During Jurassic and Cretaceous time deposition in the western interior basin was controlled by a combination of subduction-related dynamic subsidence and thrust-generated flexural subsidence. Changes in the angle of oceanic plate subduction along the western margin of North America and thrust deformation in the Cordillera governed the spatial and temporal influences of these mechanisms throughout basin history. Dynamic subsidence was the primary control on basin deposition during Early-Middle Jurassic and Late Cretaceous time. During these periods, shallow-angle oceanic plate subduction beneath the western margin of North America produced convective mantle circulation and long wavelength subsidence in the western interior. A cessation of dynamic subsidence during Early Cretaceous time, brought on by an increase in the angle of subduction, is partially responsible for the ∼20 m.y. unconformity that separates the Jurassic and Cretaceous sequences in the western interior. During Late Jurassic time, thrusting in the Cordillera resulted in flexural partitioning of the back-arc region. Statal geometries in the Upper Jurassic Morrison Formation in Utah and Colorado indicate deposition in the back-bulge and forebulge depozones of the Late Jurassic foreland basin system and suggest the coeval existence of a flexurally subsiding foredeep to the west. During Early Cretaceous time, >200 km of shortening in the thrust belt resulted in uplift and erosion of the Late Jurassic foredeep and the eastward migration of foreland-basin system flexural components. Areas occupied by the Late Jurassic forebulge were incorporated into the Early Cretaceous foredeep while the Late Jurassic back-bulge depozone became the location of the Early Cretaceous forebulge. In eastern Utah and western Colorado, migration of the forebulge enhanced the regional Early Cretaceous unconformity associated with the cessation of dynamic subsidence. During late Early Cretaceous time sediment accumulation across the entire foreland-basin system may have been facilitated by the reinitiation of dynamic subsidence in the western interior. During the Late Cretaceous, thrusting in the Cordillera resulted in continued flexural subsidence of the foredeep in east-central Utah. However, increased dynamic subsidence throughout Late Cretaceous time allowed thick accumulations of strata to be deposited in the forebulge and back-bulge depozones of the foreland-basin system.

Temporal-spatial evolution of the Central Andean foreland basin system relates directly to growth of the adjacent Andean orogenic belt during Late Cretaceous to Recent shortening. As the locus of shortening and crustal thickening propagated eastward, so too did the foreland basin system. Eastward growth of the orogenic wedge induced uplift and erosion of large portions of the basin, removing much of the detrital record of mountain building. Analyses of remnants of the Oligocene-Miocene foreland basin system in the Eastern Cordillera help define the kinematic evolution of the thrust belt in southern Bolivia. A series of north-trending depocenters, regarded collectively as a wedge-top depozone, evolved during growth of fold-thrust structures of the then-frontal part of the orogenic wedge. Growth strata and cross-cutting and onlapping relationships between contractional structures and synorogenic strata delineate the chronology of deformation. New 40Ar dates and published K-Ar dates define a minor Oligocene phase of west-vergent backthrusting followed by primarily east-vergent thrusting during Miocene time. These dates, combined with depositional histories, require synchronous and out-of-sequence thrust displacement during the Miocene. Depocenters are composed of alluvial-fan deposits on their flanks and lacustrine and braided-stream deposits in their axes. Most stratigraphic units are confined to individual depocenters, suggesting that streams rarely had sufficient power to cut across growing folds. An arid climate since ∼10-15 Ma may explain the preservation of large parts of the Late Cretaceous-Miocene foreland basin system in southern Bolivia. In contrast, northern Bolivia exhibited a humid climate over this time interval and most parts of any foreland basin were completely eroded. Critical taper theory suggests that rapid erosion in a humid fold-thrust belt may induce subcritical conditions in which thrust-front propagation is inhibited and internal deformation is promoted. An arid thrust belt may be expected to exhibit critical to supercritical conditions that favor thrust-front migration and in-sequence thrusting. Such phenomena are observed in Bolivia, suggesting that climate and erosion exert fundamental controls on the geometry and kinematics of the Andean orogenic belt.

Integrated analysis of whole-rock and mineral geochemical data from black shale and metamorphosed black shale demonstrates the importance of sulfides as trace-element hosts and reveals the influence of depositional environment on whole-rock and mineral chemistries. Detailed analysis of Fe-sulfide contents provides evidence of considerable elemental redistribution during diagenesis and metamorphism, indicating that such sulfides plausibly serve as a source of metals and other elements to epigenetic fluids. Spatial and temporal analysis of the distribution of Phanerozoic black shale, phosphorite, and ironstone suggests a related geologic origin coupled to marine upwelling. Organic-rich sedimentary rocks from diverse geologic settings in China, Canada, US Great Basin, and US Mid-Continent were studied along with regionally metamorphosed black shale (Maine) and contact metamorphosed carbonaceous argillite (Nevada). Assessment of whole-rock geochemistry in these samples was supplemented with analysis of a large geochemical database compiled from published sources. Both the studied sample suite and literature database reveal systematic elemental enrichments and depletions that can be related to depositional environment. Regionally metamorphosed black shale demonstrates trace-element loss with metamorphism (Au, As, and Sb), an observation that fits well with models proposing black-shale-derived mineralizing fluids. Compositional and textural features of sedimentary and metamorphic sulfides were investigated utilizing petrographic and in situ analysis methods. Concentrations of As, Se, Ni, Co, Cu, Zn, V, Cr, and Mo in sulfides were acquired by electron microprobe. Au, Pt, and sulfur isotope contents were measured in Fe-sulfide by SIMS. Fe-sulfide data demonstrate a complex history of pyrite growth due to diagenetic, metamorphic and hydrothermal processes. Sulfur isotopes reflect bacterially mediated growth of framboidal pyrite and redistribution of this sulfur with advanced diagenesis and metamorphism. Early framboidal pyrites are enriched in many trace metals. Later diagenetic and metamorphic pyrites are typically lower in trace metal content and demonstrate recrystallization to coarser crystals. Comparison of trace elements in framboidal and coarse overgrowth pyrites shows systematic elemental changes (losses: Au, Pt, Ni, Cu, Zn, V and Cr; gains: Se; variable: As and Mo). This pattern is found in many black shales, regardless of bulk chemistry or depositional environment. Metamorphic replacement of pyrite by pyrrhotite results in similar losses from the sulfide fraction of the rock. Mass balance of the whole-rock trace inventory indicates that Fe-sulfide is an important host for As, Se, Ni, Co, and Au. These mass balance results, combined with evidence of trace element redistribution during diagenesis and metamorphism, point to a possible sourcing of metals, sulfur and other elements from black shale.

The purpose of this dissertation is to explore the physical possibility of ancient glacial occurrences on the surface of Mars. Furthermore, I will elucidate the nature and extent of hypothetical ice sheets by modeling the ancient glacier inferred for the Hellas region. Individually, many of the proposed glacial features can indeed be interpreted as aeolian, fluvial, or another type of feature. It is, however, the spatial and temporal association of these features, and the incongruity presented by various alternative explanations, that makes the glacial theory more complete and universal than other hypotheses. The proposed glacial system has an extent on the order of two million square kilometers. My results include profiles of the Hellas glacier. In addition, calculations of erosion rates seem to imply an approximate time scale of erosion of between 110,000 and 1,440,000 years. Taking into consideration the plausible range of geothermal flux values (32 to 72 mW/m² I have also calculated the time frames to fill the Hellas pro-glacial lake, as well as lose it to the atmosphere via evaporation and/or sublimation. The majority of these values seem to point to a glacial epoch that took place over a period of 100,000 to 500,000 years. It is suggested that, similar to the Earth, Mars has two stable climate regimes whose shift is triggered at least in part by orbital forcing parameters. The warmer climate corresponds to more of a glacial climate on the Earth, while the cooler climate resembles the cold, dry environment that exists on Mars today. There is also evidence that, geologically, these features are relatively pristine, and therefore probably relatively young. This is in comparison to a Mars generally inferred to have been warmer and wetter earlier in its history. A second climatological scenario does not even call for a drastically different climate than today, with a localized hot spot or impact providing the short-lived heat and volatiles to create a glacier. Indeed, this glacier may have been cold based for a time, or warm based due to the thickness of the overlying ice combined with the geothermal gradient.

The Wallace Lake greenstone belt is located on the southern margin of the Uchi-Sachigo-Goudalie superterrane within the volcanic-rich Uchi subprovince of the Superior Province in southeastern Manitoba, Canada. Its stratigraphy consists of a Mesoarchean complex constituted of alluvial conglomerate derived from ca. 3000 Ma tonalite, overlain by a crustal contaminated mafic-ultramafic volcanic sequence. Both units were deformed and then intruded by a 2.92 Ga tonalite body and related dyke swarm. Thrust sheets of a tholeftic volcanic sequence of unknown age, of oceanic plateau affinity tectonically overlie this Mesoarchean complex. The tectonic assembly was associated with regional SW directed compression, resulting in NW-trending folding and faulting. No metamorphic break is observed within this tectonic package despite major faulting related to this event. Neoarchean (<2709 Ma) greywacke and polymictic conglomerate unconformably overlie these units, and were deformed by dextral transcurrent deformation. Finally, fault bounded low-strain alluvial greywackes mark the last recorded stratigraphic and structural event affecting this area.

Prior to now, Iittle attention has.been given to the possible contribution toward ore formation of the vast quantities of sedimentary pore water as it is squeezed out by forces of compaction during sediment accumulation. Yet in spite of the difficulty entailed in direct study, the hypothesis of ore formation by migrating connate waters appears to involve a much simpler process of metal mobilization and concentration than many of the currently favored theories. [...]

<p> This work has developed a conceptual geological model for the Pilgrim Hot Springs geothermal system supporting the exploration, assessment and potential development of this resource for direct use and electric power production. The development of this model involved the analysis of a variety of subsurface and geophysical data and the construction of a 3D lithostratigraphic block model. Interpretation of the data and block model aimed to establish the most likely scenario for subsurface geothermal fluid flow. As part of this work, well cuttings were analyzed for permeability and correlated with geophysical logs from well to well to constrain the stratigraphic architecture of the unconsolidated sediments. Hydrothermal alteration of the sediments and bedrock core was also studied through reflectance spectroscopy and methylene blue titration in order to investigate past fluid migration pathways. The structure of the basin was interpreted through geophysical surveys including aeromagnetic resistivity, isostatic gravity, and magnetotelluric resistivity. Based on temperature, well logs, geophysical surveys, and lithologic data, the system is subdivided into a shallow outflow aquifer and a deeper reservoir beneath a clay cap connected by a conduit with 91&deg;C hydrothermal fluid upflow. Stratigraphic correlations indicate several clay layers throughout the section with a dominant clay cap at 200-275 m depth. Extensive pyritization and the clay mineral assemblage suggest an argillic-style alteration facies indicative of past temperatures at or slightly elevated above current conditions of hydrothermal activity at Pilgrim Hot Springs. The conceptual model supports production from this resource in those subsurface zones where there is sufficient permeability and connectivity with the upflow zone.</p>

A Precambrian layered gabbroic intrusion about 560 km('2) in area, of the Skaergaard type, crops out on the middle north coast of Labrador. Border zones and a Layered series are recognized, / and have the following characteristics and approximate mean thicknesses: (UNFORMATTED TABLE FOLLOWS) / Upper Border zone: grey gabbro 400 m / Upper zone d: larvikite 385 m / Upper zone a, b, c: olivine gabbro 1800 m / Lower zone troctolite 4500 m / Inner Border zone b: massive gabbro 180 m / Outer Border zone a: banded gabbro 485 m(TABLE ENDS) / The intrusion displays extreme fractionation resulting in larvikite consisting of mesoperthite, fayalite, ferroaugite, and ore as the uppermost differentiate. Mineral variation and differentiation are described by means of quantitative mineralogy. Plagioclase varies from An 78 to An 2, olivine from Fo 82 to Fo 7, and clinopyroxene from Ca(,45)Mg(,43)Fe(,12) to Ca(,46)Mg(,8)Fe(,46) toward the top of the intrusion. A study of plagioclase structural state shows this mineral to be partly and variably disordered. A pyroxene trend line and pyroxene-olivine tie lines are presented, and the pyroxene solvus is discussed. Local mineral variation is discussed in the light of cumulate solidification processes. / From modal and mineral analyses, the composition of the parent magma is estimated to have been alkali-basalt. The intrusion is unique for its type in having no free quartz in any rock. The compo- sitions of successive liquids are estimated, and variation diagrams are presented. The course of crystallization related to known and deduced phase equilibria is discussed, and layers of massive oxide ore are treated in the light of oxygen partial pressure variation. / Older migmatites and metasediments are described in Part I, along with younger intermediate and granitic intrusives. Two K-A dates for the younger rocks are reported. An appendix deals with refined mineralogical techniques and their precision.

In the central Canadian Rocky Mountain thrust-fold belt, three types of first order decollements are outlined within or along the border of the present orogenic wedge: one basal decollement, three intermediate or internal decollements and one upper decollement. Structural relationships suggest that each internal decollement is the result of one of the successive forward shifts of early basal decollements to new positions within the stratigraphic pile. / Two computer programs have been developed to analyze the propagation of multiple thrust faults and their influence on the geometry of a thrust belt. The computer programs generate graphical simulations used to demonstrate a model of thrust propagation and thrust belt development that fits current knowledge about fault propagation and can replace the thrust transfer zone concept. / A structural analysis of mesoscale structures in two thrust sheets indicates that a thrust sheet consist of a series of elongated blocks separated by subtle brittle-ductile shear zones along which differential motion occurred. These shear zones are oriented perpendicular to the mean strike of the thrust faults.

The picritic volcanic suite of Baffin Island is comprised of two different types of magmas which are analogous to N and E-MORB. Although these two picritic lavas-types are spatially intermixed in the stratigraphic succession, they are distinct in terms of light rare earth elements (LREE), K/Ti and $ sp{87}$Sr/$ sp{86}$Sr ratios. N-type lavas are depleted in LREE and have K/Ti ratio 0.5 and $ sp{87}$Sr/$ sp{86}$Sr ratios ranging between 0.7032 and 0.7039. Olivine fractionation and partial melting models involving a single homogeneous source can not reproduce the trace element differences between these two magma types. The generation of N and E-type magmas is most easily explained by small scale mantle heterogeneity. A possible model for the nature of the source is that of the head of a mantle plume which has an entrained depleted mantle.