780 research outputs found
Pseudotachylytes in felsic lower-crustal rocks of the Calabrian Serre massif: A record of deep- or shallow-crustal earthquakes?
No full textPseudotachylytes (quenched frictional melts produced on a fault by seismic slip) in dry rocks exhumed from the mid-lower crust are potential indicators of earthquakes that either nucleated at, or propagated to, depths below the main shallow brittle-ductile transition zone. Establishing whether these pseudotachylytes effectively record deep-crustal earthquakes, or shallow-level earthquakes overprinting the mid-lower-crustal rocks during the exhumation path, may represent a major challenge. This challenge is mainly related to the fact that the mineral assemblage of a pseudotachylyte develops out of equilibrium during the coseismic thermal transient leading to melting and melt quenching. Here we investigate pseudotachylytes within peraluminous, sillimanite-garnet-rich, migmatitic paragneiss of the Serre Massif in Calabria (Southern Italy). These exhumed lower-crustal rocks experienced granulite-facies metamorphism (similar to 700-800 degree celsius; similar to 600-800 MPa), partial melting and dehydration during the late Variscan Orogeny (ca. 320-280 Ma). The crosscutting pseudotachylytes contain hercynite and sillimanite microlites, globular-shaped poikilitic cordierite and plagioclase, and rare cauliflower- to subhedral-shaped garnet. The pseudotachylytes are pristine, not affected by ductile deformation, recrystallisation or extensive alteration by fluid after their formation. A Rb-Sr isochron age of 51.4 +/- 5.1 Ma is obtained for the pervasively kinked biotite in the host rock immediately adjacent to the pseudotachylyte and associated with earthquake damage, while an age of 105.3 +/- 4.1 Ma is obtained for the undeformed host-rock biotite. This indicates that the granulites were cooler than the closing Rb-Sr temperature of biotite (ca. 300-400 degree celsius in the Cretaceous and that the studied pseudotachylytes formed by shallow seismic faulting. Therefore, sillimanite, hercynite, garnet, plagioclase, and cordierite all formed during quenching of the frictional melt well above the ambient temperature. Modelling of cordierite growth during melt quenching indicates that cordierite should have started to crystallise at T >900 degrees C to achieve the grain size (up to 10 mu m in diameter) observed in the pseudotachylyte. Modelling and microstructural observations allow the crystallisation sequence of microlites during melt cooling to be established. These microlites include cauliflower garnet which, in this case, did not develop in a deep-seated faulting context as commonly reported
Competition and Cooperation in the U.S. Liner Industry : A Case Study of the North Atlantic Trade Routes
No full textDTR557-P-80466RUEBEN KYLE MIDDLE TENNESSEE STATE UNIVERSITY, DEPARTMENT OF ECONOMICS AND FINANCE ADDL PLACE OF PUBLCATION: SPRINGFIELD, VA ADDL PUBLISHER: NATIONAL TECHNICAL INFORMATION SERVICE COVER TITLE SPONSORED BY THE U.S. DEPT. OF TRANSPORTATION, OFFICE OF THE SECRETARY OF TRANSPORTATION UNDER CONTRACT TO THE TRANSPORTATION SYSTEMS CENTER MARCH 1985 CONTRACT NO.: DTR557-P-80466 ADDL CORP. AUTHOR INFO: UNITED STATES. OFFICE OF THE SECRETARY OF TRANSPORTATION ADDL CORP. AUTHOR INFO: TRANSPORTATION SYSTEMS CENTER ADDL CORP. AUTHOR INFO: MIDDLE TENNESSEE STATE UNIVERSITY. DEPT. OF ECONOMICS AND FINANC
Trace-element geochemistry, isotopic and geochronological results from the Ridge Zone at the Burgundy Cu-Au Alkalic Porphyry Prospect, Golden Triangle, Northwestern British Columbia, Canada
No full textCritical raw materials (CRM) are key in the transition to green economies. Therefore, emphasis has been placed on the research of geologic deposits hosting economically significant amounts of CRM, such as alkalic porphyry deposits. As such, elucidating the characteristics of known alkalic porphyry deposits will aid in prospecting for this potentially CRM-rich deposit type.
The Burgundy prospect is a silica-undersaturated Cu-Au alkalic porphyry prospect located on the Enduro Metals’ Newmont Lake property in the Golden Triangle of British Columbia. In situ LA-ICP-MS trace-element mapping and sulfur isotope analyses of pyrite and chalcopyrite, along with in situ LA-ICP-MS Rb-Sr geochronology of biotite, provide a better understanding of the mineral paragenesis of mineralization at this poorly characterized prospect. Map results demonstrate that grain boundaries and fractures are enriched in trace-elements, indicating that Au, Ag, and CRM concentrations were upgraded by overprinting hydrothermal fluids. Sulfur isotope analyses of pyrite yield depleted rims (i.e., -6.2 ± 2.8‰; n = 62) and slightly more enriched cores (i.e., -4.2 ± 2.0‰; n = 34). Chalcopyrite grains yield marginally more enriched δ³⁴S values than pyrite (i.e., -3.9 ± 2.8‰; n = 169/172), but with no systematic rim and core zonation. Overall, the negative δ³⁴S values are indicative of sulfide mineralization from oxidized fluids. Results from Rb-Sr geochronology of biotite interpreted to be cogenetic with pyrite and chalcopyrite yield isochron dates ranging between 220.1 ± 1.2 and 196.6 ± 4.6 Ma. The youngest dates (197.8 ± 1.0 Ma and 196.6 ± 4.6 Ma) are interpreted to reflect late fluid alteration due to the chloritization of biotite in these samples. The remaining dates (220.1 ± 1.2 and 204.9 ± 1.2) are considered to record the timing of mineralization for the Burgundy prospect.
The results from this study indicate that mineralization in the Burgundy prospect occurred during infiltration of late, oxidized low-temperature hydrothermal-magmatic fluids between 220 to 205 Ma. The timing and sulfur isotope results are broadly similar to those of the nearby Galore Creek deposit and highlight the potential for discovering other alkalic porphyries in the Golden Triangle.Science, Irving K. Barber Faculty of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat
A structural and geochronological investigation of the Keno Hill area, central Yukon, Canada
No full textThe western margin of North America was shaped by the Cordilleran orogen. In the mid-Cretaceous, northeast-directed convergence resulted in compression-related structures that span the Cordillera, including the Selwyn thrust and fold belt in central Yukon. Bordering the Keno Hill area are two northwest-southeast extending thrust faults of the Selwyn thrust and fold belt. These faults are the Robert Service Thrust (RST), to the south, and the underlying Tombstone Thrust (TT), to the north. Previous detailed studies of the Keno Hill area have focussed on the late, brittle structures that host vein mineralization, leaving the structural evolution of the early, ductile structures largely unresolved. To investigate the geological evolution of the early structures, this study incorporates 1:25000 scale structural field mapping, microstructural analysis, and geochronology, including: c-axis crystallographic preferred orientation investigations, grain size piezometry, crystallographic vorticity axis investigations, in situ ⁸⁷Rb/⁸⁷Sr and ⁴⁰Ar/³⁹Ar geochronology, and Raman spectroscopy-based thermometry of carbonaceous materials. The in situ geochronology and thermometry investigations on weakly metamorphosed, clastic metasedimentary rocks from the hanging wall and footwall of the RST show a break across the approximate fault trace, with higher temperatures (>480 °C) and older dates in the hanging wall (130-102 Ma), with both the temporal and thermometry data showing a general decrease in the footwall, moving towards the approximate trace of the TT. This coincides with microstructural investigations which showed less grain boundary area reduction farther north. While the strain investigations did not show any obvious spatial or structural relationships, the area was dominated by predominantly non-coaxial constrictional strain. Contrary to other studies that have tried to date movement along the regionally extending thrust faults, the data could support that movement along the TT potentially continued until ca. 88 Ma as opposed to cessation ca. 100-104 Ma.Science, Irving K. Barber Faculty of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat
Structural evolution of the South Tibetan Detachment System in the Tsum Valley, Central Himalaya
No full textThe South Tibetan Detachment System (STDS) is a network of orogen-parallel, low-angle normal faults and shear zones traced along the entire length of the Himalayan orogen. It played a critical role in facilitating large-scale, normal-sense movement between the upper and middle crust during convergence. Despite its significance, key controls on the deformation processes of the STDS remain poorly understood. This study presents a time-resolved deformation history of the STDS in the Tsum Valley (Manaslu region, central Nepalese Himalaya), detailing its kinematics, deformation mechanisms, and stress history. In the Tsum Valley, the STDS is a ~2500 m wide zone of ductile deformation that includes Greater Himalayan Sequence (GHS) and Tethyan Sedimentary Sequence (TSS) rocks, without a discrete brittle detachment at higher levels. In situ Rb-Sr geochronology indicates that deformation and cooling within the STDS occurred between 17-13 Ma. Deformation occurred under monoclinic-dominant general shear flow. Distinct flow geometries between the rocks within the STDS and those at its boundaries imply that the boundary rocks record a different strain path, potentially linked to the onset of E-W extension in the region. STDS deformation was coupled with exhumation-driven cooling, resulting in the telescoping of isotherms from 500-600°C in the GHS to <400°C and then to <200-170°C in the TSS over ~1200m. Together with the kinematic data, deformation mechanisms indicate that the actively deforming portion of the STDS migrated to higher structural levels – from the silicate-rich GHS to the carbonate-rich TSS – during progressive shearing and cooling. In the GHS, high-temperature ductile shearing became more localized with increasing structural level, with deformation style transitioning from penetrative, involving all major minerals, to localized within quartz and mica layers/shear bands. In the TSS, marbles underwent dynamic recrystallization of calcite at high temperatures, transitioning to mechanical twinning during later stages of exhumation and cooling. The presence of carbonate rocks enabled deformation to persist in a ductile regime at relatively low temperatures and shallow crustal levels, without the formation of a discrete brittle structure. This study emphasizes that while structural level, depth, and temperature were significant factors, lithology was crucial in controlling the structural evolution of the Tsum Valley STDS.Science, Irving K. Barber Faculty of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat
Structural, geochronological, and metamorphic characterization of the Monashee décollement and its role in the tectonic evolution of the Canadian Cordillera
No full textThe Monashee décollement (MD) is a crustal-scale shear zone within the southern
Omineca belt of the Canadian Cordillera. The MD marks the contact between the autochthonous Precambrian basement core rocks of the Monashee metamorphic complex and the allochthonous rocks of the Lower Selkirk Allochthon. Both packages were metamorphosed at mid-crustal depths (>20 km) but are now exposed at ~ 2200 m elevation. The timing and style of deformation along the MD are disputed. Studies have proposed that the MD is: 1) the base of a mid-crustal ductile “channel”; 2) a complex normal-sense (top-to-the-west) extensional shear zone; or 3) a major reverse-sense (top-to-the-east) contractional shear zone that possibly forms
the basal detachment of the Rocky Mountain thrust and fold belt. This study was conducted to investigate those different interpretations through characterizing the detailed temperature-time deformation histories of the rocks within and adjacent to the MD at the Probity Peak field site, ~ 50 km northwest of Revelstoke, British Columbia. This was achieved through: 1) geological field mapping; 2) microstructural analyses of oriented thin sections; 3) quartz c-axis crystallographic preferred orientation (CPO) investigation and opening angle geothermometry; 4) titanium-in-biotite (Ti-in-Bt) geothermometry; and 5) titanite and monazite petrochronology. The data acquired from this study, combined with that from published literature indicate
that the MD was active as a reverse-sense contractional shear zone at Probity Peak between ca. 85-80 and 70-65 Ma. The MD was then crosscut by high-angle, brittle-ductile normal faults during extension between ca. 60 and 49 Ma. This extension facilitated exhumation of the Monashee Complex, which continued through Eocene time.Science, Irving K. Barber Faculty of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat
A reductive theory of justification and excuse
No full textLegal theorists commonly employ a distinction between justification defenses and excuse defenses, but there are significant theoretical disagreements about the nature of the distinction as well as about what the distinction entails. This dissertation is concerned with finding the best way to describe the distinction between the moral concepts of justification and excuse that underlie the concepts employed by legal theorists. Chapter 1 begins by examining moral defenses in general, with emphasis on their purpose, nature, function, and epistemology. Chapter 2 critically examines many of the traditional theoretical assumptions made about justification and excuse in the literature with the goal of winnowing them down to an uncontroversial core that can provide the foundation for a fuller, more specific account. Chapter 3 examines the ordinary language meaning of the words "justification" and "excuse" in order to identify any analytic constraints on what a correct theoretical account of justification and excuse may legitimately include. Finally, Chapter 4 offers and defends a reductive theory of justification and excuse which I call "the praise/blame theory." This theory identifies justified acts with those prima facie wrongful acts for which the actor is morally praiseworthy and excused acts with those prima facie wrongful acts for which the actor is merely not to blame. This simple account is consistent with the logical form of moral defenses, requires minimal elaboration on the terms' ordinary language content, avoids the conceptual mistakes that plague more traditional theories, and has the potential help resolve nagging theoretical issues in related fields.Ph.D.Includes bibliographical references (p. 232-241)by Kyle David Haide
Tectonometamorphic evolution of the Likhu Khola study area, east-central Nepal
No full textRecent models for the evolution of the Himalaya and adjacent regions have changed our understanding of how large mountain belts form. The key data that govern these models has largely been extracted from the exhumed mid-crustal core of the orogen, the Greater Himalayan sequence, and its bounding structures. Targeted mapping in the Likhu Khola region was carried out across the Greater Himalayan sequence as the initial phase of a project aimed to evaluate the viability of those models. The exhumed mid-crustal core in the study area exposes upper greenschist to upper amphibolite grade metamorphic rocks that have been pervasively deformed by ductile shearing. Mantled porphyroclasts and c, c’ and s fabrics record top-to-the-south directed shear. As with most transects across the Himalaya, metamorphic grade increases up structural section. Pressure and temperature estimates using THERMOCALC v.3.26 in average-PT mode with the internally consistent data set of Holland & Powell (1998) were conducted on eleven specimens at different structural positions. Temperatures increase slightly up structural section but become constant within error for the upper portion of the study area. Pressure estimates increase up structural section followed by an abrupt pressure decrease once partial-melting increases to form migmatitic rocks. This may indicate a potential tectonometamorphic discontinuity that separates two distinct domains that have different structural, thermal and metamorphic histories (e.g., Larson et al, 2010a; Yakymchuk and Godin, 2012). In situ U-Th-Pb Monazite geochronology was utilized on six of the specimens used for P-T analyses to constrain the P-T data. Multiple domains of ages were obtained ranging from 27.2 Ma to 15.1 Ma and are interpreted to represent several recorded metamorphic events. These metamorphic events are best interpreted in
ii
conjunction with the relative concentration of trace elements present at each U-Th-Pb data point that was collected using a split stream LA-MC-ICP-MS. More specifically, certain rare earth elements provide insight into whether garnet was growing, resorbing into melt or being homogenized at high temperatures during specific U-Th-Pb age dates. The relationships between metamorphism, crustal melting, P-T conditions and monazite/garnet growth and resorption are critical to evaluating if current models proposed for the evolution of the Himalaya are applicable in east-central Nepal
Little Shop of Horrors (2012)
No full texthttps://kent-islandora.s3.us-east-2.amazonaws.com/theatregallery/11/thumbnail.jpgDirected by: Tom Hitmar
Set Design: Tony E. Kovacic
Costume Design: Eileen Janis Larson
Actors: Kyle Merritt and company</p
Late Devonian shear zone reactivation in the Canadian Appalachian orogen
No full textAccretionary orogens are characterized by sequential collisions of buoyant crustal material with a continental margin or an oceanic arc. Because the timing, kinematics, and intensity of deformation are controlled by the obliquity of the collisions, pre-accretionary shape, and rheology of the accreted crustal material, it is often difficult to determine what processes controlled the generation or reactivation of shear zones not located in the immediate vicinity of a suture marking a collision. In the Canadian Appalachians, this problem is compounded by the lack of tectonic interpretation for the regional deformation occurring during the Late Devonian oblique collision of Meguma to composite Laurentia during the Neoacadian Orogeny.
To address these issues, this thesis targets the Eastern Highlands and Pocologan-Kennebecasis shear zones (Nova Scotia and New Brunswick, respectively) which were part of the composite margin of Laurentia at the time of the Neoacadian orogeny. Several characteristics of these shear zones are quantified including 1) the timing of deformation, through U-Pb and ⁴⁰Ar/³⁹Ar geochronology; 2) the kinematics based on field and thin section observations and quartz crystallographic preferred orientations; and 3) the potential impact of fluid-rock interaction on shear zone rheology. The new information from this work is combined with regional interpretation of aeromagnetic and gravimetric depth slices, and compilation of shear zone deformation ages and ⁴⁰Ar/³⁹Ar cooling ages to provide insight into the tectonic setting of the Neoacadian Orogeny. In the northern Appalachians, between the Late Devonian and Mississippian, regionally extensive NE-SW and ENE-WSW oriented shear zones were formed, or reactivated, with a dextral strike-slip shear sense consistent with a large-scale C-C’ system. Aeromagnetic and gravity geophysical data indicate that several of these structures are listric, and thus formed a lateral succession of transpressive and transtensive segments crosscut by antithetic sinistral shear zones. These structures appear to define a syntaxis in New England. ⁴⁰Ar/³⁹Ar age transects across the region outline Neoacadian cooling and exhumation that correlates spatially to an area of high paleo-elevation that was contemporaneous to the opening of the Maritimes and Catskills basins. Such a setting is similar to the present-day oblique collision of Yakutat terrane to Western North America.Science, Irving K. Barber Faculty of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat
- …
