TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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CONTENTS FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x CHAPTER 1: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Crustal Magma Chambers . . . . . . . . . . . . . . . . . . . . . . 6 1.2.1 Magma Chamber Processes: How Do Magmas Evolve? . . 7 1.2.2 Solidification Fronts and Partial Crystallization of Magmas 8 1.3 The Global Significance of Large Igneous Provinces (LIPs) . . . . 11 1.4 Crystal Size Distributions (CSDs): Identification and Examination of Crystal Populations . . . . . . . . . . . . . . . . . . . . . . . . 13 1.5 Crystal Stratigraphy - Microanalysis of Crystal Populations . . . . 15 1.5.1 Plagioclase as a Target for Microanalysis of Basaltic Igneous Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.6 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.6.1 Quantitative Textural Analysis: Crystal Size Distribution Measurement - CSD . . . . . . . . . . . . . . . . . . . . . 17 1.6.2 Major Element Microanalysis: Electron Probe Microanalysis - EPMA . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.6.3 Trace Element Microanalysis: Laser Ablation Inductively Coupled Plasma Mass Spectrometry - LA-ICP-MS . . . . . 18 1.6.4 Microdrilling and Sr isotope microanalysis . . . . . . . . . 19 1.7 Project Introductions . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.7.1 The Ontong Java Plateau, SW Pacific Ocean . . . . . . . . 20 1.7.2 Detroit Seamount, Part of the Emperor Seamount Chain, NW Pacific Ocean . . . . . . . . . . . . . . . . . . . . . . 22 1.7.3 The Kerguelen Plateau’s Western Salient - Elan Bank, Southern Indian Ocean . . . . . . . . . . . . . . . . . . . . . . . 24 iii
CHAPTER 2: MAGMA EVOLUTION REVEALED BY ANORTHITE- RICH PLAGIOCLASE CUMULATE XENOLITHS FROM THE ON- TONG JAVA PLATEAU: INSIGHTS INTO LIP MAGMA DYNAMICS AND MELT EVOLUTION . . . . . . . . . . . . . . . . . . . . . . . . 27 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2 Geologic Background of the Ontong Java Plateau . . . . . . . . . 30 2.3 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3.1 A Cogenetic Relationship Between Xenoliths? . . . . . . . 34 2.4 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.4.1 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . 34 2.4.2 Data Quality . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.4.3 Choosing partition coefficients (D) . . . . . . . . . . . . . 37 2.4.4 Partition Coefficients for OJP Plagioclase Crystals . . . . 39 2.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.5.1 Plagioclase Zoning Patterns . . . . . . . . . . . . . . . . . 49 2.5.1.1 Malaita Xenolith(ML-X1) . . . . . . . . . . . . . . . . . 49 2.5.1.2 Site 1183 Xenoliths . . . . . . . . . . . . . . . . . . . . . 49 2.5.1.3 Site 1183 Phenocrysts . . . . . . . . . . . . . . . . . . . 50 2.5.1.4 Site 807 Xenolith (807-X1) . . . . . . . . . . . . . . . . . 52 2.5.2 Measured compositions . . . . . . . . . . . . . . . . . . . . 61 2.5.2.1 Major Elements . . . . . . . . . . . . . . . . . . . . . . . 61 2.5.2.2 Trace Elements . . . . . . . . . . . . . . . . . . . . . . . 61 2.5.3 Parental magma compositions . . . . . . . . . . . . . . . . 63 2.5.3.1 Major Elements . . . . . . . . . . . . . . . . . . . . . . . 63 2.5.3.2 Trace Elements . . . . . . . . . . . . . . . . . . . . . . . 64 2.5.4 Resorption Features in Site 1183 xenolith Crystals . . . . . 68 2.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 2.6.1 Inferred Chemical Magma Evolution . . . . . . . . . . . . 68 2.6.1.1 Major Elements . . . . . . . . . . . . . . . . . . . . . . . 68 2.6.1.2 An-rich OJP Plagioclase: Influence of Temperature and Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 2.6.1.3 An-rich OJP Plagioclase: Influence of Water . . . . . . . 73 2.6.1.4 Trace Elements . . . . . . . . . . . . . . . . . . . . . . . 74 2.6.2 OJP Magma Chambers, Mush Layers, and Solidification Fronts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 2.7 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . 84 CHAPTER 3: SHALLOW MAGMA EVOLUTION DURING LATE CRE- TACEOUS HAWAIIAN HOTSPOT-RIDGE INTERACTION: INSIGHTS FROM INTEGRATION OF CRYSTAL SIZE DISTRIBUTIONS AND MICROANALYSIS OF PLAGIOCLASE . . . . . . . . . . . . . . . . . 86 iv
Page 1 and 2: TEXTURAL AND MICROANALYSIS OF IGNEO
Page 3 and 4: TEXTURAL AND MICROANALYSIS OF IGNEO
Page 5: DEDICATION This work is dedicated t
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 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
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44 Crystal Zone An (mol%) 63R2 phen
Page 59 and 60:
46 Crystal Zone An (mol%) TABLE 2.1
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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
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should, however, be noted that in t
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2.6.1.2 An-rich OJP Plagioclase: In
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equivocally the roles of H2O, press
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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
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Figure 3.2. Stratigraphy of basalts
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[118]. No volcaniclastic rocks were
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magmatic crystallization. Using the
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Figure 3.3. A cross polarized light
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3.4.5 Major and Trace Element Data
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3.4.6.1 Partition coefficients for
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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
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The Unit 31 plagioclase CSD is kink
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was dominated by late stage clinopy
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pressure, and growth of An-rich pla
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138 TABLE 3.3 PLAGIOCLASE PHENOCRYS
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140 TABLE 3.3 Continued Sample Zone
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Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
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Page 185 and 186:
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KP has been done via drilling at 11
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and over time crustal wall-rocks be
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flow [33]. I selected a single samp
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4.3.4 Major and Trace Element Data
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B) C) parafilm splash guard A) tape
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of these elements are the better co
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5 mm 5 mm Figure 4.4. Cross polariz
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4.4.2 Electron Probe Microanalysis
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An (mol %) An (mol %) An (mol %) An
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study exhibit their highest An at t
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4.4.3 LA-ICP-MS - Trace Elements An
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87 86 Sr/ SrI = 0.705722(8) Ba/Sr =
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and Rb (Fig. 4.11d,e). 4.4.3.3 Yttr
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Sr (ppm) Y (ppm) La (ppm) Ce (ppm)
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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
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lowing initial Elan Bank magma empl
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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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