Granitoid plutons in the Iskwasum Lake area, Manitoba: Part of the Flin Flon domain, Trans-Hudson orogen.

Abstract

Granites of the Iskwasum Lake area, Manitoba occupy greater than 60% of the exposed precambrian bedrock, and include seven different intrusive bodies. They are important indicators of the processes occurring during 1.88-1.83 Ga, a period in the formation of the Flin Flon domain of the Trans-Hudson orogen when volcanism was rare. Plagioclase, quartz, and biotite porphyritic lithologies are common. Hornblende is found in almost all instances, and alteration is ubiquitous, including varying amounts of muscovite, epidote and chlorite. Biotite is found in all but the most mafic rocks, and evidence for multiple mafic and felsic comagmatic lithologies is common. Pegmatite and aplite dikes are rare. Shear zones dominate the fabric in the Iskwasum Lake area, although only one such structure is located entirely within granitoid rocks. Some of these shear zones may represent the traces of major sutures, formed during the amalgamation of tectonic assemblages prior to pluton emplacement. The presence of zones of intrusion breccia with abundant proximal wall rock xenoliths at the margins of many plutons indicates these plutons were emplaced in their present location. Geochemical and physical properties of granitoid plutons in the Iskwasum Lake area are consistent with their derivation in a continental arc environment. (Abstract shortened by UMI.)