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Figure 2.10. Calculated major and trace element abundances of magmas that were parental to the studied plagioclase crystals plotted against the An content of each crystal from: A) ML-X1 (Malaita) and 807-X1 (130-807C-93R-1-137-139); B) ODP Site 1183 Unit 5B xenolith 59R2X1 (192-1183A-59R2 112-117 cm piece #10A); C) ODP Site 1183 Unit 6 xenolith 63R2X1 (192-1183A-63R2 25-27 cm piece #4); D) ODP Site 1183 Unit 7 xenolith 64R2X1 (192-1183A-64R2 116-120 cm piece #9B). Resorption features examined in the Unit 6 and Unit 7 xenolith crystals are noted in columns C and D. Error bars for the y-axis represent the total potential error obtained by combining the uncertainty of LA-ICP-MS measurements and that inherent in calculating the partition coefficients (D) using uncertainties reported in Bindeman et al. [7] using standard error propagation. Error bars for the x-axis represent just analytical uncertainty. 69
should, however, be noted that in their experimental studies Sano and Yamashita [123] observed crystallization of An82 plagioclase from Kroenke basalts (parental to Kwaimbaita basalts) at higher temperatures (∼1200 ◦ C) and lower pressure (0.1 MPa). Although the Mg# of a residual magma decreases with increased olivine fractionation, I see no evidence of olivine-dominated fractionation in xenolith or phenocryst parent magmas (i.e., no systematic difference of parent magma Mg# between the xenolith crystals and phenocrysts). The ranges of Mg# for parent magmas of both xenolith crystals and phenocrysts overlap the range observed for Kwaimbaita basalts (Fig. 2.9a; Table 2.3). Parent magmas of An65−79 phenocryst zones from the three Site 1183 basalt units are compositionally similar with regard to Mg number and Ti abundance (e.g., Fig. 2.9a). This first order observation suggests they share a common parent magma, although some lower An phenocryst zones (i.e., 63R2P4, 59R2P1, and 59R2P2) appear to have more evolved parent magmas (Fig. 2.9). However, when individual units from Site 1183 are considered, the Mg# of the parent magmas changes little with quite a large range in An content (Fig. 2.10b-d), suggesting that the Mg# is buffered. Parent magmas of the An-rich xenolith crystals and phenocrysts extend to more primitive compositions than the Kwaimbaita whole-rock composition (Ta- ble 2.2; Fig. 2.9a). This is contrary to the interpretation of Sano and Yamashita [123] that An-rich zones grew in a relatively evolved and H2O-rich boundary layer. It is thus necessary to elucidate other factors, in addition to growth in a water-rich boundary layer, which favor crystallization of An-rich plagioclase. 70
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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
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12 Figure 1.4: Large Igneous Provin
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distribution of crystal sizes (e.g.
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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 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: 2.5.4 Resorption Features in Site 1
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.
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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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