Petrology, mineralogy and structural geology of the Duval Lake area, Manitoba

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Pollock, Gerald Douglas
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The mapped area is in the Kisseynew gneisses west of Sherridon, Manitoba. The principal rock types are the Nokomis semipelitic paragneiss of greywacke composition; the Sherridon quartzofeldspathic paragneiss of variable composition from protoquartzite to greywacke, commonly similar to subgreywacke; layers of hornblende-plagioclase gneiss (amphibolite), most abundant in the Sherridon sequence, with compositions similar to soda-rich basalts of the olivine basalt-trachyte series; semipelitic biotite schist and staurolite schist; granitic rocks of quartz monzonite, granodiorite and tonalite composition; migmatites composed of paragneiss and granitic rocks; massive to gneissic diorites; and scattered small bodies of pyroxenite. In most of the area the rocks have been regionally metamorphosed to the sillimanite-almandine subfacies of the almandine-amphibolite facies. Staurolite schists and other rocks of the staurolite-quartz subfacies occur in the south part of the area... The rocks of the area have been complexly folded. The two large areas of Sherridon paragneiss in the north are parts of a cross-folded nappe which dips northeastward. The south margin of this nappe lies in the area and, where the axis is exposed, right sections show the form of this nappe, with a core of Sherridon paragneiss surrounded by Nokomis paragneiss and gneissoid granite. The area can be divided into domains several miles across having consistent lineation trends. Equal-area projections of foliation data show pole girdles whose axes correspond to the lineation maxima. Lineation diagrams also show partial lineation girdles dipping shallowly east or northeast and a synoptic diagram of 411 lineations shows a strong girdle that can be fitted by a small circle of large radius. This pattern might be produced by refolding about an axis plunging steeply westward.