Metamorphic petrology and gravity studies of the Archean English River subprovince, western Superior Province, Manitoba and Ontario, Canada
Date of Award
Master of Science (MS)
D. Perkins, III
The tectonic development of the English River Subprovince (ERSP) of the Superior Province in Ontario and Manitoba, as with other Archean medium-high grade metasedimentary/gneiss terranes, is an area of active research. Geochemical and geophysical data were collected during this study to determine the metamorphic conditions of formation, and the relationship between surface and subsurface geology. The results of metamorphic studies by Henke (1984), Baumann (1985), Chipera (1985) and Reeb (1987) were also integrated with those of this study. The temperatures and pressures of formation, as well as detailed gravity characteristics, constrain the postulated tectonic model for the ERSP.
Chemical data were obtained from the metasedimentary samples collected in the Lac Seul area, using an electron probe micro-analyzer for geothermobarometric calculations. The temperatures and pressures of formation were estimated using garnet-biotite geotherrnometers and garnet-cordieriteplagioclase-quartz geobarometers. Pressure, temperature, isograd and granulite occurrence maps were produced, which included results from all UNO workers in the Lac seul area.
Gravity data were collected along Highways 11, 304, 314 and 315 in Manitoba, and reduced to a Bouguer anomaly. The data were divided into five profiles. These profiles, in addition to one profile based on previously existing Bouguer data in Ontario, were modelled using a two dimensional gravity modelling program. The models were developed with a primary focus on the surficial geology.
No new isograds or mineral assemblages were identified in the Lac seul area during this study. The index minerals found are garnet, biotite, cordierite, sillimanite and orthopyroxene. The temperatures results ranged from 577 to 751 °c. The highest temperatures were found in the northeast and the lowest in the southwest. Isotherms display a pattern of domes and basins. Pressure results ranged from 2.7 to 5.7 kb, with the highest values in the northeast and lowest in the west. The pressure and temperature values of this study were intermediate compared to the range found by other UNO workers.
The gravity models display calculated profiles which closely resemble the observed anomalies. Modelling results indicate that the abundant granitoids at the surface are also pervasive at depth. There is also strong evidence that dense, mafic bodies exist at depth and may be a result of crustal underplating.
Determination of the tectonic regime operating during formation of the ERSP and adjacent subprovinces is hampered by the abundant granitoid intrusions. A potential sequence of accretionary tectonic events, distinguishing the northern and southern domains of the ERSP as individual subprovinces, is presented.
Campion, Moira E., "Metamorphic petrology and gravity studies of the Archean English River subprovince, western Superior Province, Manitoba and Ontario, Canada" (1992). Theses and Dissertations. 48.