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Acid rocks associated with an intrusive complex Coppermine River area, Northwest Territories Tedlie, William Donald

Abstract

An intrusive complex in the Coppermine River Area, Northwest Territories appears to be a greatly elongated lopolith approximately 5 miles wide and 60 miles long. Multiple intrusion and magmatic differentiation have combined to produce layers of rocks which range in composition from dunite to granophyre within the lopolith. The acid rocks of the complex were emplaced as a number of separate injections of magma after the crystallization and cooling of the basic and ultrabasic rocks. The structural relations of the acid and basic rocks indicate that the acid intrusions were accompanied by faulting and subsidence of a part of the northern end of the lopolith. A prominent textural feature of the granophyre, an oscillatory mantling of nuclei of graphic quartz and potash feldspar by quartz-free potash feldspar and plagioclase, is believed to be the result of fluctuations in water vapour pressure during crystallization of the magma. The fragments in a breccia cemented by granophyre were probably, in part, formed by fault movements which accompanied the intrusion of the acid magma.

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