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Direct-current resistivity prospecting methods have been used but rarely in the past in physical investigations of icecaps and glaciers. However these methods have the advantage of using light-weight and inexpensive equipment that is simple to operate. As part of the geophysical program of the Arctic Institute of North America's Devon Island Expedition, resistivity measurements were made in the accumulation and ablation zones of an ice-cap and on an adjoining glacier during the summers of 1961 and 1962. Depths of ice ranging from 50 to 750 meters were measured on the Sverdrup Glacier. Depth soundings on the ice-cap were not very successful owing primarily to insufficient power. However, some indication of the depth and composition of the firn was obtained. Ice resistivities were for the most part in the range from 4.10⁴ to 10⁵ ohm-meters, as compared with values of several megohm-meters found for temperate glaciers in lower latitudes. Variations of ice resistivities as a function of other physical properties were investigated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The magnetotelluric method, which depends upon the determination of impedance values over a wide frequency range (0.001-1 cps) from a pair of orthogonal electric and magnetic field components, has been used in the past by several investigators to determine the resistivity of the crust and upper mantle. Because of the diversity of the results obtained by the magnetotelluric method it was felt necessary to examine the method critically in order to obtain useful and unambiguous results. To carry this out an investigation was made of the magnetotelluric field recorded simultaneously at six stations in central Alberta during August 1961. The investigation is divided into five main sections; the recording of the magnetotelluric field, the analysis of the field records by various methods, the evaluation of the validity of the different assumptions made in the magnetotelluric method, the determination of subsurface resistivities, and the investigation of inhomogeneous and anisotropic bodies. Continuous recordings of Ey, Hx and Hz were made during August 1961 for two weeks at six stations, each approximately 100 km apart and oriented in a north-south direction (113.5° W longitude). In addition two extra components Ex, Hy were recorded at the central station, Beiseker. Estimates of the wave impedance Ey/Hx were obtained by inspection of quasi-sinusoidal events on the records from Meanook and Cardston. Using Cagniard's method an estimate of the subsurface resistivity ρ was made at Meanook. No estimate could be made at Cardston because of the large scatter of points in the plot of Ey/Hx against period T, Subsurface inhomogeneities near Cardston are believed to be the main cause of this scattering. At Beiseker, power spectra of selected lengths of records were computed and from them the ratios Ey/Hx and Ex/Hy were obtained in order to estimate subsurface resistivities. In addition a method for interpreting anisotropic bodies has been suggested and used at Beiseker to explain the differences which exist between the ratios EV/HL and Ex/Hy. A comparison between the various methods suggested by different investigators to interpret magnetotelluric data has been made and it has been shown with the help of theoretical models that these methods have no advantage over the curve matching method suggested by Cagniard. Moreover, it has been shown that such methods may give ambiguous results if applied to the interpretation of high frequency ( > 0.005 cps) magnetotelluric data. In order to judge the validity of the basic assumption of Cagniard's method, viz. that the horizontal gradients of the field vectors are negligible compared to vertical gradients, power spectra of corresponding lengths of records, used for the estimation of the resistivities, were computed at all six stations for the components Hx and Hz. Micro-pulsation activity which exhibited high coherence of Hx at all six stations yielded the least scatter in the ρ vs T plot as was expected. By carefully selecting data on the basis of this and other coherence criteria it is believed that a reliable indication has been obtained of a marked decrease in the resistivity in the upper part of the Earth's mantle. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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This dissertation consists of several distinct studies that use numerical modeling to better constrain deformation due to faulting over disparate timescales. Field mapping reveals a segment of the Lake Mead fault system, the Pinto Ridge fault, and a cluster of west-dipping normal faults located near Pinto Ridge. I suggest that this strike-slip segment was kinematically related to the Bitter Spring Valley fault, created the normal fault cluster at Pinto Ridge, and utilized these normal faults as linking structures between fault segments. Modeling results demonstrate that the location and orientations of the normal faults are consistent with having formed in the perturbed stress field around the slipping Pinto Ridge fault. Calculations of mechanical efficiency suggest that a preferred dip of normal faults in the region may reflect a crustal anisotropy at depth, such as a detachment. I present a methodology for simulating interseismic deformation in complex regions. I derive an analytical model of interseismic deformation that is equivalent to the conventional model. Based on this model, I formulate a two-step numerical simulation of geologic and interseismic deformation. I apply this technique to the Los Angeles region and find that model results match well both geologic slip rate estimates and geodetic velocities. Model results suggest that the Puente Hills thrusts are currently slipping at rates that are compatible with geologic estimates and that localized contraction in the San Gabriel basin is dominantly due to deep slip on the Sierra Madre fault. To assess the control of fault geometry and mechanical interactions on fault slip in a natural system, I create models of the Ventura region, California, using both planar and non-planar faults. I find that incorporating geologically-constrained fault surfaces into numerical models results in a better match to available geologic slip rate data than models utilizing planar faults. Because slip rates at most locations along the surface traces of Ventura faults are not likely to represent average values for the entire fault surface, I propose that well-constrained models can be used to predict slip rates at specific locations and determine whether existing slip rate estimates are representative of average fault slip rates.

This thesis contains several distinct studies aimed at better understanding fracturing in compressional fault-cored folds. At outcrops of growth strata in the Oliana anticline in the Spanish Pyrenees, the relationship of two joint sets may reflect changing mechanical properties (i.e. via diagenesis) during the folding process. Using a Schmidt hammer, I assess the rigidity contrast between the individual units and suggest that late-stage, throughgoing joints formed in strata with conditions similar to those of the present day and that early, bed-contained joints formed when the rigidity contrast between beds was significantly greater than the present day contrast. Modeling algorithms that are used for fracture prediction assume plane strain to construct, model and restore fault-cored folds. Using mechanical models that allow heterogeneous transport in three dimensions, I explore the distribution and magnitude of out-of-plane transport in plunging fault-cored anticlines and provide guidelines of where plane strain should and should not be applied. I show that out-of-plane transport is significant in the simplest non-cylindrical folds, and suggest that complex non-cylindrical structures should not be modeled using plane strain. I mapped five bed-orthogonal fracture sets associated with folding and faulting events at Sant Corneli anticline, a non-cylindrical, fault related anticline in the Spanish Pyrenees. Fold axis perpendicular, calcite healed joint sets associated with similarly oriented normal faulting both pre-date, and are cross cut by calcite healed, N-NW striking joints. Later bed strike oblique joint sets are distinguished by the presence of iron oxide mineralization that probably occurred during Paleocene-Oligocene time. This study directly links fold-related fracturing to fold evolution because fracture sets can be dated relative to the structural evolution of the anticline. I use three-dimensional restorations of Sant Corneli anticline in the Spanish Pyrenees to test the fracture prediction capability of a fully three-dimensional finite element geomechanical restoration algorithm. Reconstruction of the three-dimensional architecture of the syn-tectonic strata provides a template for incrementally unfolding the anticline. Strains predicted by the restorations are compared to the fracture sets that formed over the corresponding time intervals, which are consistent with the observed fracture patterns at Sant Corneli anticline.

<P> The Baie Verte Peninsula of Northern Newfoundland has a long history of mining and extraction. This area, which plays host to some of the oldest mines in the province, has a geologic setting favorable for Volcanogenic Massive Sulphides and is still considered to be one of the best exploration targets in Newfoundland. As less near-surface discoveries are made the requirement to look for deeper deposits becomes apparent and thus the role of geophysical modeling becomes progressively more important. This thesis examines the task of geologically supported geophysical modeling as a means to predict subsurface geological distributions and structure. Three case studies of modeling on the Baie Verte Peninsula are presented. A fourth study addresses the role of gamma attenuation for rapid density measurements in building physical property databases to be used as modeling constraint. </p> <P> A case study of the Betts Cove Ophiolite Complex along the western margins of Notre Dame Bay demonstrates the use of magnetic modeling to provide insight into the 3D nature of an area of previously significant ore extraction. While prior models have interpreted this feature to consist of a series of imbricate thrust slices, this new model suggests that the Betts Cove Ophiolite Complex is a doubly plunging syncline segmented by a several normal and high angle reverse faults. On a larger scale, this segmentation comprises a half-graben structure responsible for the morphology of Notre Dame Bay. Supported by petrophysics and a detailed structural dataset 2D forward geophysical models form the basis in the construction of a 3D geologic model of the Betts Cove Ophiolite and its cover series. </P> <P> An alternative approach to the conventional method of density measurement is presented in chapter three. Modifying an industrial gamma-gamma meter, a portable device has been constructed capable of providing rapid density measurements on bore-core. The device can be calibrated using a suite of metal alloy standards. It is possible to derive secondary empirical calibration based on a one-to-one gamma-gamma to specific gravity technique correlation. This study is one of only a very small fraction implementing this technology in an ocean-floor hard rock geologic setting. </p> <p> The second modeling case study focuses on the Rambler property in the upper Pacquet Harbour Group of the central Baie Verte Peninsula. The Rambler rhyolite is a felsic dome feature within the upper portions of an incomplete ophiolite. Ore deposits are found in association with contact between the felsic volcanics of the rhyolite and the mafic volcanic cover. 3D magnetic and gravity inversions are performed implementing the University of British Columbia Geophysical Inversion Facility's (UBC-GIF) code. A large physical property database has been constructed and used in the development of a reference model of known geologic distributions. The subsurface distribution of the Rambler rhyolite has been revealed through gravity inversions while additional structural information has been provided from magnetics. The results demonstrate the strengths of including geologic constraint within the inversion process and the ability of geophysical inversions to supplement and support current understanding and exploration techniques </p> <p> In the final case study, modeling is performed on a broader perspective in order to provide a regional geologic framework of the Baie Verte Peninsula. 2D forward models of magnetics and gravity profiles are constructed with multiple intersection points in order to enforce continuity in distribution and structure throughout. New geologic maps and a regional physical rock property database have been implemented in modeling while unconstrained 3D magnetic inversions are used as additional support. In addition to addressing such issues as regional basement morphology, the depth extent of the Cape Brule porphvry, and the nature of the Baie Verte Line, several prospective exploration targets have been revealed through this study. </p> / Thesis / Master of Science (MSc)

Selection of the paleomagnetic data base is fundamental to constructing an APW path, particularly as modelers increasingly rely on only a few studies. Substantial changes to recently constructed North American Mesozoic APW paths appear necessary based on the new data presented here. A southerly modification of the late Triassic-Early Jurassic segment of the APW path is supported by new data from the dual-polarity Late Triassic dikes in Rhode Island (paleopole 52.6$\sp\circ$N, 88.4$\sp\circ$E). The Jurassic portions of the paths are dominated by studies from the Colorado Plateau and Newark I and II poles from the east coast. Paleomagnetic data from Massachusetts and Connecticut diabases, a crucial part of the Newark I and II poles, indicate that these paleopoles should be reevaluated. The paleopoles from the early Jurassic diabases plot in three groups, one before (A) and two after (B, C) the J1 cusp: (A) 60.1$\sp\circ$N, 80.7$\sp\circ$E; (B) 66$\sp\circ$N, 92$\sp\circ$E; (C) 72.5$\sp\circ$N, 92$\sp\circ$E, all markedly different from the Newark I and II poles. From ten Cretaceous intrusions in Maine, New Hampshire, and Vermont, 514 samples were subjected to detailed thermal and alternating-field demagnetization, coupled with careful reflected-light microscopy. These have produced nine reliable VGP's of higher latitude than those previously published for the Cretaceous. Recent precise $\sp{40}$Ar/$\sp{39}$Ar ages on biotite and hornblende from the Cretaceous intrusions (Hubacher and Foland, 1991) show they are in three groups at approximately 120 Ma., 111 Ma., and 100 Ma. These constrain the calculated VGP's and the resultant paleopoles at 72.6$\sp\circ$N, 199.1$\sp\circ$E; 74.7$\sp\circ$N, 194.6$\sp\circ$E; and 76.9$\sp\circ$N, 167.4$\sp\circ$E, respectively, which in turn indicate the position of North America in the early to middle Cretaceous. When the new Cretaceous data are combined with new results from the Triassic and Jurassic rocks in New England, a considerably modified APW path for North America is indicated. Data from the Triassic and Early Jurassic intrusions is consistent with the J1 cusp. None of the data supports the J2 cusp. Instead the segment of the path from mid-Jurassic to Mid-Cretaceous is at higher latitude, and follows a smoother track toward Tertiary and younger poles.

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