Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
Tectonic and petrogenetic evolution of sub-horizontal granulite-grade fabric in lower continental crust: Constraints on lower crustal flow from the western Canadian Shield
Ductile, weak flow of continental lower crust is inferred for a number of orogenic systems, including the Andes and the Himalayan-Tibetan system. Sub-horizontal, high-temperature fabrics in rare exposures of exhumed lower continental crust provide important directly observable constraints on the physical mechanisms of lower crustal flow. This study uses m- to tens-of-km-scale examples of sub-horizontal granulite grade fabric in a large exposure of exhumed lower continental crust to constrain the conditions and timing of lower crustal flow. High-resolution electron microprobe monazite geochronology and trace element analysis in oriented tectonites reveals a protracted record of Neoarchean (ca. 2.63-2.53 Ga) garnet growth and sub-horizontal fabric development in migmatitic felsic granulites during lower crustal flow and subsequent cooling. Penetrative, sub-horizontal gneissic fabrics were over-printed by discrete steeply-dipping shear zones and upright folds. In situ dating of shear zones constrains the timing of sub-horizontal shortening and dextral shear strain to ca. 1.92-1.8 Ga. The results demonstrate the dynamic and evolving strength of continental lower crust. In this particular case, flow of relatively weak lower crust during production of sub-horizontal fabrics in the Neoarchean was followed by a period of near-isobaric cooling and strengthening. Subsequent Paleoproterozoic deformation events produced steep fabrics, outcrop- to crustal-scale steeply-dipping shear zones, and local reactivation of early sub-horizontal fabrics—a record of strain partitioning and strain hardening in an isobarically-cooled anisotropic medium.
Dumond, Gregory, "Tectonic and petrogenetic evolution of sub-horizontal granulite-grade fabric in lower continental crust: Constraints on lower crustal flow from the western Canadian Shield" (2008). Doctoral Dissertations Available from Proquest. AAI3337014.