Date of Award
1989
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The Parry Sound Shear Zone occurs between the Britt Domain and the Parry Sound Domain of the Central Gneiss Belt. The shear zone transects the Whitestone Anorthosite, located along the western margin of the Parry Sound Domain, and produces a range of new textures and paragenesis.;Two types of mylonites occur along the intersection between the Whitestone Anorthosite and the Parry Sound Shear Zone. Away from the mylonites, moderately modified anorthosite, exhibiting well-defined schistosity, and weakly modified anorthosite, exhibited relict igneous textures and ill-defined foliation, occur. Minor plant and anastomosing shear zones are superimposed on modified anorthosites.;The metamorphic mineral assemblages produced in the Whitestone Anorthosite formed under retrogressive conditions. Moderately modified anorthosite, scapolite-bearing planar shear zones and scapolite-bearing mylonites display a mineral assemblage of plagioclase (An34-60), pargasite, scapolite (Me68-75), and almandine garnet which suggests middle-upper amphibolite facies conditions of metamorphism. The anorthosites display small chemical modifications compared to the undeformed Whitestone Anorthosite; CO{dollar}\sb2{dollar} is the most prominently enhanced component. Weakly modified anorthosite, quartz-bearing anastomosing shear zones and quartz-bearing mylonites consist of plagioclase (An20-47), hornblende/pargasite, scapolite (Me57-65) and epidote or almandine garnet which suggest middle-lower amphibolite facies. The anorthosites display significant chemical modifications compared to the undeformed anorthosite; SiO{dollar}\sb2{dollar} and K{dollar}\sb2{dollar}O are the most dramatically increased components.;Under amphibolite and higher metamorphic conditions, plagioclase in the increasingly modified anorthosites underwent syntectonic recrystallization which produced non-random crystallographic orientation patterns. Quartz, present in ribbons in quartz-rich mylonites and anastomosing shear zones, deformed by dislocation creep resulting in the development of two different preferred crystallographic orientations. Isolated quartz and recrystallized plagioclase in the matrix deformed by grain boundary processes which produced random crystal orientations.;The textural and mineralogical characteristics of the Whitestone Anorthosite in the Parry Sound Shear Zone suggest a history of deformation that extended from granulite facies to lower amphibolite facies conditions. The observed sequence of chemical modifications suggests an evolutionary fluid history resulting from the inverted metamorphic gradient of an overthrust. The different orientation patterns observed in quartz grains within quartz ribbons suggest the occurrence of different regimes during the latest stages of deformation.
Recommended Citation
Koral, Hayrettin, "Ductile Deformation Of The Whitestone Anorthosite By The Parry Sound Shear Zone: Implications For Thrust Tectonics" (1989). Digitized Theses. 1787.
https://ir.lib.uwo.ca/digitizedtheses/1787