TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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TABLE 2.4 MELTS CRYSTALLIZATION MODELING <strong>OF</strong> AVERAGE OJP BASALTIC GLASSES Pressure (kbar) 0.1 0.7 0.9 Average Site 1183 Kwaimbaita basaltic glass Temperature( ◦ C) 1184 1188 1198 An content 79 79 77 Average Site 1185 Kroenke basaltic glass Temperature( ◦ C) 1200 1204 1216 An content 84 83 82 Glass 192-1185B-16R1, 64 Temperature( ◦ C) 1217 1222 1229 An content 85 84 84 Average Site 1187 Kroenke basaltic glass Temperature( ◦ C) 1200 1206 1218 An content 84 83 82 1 Glass compositions are from [121] 2 Temperature at which plagioclase starts to crystallize 3 Anorthite content of the first-formed plagioclase 71
2.6.1.2 An-rich OJP Plagioclase: Influence of Temperature and Pressure Experimental results have demonstrated that relatively albite-rich plagioclase crystallizes at elevated pressure, and growth of An-rich plagioclase is favored in high temperature magmas at lower pressure e.g., [3, 61, 123, 137]. I used the MELTS program ([2, 55]) to test the likelihood of equilibrium crystallization of An-rich (i.e., >An82) plagioclase at low pressure from relatively hot and primitive OJP magmas. Major element, H2O, and other volatile data reported by Roberge et al. [121] for unaltered Kwaimbaita and Kroenke basaltic glasses from ODP Leg 192 were used as starting compositions for equilibrium crystallization modeling using MELTS (see Table 2.4). Equilibrium crystallization modeling, which was performed to estimate initial crystallization temperature and An content of plagioclase, was run at 0.1 kbar, 0.7 kbar, and 1.9 kbar to also explore the influence of pressure on the composition of crystallizing plagioclase. These pressure estimates adhere to previous models that indicate OJP basalts experienced par- tial crystallization in the shallow crust (< 6-8 km depth) [46, 103, 121, 123]). Results of MELTS modeling demonstrate average Kroenke basaltic glasses from both Site 1187 and 1185, which are considered to be parental to Kwaimbaita basalt e.g., [46, 123], crystallize An84 plagioclase at 1200 ◦ C and 0.1 kbar pressure (see modeling results in Table 2.4). I also modeled crystallization of a single more primitive Kroenke glass with greater MgO, CaO, Al2O3 (sample 1185B-15R-1 149 of Roberge et al., 2004), which crystallized An85 plagioclase at 1217 ◦ C and 0.1 kbar (Table 2.4). There indeed may be more primitive melts, currently un- sampled, that would produce slightly An-richer initial plagioclase (i.e., to account for An86 plagioclase from Malaita xenolith ML-X1). The results of the MELTS numerical simulations suggest equilibrium crystallization a low pressure (i.e., 1 72
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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
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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 and 82: 2.5.4 Resorption Features in Site 1
Page 83: should, however, be noted that in t
Page 87 and 88: equivocally the roles of H2O, press
Page 89 and 90: ent magma requires significant clin
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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
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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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