sgr ms thesis - University of Maine

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sense of shear. Type 3 Shatter Zone must be related to Types 1 and 2, which have been confirmed as explosive. The transition from fractal to non-fractal CSD slope for Type 3 Bar Harbor clasts requires a significant change in mechanism, implying that some major secondary modification process was at work to alter the size and shape of clasts. This modification mechanism is unable to provide a self-similar size distribution, which ties in to the marked drop in Bar Harbor clast abundance. CBS and CCA data imply increased clast wear with proximity to the Cadillac Mountain Granite, which also supports the hypothesis of secondary modification having a noticeable effect on the alteration of Type 3 Bar Harbor clasts. In all cases, D r decreases and circularity increases with closer proximity to the Cadillac Mountain Granite interface. Much like CSD, one cannot interpret CBS as a complete product of the brecciation event; it is more a manifestation of secondary modification. If the clasts of Type 3 were originally as angular as Types 1 and 2, CCA data show that there is substantial clast rounding after the major explosive event. Possible modification mechanisms include thermal disaggregation, fluid assisted fracture, and thermal induced fracture. These potential mechanisms are fully discussed in the next chapter. 89
Chapter 7 MECHANISMS FOR SECONDARY CLAST MODIFICATION: A DISCUSSION The thermal influence from the intruded granitic matrix of the Shatter Zone had a significant influence on clast size distribution (CSD) data trends, specifically for Bar Harbor Formation Type 3 clasts. The marked decrease in small clast populations and boundary shape values as well as the increase in clast circularity implies a non-fractal mechanism was active in the modification of clast size, shape, and abundance. Potential mechanisms are explored for post brecciation modification and I determine that disaggregation through partial melt of clasts is the dominant mechanism at play. Transient two-dimensional models are produced in order to quantitatively characterize the migration of solidus temperatures through a conductively heated clast, and to determine the evolution of CSD as clasts begin to partially melt. I show that disaggregation of clasts can lead to a bi-fractal and eventually non-fractal CSD. Magma flow, a constraint ignored in the thermal-mechanical model, is required to physically disaggregate the melted clasts. Thermal fracture is another possible secondary mechanism and is treated in a transient two-dimensional thermal stress model. Results show that late-stage thermal fracture occurred in diorite clasts, but less is known about the thermal stress characteristics of the structurally anisotropic Bar Harbor Formation. 90
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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
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: possibilities as postulated previou
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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