sgr ms thesis - University of Maine

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t: 500 t: 5000 A B t:500 t:5000 C Figure 7.7. Time step results for thermal stress in metasedimentary and diorite clasts. A) Bar Harbor Formation clast exposed to magma at 500 seconds and B) 5000 seconds. C) diorite clast exposed to magma at 500 seconds and D) 5000 seconds. The surface plot displays the first principle stress field, with tensile stress plotted as red and compressive stress plotted as blue. Arrows designate the second principle stress direction, or the assumed direction of fracture propagation. Maximum tensile stress is the result of nonuniform expansion, first in the roots of corners, then later on in the core of the clast as it is continually heated. Stresses gradually reduce as the clast temperature equilibrates with the magma. D 113
This thermal fracture model explains the late stage fracture for diorite clasts, but it does not take into account the anisotropic nature of the Bar Harbor Formation. Rock heterogeneity creates a far more complex thermal stress problem because crack formation is not solely dependent on the thermal gradient. Clarke et al. (1998) discuss the three different possibilities for fracture development in anisotropic xenoliths. The first is determined by the thermal gradient and this is used in the above model (thermal gradient cracking). The second mechanism for crack formation in a layered material becomes operative when one layer has a differing thermal expansion coefficient than its counterpart (thermal expansion mismatch cracking). Third, a material may have an anisotropic fabric that leads to preferred crack propagation in one direction (thermal anisotropy cracking). Bar Harbor Formation rocks can exhibit all three of these fracture types due to their compositional layering, and they may be more susceptible to thermal fracture than suggested by this model. The thermal gradient cracking model therefore provides a low end-member possibility for the proliferation of thermal cracks in Bar Harbor clasts. If thermal fracture was prevalent, each clast would fracture according to a new size distribution: for thermal fracture, D s = 2.156 (Glazner and Bartley, 2006). The new value of D s is the combination of the explosive fracture event and the secondary thermal fracture event, and repeated fracture events always increase D s by a fractional amount (Jebrak, 1997). Also, field evidence suggests that not all diorite clasts experienced thermal fracture, therefore late-stage thermal fracture did not have a significant effect on diorite dike CSD results. 114
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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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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: 7.4.2. Results and Discussion COMSO
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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