TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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nent fragments of old continental crust were stranded amongst the Indian Ocean lithosphere including fragments within the KP crust. One of the scientific objectives of Leg 183 drilling was to constrain the post- melting evolution of Kerguelen magmas, of which crustal assimilation was clearly an important process. In this study I explore the timing and nature of crustal contamination of KP magmas by focusing on the compositional and isotopic record of assimilation contained within zoned plagioclase phenocrysts in two basalts from Leg 183 Site 1137 - Units 4 and 10. On the basis of whol-rock geochemistry, Ingle et al. [75] placed the Unit 4 basalt in a relatively uncontaminated upper basalt group and and the Unit 10 basalt in a relatively contaminated lower basalt group. Examination of plagioclase phenocrysts from Units 4 and 10 provide snapshots of the magmatic processes that were occurring when both when crustal contamination was significant and when it was not. Hypothesis 1: Initial LIP magma emplacement in the crust was accompanied by large amounts of crustal assimilation followed by armoring of magma chamber walls. Crystallization occurred by solidification front growth. In this case early formed plagioclase crystals or zones (i.e., cores) will contain the greatest signature of the crustal wall rocks, however the contamination signature in the crystal cores may be indistinct if contamination significantly pre-dates plagioclase crystallization. Late formed crystals or zones (i.e., rims) will contain less of a crustal signature. Hypothesis 2: Crustal assimilation occurred progressively as crystals 25
nucleated homogenously and grew throughout the magma chamber interior. Early formed crystals or zones (i.e., cores) will not necessarily bear the most contaminated signatures. Late formed crystals or zones (i.e., rims) will be equally or more contaminated than early formed crystals. 26
Page 1 and 2: TEXTURAL AND MICROANALYSIS OF IGNEO
Page 3 and 4: TEXTURAL AND MICROANALYSIS OF IGNEO
Page 5 and 6: DEDICATION This work is dedicated t
Page 7 and 8: CHAPTER 2: MAGMA EVOLUTION REVEALED
Page 9 and 10: 3.6.3.1 Crystal Population Origins
Page 11 and 12: FIGURES 1.1 Magma Chambers . . . .
Page 13 and 14: TABLES 2.1 MAJOR AND TRACE ELEMENT
Page 15 and 16: thus been debate within the volcano
Page 17 and 18: Cambrian schist) including a crysta
Page 19 and 20: explosive eruption vs. mild effusiv
Page 21 and 22: tiation (e.g., [84, 98]; Fig. 1.3).
Page 23 and 24: defined as having crystallinities b
Page 25 and 26: 12 Figure 1.4: Large Igneous Provin
Page 27 and 28: distribution of crystal sizes (e.g.
Page 29 and 30: investigating magmatic evolution us
Page 31 and 32: length dispersive spectroscopy(WDS)
Page 33 and 34: microdrilling, a pre-cleaned square
Page 35 and 36: 1.7.2 Detroit Seamount, Part of the
Page 37: lations. Reprocessing of intrusive
Page 41 and 42: With accurate partition coefficient
Page 43 and 44: uniform composition of large volume
Page 45 and 46: Figure 2.2. Hand sample and thin se
Page 47 and 48: 2.3.1 A Cogenetic Relationship Betw
Page 49 and 50: Figure 2.4. Stratigraphic section o
Page 51 and 52: Figure 2.5. Backscatter electron im
Page 53 and 54: studies of Kwaimbaita basalt by San
Page 55 and 56: 42 Crystal Zone An (mol%) TABLE 2.1
Page 57 and 58: 44 Crystal Zone An (mol%) 63R2 phen
Page 63 and 64: along the xenolith margins (e.g., F
Page 65 and 66: are more abundant in phenocrysts fr
Page 67 and 68: 54 Crystal Zone 5 ML-X1 xenolith TA
Page 69 and 70: 56 TABLE 2.2 Continued Crystal Zone
Page 75 and 76: Figure 2.7. Measured major and trac
Page 77 and 78: 2.5.3.2 Trace Elements It is diffic
Page 79 and 80: Figure 2.9. Trace element ratio plo
Page 81 and 82: 2.5.4 Resorption Features in Site 1
Page 83 and 84: should, however, be noted that in t
Page 85 and 86: 2.6.1.2 An-rich OJP Plagioclase: In
Page 87 and 88: equivocally the roles of H2O, press
Page 89 and 90:
ent magma requires significant clin
Page 91 and 92:
tion driven plumes, or stirring by
Page 93 and 94:
Yamashita, [123], and thus did not
Page 95 and 96:
erally extensive crystal-mush netwo
Page 97 and 98:
asalt at Site 1185 of ODP Leg 192 [
Page 99 and 100:
CHAPTER 3 SHALLOW MAGMA EVOLUTION D
Page 101 and 102:
magma compositions [23, 39, 98]. A
Page 103 and 104:
Figure 3.2. Stratigraphy of basalts
Page 105 and 106:
[118]. No volcaniclastic rocks were
Page 107 and 108:
magmatic crystallization. Using the
Page 109 and 110:
Figure 3.3. A cross polarized light
Page 111 and 112:
3.4.5 Major and Trace Element Data
Page 113 and 114:
3.4.6.1 Partition coefficients for
Page 115 and 116:
3.5.1.2 Site 884 CSDs I measured pl
Page 117 and 118:
Figure 3.5. Plagioclase CSDs of ODP
Page 119 and 120:
106 TABLE 3.2 CSD RESULTS Sample OD
Page 121 and 122:
ln (n) [mm -4 ] ln (n) [mm -4 ] 10
Page 123 and 124:
ulation A crystals are unzoned (An6
Page 125 and 126:
Figure 3.8. a) The majority of Site
Page 127 and 128:
3.5.4.3 Site 1203 Unit 31 and Site
Page 129 and 130:
3.5.5 Trace Elements 3.5.5.1 Measur
Page 131 and 132:
Unit 31 > Site 884 Unit 8 (Table 3.
Page 133 and 134:
3.6 Discussion 3.6.1 Evidence of Cr
Page 135 and 136:
3.6.1.1 Site 1203 Alkalic Basalts a
Page 137 and 138:
etween the different crystal popula
Page 139 and 140:
Unit 14 and 31 magmas accumulated o
Page 141 and 142:
sition is similar to parent magmas
Page 143 and 144:
Sr - low La/Ce population A parent
Page 145 and 146:
The Unit 31 plagioclase CSD is kink
Page 147 and 148:
was dominated by late stage clinopy
Page 149 and 150:
pressure, and growth of An-rich pla
Page 151 and 152:
138 TABLE 3.3 PLAGIOCLASE PHENOCRYS
Page 153 and 154:
140 TABLE 3.3 Continued Sample Zone
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
KP has been done via drilling at 11
Page 189 and 190:
and over time crustal wall-rocks be
Page 191 and 192:
flow [33]. I selected a single samp
Page 193 and 194:
4.3.4 Major and Trace Element Data
Page 195 and 196:
B) C) parafilm splash guard A) tape
Page 197 and 198:
of these elements are the better co
Page 199 and 200:
5 mm 5 mm Figure 4.4. Cross polariz
Page 201 and 202:
4.4.2 Electron Probe Microanalysis
Page 203 and 204:
An (mol %) An (mol %) An (mol %) An
Page 205 and 206:
study exhibit their highest An at t
Page 207 and 208:
4.4.3 LA-ICP-MS - Trace Elements An
Page 209 and 210:
87 86 Sr/ SrI = 0.705722(8) Ba/Sr =
Page 211 and 212:
and Rb (Fig. 4.11d,e). 4.4.3.3 Yttr
Page 213 and 214:
Sr (ppm) Y (ppm) La (ppm) Ce (ppm)
Page 215 and 216:
Unit 4 plagioclase rims plagioclase
Page 217 and 218:
204 TABLE 4.4 UNIT 4 PLAGIOCLASE PA
Page 219 and 220:
4.5 Discussion 4.5.0.1 Origin of Ma
Page 221 and 222:
4.5.0.2 Insights from Trace Element
Page 223 and 224:
that other factors influenced the a
Page 225 and 226:
C A/B / D A/B C A/B / D A/B Unit 4
Page 227 and 228:
Magma chambers tend to form at hori
Page 229 and 230:
whole-rock basalt data. Cumulate xe
Page 231 and 232:
over short time spans but may be ea
Page 233 and 234:
lowing initial Elan Bank magma empl
Page 235 and 236:
BIBLIOGRAPHY 1. C. Allegre, A. Prov
Page 237 and 238:
22. B. Charlier, J. Davidson, O. Ba
Page 239 and 240:
46. J. Fitton and M. Godard, Origin
Page 241 and 242:
68. M. Higgins, Measurement of crys
Page 243 and 244:
89. J. Longhi, D. Walker and J. Hay
Page 245 and 246:
100 of Geophysical Monograph, pages
Page 247 and 248:
129. J. Tarduno, W. Sliter, L. Kroe
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