GRANITE TECTONICS IN PART OF EDEN TOWNSHIP, SUDBURY DISTRICT, ONTARIO

Abstract

An examination of the literature demonstrates that the Grenville Front cannot be ascribed to a single tectonic event such as faulting or a zone of metamorphic transition. It may be due to faulting or metamorphic transition, or a combination of both depending on the geographic position of the observer along the Front. Southeast of Sudbury Ontario, the Grenville Front is defined by a zone of granitization of metasedimentary rocks of the Southern province, producing a zone of "pseudogranite" which supposedly extends to the southwest, separating low grade metamorphic rocks of the Southern province from high grade migmatitic and gneissic rocks of the Grenville province. The zone may be obscured by late faulting. Examination of these granitoid rocks in a small area north of Wavy Lake in Eden Township, demonstrates that they are of quartz monzonite composition and that they show well-defined igneous intrusive contact relationships with rocks of the Southern province. No evidence of meta somatism or granitization is observable. The Grenville Front in Eden Township is believed to be somewhat analogous to the Front of Quirke and Collins (1930), north of Georgian Bay. Evidence derived from fabric elements and metamorphic porphyroblasts suggests initial 'plastic' deformation of the sedimentary rocks with the production of ’low grade’ metamorphic minerals such as muscovite and epidote (greenschist facies) followed by a second phase of deformation with the development of ’high grade’ staurolite (low almandine-amphibolite facies) in fracture and flow cleavage planes produced in some pelitic rocks. A late retrograde metamorphic phase followed, characterized by the alteration of staurolite to muscovite· The age of quartz monzonite intrusion is not well defined· Retrograde metamorphism is thought to have occurred during the latter stages of the Penokean orogeny before intrusion of the quartz monzonite, rather than as a result of metamorphic effects caused by the igneous intrusion. Retrograde metamorphism of metasediments during Penokean time in the Wavy Lake area is consistent with retrograde metamorphic effects demonstrated by Card (1964) in the Agnew Lake area to the west. Two stages of gabbro intrusion are observed in Eden Township; one phase occurring after 'plastic’ deformation of the metasediments with consequent ’high grade’ metamorphism of gabbro to the almandine amphibolite facies, and a second phase, occurring after the intrusion of quartz monzonite. Metamorphism of the dike representing the second phase apparently occurred during faulting of the quartz monzonite and metasediments.