No description available.

Uplift of the Teton Range is primarily controlled by displacement across the range-front Teton normal fault. The Tetons comprise the footwall block while the hanging wall encompasses Jackson Hole valley and a portion of the Snake River. Relative to the rest of the Rocky Mountains, the Tetons experienced the majority of uplift very recently, substantiating the need for a detailed investigation integrating structural analysis and bedrock thermochronometry. New low-temperature cooling ages are documented in three vertical transects across the Teton Range and at low elevations parallel to the Teton fault. Samples adjacent to the Teton fault are consistently young (~9 Ma) and represent a minimum estimate for the onset of Teton fault-related uplift. Modeling of time-temperature histories supports a ~9-11 Ma onset of rapid uplift, indicating that the Teton fault likely originated as a Basin and Range-type structure. A maximum throw of ~8 km occurs proximal to the Grand Teton, while the average throw for the entire ~100 km along-strike fault length is ~3.3 km. Thus, the geometry of the Teton fault is comparable to traditional scaling relationships dictating a correlation between fault length and displacement. Inversion of the typical (U-Th)/He (AHe) and fission track (AFT) relationship in a few of the Teton Range samples is a result of intense zoning, primarily in apatite from Precambrian layered gneisses. Nonetheless, both the AHe and AFT ages consistently indicate slight differential uplift of the Tetons between the Late Oligocene and Middle Miocene. HeFTy models indicate that doming of the Precambrian-Paleozoic unconformity occurred prior to ~50 Ma. However, by ~15 Ma, rapid cooling of the Mount Moran section essentially "flattened" the unconformity. Thus, the modern domed shape is a result of displacement across the Teton fault, allowing the unconformity to be used as a proxy for fault deformation. Moreover, reconstruction of the unconformity and volume calculations produced an average depth to incision of ~0.3 km and a long-term erosion rate of 0.18 mm/yr. Compared to the long-term uplift rate of 0.22 mm/yr, this provides a quantitative explanation for the modern Teton topography. / Master of Science

The architecture and morphology of a mountain range is fundamentally controlled by the combination of rock uplift and distribution of precipitation. This relationship attributes fluctuations in climate to the erosion of orogens, sedimentation rates, and geodynamics of the crust. Glaciers are the most effective climate driven erosive processes, where the frequency of glacial periods has a direct impact on the structure of mountain ranges through time. The late Cenozoic global cooling period was the beginning of a series of many glaciations which increased erosion in orogens experiencing fast rock uplift. We characterize the threshold for the onset of effective glacial erosion and record the increase in erosion rate during the late Cenozoic in the Chugach and Kenai Mountains of Alaska. We utilized low temperature thermochronometry and cosmogenic dating to constrain the spatial and temporal distribution of exhumation and glacial history in order to characterize the net effect of glaciers on an orogen that experiences slow rock uplift. We constrain the spatial distribution of exhumation and characterize the landscape along the Kenai Peninsula, underlain by the transition from flat slab to normal subduction. The region is characterized by old AHe ages which mimic the subduction angle of the down going plate and decrease away from an exhumational hotspot at a syntax in the Chugach Mountains. We attribute the long term exhumational characteristic of the Kenai Peninsula to subduction and underplating of sediment shed from the accreting Yakutat microplate to the east. A delineation of the glacial history using 10Be cosmogenic dating depict a series of glacial advances which date to the early and late Wisconsin. We find that the asynchronuity of glaciation across maritime and continental Alaska is controlled by steep orographic precipitation gradients which result from upper plate deformation. Finally, we observe an increase in erosion since the late Cenozoic using both AHe and cosmogenic dating and conclude that it is possible for the onset of effective glacial erosion in regions that experience slow to moderate rock uplift and that climate drives erosion rates in these regions. / Ph. D. / The formation of mountain ranges is controlled by how fast they grow and the precipitation they receive. Fluctuations in climate change influence the architecture and erosion of the crust, especially in regions where there are glaciers. The beginning of global glacial activity approximately five million years ago, increased erosion in mountain ranges that experience fast growing rates. We characterize the effect of glaciers on mountain growth and record the related erosion in the Chugach and Kenai Mountains of Alaska. We used dating techniques to measure the spatial and temporal distribution of erosion in mountain ranges that grow slowly. We measured erosion rate variations in the Kenai Mountains, and discovered that erosion rate mimics the change in tectonic morphology along the subduction zone. The glacial history of the Chugach Mountains was delineated and shows a series of glacial advances from 50-14 thousand years ago. We found that the characteristics of the glacial advances were dependent upon the distribution of precipitation along the mountain ranges, and that the latest glacial ice age was dryer than older events. Finally, we observed an increase in erosion in the mountain ranges and concluded that it is possible for glaciers to effectively erode slowly growing mountains.

The Tatric crystalline unit of the Western Carpathians in northern Slovakia displays an inverted metamorphic sequence where high-grade migmatite and orthogneiss units are overlying lower-grade mica schists. Enclosed within the migmatites are lenses of eclogite-bearing amphibolites. Conventional geothermobarometry coupled with isochemical modeling constrained P-T paths that exhibit contrasting metamorphic histories for rock units that are now heterogeneously interleaved. Relict eclogite facies assemblages with occasionally preserved omphacite record post-peak pressure conditions of 1.7-1.8 GPa followed by near isothermal decompression at ~750 °C leading to intensive re-equilibration of eclogites at high-pressure granulite facies conditions and development of diopside + plagioclase symplectitic textures. New ID-TIMS Sm-Nd dating of garnet separated from the omphacite-bearing eclogite yields a whole rock-garnet isochron age of 337 ± 10 Ma, with an epsilon Nd isotopic composition of +8.3. While major element profiles across the garnets display little variation, the trace element distribution shows a typical HREE enrichment profile and a slight core to rim disparity with LREE and MREE concentrations higher in the cores and higher HREE in the rims. Granulite-facies migmatites that host the eclogite boudins record lower pressure metamorphic conditions of 1.2 GPa at ~750 °C and a similar retrograde path. The lower-grade micaschists reached metamorphic conditions of 0.8 GPa at ~650 °C. Monazite U-Pb analysis from a migmatite surrounding the eclogite boudins yields one population of ca. 380 Ma age. Another migmatite away from the eclogite yields two populations monazite ages. A robust 340 ± 11 Ma monazite U-Pb age is indistinguishable from our garnet age and U-Pb SIMS age of zircons in the anatectic leucosome of the migmatite (347 ± 7 Ma). We interpret the ca. 340 Ma ages to represent the exhumation of the deep crustal root of the Variscan orogen into the middle crust coeval with anatexis. A younger monazite U-Pb age of 300 ± 16 Ma is consistent with 40Ar/39Ar thermochronology data of ca. 310 Ma that is likely indicative of the Late Carboniferous I-type magmatism and cooling in the Tatric block. Cooling rates calculated by garnet diffusion modeling yield estimates of ~30 °/Ma. This exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid-crustal levels at a time coeval with anatexis and subsequently extruded with mid-crustal material to the upper crust.

The Tatric crystalline unit of the Western Carpathians in northern Slovakia displays an inverted metamorphic sequence where high-grade migmatite and orthogneiss units are overlying lower-grade mica schists. Enclosed within the migmatites are lenses of eclogite-bearing amphibolites. Conventional geothermobarometry coupled with isochemical modeling constrained P-T paths that exhibit contrasting metamorphic histories for rock units that are now heterogeneously interleaved. Relict eclogite facies assemblages with occasionally preserved omphacite record post-peak pressure conditions of 1.7-1.8 GPa followed by near isothermal decompression at ~750 °C leading to intensive re-equilibration of eclogites at high-pressure granulite facies conditions and development of diopside + plagioclase symplectitic textures. New ID-TIMS Sm-Nd dating of garnet separated from the omphacite-bearing eclogite yields a whole rock-garnet isochron age of 337 ± 10 Ma, with an epsilon Nd isotopic composition of +8.3. While major element profiles across the garnets display little variation, the trace element distribution shows a typical HREE enrichment profile and a slight core to rim disparity with LREE and MREE concentrations higher in the cores and higher HREE in the rims. Granulite-facies migmatites that host the eclogite boudins record lower pressure metamorphic conditions of 1.2 GPa at ~750 °C and a similar retrograde path. The lower-grade micaschists reached metamorphic conditions of 0.8 GPa at ~650 °C. Monazite U-Pb analysis from a migmatite surrounding the eclogite boudins yields one population of ca. 380 Ma age. Another migmatite away from the eclogite yields two populations monazite ages. A robust 340 ± 11 Ma monazite U-Pb age is indistinguishable from our garnet age and U-Pb SIMS age of zircons in the anatectic leucosome of the migmatite (347 ± 7 Ma). We interpret the ca. 340 Ma ages to represent the exhumation of the deep crustal root of the Variscan orogen into the middle crust coeval with anatexis. A younger monazite U-Pb age of 300 ± 16 Ma is consistent with 40Ar/39Ar thermochronology data of ca. 310 Ma that is likely indicative of the Late Carboniferous I-type magmatism and cooling in the Tatric block. Cooling rates calculated by garnet diffusion modeling yield estimates of ~30 °/Ma. This exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid-crustal levels at a time coeval with anatexis and subsequently extruded with mid-crustal material to the upper crust.

The Tatric crystalline unit of the Western Carpathians in northern Slovakia displays an inverted metamorphic sequence where high-grade migmatite and orthogneiss units are overlying lower-grade mica schists. Enclosed within the migmatites are lenses of eclogite-bearing amphibolites. Conventional geothermobarometry coupled with isochemical modeling constrained P-T paths that exhibit contrasting metamorphic histories for rock units that are now heterogeneously interleaved. Relict eclogite facies assemblages with occasionally preserved omphacite record post-peak pressure conditions of 1.7-1.8 GPa followed by near isothermal decompression at ~750 °C leading to intensive re-equilibration of eclogites at high-pressure granulite facies conditions and development of diopside + plagioclase symplectitic textures. New ID-TIMS Sm-Nd dating of garnet separated from the omphacite-bearing eclogite yields a whole rock-garnet isochron age of 337 ± 10 Ma, with an epsilon Nd isotopic composition of +8.3. While major element profiles across the garnets display little variation, the trace element distribution shows a typical HREE enrichment profile and a slight core to rim disparity with LREE and MREE concentrations higher in the cores and higher HREE in the rims. Granulite-facies migmatites that host the eclogite boudins record lower pressure metamorphic conditions of 1.2 GPa at ~750 °C and a similar retrograde path. The lower-grade micaschists reached metamorphic conditions of 0.8 GPa at ~650 °C. Monazite U-Pb analysis from a migmatite surrounding the eclogite boudins yields one population of ca. 380 Ma age. Another migmatite away from the eclogite yields two populations monazite ages. A robust 340 ± 11 Ma monazite U-Pb age is indistinguishable from our garnet age and U-Pb SIMS age of zircons in the anatectic leucosome of the migmatite (347 ± 7 Ma). We interpret the ca. 340 Ma ages to represent the exhumation of the deep crustal root of the Variscan orogen into the middle crust coeval with anatexis. A younger monazite U-Pb age of 300 ± 16 Ma is consistent with 40Ar/39Ar thermochronology data of ca. 310 Ma that is likely indicative of the Late Carboniferous I-type magmatism and cooling in the Tatric block. Cooling rates calculated by garnet diffusion modeling yield estimates of ~30 °/Ma. This exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid-crustal levels at a time coeval with anatexis and subsequently extruded with mid-crustal material to the upper crust.

In Rwanda, graves containing the bodies of those killed during conflict and the 1994 genocide hold great significance both for the Rwandan state and for individuals caught up in the violent conflicts that have troubled the country over the last century. The ruling Rwandan Patriotic Front (RPF) has initiated a national exhumation program, unearthing thousands of genocide victims. The exhumations are undertaken by genocide survivors and local community members who unearth the bodies, disarticulate the corpses, wash and layout the bones for re-internment together. The destruction of graves and/or the reconstruction of memorials takes place alongside this process, a transformation into collective spaces of genocide ‘remembrance’. My thesis interrogates these processes and considers a conundrum: in as much as these are revealing acts, making visible the horrors of a violent death, that also conceal and complicate. Understanding the multiple intentions behind this work requires a delicate unpacking of the everyday presence of uncertainty within Rwanda post-genocide and a careful consideration of the properties of materials through which troubling memories are made visible. These are inherently risky projects and thinking through the transformations that are enacted upon the recovered items invites fresh review of the potential for material remains of the dead to evoke destabilizing pasts or assist in the imagining of the future at a salient moment for Rwanda.

This study presents an integrated evaluation of the burial and thermal history of an exhumed (uplifted and eroded) basin, and investigates the implications for the evolution of reservoir quality of the Ordovician sandstone in the Illizi Basin, Algeria. Complementary techniques including sonic compaction analysis, apatite fission track analysis, thermal maturity analysis, fluid inclusion microthermometry, and sandstone petrography are integrated to provide calibration for burial and thermal history models and diagenetic forward modelling, in order to predict variations in sandstone reservoir quality across the study area. The Illizi Basin has been structurally modified due to multiple exhumation events, including the uplift of the Hoggar Massif, which resulted in exhumation of the flanking sedimentary basins over a distance of 1,500 km from north to south. This study presents new apatite fission track data and analyses that constrain the onset of major exhumation in the Illizi Basin to the Eocene with exhumation magnitudes estimated to be 1-1.4 km in the study area. The study area contains a multi trillion cubic foot gas-condensate accumulation within a large four way dip closure. Hydrocarbon generation occurred during two main phases in the Carboniferous and the Mesozoic, but ceased during Cenozoic exhumation. Due to the Cenozoic tilting of the Illizi Basin in response to the uplift of the Hoggar Massif to the south, the present-day structural trap is interpreted to have formed after the main hydrocarbon generation phases. Therefore, alternative charging mechanisms of this post-peak burial trap are required and explored. In addition, new fluid inclusion data provides evidence of a significant fluid flow event within the Illizi basin, triggered by Cenozoic exhumation. Brines hosted present-day in the Ordovician sandstone in the study area are shown to be genetically linked to Triassic-Liassic evaporites deposited over 400 km to the north. Overpressure dissipation during exhumation is proposed to be a potential driving mechanism for the late stage remobilization of deep brines. A major pre-drill risk in many North African Paleozoic plays relates to sandstone reservoir quality, largely due to extensive quartz diagenesis. The Ordovician reservoir in the study area is characterised through petrography and core analysis, and the impact of burial and thermal history on the reservoir quality is investigated through diagenetic forward modelling. Results indicate that facies and variations in thermal history are a major control on preserving reservoir quality. This study demonstrates the importance of integrating the burial and thermal history, depositional facies and diagenetic history during predictive reservoir quality studies, particularly in exhumed basins where the burial and exhumation history may be complex, and present-day depth or geometry is not indicative of the past. Methodologies and implications from this study could be applied to exhumed basins in general.

The Tatric crystalline unit of the Western Carpathians in northern Slovakia displays an inverted metamorphic sequence where high-grade migmatite and orthogneiss units are overlying lower-grade mica schists. Enclosed within the migmatites are lenses of eclogite-bearing amphibolites. Conventional geothermobarometry coupled with isochemical modeling constrained P-T paths that exhibit contrasting metamorphic histories for rock units that are now heterogeneously interleaved. Relict eclogite facies assemblages with occasionally preserved omphacite record post-peak pressure conditions of 1.7-1.8 GPa followed by near isothermal decompression at ~750 °C leading to intensive re-equilibration of eclogites at high-pressure granulite facies conditions and development of diopside + plagioclase symplectitic textures. New ID-TIMS Sm-Nd dating of garnet separated from the omphacite-bearing eclogite yields a whole rock-garnet isochron age of 337 ± 10 Ma, with an epsilon Nd isotopic composition of +8.3. While major element profiles across the garnets display little variation, the trace element distribution shows a typical HREE enrichment profile and a slight core to rim disparity with LREE and MREE concentrations higher in the cores and higher HREE in the rims. Granulite-facies migmatites that host the eclogite boudins record lower pressure metamorphic conditions of 1.2 GPa at ~750 °C and a similar retrograde path. The lower-grade micaschists reached metamorphic conditions of 0.8 GPa at ~650 °C. Monazite U-Pb analysis from a migmatite surrounding the eclogite boudins yields one population of ca. 380 Ma age. Another migmatite away from the eclogite yields two populations monazite ages. A robust 340 ± 11 Ma monazite U-Pb age is indistinguishable from our garnet age and U-Pb SIMS age of zircons in the anatectic leucosome of the migmatite (347 ± 7 Ma). We interpret the ca. 340 Ma ages to represent the exhumation of the deep crustal root of the Variscan orogen into the middle crust coeval with anatexis. A younger monazite U-Pb age of 300 ± 16 Ma is consistent with 40Ar/39Ar thermochronology data of ca. 310 Ma that is likely indicative of the Late Carboniferous I-type magmatism and cooling in the Tatric block. Cooling rates calculated by garnet diffusion modeling yield estimates of ~30 °/Ma. This exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid-crustal levels at a time coeval with anatexis and subsequently extruded with mid-crustal material to the upper crust.

No description available.