TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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Figure 2.8. Measured MgO (wt %) abundance versus An content of all xenolith plagioclase crystals and plagioclase phenocrysts examined in this study. All data were obtained by EPMA. Magnesium partitioning is weakly affected or unaffected by plagioclase composition e.g., [7]. I suggest low pressure (depth range shallower than 7 km) crystallization of relatively primitive OJP magmas can generate low MgO, An-rich plagioclase. 2.5.3 Parental magma compositions 2.5.3.1 Major Elements Parent magmas of the An-rich xenolith interiors tend to have lower Ti at a given Mg number (Mg/[Mg+Fe]) than phenocryst parent magmas. On a plot of Mg number vs. Ti, phenocryst parent magmas overlap the Kwaimbaita whole-rock basalt field, whereas the An-rich xenolith interiors trend below the fields defined by OJP basalts (Fig. 2.9a; Table 2.3). 63
2.5.3.2 Trace Elements It is difficult to accurately quantify the amount of error introduced by chosen or calculated partition coefficients. Error bars displayed in figures 2.9 and 2.10, which can be compared to analytical uncertainty displayed in figure 2.7, repre- sent the combined potential error related to analytical uncertainty and calculation of partition coefficients using uncertainty on constants reported by Bindeman et al. [7]. Parent magmas of xenolith interiors typically exhibit lower La/Y and Ba/Sr ratios and slightly higher Sr/Ti ratios than phenocryst parent magmas (Tables 2.2and2.3; Fig. 2.9). Parent magmas of the An-rich xenolith interiors are also enriched in Sr, Eu, and Y and relatively depleted in Ba, La, Ce, and Nd rela- tive to phenocryst parent magmas (Tables 2.2, 2.3; Fig. 2.10). Parent magmas of both xenolith crystals and phenocrysts have Sr, Ba, and Eu abundances that overlap published Kwaimbaita and Kroenke basalt whole-rock values, but generally have lower La, Ce, and Nd abundances (see Table 2.3). Given the potential error in calculated D values (compare error bars in Figs. 2.7 and 2.10), OJP plagioclase parent magmas plot in a reasonably consistent manner in terms of La/Y, Sr/Ti, and Ba/Sr ratios, Mg number, Eu and Sr, compared to the Kroenke, Kwaim- baita, and Singgalo whole-rock basalt fields (Fig. 2.9; Table 2.3). For example, the compositions of parent magmas of xenolith interiors from Malaita and Unit 7 of Site 1183 overlap Kroenke and Kwaimbaita basalt fields (see Fig. 2.9). Par- ent magma compositions of xenolith exteriors and phenocrysts from all three Site 1183 Units and xenolith interior parent magmas from Units 5B and 6 consistently trend outside of the fields defined by the whole-rock compositions (Fig. 2.9). Par- ent magmas of the core and rim of phenocryst 63R2P4, the core of 59R2P1, the rim of 59R2P2, and an exterior zone of xenolith 59R2X-1 are unique, because they 64
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TEXTURAL AND MICROANALYSIS OF IGNEO
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TEXTURAL AND MICROANALYSIS OF IGNEO
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DEDICATION This work is dedicated t
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CHAPTER 2: MAGMA EVOLUTION REVEALED
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3.6.3.1 Crystal Population Origins
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FIGURES 1.1 Magma Chambers . . . .
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TABLES 2.1 MAJOR AND TRACE ELEMENT
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thus been debate within the volcano
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Cambrian schist) including a crysta
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explosive eruption vs. mild effusiv
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tiation (e.g., [84, 98]; Fig. 1.3).
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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 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: Figure 2.7. Measured major and trac
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
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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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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
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22. B. Charlier, J. Davidson, O. Ba
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46. J. Fitton and M. Godard, Origin
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68. M. Higgins, Measurement of crys
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89. J. Longhi, D. Walker and J. Hay
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100 of Geophysical Monograph, pages
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129. J. Tarduno, W. Sliter, L. Kroe
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