sgr ms thesis - University of Maine

More documents

Recommendations

Info

FRACTAL ANALYSIS AND THERMAL-ELASTIC MODELING OF A SUBVOLCANIC MAGMATIC BRECCIA: THE SHATTER ZONE, MOUNT DESERT ISLAND, MAINE By Samuel Geoffrey Roy Thesis Advisor: Dr. Scott E. Johnson An Abstract of the Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science (in Earth Sciences) May, 2011 The Shatter Zone of Mount Desert Island, Maine, is a 450-1000m thick magmatic breccia that defines the perimeter of the Cadillac Mountain Intrusive Complex. The 400 Ma complex consists of gabbro-diorite sheets overlain by three different granites, the largest of which is an A-type granite emplaced at high temperature (~900 o C) and at shallow crustal depth (
emplacement of mafic magma, resulting in elastic failure of the metasedimentary and diorite wall rock and virtually instantaneous fragmentation and entrainment of the clasts in hot granitic magma. The degree of brecciation is gradational, with clast supported breccias at the outer margin of the zone grading inward to granitic-matrix supported breccia, and finally into clast-free Cadillac Mountain Granite. Field observations point to an explosive breccia mechanism, and clast size distribution analysis yields fractal dimensions (D s > 3) that agree with those known to result from explosion (D s > 2.5). Field and microstructural data and observations suggest that the clast sizes and shapes of the metasedimentary host rocks reflect post-brecciation modification by partial melting and thermal fracture, while diorite dike fragments experienced little modification after the original brecciation event. Clast circularity increases with proximity to the magma reservoir, whereas clast boundary shape decreases; this implies thermal wear on clast surfaces. Numerical modeling is employed to explore the possible thermalmechanical effects on the size distribution of clasts. Instantaneous immersion is assumed for metasedimentary clasts (650°C) in a hot granitic matrix (800°C - 900°C), and our thermal analysis is restricted to conductive heat transfer corrected for latent heat. The amount of clast melt is primarily dependent on the melt temperature of the clast, the matrix to clast volume ratio, and the initial magma intrusion and clast temperatures. Results show that thermal fracture and clast melt were viable secondary modification processes, and magma flow was necessary for disaggregation of melted clasts to occur. Angular clasts are highly susceptible to corner break-off owing to large tensile stresses associated with
Page 1 and 2: FRACTAL ANALYSIS AND THERMAL-ELASTI
Page 3: LIBRARY RIGHTS STATEMENT In present
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 and 50: 4.3.1. Model Setup The model is use
Page 51 and 52: 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 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.;
show all

sgr ms thesis - University of Maine

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?