| Summary: | The first part of this thesis focuses on the tectono-metamorphic evolution of the Selkirk
Allochthon, a welt of supracrustal rocks deformed and metamorphosed during Mesozoic to early
Cenozoic time as a result of terrane collision at the western edge of North America. The studied area is
part of the Selkirk Allochthon. Pelitic rocks in the area record a Barrovian metamorphic field gradient.
Detailed mapping of metamorphic assemblage distribution and textural analysis of pelitic rocks has
unraveled two distinct metamorphic events (M1 and M2). Emplacement of the Bigmouth Creek stock,
which intrudes rocks of the Big Fish Creek area was dated as mid-Jurassic, with evidence for substantial
reheating in early Cretaceous time. Based on regional correlation, M1 is assigned a mid-Jurassic age,
synchronous with emplacement of the Bigmouth Creek stock. M2 is interpreted to have resulted from the
early Cretaceous thermal event. The development of early-M2 kyanite and late-M2 andalusite indicates
decompression over at least 3 kbar, implying at least 10 km of denudation. Detailed analysis of structural
elements suggests that the area was part of a long-lived, mid-crustal zone of intense distributed strain.
Uplift and denudation of metamorphic rocks by tectonic extension and coaxial thinning were synchronous
with continued contraction. A tectono-thermal model is proposed for the Allochthon as a long-lived,
dynamic orogenic wedge within which deformation accommodated contraction due to terrane
convergence and accretion, and polycyclic metamorphism resulted from thickening and maintenance of
the wedge over at least 20 My. Significant early Cretaceous thinning of the wedge recorded by
extensional strain and late-M2 decompression resulted from waning of far-field contraction, and/or from
rheological modification of the wedge due to thermal relaxation.
The second part of this thesis reports on a study of heterogeneous reactive transport of H2O-CO2
fluids during contact metamorphism of siliceous dolomites. Comparison of mineral assemblage
distributions resulting from numerical simulations of heterogeneous flow with assemblage distribution in
the Alta (Utah) contact aureole indicates that mineral reactions record flow through highly heterogeneous
permeability. This is interpreted to result from positive feedback between reaction enhancement of
permeability and flow-focusing. Comparison with other contact aureoles suggests that this is a common
mechanism of permeability evolution during contact metamorphism of carbonate rocks. More
homogeneous permeability recorded in regional metamorphic rocks may reflect fundamental differences
in the relative rates of fluid flow and compaction in regional and contact metamorphic environments. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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