sgr ms thesis - University of Maine

mesh to better evaluate large thermal gradients at these boundaries. All models
portray the transient behavior of thermal diffusion, and time steps were used to
collect thermal data for clast sizes that cover 3 orders of magnitude. Although
there was obviously some magmatic flow to fully disaggregate clasts, field
evidence does not suggest large-scale flow. Therefore, these models are limited
to conductive heat transfer. The ideal isolated spherical clast model was used to
define an ideal trend for phase boundary migration without geometric
interference. The outcrop-scale model was used to plot cooling patterns for the
observed geometry. Models are defined by the parameters in Table 7.1.
Geometry is the dominant factor that determines the pattern of conductive
heat transfer (Jaeger, 1961). Conductive heat transfer across a boundary is
fastest when surface area to volume ratios and thermal gradients are large
(Jaeger, 1961; Bowers et al., 1990; Furlong et al., 1991; Stuwe, 2002). I assume
a kinetically static interface between the clast and its granitic matrix; therefore the
rate of heat transfer is entirely dependent on the thermal diffusivities of the
granitic magma and the metasedimentary clast.
Initial temperatures for clast and magma must be determined to solve the
conductive heating equation. The relatively sparse occurrence of pyroxene
implies that the rocks were heated to the lower-temperature end of
orthopyroxene hornfels facies, so initial clast temperature is set to T clast = 650°C
(e.g. Spear et al., 1999; Milford et al., 2001; Blatt et al., 2006, Kriegsman and
Alvarez-Valero, 2010). Magmatic temperatures are modeled at T magma = 900°C
(Wiebe et al., 1997a). The outcrop-scale model contains 75% matrix by volume,
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