Metamorphic and structural evolution of Archean rocks in the Keskarrah Bay area, Point Lake, District of Mackenzie, N.W.T

• Main Author: Jackson, Valerie A.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1989
• Subjects: Yellowknife; Keskarrah Bay; Itchen Lake
• Online Access: https://research.library.mun.ca/6870/; https://research.library.mun.ca/6870/1/ValerieAJackson.PDF; https://research.library.mun.ca/6870/2/ValerieAJackson.pdf

The Keskarrah Bay area, Point Lake, N.W.T. is underlain by Archean rocks of the Slave Province that form two distinct lithotectonic elements: a sialic basement terrane, consisting of high-grade gneisses and granodiorite, and a supracrustal terrane, known as the Itchen Lake region supracrustal belt, comprising metavolcanic and metasedimentary rocks of the Yellowknife Supergroup. -- Conditions of regional metamorphism are documented mainly from metamorphic mineral assemblages in turbidites, which comprise greywacke-mudstone and subordinate iron formation and Fe-rich sediments. The sequential development of the key metamorphic index minerals chlorite, biotite, cordierite, andalusite and sillimanite in pelitic lithologies and garnet, staurolite or Ca and Fe-rich clino-amphibole in Fe-rich sediments occurred dominantly through continuous rather than discontinuous metamorphic reactions. The measured trends of increasing Mg:Fe ratios of the index minerals (cordierite > muscovite > chlorite > biotite > amphibole > staurolite > garnet) are used to demonstrate changes in AFM topology, from which the continuous reactions are interpreted. -- The pattern of metamorphic isograds is attributed to a single, progressive low pressure regional metamorphic event. Metamorphic grade increases both eastwards towards the Yamba batholith, and westwards towards the basement gneisses and the Pointless batholith. Prograde metamorphism in the supracrustal rocks was synchronous with retrograde metamorphism in the basement terrane. Peak metamorphic conditions, which reached a maximum of about 600°C +/- 50°C and 4.0 +/- 1.6 kbar, were attained toward the end of deformation. The P-T distribution throughout the area is consistent with the presence of a distant thermal dome that formed in the area of eventual batholith emplacement. -- Three or possibly four phases of deformation have been recognized in the supracrustal terrane. Proximity to basement is considered to have had an influence on the orientation and intensity of ...