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http://hdl.handle.net/11375/19662
Title: | The Nature of Anorthosite - Country Rock Interaction During Granulite Facies Metamorphism: An Example From the Whitestone Anorthosite |
Authors: | Thompson, Danny Lee |
Advisor: | Grundy, H. D. |
Department: | Geology |
Keywords: | nature of anorthosite;Country rock interaction;Granulite facies metamorphism;Whitestone Anorthosite;Parry Sound;metasomatic interaction;Western Grenville Province, Ontario |
Publication Date: | Jun-1983 |
Abstract: | <p> The Whitestone Anorthosite is a relatively small anorthosite body (160 km2 ) located within the Parry Sound structural domain, Western Grenville Province, Ontario. Both the anorthosite and the surrounding gneisses have been affected by a granulite grade metamorphic event which predates the Grenville Orogeny. The outer margin of the anorthosite body has been strongly deformed and recrystallized and is characterized by a pervasive metasomatic alteration consisting of garnet, scapolite, hornblende, apatite, biotite, sphene, carbonate and opaques. The country rock gneisses exhibit a corresponding discontinuous, and highly variable, reaction aureole. Pre-existing mafic gneisses are particularily affected, being characterized by the breakdown of orthopyroxene and hornblende, an increase in garnet, clinopyroxene, apatite and opaques, and enrichment in Fe, Ti and P. </p> <p> The metasomatic alteration exhibited by the Whitestone Anorthosite is thought to be due to a combination of two processes: 1. Mechanical mixing at the anorthosite/country rock contact during intense deformation (tectonic assimilation), and 2. Widespread absorption of mobile components (predominantly volatiles) from both included material and the surrounding gneisses. </p> <p>The formation of the country rock reaction aureole is a continuous solid state metamorphic process, whereby mobile components are preferentially leached from the rock leaving a mafic restite. Post-deformation cooling of the anorthosite, combined with an increased volatile flux, has imparted a polygonal mosaic texture suggestive of contact metamorphism. The typical garnet-clinopyroxene assemblage exhibited by mafic gneisses within the reaction aureole, is a consequence of the increased Fe/Mg ratio which stabilizes this assemblage at lower P, T conditions. The temperature of final equilibration and recrystallization is estimated to be 750 ± 70 °C, based on clinopyroxene-garnet geotherrnometry. </p> <p> A similar metasomatic interaction, to the one outlined in this thesis, is to be expected at all anorthosite/country rock contacts which have been overprinted by granulite metamorphism. </p> |
URI: | http://hdl.handle.net/11375/19662 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Thompson_Danny Lee_1983June_Master of Science.pdf | 70.28 MB | Adobe PDF | View/Open |
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