sgr ms thesis - University of Maine

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causing contact aureoles to become wider and achieve higher peak metamorphic temperatures over far longer timescales compared to those with a single intrusive sequence (Hanson and Barton, 1989). The model is limited by assuming a single instantaneous intrusion in a conduction dominated system, but the results will provide a foundation for future studies with more realistic constraints (e.g., Attoh and van der Muellen, 1984). For the conduction dominated model, I assume that the Bar Harbor Formation was metamorphosed before wall-rock brecciation and there was a single, instantaneous intrusion event that was allowed to thermally equilibrate with the wall rock. Latent heat correction was included during magma solidification within the range of 700-800°C, producing 400kJ kg -1 °K -1 of extra heat energy (see Chapter 7 for a more detailed explanation on how latent heat of crystallization is calculated). I disregard the expenditure of heat energy by endothermic metamorphic reactions, which can account for 60-110 kJ per mole of H 2 O or CO 2 released from a dehydrating pelite (Furlong et al., 1991). Intrusion geometry plays a major role in the resulting spatial distribution of the thermal gradient. The rate of conduction is entirely dependent on the material’s thermal diffusivity and the thermal gradient, but an object with high surface area to volume ratio is more exposed to the diffusive contact, allowing much faster heat transfer (Jaeger, 1961). It is important that the model geometry closely approximates that of the real intrusive system. Therefore, I produce a 3 dimensional model by digitally tracing the Cadillac Mountain Granite in map view, simplifying the geometry for use in COMSOL, and extruding it 2km into z space 35
to make a “hockey puck” style geometry (figure 4.3). The gabbro-diorite unit is added to the base and is given the same shape and thickness of 1km. Model boundaries must be placed at a substantial distance from the region of interest so as to not interfere with the heat transfer model. Therefore, the outer model boundaries lie 100 km away from the pluton center and are thermally insulated. The interface between the intrusion and the country rock is open and allows for free conductive heat transfer. A tetragonal mesh is used, with a fine boundary mesh located at the intrusive contact for increased resolution of the thermal evolution adjacent to the heat source. Initial wall rock temperature is 150°C at an emplacement depth of 5km based on a typical upper crustal geotherm of 30°C/km. I am concerned with the lateral evolution of the thermal gradient, so there is no need to calculate the local geothermal gradient for this model. The intrusion temperature was approximately 900°C, higher than average for a granitic magma (Wiebe, 1997). The gabbro diorite sheet is given an initial temperature of 1200°C. The thermal diffusivity ( ) of Bar Harbor Formation is set at 1.30E-6 m 2 /s calculated from (4.1) Where is thermal conductivity, is density, and is specific heat. Thermal diffusivities for Cadillac Mountain Granite and gabbro are given values of1.34E-6 m 2 /s and 1.01E-6 m 2 /s, respectively. A series of 300 time steps are taken from time = 0s to time = 1E14s, producing solutions for the evolving thermal gradient nearly up to a point of thermal equilibrium (Figure 4.4). 36
Page 1 and 2: FRACTAL ANALYSIS AND THERMAL-ELASTI
Page 3 and 4: LIBRARY RIGHTS STATEMENT In present
Page 5 and 6: emplacement of mafic magma, resulti
Page 7 and 8: © 2011 Samuel Geoffrey Roy All Rig
Page 9 and 10: TABLE OF CONTENTS ACKNOWLEDGEMENTS
Page 11 and 12: 5.3.5. Clast Circularity Analysis .
Page 13 and 14: LIST OF FIGURES Figure 2.1. Figure
Page 15 and 16: LIST OF TABLES Table 6.1. Table 7.1
Page 17 and 18: subvolcanic magmatic systems, the l
Page 19 and 20: Chapter 2 GEOLOGIC SETTING 2.1. Reg
Page 21 and 22: Somesville granite suite to the wes
Page 23 and 24: Biotite is metamorphic in origin, a
Page 25 and 26: Chapter 3 PHYSICAL DESCRIPTION OF S
Page 27 and 28: thinned lithosphere allows for part
Page 29 and 30: A B C Figure 3.1. Formation of a la
Page 31 and 32: 1997; Branney and Kokelaar, 1998; J
Page 33 and 34: Effusive-Type Eruption max 10 0 - 1
Page 35 and 36: magma quickly intrudes the develope
Page 37 and 38: Piston Downsag Piecemeal Funnel Tra
Page 39 and 40: fragmentation, and thermal energy h
Page 41 and 42: Chapter 4 THERMAL FRAMEWORK FOR CON
Page 43 and 44: contrast, conduction is heat transf
Page 45 and 46: A B Grt C Grt D Crd Crd E 1 mm F Cr
Page 47 and 48: ! ! ! ! Biotite Zone Garnet Zone !
Page 49: 4.3.1. Model Setup The model is use
Page 53 and 54: t = 0s t = 1E11 t = 1E12s t = 1E13s
Page 55 and 56: 850 750 650 550 450 400m Into Chamb
Page 57 and 58: approximately 140m thinner. The Sha
Page 59 and 60: Chapter 5 ROCK MECHANICS AND THE FR
Page 61 and 62: A β δ σ 1 σ 3 σ t c a σ 1 σ
Page 63 and 64: friction along the closed crack sur
Page 65 and 66: h h/2 h/4 Figure 5.2. A cube displa
Page 67 and 68: where N (≥r) is the count of clas
Page 69 and 70: to place a minimum size limit when
Page 71 and 72: moment of sudden fracture tip failu
Page 73 and 74: produced results in a self-similar
Page 75 and 76: 13 ln(area) (pixels) 12 11 10 9 ln(
Page 77 and 78: eaction processes were involved in
Page 79 and 80: Chapter 6 ANALYSIS AND RESULTS The
Page 81 and 82: Type 1 Type 2 500 m N Type 1 Type 2
Page 83 and 84: A B Figure 6.3. Type 2 Shatter Zone
Page 85 and 86: A B Figure 6.5. Centimeter-scale bo
Page 87 and 88: A B Figure 6.6. Brecciation texture
Page 89 and 90: The final breccia classified in thi
Page 91 and 92: esolution images of each box were s
Page 93 and 94: Clast circularity data were produce
Page 95 and 96: A 1000 Clast Size Distribu on: Type
Page 97 and 98: diorite dike with D s = 2.62 and R
Page 99 and 100: 6.3.3. Clast Circularity Analysis (
Page 101 and 102:
with decreasing clast size in all T
Page 103 and 104:
possibilities as postulated previou
Page 105 and 106:
Chapter 7 MECHANISMS FOR SECONDARY
Page 107 and 108:
magma. To prove the viability of th
Page 109 and 110:
mesh to better evaluate large therm
Page 111 and 112:
consistent with Type 3 breccias. Th
Page 113 and 114:
A temperature versus time plot was
Page 115 and 116:
Dimensionless time 0 0.05 0.1 0.15
Page 117 and 118:
Figure 7.4 displays model results f
Page 119 and 120:
thermal model ignores advection of
Page 121 and 122:
Zone experienced a relatively weake
Page 123 and 124:
7.4. Thermal-Induced Fracture Field
Page 125 and 126:
Metapelite/hornfels Diorite dike E
Page 127 and 128:
7.4.2. Results and Discussion COMSO
Page 129 and 130:
This thermal fracture model explain
Page 131 and 132:
disaggregation of Bar Harbor clasts
Page 133 and 134:
REFERENCES Acocella, V. (2007). Und
Page 135 and 136:
Billen, M.I. and Gurnis, M. (2001).
Page 137 and 138:
Clarke, D. B. (2007). Assimilation
Page 139 and 140:
Fisher, R.V. (1960). Classification
Page 141 and 142:
Hartmann, W.K. (1969). Terrestrial,
Page 143 and 144:
Johnson, S.E.; Paterson, S.R.; Tate
Page 145 and 146:
Mandelbrot, B.B. (1967). How long i
Page 147 and 148:
Oliver, N.H.S.; Rubenach, M.J.; Fu,
Page 149 and 150:
Schoutens, J.E. (1979). Empirical A
Page 151 and 152:
Wiebe, R.; Holden, J.; Coombs, M.;
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