Muscovite 40Ar/39Ar Geochronology of the Western Parry Sound and Britt Domains, Central Gneiss Belt, Grenville Province
McKenzie, Kenneth J.
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40Ar/39Ar analysis of ten muscovite samples from the western Central Gneiss Belt, Grenville Province, Ontario, yielded good argon spectra. The ages calculated show a trend of decreasing age southward into the orogenic interior. These new ages necessitate reinterpretation of previous data from the same area. Combined, the two data sets show an age gradient of -0.23 Ma / km along an 85 km transect through the Britt Domain and northern Parry Sound Domain, perpendicular to the strike of the orogen. The samples reached muscovite closure temperature more than 70 Ma after deformation ceased. The data record events in the post-tectonic thermal history occurring during the erosional degeneration of the mountain belt. Two models of post-tectonic thermal behaviour offer possible explanations of this trend in ages. One model assumes erosion-controlled variable uplift rates and a constant geothermal gradient across the transect. The northern end of the transect experiences rapid uplift relative to the south. A greater erosion rate at the margin of the orogen could explain this. The second model assumes a variable geothermal gradient and constant uplift rate across the transect. The northern end passes through the depressed end of the muscovite closure temperature isotherm first. A combination of both models may best explain the observed trend in ages. Keywords: Grenville Province, Central Gneiss Belt, orogen, uplift, geothermal gradient, argon, geochronology, muscovite, radiogenic, closure temperature, plateau Pages: 110 Supervisor: Nicholas Culshaw