TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 3.1.1 Magma Evolution in the Crustal Magma Chambers . . . . 87 3.2 The Emperor Seamount Chain . . . . . . . . . . . . . . . . . . . . 91 3.3 Detroit Seamount . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.1 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.2 Volcanic history of Detroit Seamount . . . . . . . . . . . . 92 3.3.3 Sampling Strategy . . . . . . . . . . . . . . . . . . . . . . 93 3.4 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 94 3.4.1 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . 94 3.4.2 Crystal Size Distribution (CSD) Measurement . . . . . . . 94 3.4.3 Electron Probe Microanalysis (EPMA) and Scanning Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . . . 95 3.4.4 Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) . . . . . . . . . . . . . . . . . . . . . . 97 3.4.5 Major and Trace Element Data quality . . . . . . . . . . . 98 3.4.6 Choosing partition coefficients (D) . . . . . . . . . . . . . 98 3.4.6.1 Partition coefficients for DSM plagioclase crystals . . . . 100 3.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 3.5.1 Crystal Size Distributions . . . . . . . . . . . . . . . . . . 101 3.5.1.1 Site 1203 CSDs . . . . . . . . . . . . . . . . . . . . . . . 101 3.5.1.2 Site 884 CSDs . . . . . . . . . . . . . . . . . . . . . . . . 102 3.5.2 CSDs as Guides for Microanalysis . . . . . . . . . . . . . . 107 3.5.3 Petrography and Crystal Zoning Patterns of Microanalysis Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 3.5.3.1 Site 1203 Unit 3 . . . . . . . . . . . . . . . . . . . . . . 107 3.5.3.2 Site 1203 Unit 14 . . . . . . . . . . . . . . . . . . . . . . 109 3.5.3.3 Site 1203 Unit 31 . . . . . . . . . . . . . . . . . . . . . . 111 3.5.3.4 Site 884 Unit 8 . . . . . . . . . . . . . . . . . . . . . . . 111 3.5.4 Major Elements . . . . . . . . . . . . . . . . . . . . . . . . 113 3.5.4.1 Site 1203 Unit 3 . . . . . . . . . . . . . . . . . . . . . . 113 3.5.4.2 Site 1203 Unit 14 . . . . . . . . . . . . . . . . . . . . . . 113 3.5.4.3 Site 1203 Unit 31 and Site 884 Unit 8 . . . . . . . . . . 114 3.5.4.4 Ti variations between crystal populations and Units . . . 114 3.5.5 Trace Elements . . . . . . . . . . . . . . . . . . . . . . . . 116 3.5.5.1 Measured Compositions . . . . . . . . . . . . . . . . . . 116 3.5.5.2 Inferred Parent Magma Compositions . . . . . . . . . . . 116 3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 3.6.1 Evidence of Crystal Sorting . . . . . . . . . . . . . . . . . 120 3.6.1.1 Site 1203 Alkalic Basalts and Tholeiitic Sheet Flows . . 122 3.6.1.2 Site 1203 Pillow Basalts . . . . . . . . . . . . . . . . . . 122 3.6.2 Insights from Plagioclase Major Element Compositions . . 124 3.6.3 Crustal Magma Evolution: Insights from Trace Elements . 127 v
3.6.3.1 Crystal Population Origins . . . . . . . . . . . . . . . . . 127 3.6.4 The Crystal Record of Highly Evolved Magmas . . . . . . 133 3.6.5 Ba and Sr variations: Evidence for Polybaric Crystallization?134 3.7 Summary and Conclusions: Insights Into the Petrogenesis of Depleted Detroit Seamount Basalts . . . . . . . . . . . . . . . . . . . 136 CHAPTER 4: CRUSTAL CONTAMINATION OF BASALTIC MAGMAS REVEALED THROUGH MICROANALYSIS OF MAJOR, MINOR, AND TRACE ELEMENTS AND Sr ISOTOPES IN PLAGIOCLASE: IMPLI- CATIONS FOR ELAN BANK MAGMAS, KERGUELEN PLATEAU, INDIAN OCEAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 4.1.1 Geologic Background of the Kerguelen Plateau and Elan Bank176 4.2 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 4.3 Analytical Techniques . . . . . . . . . . . . . . . . . . . . . . . . 178 4.3.1 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . 178 4.3.2 Electron Probe Microanalysis (EPMA) and Scanning Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . . . 178 4.3.3 Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) . . . . . . . . . . . . . . . . . . . . . . 179 4.3.4 Major and Trace Element Data quality . . . . . . . . . . . 180 4.3.5 Microdrilling and Sr isotope microanalysis . . . . . . . . . 180 4.3.6 Choosing Partition Coefficients (D) . . . . . . . . . . . . . 181 4.3.6.1 Partition coefficients for Elan Bank Plagioclase Crystals 183 4.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 4.4.1 Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . 185 4.4.2 Electron Probe Microanalysis (EPMA) - Major Elements . 188 4.4.3 LA-ICP-MS - Trace Elements . . . . . . . . . . . . . . . . 194 4.4.3.1 Scandium, Ti, V, and Pb . . . . . . . . . . . . . . . . . 194 4.4.3.2 Barium, Sr, and Rb . . . . . . . . . . . . . . . . . . . . 194 4.4.3.3 Yttrium and the Rare Earth Elements La, Ce, Pr, Nd, Sm, and Eu . . . . . . . . . . . . . . . . . . . . . . . . . 198 4.4.4 Sr Isotope Microdrilling . . . . . . . . . . . . . . . . . . . 198 4.4.5 Inferred Parent Magma Compositions . . . . . . . . . . . . 202 4.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 4.5.0.1 Origin of Major Element Zoning and Resorption Surfaces 206 4.5.0.2 Insights from Trace Elements and Inverted Parent Magma Compositions . . . . . . . . . . . . . . . . . . . . . . . . 208 4.5.0.3 Diffusive Redistribution of Trace Elements . . . . . . . . 210 4.5.0.4 Petrogenetic Insights from Plagioclase 87 Sr/ 86 SrI Ratios and the Timing of Crustal Contamination at Elan Bank 213 vi
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: CHAPTER 2: MAGMA EVOLUTION REVEALED
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 and 38: lations. Reprocessing of intrusive
Page 39 and 40: nucleated homogenously and grew thr
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 59 and 60:
46 Crystal Zone An (mol%) TABLE 2.1
Page 61 and 62:
48 Crystal Zone An (mol%) TABLE 2.1
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along the xenolith margins (e.g., F
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are more abundant in phenocrysts fr
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54 Crystal Zone 5 ML-X1 xenolith TA
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56 TABLE 2.2 Continued Crystal Zone
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Figure 2.7. Measured major and trac
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2.5.3.2 Trace Elements It is diffic
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Figure 2.9. Trace element ratio plo
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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
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tion driven plumes, or stirring by
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Yamashita, [123], and thus did not
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erally extensive crystal-mush netwo
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asalt at Site 1185 of ODP Leg 192 [
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CHAPTER 3 SHALLOW MAGMA EVOLUTION D
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magma compositions [23, 39, 98]. A
Page 103 and 104:
Figure 3.2. Stratigraphy of basalts
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[118]. No volcaniclastic rocks were
Page 107 and 108:
magmatic crystallization. Using the
Page 109 and 110:
Figure 3.3. A cross polarized light
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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
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Figure 3.5. Plagioclase CSDs of ODP
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106 TABLE 3.2 CSD RESULTS Sample OD
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ln (n) [mm -4 ] ln (n) [mm -4 ] 10
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ulation A crystals are unzoned (An6
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Figure 3.8. a) The majority of Site
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3.5.4.3 Site 1203 Unit 31 and Site
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3.5.5 Trace Elements 3.5.5.1 Measur
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Unit 31 > Site 884 Unit 8 (Table 3.
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3.6 Discussion 3.6.1 Evidence of Cr
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3.6.1.1 Site 1203 Alkalic Basalts a
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etween the different crystal popula
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Unit 14 and 31 magmas accumulated o
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sition is similar to parent magmas
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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
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140 TABLE 3.3 Continued Sample Zone
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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
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flow [33]. I selected a single samp
Page 193 and 194:
4.3.4 Major and Trace Element Data
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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
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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
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204 TABLE 4.4 UNIT 4 PLAGIOCLASE PA
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4.5 Discussion 4.5.0.1 Origin of Ma
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4.5.0.2 Insights from Trace Element
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that other factors influenced the a
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C A/B / D A/B C A/B / D A/B Unit 4
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Magma chambers tend to form at hori
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whole-rock basalt data. Cumulate xe
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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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TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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