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The biotites from 24 samples of granodioritic and adamellitic rocks (13 Stallard, 11 McKenzie) of the South Mountain Batholith, N. S. were analyzed for nine major elements using the Electron Microprobe. Wet chemical analyses were done on eighteen of the biotites to obtain the Fe2+/Fe3+ ratio. The Ti, Fe2+, Fe3+, Mg and Al relationships in particular are examined in detail in order to assess the role of biotite as an indicator of differentiation and to estimate fugacities of oxygen and water in the crystallization of the South Mountain batholith. These elements are also used to examine the variation of biotite chemistry in the one-mica granodiorites and two-mica andalusite-free adamellites and the two-mica andalusite bearing adamellites. It appears from a plot of Fe2+-Fe3+-Mg that the oxygen fugacity of the South Mountain batholith was unbuffered during crystallization, and it increased with decreasing temperature. However, since the adamellites have been affected by hydrothermal processes, which may have caused oxidation, it is likely that only the granodiorites give the true estimate of oxygen fugacity.

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Pages: 43
Supervisors: D.B. Clarke