TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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Figure 2.3. Hand sample and thin section photographs of plagioclase rich xenoliths hosted in Kwaimbaita basalt from ODP Site 807 and Malaita. A) A boulder of Kwaimbaita basalt (SGB-21) from along the Singgalo River, Malaita exhibiting large plagioclase-rich xenoliths. Note rock hammer for scale; B) Mosaic photomicrograph of the interior of Malaita xenolith ML-X1, exhibiting oscillatory zoning; C) Rim of xenolith ML-X1 illustrating destruction of the rim zones by alteration and a clinopyroxene crystal present along the rim; D) Small melt inclusions within ML-X1 that run parallel to zoning features; E) Mosaic photomicrograph of xenolith 807-X1 from ODP Site 807 (130-807C-93R-1-137-139). Note olivine and clinopyroxene along the xenolith margins; F) Altered olivine along the margin of 807-X1. (see 2.3e). I also measured major and trace element data at select points in a variety of phenocrysts from Site 1183 Units 5B, 6, and 7 basalts (Fig. 2.5a-d). I did not examine any plagioclase phenocrysts from Kwaimbaita basalt SGB-21 from Malaita or the Site 807 Kwaimbaita basalt. Detailed descriptions of zoning patterns of the xenolith plagioclase crystals and phenocrysts are provided in the results section. 33
2.3.1 A Cogenetic Relationship Between Xenoliths? Isotopic studies were not conducted on any of the plagioclase crystals in this study. Tejada et al. [133] reported isotopic data for a single OJP plagioclase xenolith, which was isotopically indistinguishable from its Kwaimbaita host basalt (SGB-21, see sample description below). I therefore assume for this study that the plagioclase-rich xenoliths, all in Kwaimbaita host basalt, are indistinguishable from Kwaimbaita-type basalt. 2.4 Methods 2.4.1 Analytical Methods Samples were prepared as polished thick sections (80-100 µm) with Bi-doped epoxy to signal when the sample had been penetrated during LA-ICP-MS analyses e.g., [76]. Bismuth was chosen as a dopant because naturally occurring Bi is well below analytical detection limits in plagioclase. Backscatter electron images and major element analyses were performed using a JEOL JXA-8600 Superprobe electron microprobe at the University of Notre Dame. Backscatter electron images were taken using a 1 µm beam, an accelerating voltage of 20 kV, and a probe current of 25-50 nA. Microprobe analyses were performed using a 5 µm defocused beam, accelerating voltage of 15 kV or 20 kV depending upon samples, a probe current of 20 nA, 15 second on-peak counting time, and two background measurements per peak. I measured Na first to minimize loss via volatilization. Microprobe data were corrected for matrix effects using a ZAF correction method. Data points near Fe-rich phases such as melt inclusions and alteration-filled frac- tures were discarded due to Fe fluorescence effects. Titanium was quantified by EPMA. Strontium, Y, Ba, La, Ce, Nd, and Eu were measured in plagioclase 34
Page 1 and 2: TEXTURAL AND MICROANALYSIS OF IGNEO
Page 3 and 4: TEXTURAL AND MICROANALYSIS OF IGNEO
Page 5 and 6: DEDICATION This work is dedicated t
Page 7 and 8: CHAPTER 2: MAGMA EVOLUTION REVEALED
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: Figure 2.2. Hand sample and thin se
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 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
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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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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
Page 247 and 248:
129. J. Tarduno, W. Sliter, L. Kroe
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