Date of Award

8-2015

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Christopher Gerbi

Second Committee Member

Scott Johnson

Third Committee Member

Edward Grew

Abstract

Our understanding of deep crustal processes is limited because we cannot directly observe rocks at depth or reproduce those conditions at a large scale in a lab. We can, however, infer deep crustal processes recorded in structures of exhumed mid to lower crustal rocks. We discovered six cathodoluminescent (CL) quartz microstructures in rocks from the Parry Sound Domain, Grenville Province, Ontario; this domain contains many amphibolite shear zones in granulite host rock. The purpose of this study is to (a) fully characterize the CL microstructures, (b) determine how and when they formed, and (c) evaluate their role in orogenic processes, especially their rheological significance. We characterize and interpret the six microstructures as follows. (1) Straight lines are fluid inclusion trails and thus healed fractures formed at cool temperatures (<300 >°C) during uplift. (2) Sinuous lines are subgrain boundaries formed by rotation recrystallization at the end of or just after amphibolite shearing ceased (~650 °C). (3 and 4) Sharp mantles and dark patches formed by a water-facilitated mechanism such as recrystallization or dissolution-precipitation after grain shape change associated with the amphibolite shearing event had occurred, yet while still within amphibolite facies (~650-550 °C). They provide evidence for post-kinematic grain boundary alteration. (4 and 5) Diffuse mantles and medium-dark grains formed as products of shear-related recrystallization at mid-amphibolite facies, whereas grains that maintain bright CL ceased recrystallization at higher amphibolite facies. They provide evidence for extended shearing in some locations. This study is an example of how CL provides evidence for processes and events that may otherwise be elusive.

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