TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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in Detroit Seamount basalts. Unit 14 magma mixing does suggest, however, that subtle variations in partial melting or source compositions do occur over relatively short time spans but may be easily overlooked in whole-rock compositional studies. I suggest this variation is consistent with subtle variations in partial melting of a heterogeneous mantle source that consisted of relatively depleted and relatively enriched components (cf. [50, 72, 119]) Subtle variations in partial melting are consistent with enhanced mantle flow and complex mantle dynamics in the near ridge hotspot environment as discussed by Pearce [114]. The nature of the depleted component in Detroit Seamount basalts is prominent in tholeiitic basalts from Site 884, and perhaps most prominent in the cm-size plagioclase phenocrysts. These large crystals have low Sr parent magmas suggesting they were less evolved than their host basalt. A fruitful continuation of this research would be to conduct Sr and Pb isotope studies on these large crystals by in-situ microdrilling (e.g., [39]) or plagioclase separation (e.g., [16]). 137
138 TABLE 3.3 PLAGIOCLASE PHENOCRYST MAJOR <strong>AND</strong> TRACE ELEMENT DATA Sample Zone 1 2 Pop. An FeOT P2O5 K2O TiO2 Na2O CaO MgO SiO2 Al2O3 Total Mg# Ti Rb Sr Y Ba La Ce Nd Sm Eu (mol%) 3 Site 1203 Unit 3 A C B 80 0.63 0.15 0.03 0.06 2.20 15.91 0.19 47.15 33.81 100.13 0.19 275.2 – 393 0.14 10.2 0.28 0.76 0.33 0.05 0.23 A I B 74 0.67 0.15 0.06 0.06 2.88 15.04 0.19 48.82 32.75 100.62 0.18 – – 378 0.15 10.4 0.28 0.77 0.26 0.08 0.28 A I B 75 0.67 0.13 0.04 0.06 2.72 15.08 0.18 48.62 32.87 100.37 0.18 269.2 – 369 0.14 9.89 0.28 0.75 0.29 0.09 0.25 A I B 80 0.71 0.13 0.02 0.01 2.20 16.16 0.21 46.89 33.47 99.80 0.18 277.0 – 391 0.10 9.92 0.29 0.72 0.30 0.05 0.25 A I B 80 0.62 0.15 0.03 0.04 2.25 16.05 0.17 46.57 33.33 99.22 0.18 288.4 – 395 0.13 10.4 0.32 0.72 0.26 0.08 0.25 A I B 80 0.64 0.15 0.02 0.07 2.20 16.03 0.18 46.44 33.68 99.41 0.18 293.2 – 400 0.14 10.5 0.31 0.77 0.33 0.08 0.25 A I B 79 0.66 0.16 0.04 0.04 2.27 15.51 0.17 47.69 32.97 99.50 0.17 299.2 – 369 0.11 9.54 0.27 0.71 0.27 0.07 0.22 A I B 78 0.64 0.16 0.03 0.03 2.34 15.60 0.18 46.43 34.05 99.46 0.18 277.0 – 360 0.11 9.43 0.28 0.68 0.25 0.03 0.23 A I B 78 0.65 0.16 0.02 0.05 2.43 15.61 0.19 47.38 32.91 99.41 0.19 – – – – – – – – – – A R B 70 0.77 0.13 0.05 0.05 3.20 13.91 0.22 49.15 32.06 99.55 0.18 – – – – – – – – – – B C B 79 0.64 0.16 0.03 0.03 2.29 15.53 0.18 47.93 32.61 99.40 0.18 257.2 – 355 0.10 9.23 0.28 0.63 0.25 0.09 0.24 continued...
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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)
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microdrilling, a pre-cleaned square
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1.7.2 Detroit Seamount, Part of the
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lations. Reprocessing of intrusive
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nucleated homogenously and grew thr
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With accurate partition coefficient
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uniform composition of large volume
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Figure 2.2. Hand sample and thin se
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2.3.1 A Cogenetic Relationship Betw
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Figure 2.4. Stratigraphic section o
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Figure 2.5. Backscatter electron im
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studies of Kwaimbaita basalt by San
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42 Crystal Zone An (mol%) TABLE 2.1
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44 Crystal Zone An (mol%) 63R2 phen
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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 [
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
Page 135 and 136: 3.6.1.1 Site 1203 Alkalic Basalts a
Page 137 and 138: etween the different crystal popula
Page 139 and 140: Unit 14 and 31 magmas accumulated o
Page 141 and 142: sition is similar to parent magmas
Page 143 and 144: 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: pressure, and growth of An-rich pla
Page 153 and 154: 140 TABLE 3.3 Continued Sample Zone
Page 187 and 188: KP has been done via drilling at 11
Page 189 and 190: and over time crustal wall-rocks be
Page 191 and 192: flow [33]. I selected a single samp
Page 193 and 194: 4.3.4 Major and Trace Element Data
Page 195 and 196: 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
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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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