Primary structures of the Falcon Lake Intrusive Complex, southeastern Manitoba
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Date
1989
Authors
Mandziuk, William Stanley
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Abstract
The Falcon Lake Intrusive Complex is a composite intrusive body, approximately 10 square kilometers in area, located near the western edge of the Wabigoon Subprovince in the Superior Province of the Canadian Precambrian Shield. The complex has an elliptical shaped core, and tapering extensions to the southwest and northeast. The complex consists of a series of intrusions ranging from oldest gabbroic rocks in the extensions, through younger diorite-granodiorite in the outer areas of the core, to youngest quartz monzonite in the centre. All of the rocks of the complex are characterized by cumulate or porphyritic textures. The compositions, distribution, and relative ages of the component intrusions suggest a, separate differentiating magma chamber from which the intrusions were drawn sequentially. Successive intrusions of progressively more differentiated magma were intruded more or less into the centre of its less differentiated predecessor. The initial intrusion was dyke-like, and succeeding intrusions gave the complex a more equant and cylindrical shape. Relationships throughout the complex suggest that the complex was a magma conduit in which magmas were periodically transported from a source at depth to higher level intrusive or extrusive features. Each intrusion of the complex is characterized by its own set of primary fabric structures which may include the preferred orientation of primary minerals, layering, discordant intrusive contacts similar to angular unconformities, scour and trough-banded structures, mineral clots and segregations of various compositions, xenoliths and cognate inclusions, and breccia pipes. The form and arrangement of these primary structures. as well as relationships between structures, suggest that each intrusion initially consisted of a crystal-liquid mixture, and that magmatic flow processes were responsible for the development of the structures. The origin of the flow is related to intrusive emplacement mechanisms rather than convection processes after emplacement.