Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 162-176).

Thesis (M.Sc.)--Memorial University of Newfoundland, 1995. / Bibliography: leaves 189-196. Also available online.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography: leaves 51-56. / by Waris E.K. Warsi. / M.S.

An interpretation of gravity and magnetic anomalies of the Butte district, Montana, is based on the analysis of five gravity profiles constructed from Bouguer gravity data of the Butte district observed during the summer of 1974 and give concurrent magnetic profiles constructed from U.S. Geological Survey high-level aeromagnetic data of the district. Of primary concern in this analysis is the interpretation of the Bouguer gravity high and aeromagnetic low associated with the Butte orebody. Results of this interpretation yield a configuration for the Butte orebody characterized by vertical contacts extending from the surface or directly beneath Cenozoic basin fill to 4,500 feet below sea level, with a central core, elongate in the north -south direction, surrounded by a variable outer zone, which is more pronounced in the southern and western portions of the district. The central core is interpreted as a region of zero magnetic susceptibility with three density distributions, all of which are of higher densities than the surrounding host rock and are related to the varying degrees of mineralization and alteration present in this region. The laterally variable outer zone is interpreted as a zone of low magnetic susceptibility with a density equal to that of the host rock. This zone is related to the peripheral mineralization and alteration of the Butte orebody.

No description available.

published_or_final_version / Earth Sciences / Master / Master of Philosophy

The Queen Charlotte Fault system is a segment of the North America - Pacific plate boundary. From 45 Ma - 5 Ma, plate motion has been primarily translational. Since 5 Ma, transpression has been the dominant mode of interaction. The plate boundary west of the Queen Charlotte Islands is characterized by an approximately 30- km wide terrace, flanked to the west by a topographic trough and to the east by the seismically active Queen Charlotte Fault. At 53.4°N the fault bends eastward and the terrace becomes wider and discontinuous, forming triangular shaped highs and intervening lows. Approximately 300 km of multichannel seismic reflection and gravity data along and across the Queen Charlotte Fault off Dixon Entrance were collected as part of the ACCRETE experiment in 1994. Structural interpretation of the five new profiles reveals the presence of faults and folds within the terrace, which form an angle of 20° to the strike of the Queen Charlotte Fault. The direction of these structures corresponds to the trend of the plate boundary south of the bend and west of the Queen Charlotte Islands, implying that through complex compression and shear, material must have been carried from south to north along the margin during oblique plate motion. Based on this observation and on forward gravity modeling, which places limits on the possible plate configuration at depth, a four-dimensional model has been developed to explain the temporal and spatial evolution of structural styles in this region. Considering the amount of shortening that must be accommodated within the past 5 Ma (a maximum of 100 km), a model of an underthrusting Pacific plate is preferred over one of pure upthrusting. About 5-6 Ma ago, when transpression began, oceanic crust was flexed and thrust upward at the plate boundary to eventually reach a steady-state configuration of a subducting slab. Fractured basement rock and consolidated, deformed sediments underlie the terrace and form its foundation. As a result of strain partitioning, the terrace is now decoupled and moves both parallel to the continent and perpendicular to the underthrusting Pacific plate. North of the bend in the Queen Charlotte Fault, underthrusting north of it occurs obliquely along preexisting fractures at the base of the terrace. The repetitive pattern of triangular terrace slivers is the result of continuing uplift and shear along these trends. Active tectonism influences sediment dispersal and creates traps. A N-S trending fault was also identified in the trough segment and possibly involves oceanic basement. Its origin is thought to be due to distributed shear that was transmitted across the plate boundary. Sea-floor spreading magnetic anomalies trend north-south as well. Along these zones of weakness, synthetic strike-slip faults of a transpressional strain ellipse could has been initiated during early stages of subduction. Reactivation of such faults may occur when oceanic crust approaches the outer terrace boundary, as is the case in the study region. Gravity modeling confirmed the existence of thin (24 km) continental crust and an increase in oceanic Moho dip beneath the terrace, which is topped by unconsolidated sediments and underlain by material of near-basement densities. It could not be determined using gravity modeling whether oceanic crust exists beneath the continent, but if it does, it must be welded to the North American plate in shallow subduction. / Graduation date: 1998

No description available.