sgr ms thesis - University of Maine

More documents

Recommendations

Info

7.5. Final Discussion Results from clast size distribution imply that the Shatter Zone originally formed from a subvolcanic explosion. The volcanic eruption was likely triggered by replenishment of mafic magma at the chamber base, which reinvigorated the overlying granite (Wiebe, 1994). The explosion was triggered by rapid volume expansion of volatiles within the chamber. Overpressure of the chamber led to immediate wall rock failure, providing channel ways for incoming magma. Size distributions for clasts above ~1.5cm radius in Types 1 and 2 record the explosive origin of the chamber walls, whereas distributions for clasts below 1.5 cm radius imply a secondary mechanism related to disaggregation and hydraulicthermal fracture during magma introduction. Diorite clast size distributions in Type 3 digress from D s values seen for Types 1 and 2, but they are still also thought to have an explosive origin. The decrease in D s between Types 1 and 2 and Type 3 is likely related to a change in dominant wall rock type as a function of rock strength differences rather than a difference in brecciation mechanism. Type 3 Bar Harbor clasts show a non-fractal size distribution trend, implying a secondary modification process that effectively reduced clast size and abundance. Data from clast boundary shape and clast circularity analysis also argue that clast modification has occurred from type 1 to type 3, showing relative decrease in clast surface complexity and increase in clast compactness with proximity to the Cadillac Mountain Granite. I suggest that clast modification was dominantly caused by thermal attrition: the thermal fracture, melt, and 115
disaggregation of Bar Harbor clasts driven by the intruding 900°C magma. I explored the possibility of thermal attrition by thermal-mechanical modeling of clast geometries instantaneously immersed in an intruding magma. Thermal fracture and partial melt are likely to occur during magma intrusion, but my conclusions are limited by the thermal conduction model because disaggregation requires some component of viscous flow of the matrix magma to mechanically disintegrate a clast. Results from the phase boundary migration model show that all Bar Harbor clasts of appropriate composition had potential to melt. Assuming that the volcanic eruption underwent days of activity, this would be enough time to melt and disaggregate a large component of the smallest Bar Harbor clast size populations. This agrees with the trend that is seen in clast size distribution for Type 3 Bar Harbor Formation clasts. Thermal fracture was driven by the immediate intrusion of magma after explosive wall rock fragmentation. Late-stage fractures in diorite clasts are likely caused by the large thermal gradients caused by the granitic intrusion into the Shatter Zone. Rapid thermal expansion in clasts provided great enough tensile stresses to cause fracture propagation of corners. Although the thermal fracture effect on clast size distribution is not as well understood, D s will increase slightly with repeated fracturing events, assuming that there is no removal of any clast populations through melting. The contribution from thermal fracture is small and had little effect on diorite clast D s . Diorite clasts did not reach their solidus temperatures, therefore D s represents the initial fracturing event plus thermal fracture, presumably creating a fractionally higher D s . Thermal fracture in a 116
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 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: This thermal fracture model explain
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

Create successful ePaper yourself

Delete template?

Save as template?