZ) and the Madison mylonite zone (MMZ), South Madison Range, Montana. Comparison of U-Pb and U-Th-Pb ages yielded by monazite grains from both shear zones and zircon rims from SSZ, a new timing for major SE-directed thrusting and formation of the MMZ and SSZ has been identified at ~2550 Ma. The collinearity of these two shears indicates the formation of a much larger single shear zone that extends from the North Snowy block (NE), Beartooth Mountains, through the South Madison range (SW), and is paralleled to the immediate NW by the Mirror Lake and Big Brother shear zones. A detrital zircon study of two quartzites, from the westernmost North Snowy block units, yielded concordant age populations ranging in age from 3556 ± 10 to 2752 ± 9 Ma indicating that these sediments were derived either from older crust located in the Beartooth Mountains or from another source that was relatively close to the region prior to ~2750 Ma. The youngest magmatic zircon core found among these quartzites yielded a U-Pb age of 2690 ± 12 Ma, setting a new maximum age for sandstone deposition, additionally 10 metamorphic zircon rims and one monazite grain provide a new minimum U-Pb age of deposition and metamorphism at 2545 ± 2 Ma. Driving forces behind the ~2550 Ma SE-directed thrusting in the NW Wyoming craton may have been the final stages of supercontinent Kenorland assembly, whereas the ~2450 Ma reactivation, recorded by monazite rim growth, along the SSZ-MMZ may relate to the incipient supercontinent break-up, which has been suggested to have occurred at about this time by other studies.<br>Master of Science
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Mehl, Luc. "Plagioclase preferred orientation in the layered mylonites : evaluation of flow laws for the lower crust." Thesis, Online version of original thesis, 2008. http://hdl.handle.net/1912/2324.
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Jarrett, Corey. "Analysis of an Exposed Portion of the Badwater Turtleback Shear-zone, Death Valley, California, USA." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23181.
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The exposed shear zone within the footwall of the Badwater turtleback presents an excellent opportunity to explore the brittle-ductile transition. Within this shear zone, a variety of lithologies preserve the last stages of crystal-plastic deformation concurrent with exhumation of the turtleback. The included field study captures a snapshot of each lithologic element during the last stages of ductile deformation.
The exposed shear zone's journey through the brittle-ductile transition is analyzed using the deformation mechanisms of calcite and quartz. A history of strain partitioning is constructed through comparison of the strain and temperature environments needed to facilitate each mechanism of crystal-plastic deformation. As the shear zone cooled, strain was partitioned from quartz-rich mylonitic gneiss to the calcite-dominated marbles and mylonites. Correlation of deformation temperatures with previous studies further constrains the timing of the last stage of ductile deformation to between 13 and 6 Ma.
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Tatarin, Triffon Joseph, and Triffon Joseph Tatarin. "Interrelationships of cataclasite, mylonite, and leucocratic bodies associated with the Catalina detachment fault, dual wash area, Saguaro National Park east, Rincon Mountains." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/626821.
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The Dual Wash area is comprised of two west-northwest-trending washes (Deer Valley and Carillo), which provide excellent cross-section exposures of metamorphic core complex fault rock units. The structural components of metamorphic core complexes consist of upper plate rocks, a detachment fault, cataclasite and chlorite breccia, subdetachment fault, and mylonites. Within the Carillo Wash, the Catalina detachment fault dips ~13° NW, which is consistent with its overall dip in this part of the Rincon Mountains. However, exposed along the Deer Valley Wash, the Catalina detachment fault dips more steeply at ~60° NW. Beneath the detachment fault, in the lower plate, the structurally highest rock is a highly-fractured chlorite cataclasite which lies above two different units of mylonites. Embedded in these unit is leucocratic granitic unit which floods the cataclasite and mylonites. Evidence of brittle faulting and fracturing show evidence of this being a late-stage intrusion.
The structural geology of the Dual Wash area proves to be somewhat structurally anomalous. The cause for much of these anomalies within the lower plate may be credited to the presence of this abundant leucogranite unit. This may be because it is a late-stage intrusion as well as a potential driver of core complex development.
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Adriao, de Brito Alden. "Mélange mécanique et métamorphisme des lithologies basiques et ultrabasiques au cours de la mylonitisation dans le système transformant de St. Paul, Dorsale Médio-Atlantique." Thesis, Brest, 2019. http://www.theses.fr/2019BRES0012.
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Le système transformant de St. Paul (SPTS) affiche l’un des contextes tectoniques les plus complexes, composé de quatre failles transformantes, trois segments de dorsale (intra-transformants) qui décalent de 630 km la dorsale équatoriale médio-atlantique. Cette région est connue pour ses roches mantelliques uniques qui émergent dans les îlots Saint-Pierre et Saint-Paul, toujours en cours d’élévation. Le SPTS montre une transition depuis une zone de cisaillement régionale au nord vers une région dominée par des Ocean Core Complexes (OCCs) au sud. Les tectonites recueillies tout le long du système transformant ont subi une déformation généralisée dans des conditions ductiles et fragiles et ont été regroupées de la façon suivante : des ultramylonites ultrabasiques, basiques et intermédiaires. Les mylonites ultrabasiques sont des harzburgites porphyroblastiques à porphyroclastiques avec des restes d’amphiboles équilibrées dans le faciès granulite. Les mylonites basiques sont principalement des gabbros porphyroclastiques fortement transformés en amphibolites. Les mylonites intermédiaires sont des schistes riches en talc-chlorite composés de proportions variables de roches basiques et ultrabasiques fortement déformées et hydratées. Toutes les roches ont une matrice très fine (<0.1 mm), une foliation à bandes très marquées qui ont subi une altération tardive à faible température. La géothermométrie donne des températures d'équilibre comprises entre 700 et 900 ° C pour les péridotites et entre 700 et 850 ° C pour les roches gabbroiques. Les teneurs en éléments majeurs et traces des mylonites ultrabasiques se situent dans le champ des péridotites abyssales épuisé, provoquées par une faible fusion fractionnelle (jusqu’à 9%), mais elles présentent un enrichissement marqué en terres rares légères et une anomalie positive en Eu. Les mylonites basiques et intermédiaires présentent des spectres de terres rares plats à enrichis (jusqu'à 100 fois les chondrites de classe CI) et des anomalies variables en Eu. Une interaction entre les roches et le fondu est suggérée pour l’enrichissement en terres rares légères pour les mylonites péridotitiques et les fluides hydrothermaux, en particulier pour l’enrichissement global en terres rares des mylonites serpentinisées. Ces caractéristiques de composition suggèrent une assimilation variable de N-MORB et d’E-MORB au cours de la mylonitisation ou au cours d’une interaction précoce entre la fusion et le magma et une évolution hydrothermale dans des conditions métamorphiques variables. Les failles transformantes sont des milieux mécaniquement résistants qui ne sont pas affaiblis par les minéraux lubrifiants comme le talc ou la serpentine et la déformation se produit principalement en milieu anhydre. Le premier profil de contrainte pour cette région est présenté et suggère une transition plastique-fragile à une profondeur d'environ 15 km<br>The St. Paul Transform System (SPTS) displays one of the most complex tectonic settings composed by four transform faults, three intra-transform ridge segments that offset by 630 km the Equatorial Mid Atlantic Ridge. This region is known by having unique mantle rocks exposed above the sea level, the St. Peter and St. Paul islets that are still rising. The SPTS shows a transition from a transpressive, hot spot affected, regional-scale shear zone to the North to a region dominated by a particular oceanic core complex spreading to the South. The tectonized samples collected along the whole transform system experienced pervasive deformation at both ductile and brittle conditions, and are grouped in ultramafic, mafic and intermediate mylonites. Ultramafic mylonites are porphyroblastic to porphyroclastic harzburgites with remnants of amphiboles equilibrated at granulite facies. Mafic mylonites are mainly porphyroclastic gabbros strongly transformed to amphibolites. Intermediate mylonites are talc-chlorite rich schist with composed by variable proportions of highly deformed and hydrated mafic and ultramafic rocks. All rocks have micrograin size groundmass, banded foliation and are overprinted by late low-T alteration.Geothermometry yield temperatures of equilibration between 700 and 900 °C for the peridotites and 700 to 850 °C for the gabbroic rocks. Major and trace element contents of the ultramafic mylonites plot in the depleted field of the abyssalperidotites originated by low degrees of fractional melting (up to 9%), however, they present marked LREE enrichment and Eu positive anomaly. Mafic and intermediate mylonites display REEenriched flat patterns (up to 100 x CI) and variable Eu anomalies. Rock-melt interaction is suggested for the enrichmentof the LREE for the peridotitic mylonites and hydrothermal fluids specifically for the overall REE enrichment of the serpentinized mylonites. These compositional characteristics suggest variable assimilation of N-MORB and E-MORB during mylonisis or early melt-rock interaction and hydrothermal evolution at variable metamorphic conditions. Transform faults are resistant and not weakened by lubricating minerals as talc or serpentine and the deformation takes place mainly under dry conditions. The first stress profile for this region is presented and suggests a deep Brittle Plastic Transition at depth of around 15 km
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Toy, Virginia Gail, and n/a. "Rheology of the Alpine Fault Mylonite Zone : deformation processes at and below the base of the seismogenic zone in a major plate boundary structure." University of Otago. Department of Geology, 2008. http://adt.otago.ac.nz./public/adt-NZDU20080305.110949.
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The Alpine Fault is the major structure of the Pacific-Australian plate boundary through New Zealand�s South Island. During dextral reverse fault slip, a <5 million year old, ~1 km thick mylonite zone has been exhumed in the hanging-wall, providing unique exposure of material deformed to very high strains at deep crustal levels under boundary conditions constrained by present-day plate motions. The purpose of this study was to investigate the fault zone rheology and mechanisms of strain localisation, to obtain further information about how the structural development of this shear zone relates to the kinematic and thermal boundary constraints, and to investigate the mechanisms by which the viscously deforming mylonite zone is linked to the brittle structure, that fails episodically causing large earthquakes.
This study has focussed on the central section of the fault from Harihari to Fox Glacier. In this area, mylonites derived from a quartzofeldspathic Alpine Schist protolith are most common, but slivers of Western Province-derived footwall material, which can be differentiated using mineralogy and bulk rock geochemistry, were also incorporated into the fault zone. These footwall-derived mylonites are increasingly common towards the north.
At amphibolite-facies conditions mylonitic deformation was localised to the mylonite and ultramylonite subzones of the schist-derived mylonites. Most deformation was accommodated by dislocation creep of quartz, which developed strong Y-maximum crystallographic preferred orientation (CPO) patterns by prism (a) dominant slip. Formation of this highly-oriented fabric would have led to significant geometric softening and enhanced strain localisation. During this high strain deformation, pre-existing Alpine Schist fabrics in polyphase rocks were reconstituted to relatively well-mixed, finer-grained aggregates. As a result of this fabric homogenisation, strong syn-mylonitic object lineations were not formed. Strain models show that weak lineations trending towards ~090� and kinematic directions indicated by asymmetric fabrics and CPO pattern symmetry could have formed during pure shear stretches up-dip of the fault of ~3.5, coupled with simple shear strains [greater than or equal to]30. The preferred estimate of simple:pure shear strain gives a kinematc vorticity number, W[k] [greater than or equal to]̲ 0.9997.
Rapid exhumation due to fault slip resulted in advection of crustal isotherms. New thermobarometric and fluid inclusion analyses from fault zone materials allow the thermal gradient along an uplift path in the fault rocks to be more precisely defined than previously. Fluid inclusion data indicate temperatures of 325+̲15�C were experienced at depths of ~45 km, so that a high thermal gradient of ~75�C km⁻� is indicated in the near-surface. This gradient must fall off to [ less than approximately]l0�C km⁻� below the brittle-viscous transition since feldspar thermobarometry, Ti-inbiotite thermometry and the absence of prism(c)-slip quartz CPO fabrics indicate deformation temperatures did not exceed ~ 650�C at [greater than or equal to] 7.0-8.5�1.5 kbar, ie. 26-33 km depth.
During exhumation, the strongly oriented quartzite fabrics were not favourably oriented for activation of the lower temperature basal(a) slip system, which should have dominated at depths [less than approximately]20 km. Quartz continued to deform by crystal-plastic mechanisms to shallow levels. However, pure dislocation creep of quartz was replaced by a frictional-viscous deformation mechanism of sliding on weak mica basal planes coupled with dislocation creep of quartz. Such frictional-viscous flow is particularly favoured during high-strain rate events as might be expected during rupture of the overlying brittle fault zone. Maximum flow stresses supported by this mechanism are ~65 Mpa, similar to those indicated by recrystallised grain size paleopiezometry of quartz (D>25[mu]m, indicating [Delta][sigma][max] ~55 MPa for most mylonites). It is likely that the preferentially oriented prism (a) slip system was activated during these events, so the Y-maximum CPO fabrics were preserved. Simple numerical models show that activation of this slip system is favoured over the basal (a) system, which has a lower critical resolved shear stress (CRSS) at low temperatures, for aggregates with strong Y-maximum orientations. Absence of pervasive crystal-plastic deformation of micas and feldspars during activation of this mechanism also resulted in preservation of mineral chemistries from the highest grades of mylonitic deformation (ie. amphibolite-facies).
Retrograde, epidote-amphibolite to greenschist-facies mineral assemblages were pervasively developed in ultramylonites and cataclasites immediately adjacent to the fault core and in footwall-derived mylonites, perhaps during episodic transfer of this material into and subsequently out of the cooler footwall block. In the more distal protomylonites, retrograde assemblages were locally developed along shear bands that also accommodated most of the mylonitic deformation in these rocks. Ti-in-biotite thermometry suggests biotite in these shear bands equilibrated down to ~500+̲50�C, suggesting crystal-plastic deformation of this mineral continued to these temperatures. Crossed-girdle quartz CPO fabrics were formed in these protomylonites by basal (a) dominant slip, indicating a strongly oriented fabric had not previously formed at depth due to the relatively small strains, and that dislocation creep of quartz continued at depths [less than or equal to]20 km. Lineation orientations, CPO fabric symmetry and shear-band fabrics in these protomylonites are consistent with a smaller simple:pure shear strain ratio than that observed closer to the fault core (W[k] [greater than approximately] 0.98), but require a similar total pure shear component. Furthermore, they indicate an increase in the simple shear component with time, consistent with incorporation of new hanging-wall material into the fault zone. Pre-existing lineations were only slowly rotated into coincidence with the mylonitic simple shear direction in the shear bands since they lay close to the simple shear plane, and inherited orientations were not destroyed until large finite strains (<100) were achieved.
As the fault rocks were exhumed through the brittle-viscous transition, they experienced localised brittle shear failures. These small-scale seismic events formed friction melts (ie. pseudotachylytes). The volume of pseudotachylyte produced is related to host rock mineralogy (more melt in host rocks containing hydrated minerals), and fabric (more melt in isotropic host rocks). Frictional melting also occurred within cataclastic hosts, indicating the cataclasites around the principal slip surface of the Alpine Fault were produced by multiple episodes of discrete shear rather than distributed cataclastic flow. Pseudotachylytes were also formed in the presence of fluids, suggesting relatively high fault gouge permeabilities were transiently attained, probably during large earthquakes. Frictional melting contributed to formation of phyllosilicate-rich fault gouges, weakening the brittle structure and promoting slip localisation. The location of faulting and pseudotachylyte formation, and the strength of the fault in the brittle regime were strongly influenced by cyclic hydrothermal cementation processes.
A thermomechanical model of the central Alpine Fault zone has been defined using the results of this study. The mylonites represent a localised zone of high simple shear strain, embedded in a crustal block that underwent bulk pure shear. The boundaries of the simple shear zone moved into the surrounding material with time. This means that the exhumed sequence does not represent a simple 'time slice' illustrating progressive fault rock development during increasing simple shear strains. The deformation history of the mylonites at deep crustal P-T conditions had a profound influence on subsequent deformation mechanisms and fabric development during exhumation.
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Orndorff, William D. "Crystalline bedrock geology of the lower Susquehanna Gorge: Conowingo to Havre de Grace, Maryland." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36167.
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Jackson, Christopher. "A microstructural kinematic study of selected shear zones in the Hartbees River Thrust Belt, northeastern Namaqua Tectonic Province." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005588.
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The Hartbees River Thrust Belt (HRTS) is a 40-60 km wide, southwest-vergent zone of complex structure, lithostratigraphy and high-grade metamorphism in the northeastern part of the mid-Proterozoic Namaqua Tectonic Province. The HRTS comprises the boundary zone separating the Bushmanland and Gordonia Subprovinces of the Namaqua Province. A knowledge of the movement histories of major ductile shear zones within the HRTS is fundamental to understanding the tectonic development of the belt, and Namaqua tectogenesis as a whole. In spite of this, no detailed microstructural kinematic studies have been attempted and the movement histories and age relationships of these shear zones have not been described in detail. This thesis represents a detailed microstructural kinematic study of a representative suite of orientated samples of mylonitic rocks, collected from five ductile shear zones within the HRTS. These shear zones include the Neusspruit Lineament, the Kakamas shear zone (KSZ), the Hugosput shear system (HSS), the Rozynenbosch-Ganzenmond shear zone (RGSZ) and the Graafwater shear system (GSS). Accepted modern methods of microstructural kinematic analysis were applied to samples of mylonite from these shear zones, in order to determine the precise orientation of the kinematic vectors, and the sense and relative ages of movements on each of the shear zones. Shear sense criteria, including composite SoC planar fabrics and shear band foliations, asymmetrical porphyroclast systems, mica-fish, oblique grain-shape and subgrain fabrics, asymmetrical microfolds, and the displacement of fractured rigid grains, together with a well-developed mylonite elongation lineation, conclusively indicate that SSW-directed thrusting occurred along the HSS, RGSZ, GSS and possibly along the Neusspruit Lineament, while normal, top-to-NE movements occurred on the Neusspruit Lineament, KSZ and HSS. Rare transposition criteria, and textural and paragenetic contrasts between syn-kinematic fabrics, strongly suggest that the phase of normal, top-to-NE movement seen in the northeastern HRTS shear zones is younger than the more widespread top-to-SW thrusting event. On the basis of mesoscopic structural criteria, SSW-directed thrusting is correlated with the D₂ deformation event in the HRTS. The mylonite zones have been refolded by ENE-SSW trending F₃ crossfolds, whose demonstrated coaxial relationship to the mylonite elongation lineation precluded reorientation of primary kinematic vectors. In the southwestern HRTS, primary thrust vectors have been reoriented by right-lateral, strike-slip shearing adjacent to the Pofadder Lineament during D₄. Simple shear dispersion of mylonite lineations related to normal movement, suggests that they too have been modified by D₄ shearing, and this constrains the timing of extensional movements to post-D₂ and pre- or syn-D₄. Syn-kinematic mineral assemblages, rheological criteria and the annealing states of the mylonites, provide insight into the thermotectonic evolution of the shear zones. A model is proposed in which the movement histories of shear zones within the HRTS are explained in terms of a typical orogenic cycle, involving crustal thickening by thrusting during a compressional orogenic phase, followed by collapse of the thickened crust during an extensional taphrogenic phase.
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MAUREL, Olivier. "L'exhumation de la Zone Axiale des Pyrénées orientales : Une approche thermo-chronologique multi-méthodes du rôle des failles." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2003. http://tel.archives-ouvertes.fr/tel-00003429.
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La structuration de la Zone Axiale des Pyrénées Orientales est le résultat d'une évolution thermique et tectonique complexe depuis plus de 300 Ma, synthétisée dans le premier chapitre de ce mémoire. Dans le but de mieux appréhender cette évolution à l'échelle des différents massifs de cette Zone Axiale, une approche thermochronologique multi-méthodes (U-Pb, 40Ar/39Ar, traces de fission et (U-Th)/He) a été mise en œuvre afin de dater et quantifier les processus thermiques et mécaniques qui participent à leur exhumation (Second chapitre). L'activité essentiellement alpine de la faille de la Têt fait l'objet du troisième chapitre, par la reconstitution de l'histoire thermique des massifs du Canigou et de Mont-louis, respectivement au mur et au toit de la faille. Un réchauffement généralisé du socle gneissique du Canigou au Crétacé moyen-supérieur, une exhumation du massif de Mont-Louis synchrone des chevauchements pyrénéens éocènes et une surrection importante du Canigou lors de la phase extensive oligo-miocène sont les principaux résultats obtenus. Le quatrième chapitre fait état des données thermochronologiques obtenues sur les massifs de Saint-Laurent et des Albères qui attestent également d'une exhumation différentielle au cours du cycle alpin. La datation 40Ar/39Ar par sonde laser des mylonites jalonnant les zones de failles globalement E-W à NW-SE qui parcourent l'ensemble de la chaîne pyrénéenne fait l'objet du cinquième chapitre. Une importante phase de recristallisation statique d'âge crétacé moyen à supérieur se localise sur ces zones mylonitiques probablement en partie héritées de l'histoire hercynienne de la Zone Axiale. Une déformation ductile globalement chevauchante vers le Sud et relativement froide (< 400°C), que nous relions à l'événement compressif pyrénéen s.s., a été datée à 58 Ma sur l'accident de Mérens et à 38 Ma sur celui du Boulou-Le Perthus, ce qui témoigne de la pérennité du régime compressif. Pour conclure, l'ensemble des données a été replacé dans un cadre général d'évolution de la chaîne des Pyrénées. L'utilisation de plusieurs thermochronomètres pour l'établissement des chemins température-temps nous a permis de mieux tester la validité des âges obtenus et de discuter les causes possibles des quelques incohérences observées dans l'enregistrement des principaux événements thermo-tectoniques.
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Degli, Alessandrini Giulia. "Deformation mechanisms and strain localization in the mafic continental lower crust." Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/12799.
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The rheology and strength of the lower crust play a key role in lithosphere dynamics, influencing the orogenic cycle and how plate tectonics work. Despite their geological importance, the processes that cause weakening of the lower crust and strain localization are still poorly understood. Through microstructural analysis of naturally deformed samples, this PhD aims to investigate how weakening and strain localization occurs in the mafic continental lower crust. Mafic granulites are analysed from two unrelated continental lower crustal shear zones which share comparable mineralogical assemblages and high-grade deformation conditions (T > 700 °C and P > 6 Kbar): the Seiland Igneous Province in northern Norway (case-study 1) and the Finero mafic complex in the Italian Southern Alps (case-study 2). Case-study 1 investigates a metagabbroic dyke embedded in a lower crustal metasedimentary shear zone undergoing partial melting. Shearing of the dyke was accompanied by infiltration of felsic melt from the adjacent partially molten metapelites. Findings of case-study 1 show that weakening of dry and strong mafic rocks can result from melt infiltration from nearby partially molten metasediments. The infiltrated melt triggers melt-rock reactions and nucleation of a fine-grained (< 10 µm average grain size) polyphase matrix. This fine-grained mixture deforms by diffusion creep, causing significant rheological weakening. Case-study 2 investigates a lower crustal shear zone in a compositionally-layered mafic complex made of amphibole-rich and amphibole-poor metagabbros. Findings of case-study 2 show that during prograde metamorphism (T > 800 °C), the presence of amphibole undergoing dehydration melting reactions is key to weakening and strain localization. Dehydration of amphibole generates fine-grained symplectic intergrowths of pyroxene + plagioclase. These reaction products form an interconnected network of fine-grained (< 20 µm average grain size) polyphase material that deforms by diffusion creep, causing strain partitioning and localization in amphibole-rich layers. Those layers without amphibole fail to produce an interconnected network of fine grained material. In this layers, plagioclase deforms by dislocation creep, and pyroxene by microfracturing and neocrystallization. Overall, this PhD research highlights that weakening and strain localization in the mafic lower crust is governed by high-T mineral and chemical reactions that drastically reduce grain size and trigger diffusion creep.
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Ceccato, Alberto. "Structural Evolution of Periadriatic Plutons and its implications on solid-state deformation of granitoid rocks." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3427142.
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Exhumed granitoid plutons are an ideal natural research target for studying the processes of nucleation and evolution of ductile and brittle deformation structures. Granitoid plutons, unaffected by later tectono-metamorphic cycles, preserve pristine deformation structures developed during cooling from magmatic to host rock ambient temperatures, that can be assumed as representatives of structures that at different structural levels of the continental crust. The main focus of this Ph.D. project is the analysis of deformation structures of the Rieserferner pluton – one of the major Periadriatic intrusions. The aim of the study is two-fold: (i) reconstruct the tectonic framework during the different stages of the pluton structural evolution, and (ii) determine the processes controlling localized ductile strain at different scales and the environmental conditions at which they occurred.
The structural evolution during pluton cooling consists of 5 main deformation stages, that have been bracketed in time and thermal conditions according to microstructural and textural analysis, literature and field data: (i) steeply dipping joints, leucocratic dykes and quartz-feldspar veins and associated ductile shear zones; (ii) shallowly dipping joints with associated epidote and quartz veins and ductile shear zones; (iii) steeply dipping mafic dykes and calcite-white mica-bearing brittle-ductile faults; (iv) steeply dipping pseudotachylyte-bearing cataclastic faults; and (v) zeolite-bearing faults. Integrating new field, microstructural and geothermo-chronological data with published data we have related the deformation sequence to the Tertiary tectonics of the Eastern Alps. (i) three main ductile deformation stages developed during Oligocene, followed by two brittle deformation stages during Miocene; (ii) paleostress inversion from kinematic analyses suggest a complex stress field variation during the structural evolution mainly due to switch in relative magnitudes of principal stress components; (iii) the described paleostress evolution reflect the sequence of tectonic processes occurred during Oligocene and Miocene at the scale of the Eastern Alps, from slab break-off to indentation and lateral escape tectonics.
Microstructural investigations were mainly focused on the analysis of ductile shear zones exploiting epidote- and quartz-rich veins. Softening and localization in quartz veins was mainly controlled by grain size reduction by recrystallization. EBSD mapping and image analyses have shown that different crystallographic orientations of quartz vein crystals controlled the evolution of microstructures and crystallographic preferred orientations (CPO) during vein-parallel simple shear up to high shear strains ( ≈ 10). Recrystallization by Subgrain Rotation (SGR) lead to the development of fine-grained ultramylonitic quartz veins, in which, the observed CPO banding have been inherited from the original crystallographic orientation of the vein crystals. Localization of ductile strain within heterogeneous shear zones exploiting epidote veins was mainly obtained through myrmekite development and following shearing. EBSD investigations suggest that myrmekite induced a switch in the dominant deformation mechanism, from dynamic recrystallization by SGR to diffusion-assisted grain boundary sliding (GBS) during shearing of plagioclase + quartz aggregates.
Thermodynamic modelling was aimed to define the temperature-pressure-fluid conditions under which deformation these processes occurred. Pseudosections computed for the chemical systems NaCaKFMASHO and MnNaCaKFMASHO suggest that: (i) the epidote-veining event in the RFP likely occurred at temperatures between 520°C and 490°C at water-saturated conditions; (ii) the main deformation phase likely occurred at 460±40°C and 0.35 ± 0.05 GPa, lasting probably during pluton cooling down to 350°C at slightly under-saturated water-conditions.<br>I plutoni granitoidi esumati sono un target di ricerca ideale per la caratterizzazione dei processi di nucleazione e sviluppo delle strutture deformative sia duttili che fragili. I plutoni granitoidi sono corpi magmatici che per definizione, sono privi della moltitudine di strutture pervasive derivanti dagli intensi processi tettono-metamorfici che caratterizzano le rocce metamorfiche in generale. Per cui, le strutture deformative sviluppate durante il raffreddamento dei plutoni da condizioni magmatiche alle temperature della roccia incassante, sono preservate nei loro stadi incipienti. Tali strutture possono essere prese come esempio per lo sviluppo di strutture deformative a differenti livelli strutturali della crosta continentale. Il principale soggetto di ricerca trattato in questa tesi di dottorato è l'analisi delle strutture deformative del plutone di Vedrette di Ries – Rieserferner – una delle più importanti intrusioni Periadriatiche. Gli obbiettivi dell'analisi sono molteplici: (i) ricostruzione del contesto tettonico durante lo sviluppo dei diversi stage dell'evoluzione strutturale del plutone, e (ii) definizione dei processi alla base della localizzazione della deformazione duttile a varie scale e definizione delle condizioni alle quali questi processi avvengono.
L'evoluzione strutturale durante il raffreddamento e successiva esumazione del plutone delle Vedrette di Ries comprende 5 fasi principali di deformazione: (i) joint, filoni leucocratici e vene a quarzo-feldspato ad alto angolo e zone di taglio associate; (ii) joint a basso angolo e associate vene a quarzo e vene a epidoto e associate zone di taglio duttili; (iii)faglie duttili-fragili ad alto angolo, associate a mineralizzazione a calcite e mica bianca e all'intrusione di filoni mafici; (iv) faglie cataclastiche e pseudotachylyti ad alto angolo; (v) faglie cataclastiche a zeoliti. Tali fasi sono state vincolate in termini di temperature e cronologia assoluta in questo lavoro tramite la comparazione di analisi microstrutturali, dati di letteratura e dati di rilevamento geologico. Tale vincolo ci ha permesso di collegare l’evoluzione descritta con la tettonica del Terziario delle Alpi Orientali. I principali risultati del nostro lavoro possono essere così riassunti: (i) Tre fasi principali di deformazione duttile sono avvenute durante il raffreddamento del plutone nell’Oligocene; in seguito, due fasi fragili si sono sviluppate durante l’esumazione regionale nel Miocene; (ii) l'analisi della cinematica delle strutture e l'inversione del paleostress suggeriscono una variazione complessa del campo di sforzi, principalmente legato alla variazione delle intensità relative delle componenti principali di sforzo; (iii) l'evoluzione del paleostress riflette la sequenza di processi tettonici avvenuti durante l'Oligocene ed il Miocene alla scala delle Alpi Orientali, dai processi legati allo slab break-off, alla tettonica di indentazione e di estrusione laterale.
Le indagini microstrutturali sono state principalmente indirizzate all'analisi delle zone di taglio derivanti da vene a quarzo ed epidoto. I processi di softening e localizzazione nelle vene a quarzo sono principalmente controllati da processi di grain-size reduction per ricristallizzazione dinamica. Le analisi dei campioni raccolti tramite electron-backscattered diffraction (EBSD) ed analisi di immagine hanno mostrato che l'orientazione cristallografica dei cristalli di quarzo della vena hanno controllato l'evoluzione microstrutturale e dell'orientazione cristallografica preferenziale (CPO) durante la deformazione di taglio semplice parallela alla vena fino ad elevate deformazione (>10). La ricristallizzazione tramite subgrain rotation (SGR) ha portato allo sviluppo di vene di quarzo ultramilonitiche a grana fine, nelle quali, la struttura a bande della CPO è stata ereditata della orientazione cristallografica originale dei cristalli di vena. La localizzazione della deformazione duttile su zone di taglio eterogenee nucleate sulle vene a epidoto, invece, è stata principalmente ottenuta tramite lo sviluppo di myrmekiti e successiva deformazione. Analisi EBSD suggeriscono che lo sviluppo di myrmekiti ha indotto uno scambio nei processi di deformazione dominanti, dalla ricristallizzazione dinamica per mezzo di dislocation creep, a processi di diffusion-assisted grain boundary sliding durante la deformazione degli aggregati di plagioclasio + quarzo derivanti dalle myrmekiti.
La modellizzazione termodinamica ha permesso di definire le condizioni di pressione-temperatura-fluidi alle quali questi processi furono attivi. Le risultanti pseudosezioni calcolate per i sistemi chimici NaCaKFMASHO e MnNaCaKFMASHO suggeriscono che: la formazione delle vene ad epidoto avviene a temperature comprese tra 520°C e 490°C in condizioni di saturazione della fase fluida; (ii) la fase di deformazione principale probabilmente avviene a 460 ± 40 °C e 0.35 ± 0.05 GPa, perdurando durante il raffreddamento del plutone probabilmente fino a 350°C in condizioni di quasi-saturazione della fase fluida.
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Grotenhuis, Saskia Martine ten. "Mica fish in mylonites deformation mechanisms and implications for rheology /." [S.l. : s.n.], 2000. http://ArchiMeD.uni-mainz.de/pub/2001/0033/diss.pdf.
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Lamouroux, Christian. "Les mylonites des Pyrénées : classification, mode de formation et évolution." Toulouse 3, 1987. http://www.theses.fr/1987TOU30312.
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Les zones mylonitiques, trait majeur des pyrenees, appartiennent a deux familles principales: les zones longitudinales senestres ; les zones obliques dextres deformant les precedentes. L'analyse des materiaux permet de definir plusieurs types de mylonites dont la repartition au sein des zones ne presente aucune rythmicite. Leurs caracteres autorisent une classification avec la definition de: i) sequences de mylonites (mineralogie) ; ii) types mylonitiques dans chaque sequence en fonction de la valeur de la deformation et des processus de deformation actives pour un mineral-reference. Le mode de genese des zones necessite une analyse du contexte structural regional. Les zones mylonitiques obliques sont associees a des bandes de plis alpines a rotation interne senestre dont la partie centrale est occupee par un noyau peu deformable. Ces relations conduisent a relier leur formation a l'evolution de ces bandes. L'evolution de ces bandes de plis analysee en utilisant les resultats theoriques et experimentaux de ghosh et ramberg (1976) amene a proposer un schema d'evolution de la chaine
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Lamouroux, Christian. "Les Mylonites des Pyrénées classification, mode de formation et évolution /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376177993.
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NARUK, STEPHEN JOHN. "KINEMATIC SIGNIFICANCE OF MYLONITIC FOLIATION (METAMORPHIC)." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184087.
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Geometric analyses of three mylonite zones, including two metamorphic-core-complex SC-mylonite zones, show that the mylonitic foliation surfaces (S-surfaces) are consistently discordant to the margins of the shear zones. Finite-strain analyses show that the foliation surfaces in each zone are consistently oriented parallel to the XY-plane of the finite strain ellipsoid. The shear bands within the mylonites (C-surfaces, C'-surfaces, extensional crenulations, and shear-band cleavages) are uniformly oriented subparallel to the margins of the shear zones. The finite lengths and discontinuous natures of the shear bands require that the displacement along them be accommodated by the S-surfaces at the tips of the shear bands. Thus the S-surface elongations and orientations represent the total bulk rock strain, rather than some minimum measure of inter-C-surface strain. General stress and strain considerations indicate that the shear bands are planes of maximum shear stress, and that they are not only simple-shear slip planes. This interpretation implies that in simple-shear deformation, a single, irrotational set of shear bands will develop parallel to the shear-zone boundaries. In deformations involving significant components of coaxial strain, however, shear bands may develop in other orientations or in conjugate sets and rotate with progressive deformation.
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Prior, D. J. "Deformation processes in the Alpine Fault mylonites, South Island, New Zealand." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384072.
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Bürgi, Christoph. "Cataclastic fault rocks in underground excavations : a geological characterisation /." [S.l.] : [s.n.], 1999. http://library.epfl.ch/theses/?nr=1975.
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Wane, Ousmane. "Étude géologique du Birimien de la région de Massigui (Paléoprotérozoïque du Mali méridional) : la zone de cisaillement du Banifing, structure majeure du craton ouest-africain." Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10093.
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Le Degré Carré de Massigui (Mali Sud) est composé de roches métavolcano-sédimentaires et de grandes masses de roches plutoniques d’âge paléoprotérozoïque. Il est traversé par une zone de cisaillement d’échelle crustale qui se localise à l’interface du batholite de Massigui et des roches métavolcano-sédimentaires encaissantes. Cette zone de cisaillement est jalonnée de corps dioritiques et granitoïdiques. Sa compréhension représente un enjeu au niveau régional.Les roches paléoprotérozoïques sont peu affleurantes et la région est recouverte par d’abondantes formations latéritiques qui empêchent de voir les contacts entre les différents ensembles lithostructuraux et peu d’études géologiques fondamentales ont été faites sur la région malgré son fort potentiel minier. La compréhension de la géologie de la région requiert une approche multidisciplinaire alliant des travaux de terrain et en laboratoire (étude pétrostrucurale, observations microscopiques, géochimie des roches et des minéraux), utilisée dans cette thèse.Les données récoltés dans le cadre de cette thèse, indiquent une mise en place parentée des roches dioritiques et granitoïdiques qui jalonnent la zone de cisaillement du Banifing. Cette mise en place se fait à la faveur du fonctionnement de l’accident cisaillant du Banifing le long duquel se met en place une suite magmatique qui montre une évolution complète depuis les diorites jusqu’aux granites en passant par les monzodiorites et les granodiorites. Cette suite magmatique a été appelée suite plutonique du Banifing<br>The Massigui degree sheet (South Mali) is composed of metavolcano sedimentary rocks and large masses of plutonic rocks of Paleoproterozoic age. It is crossed by a shear zone of crustal scale, which is set up in the interface of the batholith and metavolcano sedimentary sequences. The shear zone is littered with bodies of dioritic and granitoid rocks. The understanding and studying of such matter have become a regional issue.Paleoproterozoic rocks don’t crop out well and the area is covered by abundant lateritic formations, which prevent us from seeing the contacts between different units and few academic geological studies have been done on the region despite its high mineral potential. The understanding of the geology of the region required a multidisciplinary approach combining both field work and laboratory, (e.g. petrostructural study, microscopic observations, geochemistry of rocks and minerals) which were undertaken in this thesis.The data collected as part of this thesis, indicate a fundamental link between dioritic rocks and granitoid that line the shear zone Banifing. This establishment is to support the functioning of the occurrence of shearing Banifing along magmatic suite implements, which shows a complete evolution from diorites to the granites through the monzodiorites and granodiorites. This suite has been called magmatic plutonic suite of Banifing
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Roth, Benjamin Louis. "Flow Properties of Moine Thrust Zone Mylonites in Northern Assynt, NW Scotland." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/46210.
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Quartz-rich mylonites present along the Moine Thrust Zone are well suited for the application of various analytical techniques designed for investigating the flow processes by which rock deformation occurred. These analytical techniques were applied to a suite of samples from the footwall and hangingwall of the Moine thrust exposed along the Allt Pol aâ Mhadaich stream located in the northern part of the Assynt window. Vorticity analyses were performed to determine the relative contributions of pure and simple shear deformation within the penetratively deforming thrust sheets. Integration of vorticity data with 3D strain analyses demonstrated that sub-vertical shortening perpendicular to the flow plane, accompanied by thrust transport parallel extension, occurred during mylonitization, and was driven by emplacement of the overlying Moine nappe. Quartz c-axis fabrics in the mylonites are characterized by well-defined asymmetric Type-1 cross girdles in which internal and external skeletal asymmetries are indicative of a top-to-the-WNW shear sense, compatible with regional thrusting. These c-axis fabrics were also used to estimate deformation temperatures. Differential flow stresses associated with mylonitization were estimated from the grain size of dynamically recrystallized quartz. Deformation temperature and flow stress data were then incorporated into a dislocation creep flow law for quartz to estimate strain rates. Finally, along strike variation in these flow properties at the base of the Moine nappe to the north and south of the APM section were investigated and results from the APM section compared with previously published studies of mylonites exposed in eastern Assynt that occupy similar structural positions.<br>Master of Science
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BOLOGNESI, FRANCESCA GIOVANNA. "Brittle deformation in phyllosilicate-rich mylonites: implications for failure modes, mechanical anisotropy, and fault weakness." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2015. http://hdl.handle.net/10281/69725.
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Phyllosilicates, even in relatively small quantities, dramatically influence the mechanical behavior of rocks. In laboratory triaxial tests on foliated rocks, for content in phyllosilicates greater than 20-25%, a relevant mechanical anisotropy appears, as the internal friction coefficient (tangential stress/normal stress at failure) varies between 0.3 and 0.7 with orientation of the sample with respect to the maximum compressive stress. This reflects different fracture modes: when the foliation is favorably oriented, fractures develop along it and the rocks are weak, whilst when fractures cut the foliation at a high angle, rocks are stronger.
This kind of mechanical anisotropy is one possible explanation for the relative and absolute fault weakness shown by non-Andersonian misoriented faults (i.e. faults with an orientation, with respect to the regional stress field, not fulfilling Anderson’s theory of faulting). Examples of misoriented faults are low angle normal faults (LANFs), high angle reverse faults and strike slip faults developed at a high angle with the most compressive regional stress axis.
In this thesis I have considered two field examples of misoriented faults represented by the Simplon Line Fault Zone (SFZ), in the Swiss Alps, and a zone of (ultra)cataclastic bands in the Grandes Rousses Massif of the French Alps (GRM). These structures have been characterized from the regional scale (paleostress), to the meso-scale (fault zone architecture), and micro-scale (optical microscope, SEM and micro-CT). Moreover, I have characterized the petrophysical properties and mechanical anisotropy of the GRM rocks with density, porosity, uniaxial (UCS) and triaxial (TXT) lab tests performed at the Environmental Science Centre of the British Geological Survey in Keyworth (Nottingham,UK).
Both fault zones have been involved in Alpine brittle deformations, which acted on rocks characterized by a pre-existing schistosity. The SFZ is a LANF developed in mylonitic phyllosilicate-rich paragneiss and orthogneiss, characterized by the alternation of anastomosing phyllosilicate films and quartz and feldspar lithons/layers. The schistosity is misoriented for brittle reactivation (high angle with respect to σ1), and its weakness is demonstrated by its brittle activation with the progressive development of cataclasites, which nucleate in the phyllosilicate levels.
Brittle deformation in the GRM micaschists, around the glacial plain of the Saint Sorlin Lakes, shows two different failure modes, depending on the schistosity orientation. For a σ1/foliation ẞ angle of ca. 80°, we observe the development of Andersonian conjugated fractures, with a stair-stepping failure path controlled by either [001] mica planes or brittle fractures crosscutting the more competent quartz and feldspar layers. With a ẞ angle of ca. 72° we observe no Andersonian fractures and the complete brittle activation of the schistosity, along which penetrative ultracataclastic seams are developed.
The mechanical characterization of GRM’s samples with UCS and TXT highlights the relationships between elastic moduli, peak strength, and failure modes, as a function of the ẞ angle. Peak strength follows a continuously varying anisotropy model, since we observe a progressive and continuous strength decrease from ẞ = 0° to ẞ = 45°, and a similarly smooth and continuous increase up to ẞ = 90°. If we consider the different failure modes, we can see a progressive transition from an Andersonian behavior (ẞ = 0° or 90°), a hybrid failure mode dominated by stair-stepping fractures, and a failure mode dominated by slip along phyllosilicate films (20° < ẞ < 70°).
Field and lab results evidence the primary role of phyllosilicate rich foliation in nucleation and development of fracturing and faulting.
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Dempsey, Edward Damien. "The kinematics, rheology, structure and anisotropy of the Alpine schist derived Alpine fault zone mylonites, New Zealand." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539562.
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Ebert, Andreas. "Microfabric evolution in pure and impure carbonate mylonites and their role for strain localization in large-scale shear zones /." Bern : Universität Bern, Philosophisch-naturwissenschaftlichen Fakultät, 2006. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Swanson, Erika M. "The Day Nui Con Voi mylonitic belt in Southwestern China and Its implications for the early Cenozoic extrusion of Indochina." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/114337.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2007.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 42-43).<br>The early Cenozoic India-Asia collision resulted in the extrusion of large crustal fragments southeast from the Eastern Himalayan syntaxis, with large shear zones at their boundaries that could have accommodated displacements of hundreds to perhaps a thousand kilometers. Along the northeastern edge of the Indochina extruded fragment, the belt of mylonitic metamorphic rocks generally referred to as the Ailao Shan/Red River shear zone forms the extrusion boundary. This shear zone actually consists of at least two belts, the Ailao Shan and the Day Nui Con Voi, which are separated by a narrow belt of unmetamorphosed Triassic sedimentary rocks. In the Chinese extension of the Day Nui Con Voi, the presence of sillimanite and garnet indicates the shear zone formed at amphibolite grade, and the mylonitic fabric defined by muscovite and biotite indicate left-lateral shearing. Ar/Ar cooling ages indicate the metamorphic rocks reached the cooling temperature of muscovite and biotite 26.07 ± 0.20 to 32.46 ± 0.25 Ma, ages that match those in the Day Nui Con Voi in north Vietnam. These data come from both the core orthogneiss of the shear zone as well as a narrow carapace of metasedimentary rocks of unknown age. Both rock units form an antiform in southern China that plunges below Triassic sedimentary rocks of South China. These relations show that: 1) the Day Nui Con Voi in China is the direct continuation of the same belt in north Vietnam, 2) the Day Nui Con Voi does not directly connect with the Ailao Shan shear zone, 3) the Day Nui Con Voi shear zone has a structural (?) cover of South China Mesozoic sedimentary rocks, 4) structural relations limit the amount of late stage left-lateral shear on the Indochina boundary, and 5) the structural relations require a more complex history for the shear zone along the NE boundary of the extruded Indochina crustal fragment than proposed by all earlier workers.<br>by Erika Swanson.<br>S.B.
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Hentschel, Felix [Verfasser], and Claudia [Akademischer Betreuer] Trepmann. "Deformation and reactions in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window / Felix Hentschel ; Betreuer: Claudia Trepmann." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1205665196/34.
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Tu, Ching. "Mean kinematic vorticity of retrograde mylonite in the Brevard fault zone, South Carolina." 2009. http://etd.utk.edu/2009/May2009Theses/TuChing.pdf.
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Thesis (M.S.)--University of Tennessee, Knoxville, 2009.<br>Title from title page screen (viewed on Nov. 4, 2009). Thesis advisors: Robert D. Hatcher, Micah J. Jessup. Vita. Includes bibliographical references.
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Wang, Zhijing. "GIS-based fractal/multifractal modelling of texture in mylonites and banded sphalerite ores /." 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR46019.
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Thesis (Ph.D.)--York University, 2008. Graduate Programme in Earth and Space Science and Engineering.<br>Typescript. Includes bibliographical references (leaves123-134). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR46019
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Regan, Sean P. "Deciphering the Age and Significance of the Cora Lake Shear Zone: Athabasca Granulite Terrane, Northern Saskatchewan." 2013. https://scholarworks.umass.edu/theses/988.
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Interpreting the tectonic significance of high strain zones requires detailed knowledge of the P-T-t-D history of rocks on either side and of tectonized rocks within the shear zone. In-situ monazite geochronology is particularly useful because it generates a time-integrated framework of metamorphism and fabric development. This can be achieved by correlating monazite compositional domains with the growth and consumption of major phases. Furthermore, monazite can be a fabric forming mineral, and can be directly linked to structural fabrics and kinematics. The Cora Lake shear zone (CLsz) represents a major lithotectonic discontinuity within the deep crustal Athabasca Granulite terrain, and preserves intense mylonitic to ultramylonitic fabrics. The 3-5 km wide CLsz strikes ~231°, and dips ~62° to the Northwest, has a moderately plunging stretching lineation (SW trend) with abundant sinistral kinematic indicators. These data indicate oblique extension with NW hanging wall down and to the SW relative to the SE footwall. The NW hangingwall is dominated by the ca. 2.6 Ga charnockitic Mary batholith. The southeastern footwall is primarily underlain by the heterogeneous ca. 3.3-3.0 Ga Chipman tonaite straight gneiss. Although both share common Archean (ca. 2.55 Ga) and Paleoproterozoic (ca. 1.9 Ga) deformation events, the style and P-T conditions of deformation are different. The earliest phase of deformation within the NW hangingwall consists of a penetrative subhorizontal flow fabric at 0.9 GPa and ~725°C (2.56 Ga), but folding in the SE footwall associated with the development of a strong upright axially planar fabric at 1.35 GPa and 850°C. Deformation at ca 1.9 Ga was characterized by upright folding, similar in orientation, in both hangingwall (0.9 GPa; 725°C) and footwall (1.17 GPa; 825°C). Deformation related to the CLsz occurred at 1880 Ma (0.9-1.06 GPa; ~775°C), and is responsible for juxtaposing two levels of lower crust. The Cora Lake shear zone is interpreted to be the culmination of a trend of increased strength, localization, strain partitioning, and vertical coupling. Furthermore, the CLsz overprints fabrics from each wall, marks the development of a major lateral lithotectonic discontinuity, and an introduction of major structural and compositional heterogeneity within the lower continental crust.
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Joye, Jean Bernard. "L'évolution pression-température-déformation dans le massif des Aiguilles Rouges, massif externe alpin." Phd thesis, 1989. http://tel.archives-ouvertes.fr/tel-00822947.
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L'analyse structurale de la géométrie et de la cinématique ainsi que le métamorphisme d'un secteur du massif des Aiguilles Rouges permettent de reconstruire l'évolution tectonométamorphlque du massif au cours de l'orogenèse varlsque. Cette évolution correspond à des événements orogéniques d'âge Dévonien et d'âge Carbonifère qui sont nettement distingués. Les événements d'âge Dévonien sont caractérisés par deux phases de déformation DI et D2. La schistoslté SI est relictuelle, préservée dans des mlcrolithons dans la schlstoslté S2. La déformation D2 se marque par une forte schistoslté S2 supportant une linéatlon d'étirement L2. De nombreux plis non-cylindriques P2 se développent. L'étude des microstructures indiquent une déformation non-coaxiale. Ces structures ont été acquises lors d'un mouvement tangentiel de sens S - N. Ces deux phases de déformation DI et D2 sont associées aux épisodes de métamorphisme MI et M2 qui sont continus dans le temps. M l, conservé dans des microlithons, marque le métamorphisme prograde. M2, l'épisode principal du métamorphisme, définit le métamorphisme rétrograde. L'établissement du chemin pression - température - temps - déformation (P-T-t-d) dans les paragneiss et les amphiboliles révèle un contexte géodynamique de collision continentale: épaississement crustal - remontée - érosion. Les événements d'âge Carbonifère (déformation D3) résultent principalement du fonctionnement d'une zone de cisaillement transcurrente dextre. L'ensemble des roches est déformé en mégaplis en échelon dextre très serrés dans le secteur étudié. La linéatlon d'étirement L2 est déformée dans ce mouvement en forme de sigmoïde. Le granite de Vallorcine s 'est mis en place dans cette zone de cisaillement à la fin de la déformation D3. L'évolution mise en évidence dans ce travail s'intrègre parfaitement dans le modèle actuel de la chaine varlsque.
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Singleton, John Selwyn. "Kinematic and geometric evolution of the Buckskin-Rawhide metamorphic core complex, west-central Arizona." 2011. http://hdl.handle.net/2152/14374.
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Reconstructing the structural evolution of metamorphic core complexes is critical to understanding how large-magnitude extension is accommodated in the middle to upper crust. This dissertation focuses on the Miocene geometric and kinematic evolution of the Buckskin-Rawhide metamorphic core complex in west-central Arizona, addressing controversial topics including the geometric development of mid-crustal shear zones, the formation of detachment fault corrugations, and the transition from detachment faulting to more distributed deformation. Detailed microstructural data from mylonites in the lower plate of the Buckskin-Rawhide detachment fault indicate that early Miocene mylonitization was characterized by consistent top-NE-directed shear and ~450-500°C deformation temperatures that varied by [less-than or equal to]50°C across a distance of ~35 km in the extension direction. The relatively uniform deformation conditions and strain recorded in mylonitized ~22-21 Ma granitoids are incompatible with models in which the lower plate shear zone represents the down-dip continuation of a detachment fault. Instead, lower plate mylonites initiated as a subhorizontal shear zone that was captured and rapidly exhumed by a moderately to gently dipping detachment fault system. Structural data and geologic mapping demonstrate that the prominent NE-trending Buckskin-Rawhide detachment fault corrugations are folds produced by extension-perpendicular (NW-SE) shortening during core complex extension. Dominant NE-directed slip on the detachment fault was progressively overprinted by NW- and SE-directed slip associated with corrugation folding. Orientation patterns of upper plate bedding across the corrugations are compatible with folding about a NE-trending axis. Extension-perpendicular shortening in the lower plate is recorded by synmylonitic constriction and folding. Upright m-scale and km-scale lower plate folds parallel the detachment fault corrugations and developed primarily by postmylonitic flexural slip that was coeval with detachment faulting. The total amount of NW-SE shortening across the lower plate is ~10%, but the amount of NW-SE shortening recorded by the younger detachment fault is only ~1%. The relatively late-stage development of corrugations in the Buckskin-Rawhide metamorphic core complex suggests that extension-perpendicular shortening was primarily driven by a reduction of vertical stresses through crustal thinning and tectonic denudation. Brittle fault data document the transition from large-magnitude, NE-directed extension to distributed E-W extension and right-lateral faulting. Following exhumation to brittle conditions, lower plate mylonites were extended up to ~20-30% by NE-dipping, syndetachment normal faults. Towards the end of detachment faulting, the extension direction rotated clockwise, and some portions of the Buckskin detachment fault record a transition from dominant top-NE slip to ENE- and E-directed slip. After detachment faulting ceased, E-W extension was accommodated primarily by steeply NE-dipping, right-lateral and oblique right-lateral-normal faults. The cumulative amount of right-lateral shear across the core complex is probably 7-9 km, which is the amount needed to restore the topographic trend of lower plate corrugations into alignment with the dominant extension direction. Postdetachment right-lateral/transtensional faulting across the Buckskin-Rawhide metamorphic core complex reflects the increasing influence of the Pacific-North American transform plate boundary towards the end of the middle Miocene.<br>text
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Simpson, C. A. "Constraints on Proterozoic crustal evolution from an isotopic and geochemical study of clastic sediments of the Gawler Craton, South Australia." Thesis, 1994. http://hdl.handle.net/2440/88297.
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This item is only available electronically.<br>The Gawler Craton comprises tocks varying in age from Archaean to more recent Phanerozoic sediments. The rocks of greatest interest in defining processes of early crustal formation and evolution in the Australian continent, are the basement material older than approximately 1400 Ma (pre-cratonisation), comprising deformed and metamorphosed rocks suites of Archaean and Proterozoic metasediments and gneisses. These suites span an immense period of intense geological history, and as such are a topic of much past and present study.
Detailed mapping in the Tumby Bay region of eastern Eyre Peninsula outlines stratigraphic and structural evolution of a sequence of Proterozoic rock suites, these are proposed to be related to other recognised deformation episodes elsewhere within the Gawler Craton, thus regional correlation is inferred. A new theory for development of two lineations within the map region is postulated by two movement directions along the Kalinjala Mylonite Zone.
Geochemically the Proterozoic sediments of the Gawler Craton are similar to upper crustal average values of Taylor & McClennan (1985). However, characteristic depletions in Nb and Sr are recognised. Consistency in trace element compositions for Archaean and Proterozoic samples would suggest recycling of older Archaean crust into Proterozoic sediments and granitoids. Analysis of representative trace element ratios and indices of alteration and weathering suggest some change in geochemistry throughout the Proterozoic period.
Selected Proterozoic elastic sedimentary suites were geochemicaly and isotopically (Sm-Nd) analysed, with the data being presented within this thesis. The most interesting of these being the Pandurra Formation, red-bed sediments deposited within the north-eastern Stuart Shelf region of the Gawler Craton. These sediments exhibit a change in measured isotopic values, with younger epsilon neodymium (ENd), and higher Sm/Nd ratios observed (ENd(O) = -14.67, Sm/Nd = 0.2441), than typical older Gawler Craton rocks (average Proterozoic sediments ENd(O) = -21.85, Sm/Nd = 0.1847). This isotopic shift is also recognised within the Adelaide Fold Belt to the east of the Gawler Craton (average shales ENd(O) = -16.20, Sm/Nd = 0.1942). A source for these younger signatures is not recognised within the Gawler Craton, and therefore more distal province sources, OR isotopic alteration in the originally considered 'robust' Sm-Nd isotopic system, are proposed.<br>Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 1994
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Kopf, Christopher Frederick. "Deformation, metamorphism, and magmatism in the East Athabasca mylonite triangle, northern Saskatchewan: Implications for the Archean and Early Proterozoic crustal structure of the Canadian Shield." 1999. https://scholarworks.umass.edu/dissertations/AAI9932323.
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The East Athabasca mylonite triangle (EAMT) is a well exposed region of granulite facies mylonitic rocks along the trace of the Snowbird tectonic zone in northern Saskatchewan. The region was deformed and metamorphosed in a lower crustal shear zone during an episode of intense magmatic intrusion and advective heating at 2.6 Ga. The EAMT can be divided into three major domains which are remarkably different in rock type, structural fabric orientation, and metamorphic history. Rocks in the southeastern domain consist mainly of early tonalitic gneisses and syntectonic mafic dikes that were metamorphosed at approximately 1.0 GPa and 700–800°C. The northwestern domain contains numerous syntectonic felsic and mafic intrusions which record metamorphic conditions of approximately 0.9 GPa, 700–800°C during cooling from higher igneous temperatures. Metamorphism in both of these domains appears to have occurred during localized heating and deformation associated with voluminous additions of new magma to an isostatically stable region of the lower crust. The third domain is dominated by highly deformed felsic gneisses in the north and overlying mafic intrusions in the south. The mafic rocks intruded during 2.6 Ga thermotectonism, possibly as part of a larger mafic underplate of the lower crust. They preserve spectacular coronitic growths of clinopyroxene, orthopyroxene, plagioclase and garnet that formed during and subsequent to 2.6 Ga deformation. Consistent reaction textures in the mafic rocks suggest that the corona assemblages developed during early deformation at 1.1–1.2 GPa and 750°C, followed by rapid heating to greater than 900°C (and possible decompression) during juxtaposition with the northeastern and southwestern domains. Late symplectite assemblages record retrograde conditions of 0.7–0.8 GPa and 700°C during rapid decompression of the zone during a previously unknown Early Proterozoic uplift event. This metamorphic sequence sets the mafic rocks apart from the felsic gneisses which record earlier high P-T metamorphism above 1000°C and 1.6 GPa. The metamorphic history of the mafic rocks reflects a significant thermal and magmatic event within the lower crust at 2.6 Ga, similar to that recorded in the southeastern and northwestern domains. All three domains show almost no affect of Early Proterozoic metamorphism or deformation. The intense episode of 2.6 Ga metamorphism and magmatism recorded in the East Athabasca mylonite triangle is not preserved in the adjacent regions of the Hearne and Rae Archean provinces. Extensive Archean granite-greenstone belts in the Hearne province suggest the presence of a sharp metamorphic boundary east of the EAMT. Rocks of the western Rae province are marked by domains of felsic intrusions and high metamorphic grade gneisses separated by steeply dipping shear zones. One domain in the Neil Bay region of Lake Athabasca records an intense period of deformation, magmatism, and high temperature metamorphism similar to that preserved in the EAMT, but at 1.9 rather than 2.6 Ga. The domainal partitioning of metamorphic and magmatic events among shear-zone-bounded regions may indicate the existence of a block-style architecture in the lower crust of the Canadian Shield similar to that proposed for the middle crustal terranes of the American southwest.
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Cao, Shuyun. "Cenozoic tectonic deformation, thermochronology and exhumation of the Diancang Shan metamorphic massif along Ailao Shan-Red River shear zone, southeastern Tibet, China." Thesis, 2010. http://hdl.handle.net/11858/00-1735-0000-0006-B2FA-8.
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Pollard, Brittney Maryah. "Reactivation of fractures as discrete shear zones from fluid enhanced reaction softening, Harquahala metamorphic core complex, west-central Arizona." Thesis, 2014. http://hdl.handle.net/2152/25744.
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Discrete (mm- to m-scale) mylonitic shear zones in the northeastern Harquahala metamorphic core complex, Arizona, show evidence of fluid-mineral interactions catalyzing deformation and metamorphism. Many contain a deformed central epidote vein with adjacent bleached haloes and flanking paired shear zones that indicate significant fluid-rock interaction during deformation. An integration of structural and geochemical methods was employed to understand timing, metamorphic conditions, and physiochemical processes responsible for producing the discrete shear zones. Field and microstructural evidence suggest the zones initiated on antecedent fractures. Electron backscatter diffraction (EBSD) analyses show a significant coaxial contribution to the shear, and quartz deformation predominately by prism <a> slip, along with some rhomb <a> slip, suggesting amphibolite-facies conditions during shearing. Fourier Transform Infrared spectroscopy analyses of quartz reveal higher water contents within shear zones than within country rocks, indicating fluid infiltration synchronous with shearing. Stable isotope analyses of quartz and feldspar from mylonites are consistent with an igneous or metamorphic fluid origin. Microstructural observations suggest that the zone morphology with epidote veins, bleached haloes, and flanking discrete paired shear zones was developed predominantly from reaction softening mechanisms. The increase in deformation from bleached rock to flanking shear zones is marked by progressive modal increases in biotite and myrmekite, and modal decreases in K-feldspar, and locally epidote and titanite. Myrmekitic textures recrystallized readily and resulted in progressively greater grain size reduction of feldspar, which aided in the progressive alignment and linkage of the biotite grains, which together concentrated the deformation in bands. Volume reduction resulting from some of the metamorphic reactions may have led to a positive feedback cycle among fluid infiltration, metamorphism and deformation. U-Pb isotope analyses of syn-metamorphic titanite yield an age of ~70 Ma, suggesting the shear zones formed during cooling of the Late Cretaceous (75.5±1.3 Ma) Brown’s Canyon pluton, consistent with their top-to-the-southwest sense of shear, rather than during top-to-the-northeast directed Miocene metamorphic core complex exhumation. Petrography, EBSD analyses, and U-Pb dating of titanite from other (non-discrete) mylonites in the area imply most formed synchronously with the discrete shear zone mylonites. Only rare, scattered mylonites show features consistent with metamorphic core complex exhumation.<br>text
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Grotenhuis, Saskia Martine ten [Verfasser]. "Mica fish in mylonites : deformation mechanisms and implications for rheology / Saskia Martine ten Grotenhuis." 2000. http://d-nb.info/96136288X/34.
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Stopen, Lynne E. "Geometry and Deformation History of Mylonitic Rocks and Silicified Zones Along the Mesozoic Connecticut Valley Border Fault, Western Massachusetts." 1988. https://scholarworks.umass.edu/theses/3525.
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The Connecticut Valley border fault is a major, probably listric, west-dipping normal fault, that uplifted Precambrian to Devonian schists and gneisses of the Pelham Dome on the east, and formed a lowland to the west where Triassic and Jurassic sediments accumulated. It extends from northwestern New Hampshire south to Long Island Sound. Five kilometers of vertical displacement, and dips of 20 to 40 degrees have been estimated for central Massachusetts.
Mylonitic and silicified rocks were examined from the Village of Millers Falls, in north-central Massachusetts, south to Belchertown, in central Massachusetts. Silicified rocks occur on the footwall of the fault in seven locations, and mylonitic rocks were studied in one location.
Mylonitic rocks involve protomylonite with small areas of rock that have characteristics of orthomylonite and ultramylonite. This indicates that some rocks were affected ally by the faulting process at depth in a ductile environment with heterogeneous strain rates. S - C fabrics (schistosite-cisaillement) within the mylonites indicate a west-side-down motion direction, supporting the usual observation that the border fault is a normal fault. The mylonites were cut by a cataclastic intrusion breccia which was subsequently mylonitized, developing an S-C fabric Similar to that in the host mylonite rock. Mylonites are indicative of low strain rates in a ductile regime, while cataclasites indicate higher strain rates. This suggests that the fault surface was not a smooth plane, but had irregularities that temporarily changed the strain rates imposed on the rocks.
Conditions nearer to the surfaces involved a brittle extensional environment where volumes of rock borderin the fault in the footwall were brecciated. The mylonites also were uplifted into the brittle regime. Joints, veins and minor normal faults were developed within the mylonites, cutting previous ductile features. Silicification occurred in the brecciated rock masses where hydrothermal fluids circulated through the fractured volumes of rock replacing primary metamorphic and igneous minerals with new minerals, primarily quartz.
Several groups of joints and veins within the silicified rocks have north-south strikes similar to the trend of the border fault in many areas. One style of joint strikes northeast to northwest, dips west, has a platy character, and appears to mimic the local fault plane orientation. Fluids that initially silicified the breccia masses also produced the quartz, and later, hematite veins in at least two subsequent hydrothermal pulses. Combined joint data show no conclusive evidence as to whether joint development and orientation was controlled by the geometry of the border fault, or by regional stresses. Combined vein data, however, show strong evidence that vein orientation was controlled by a regional stress field and not directly by border fault geometry. A mean strike for the veins of N15E suggests an extensional stress of N75W-S75E for the region at the time of vein formation. Extensional stresses of N60W-S60E and N68W-S68E have been estimated in previous studies for the Northfield basin and Amherst areas during the early Mesozoic. Vein formation was later and suggests that the regional stress field rotated counterclockwise over time.
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Trullenque, Ghislain. "Tectonic and microfabric studies along the Penninic Front between Pelvoux and Argentera massifs (Western Alps, France)." Phd thesis, 2005. http://tel.archives-ouvertes.fr/tel-00769805.
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