麻豆传媒

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Digital topographic contours from twenty-four 1:250,000 scale maps have been gridded to produce a digital terrain model (DTM) for Ellesmere and Axel Heiberg islands in the Canadian Arctic. Gradient calculations were used to define coherent topographic dip vectors (TDV) to compare orientations with structural information digitally extracted from nineteen 1:250,000 scale geological maps. TDV, thrust fault dips directions, normal fault dip directions, and fold axis tangent vectors were binned into thirty-seven 100 km square cells with angular orientations calculated with respect to the convergence direction defined by the kinematic pole of rotation for the Greenland Plate relative to the North American Plate between 56 Ma and 35 Ma (anomaly 24 to 13). Histograms of these angular orientations have been used to quantify internal relationships as well as variability from cell to cell. In ice-covered areas, where geological mapping was not possible, TDV have been used to correlate extensions of fault patterns. The style of offset for the faults have been inferred based on their orientation for comparison with available field observations.

Five topographic zones have been identified, each with unique dip orientations suggesting different structural regimes. In Zone 1, TDV have a dominant single peak at -90o (+/-10o), relative to the rotation pole, and correspond to a pure-compressive area. In northern Ellesmere Island, histograms of TDV are predominantly bimodal with highly asymmetric antithetic peaks. Principle orientations are -170o/+10o (+/-10o) indicating dextral transpression and minor secondary peaks at -70o/+110o (+/-10o)indicating sinistral transpression. On Axel Heiberg Island, Zone 3, TDV are oriented at -150o (+/-10o), usually with a minor antithetic peak at +30o, and indicate sinistral transpression. Zone 4 has highly asymmetric TDV with a principal orientation of -60o (+/ -5o, suggesting dextral transpression, with both antithetic (+120o) and cross-cutting peaks (+160o). In southern Ellesmere Island, Zone 5 has TDV oriented at +30o, suggesting strike-slip faulting. Multiple cross-cutting patterns are observed with no preferred orientation.

Orientations of fault systems are generally compatible with the topographic "predictions", and together have been used to modify the existing classification of Eurekan structural domains. The Central Ellesmere Domain is subdivided into a northern transpressional zone and a southern compressive front. The compressive front is terminated to the south by the Vendom Fiord Fault Zone. The boundary between the Northern Ellesmere Domain and the Sverdrup Islands Domain is a broad region with sinistral splay faults. In southern and northern Ellesmere Island, fold axis are identified requiring a shortening axis incompatible with the Tertiary convergence of Greenland and are the result of an older tectonic event, presumably the Ellesmerian orogeny. This study confirms, for the first time, an excellent compatibility between geological and geophysical constraints for the timing and geometry of the Eurekan Orogeny.

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Supervisor: Ruth Jackson