sgr ms thesis - University of Maine

4.3.2. Results and Discussion
Results (figure 4.5) show temperature versus time curves for 100m
interval points from the chamber-wall rock contact, points located at the observed
isograds, and a point 400m into the intrusion. The peak metamorphic
temperature, 635°C, occurred at the intrusive contact at t = 1.9E11s (~6000
years). Peak temperature 500m from contact was 510°C at t = 3.2E12s (~1E5
years), and 1000m from the contact, peak temperature was 458°C at t = 6.2E12
(~2E5 years).
The single intrusion model provides a similar gradient trend within the
metamorphosed zone, but the model did not attain the temperatures required to
form the observed peak metamorphic facies (figure 4.6a). For this model, Garnet
and cordierite are stable at temperatures as low as 460°C, which is possible for
low pressure metamorphism (Blatt et al., 2006). This simplified conductive model
cannot fully explain the metamorphic pattern seen for pyroxene, however.
Metamorphic orthopyroxene requires a temperature of at least 650°C at 1.5 kbar
pressure or ~5 km depth (Spear et al., 1999; Blatt et al., 2006).
If the pluton contact is not actually vertical, the surface exposures of the
metamorphic zones may be oblique from their true thicknesses (figure 4.6b). This
could explain the wider than expected thickness of the pyroxene zone and it may
provide a constraint on the geometry of the magma reservoir and the Shatter
Zone. If the metamorphic aueole dips outward or inward with respect to the
chamber by 45 degrees, the “true” thickness of the pyroxene zone is
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