Gordon Check

B. Sc. Honours Thesis

⁴⁰Ar/³⁹Ar Thermochronology of the Britt Domain Grenville Province - Georgian Bay, Ontario

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The ⁴⁰Ar/³⁹Ar thermochronology of a transect of the Britt domain, Central Gneiss Belt, Grenville Province has been examined in this study. In total, twelve argon gas analyses were obtained. These came from five locations within co-genetic, single-cycle plutonic bodies which were metamorphosed during the Grenville Orogeny. Argon gas spectra were obtained for the minerals hornblende, biotite and K-feldspar separated from the plutonic rock samples. Diffusion experiments were carried out on the K-feldspars. This data yielded a calculated closure temperature for K-feldspar of 221^oC (+/-14^o). The presence of excess argon was implicated in most of the biotite analyses. A cooling history diagram was obtained for the Britt domain. The rate of cooling from hornblende closure temperatures to K-feldspar closure temperatures, subsequent to the Grenville Orogeny was calculated at 7.5^o C/Ma. The corresponding rate of exhumation would be about 0.25 km/Ma. These values are two to three times higher than values obtained from neighbouring areas but are much lower than values for young, active thrust orogens such as the Swiss Alps. It is believed that this area of the Britt domain underwent uniform cooling and exhumation after its metamorphism during the Grenville Orogeny. The relatively high rates, compared to nearby regions, may be due to the proximity to the Grenville Front.

Kwywords:
Pages: 83
Supervisors:  Nicholas Culshaw and Peter Reynolds