• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1
  • Tagged with
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Structural evolution of the northern Thor–Odin Culmination, Monashee Complex southern Canadian Cordillera

Kruse, Stefan January 2007 (has links)
The Monashee Complex is a structural culmination which exposes rocks from the lowest stratigraphic levels of the Canadian Cordillera. The Monashee Complex is subdivided into two lesser structural culminations; the Frenchman Cap and Thor–Odin culminations. The lithostratigraphic succession of the Thor–Odin Culmination is completely transposed by penetrative isoclinal folds with amplitudes from microscopic (<1 mm) to regional (10’s km). Lower structural levels are occupied by Proterozoic gneisses and migmatites of the Monashee basement assemblage. These are infolded with overlying metasedimentary rocks of the Monashee cover assemblage, which are Proterozoic to possibly Paleozoic in age. The basement and cover assemblages were subsequently intruded by Eocene granitic pegmatite, aplite and lamprophyre dykes. Regional metamorphism of the basement and cover assemblages reached upper amphibolite to lower granulite facies. The northeastern portion of the Thor–Odin Culmination of the Monashee Complex contains a suite of structures and fabrics, which are classified into four sets, based on their interpreted kinematic significance. These are: 1) transposition related structures (DT); 2) open, upright folds (DO); 3) exhumation related structures (DE); and 4) brittle faults (DB). Each successive set of structures exerted a control on the geometry of the next set. The large-scale geometry of the culmination is an interference structure between DT folds, a DE arch and high-strain zones, and a DB brittle horst. Early, DT fold style varies from intrafolial isoclinal “mature” style folds to upright or inclined asymmetric “immature” folds. This continuum of fold styles, along with evidence of anticlockwise rotation (looking down a vertical axis toward the shear plane) of fold axes and lineations is interpreted as being a result of penetrative triclinic non-coaxial flow. DO upright, symmetrical folds overprint early structures and fabrics, but are only preserved at low structural levels in the culmination where the DE coaxial stretching overprint is weak. DE normal shear bands and boudins overprint all earlier structures. A complex high-strain zone, the Thor–Odin High-Strain Zone, outcrops at high structural levels and along the margins of the culmination. The Thor–Odin High- Strain Zone developed as a result of material moving away from the crest of the culmination, outwards toward the flanks. Eocene brittle faults (DB) and fractures within the Thor–Odin Culmination of the Monashee Complex are divisible into three distinct sets. Initial 340–010º trending strikeslip faults (Set 1) were locally overprinted and reactivated by normal faults with a 325– 020º trend (Set 2). A third set of 255–275º trending fractures (Set 3) are interpreted as conjugates to Set 1, reactivated as transfer faults to the Set 2 normal faults. Large regional faults weather recessively forming topographic lineaments that transect the Monashee Complex. The Victor Creek Fault defines one such lineament. Detailed mapping within the northern Thor–Odin Culmination, reveals piercement points (fold hinges) on the east side of the fault, which are not readily matched on the west side. The minimum displacement required on the Victor Creek Fault to down-drop the fold hinge below the level of exposure on the west side is 1370 m, assuming normal down-to-the west displacement. However, the geometry of the fault is consistent with a Set 1 dextral strike-slip fault. Matching the piercement points in the study area with possible equivalents to the north indicates 55–60 kms of dextral strike-slip displacement. The Monashee Reflection (MR) is a major crustal-scale, cross-cutting reflection appearing on two mutually perpendicular Lithoprobe seismic profiles in the southern Omineca Belt of the Canadian Cordillera. It has previously been interpreted as the downplunge extension of an arched regional ductile thrust fault, the Monashee Décollement, and is described as separating the Monashee Complex from the overlying Selkirk Allochthon. Recent mapping demonstrates that this boundary is not a discrete ductile thrust, but rather transposed and gradational. Overprinting the transition zone is a complex, outward-dipping, normal, structure; the Thor−Odin High-Strain Zone. Three alternative 3-D geometric models have been developed for the MR in order to project the reflection to the surface. The favoured model correlates the surface trace of the Thor−Odin High-Strain Zone with MR. Normal shear sense kinematics are interpreted for the MR based on: 1) the overall geometry and asymptotic relationship between the MR and reflections in the hanging wall and footwall; 2) offset of metamorphic and geochronological gradients, consistent with an extensional zone, rather than with thrust fault interpretation and 3) the cross-cutting nature of the MR is consistent with normal structures throughout the region.

Page generated in 0.0649 seconds