sgr ms thesis - University of Maine

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Figure 7.6. Clast geometry used for thermal stress analysis. Box is 1.25x1.25m. 111
7.4.2. Results and Discussion COMSOL follows engineering convention, meaning that tensile stress is positive and compressive stress is negative. The first principal stress relates to maximum tensile stress, while the second principal stress relates to minimum tensile stress for a two-dimensional model. Figure 7.7 shows transient development of the first principal stress distribution in the clast (also see Animation 2, 3). Local tensile stress buildup begins in the roots of sharp corners and moves inward as the clast heats up. Two patterns of fracture are evident from the experiment. The first phase of thermal fracture shows preference for edge break off. Arrows denote the direction of the second principal stress, or the direction of minimum tensile stress that a tensile fracture would prefer to follow. For this clast there is a preferred cuspate-shaped fracture pattern that would produce more corners. Eventually the number of corners would be reduced by successive fragmentation and circularity would increase. Next, as the clast continues to warm, tensile stress in the center of the clast reaches a critical value, allowing larger fractures to nucleate from the center and break the clast in half. The clast is slightly elongate, and increases inward and parallel to elongation. The first principal stress directions run perpendicular to elongation, preferring to fracture along the short axis. At this time of thermal exposure, originally elongate clasts would be preferentially broken up into more equant fragments, and each new fracture surface provides a fresh face to repeat the process. The potential for thermal fracture declines as the clast heats up and the thermal gradient is reduced. 112
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FRACTAL ANALYSIS AND THERMAL-ELASTI
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LIBRARY RIGHTS STATEMENT In present
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emplacement of mafic magma, resulti
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© 2011 Samuel Geoffrey Roy All Rig
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TABLE OF CONTENTS ACKNOWLEDGEMENTS
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5.3.5. Clast Circularity Analysis .
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LIST OF FIGURES Figure 2.1. Figure
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LIST OF TABLES Table 6.1. Table 7.1
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subvolcanic magmatic systems, the l
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Chapter 2 GEOLOGIC SETTING 2.1. Reg
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Somesville granite suite to the wes
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Biotite is metamorphic in origin, a
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Chapter 3 PHYSICAL DESCRIPTION OF S
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thinned lithosphere allows for part
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A B C Figure 3.1. Formation of a la
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1997; Branney and Kokelaar, 1998; J
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Effusive-Type Eruption max 10 0 - 1
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magma quickly intrudes the develope
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Piston Downsag Piecemeal Funnel Tra
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fragmentation, and thermal energy h
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Chapter 4 THERMAL FRAMEWORK FOR CON
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contrast, conduction is heat transf
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A B Grt C Grt D Crd Crd E 1 mm F Cr
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! ! ! ! Biotite Zone Garnet Zone !
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4.3.1. Model Setup The model is use
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to make a “hockey puck” style g
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t = 0s t = 1E11 t = 1E12s t = 1E13s
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850 750 650 550 450 400m Into Chamb
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approximately 140m thinner. The Sha
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Chapter 5 ROCK MECHANICS AND THE FR
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A β δ σ 1 σ 3 σ t c a σ 1 σ
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friction along the closed crack sur
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h h/2 h/4 Figure 5.2. A cube displa
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where N (≥r) is the count of clas
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to place a minimum size limit when
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moment of sudden fracture tip failu
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produced results in a self-similar
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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: Metapelite/hornfels Diorite dike E
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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