Geochemistry and Petrogenesis of the Mcelroy and Larder Lake Assemblages, Abitibi Greenstone Belt, Northeastern Ontario by Chris
Geochemistry and Petrogenesis of the McElroy and Larder Lake assemblages, Abitibi Greenstone Belt, Northeastern Ontario by Christopher T. Kimmerly, B.Sc. A Thesis submitted to the Department of Geological Sciences in partial fulfIllment of the requirements for the degree of Master of Science September 1992 Brock University St. Catharines, Ontario © Christopher T. Kimmerly, 1992 2 Abstract The McElroy and Larder Lake assemblages, located in the southern Abitibi Greenstone Belt are two late Archean metavolcanic sequences having markedly contrasting physical characteristics arid are separated from one another by a regional fault. An assemblage is an informal term which describes stratified volcanic and/or sedimentary rock units built during a specific time period in a similar depositional or volcanic setting and are commonly bounded by faults, unconformities or intrusions. The petrology and petrogenesis of these assemblages have been investigated to determine if a genetic link exists between the two adjacent assemblages. The McElroy assemblage is homoclinal sequence of evolved massive and pillowed fl.ows, which except for the basal unit represents a progressively fractionated volcanic pile. From the base to the top of the assemblage the lithologies include Fe-tholeiitic, dendritic flows; komatiite basaltic, ultramafic flows; Mg-tholeiitic, leucogabbro; Mg-tholeiitic, massive flows and Fe-tholeiitic, pillowed flows. Massive flows range from coarse grained to aphanitic and are commonly plagioclase glomerophyric. The Larder Lake assemblage consists of komatiitic, Mg-rich and Fe-rich tholeiitic basalts, structurally disrupted by folds and faults. Tholeiitic rocks in the Larder Lake assemblage range from aphanitic to coarse grained massive and pillowed flows. Komatiitic flows contain both spinifex and massive textures.
[Show full text]