TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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and is most apparent near population B crystal rims where there are changes of up to > 10 mole % An. Population A and B crystals have thin (< 10 µm) rims that are as low as An62. The majority of the population A crystals in Unit 3 samples are unzoned or normally zoned (Fig. 3.7b). There is a small proportion of crystals exhibiting reverse zonation that have chaotic zoning in their crystal cores that on average have lower An than the rims (Fig. 3.8b). Small reverse zoned plagioclase crystals are commonly present in clots of clinopyroxene and plagioclase crystals, where the small clinopyroxene crystals also exhibit reverse zonation (see inset image in Fig. 3.8b). Of the two Unit 3 basalt samples I examined, the sample from the bottom of the flow has a 17% modal abundance of plagioclase and the sample from the top of the flow has 23% modal plagioclase. I did not measure olivine modal abundances in the Unit 3 samples but were estimated to be 3-5 % by Tarduno et al. [128]. 3.5.3.2 Site 1203 Unit 14 The Unit 14 basalt I examined has a massive texture and population B crystals that occur as clusters of euhedral crystals and as occasional individual rounded crystals (e.g., Fig. 3.7b). Population B crystals exhibit oscillatory zoning (e.g., Fig. 3.8e,f) superimposed upon normal zonation with distinct changes in An con- tent near the rims, often a > 10 mole % An change (e.g., Fig. 3.8e,f). The majority ( 95%) of the population A crystals exhibit the zoning pattern displayed in figure 3.8g. This pattern, which is characterized by a change from An69−71 in the core to a thin (2-5 µm) higher An zone then an outermost rim that is An69−71, is similar to the zoning pattern observed along the rims of the population B crystals (e.g., rims in Figs. 3.8e,f vs. Fig. 3.8g). The remaining proportion of the pop- 109
ulation A crystals are unzoned (An64−79) and normal zoned with cores up An82 (e.g., Fig. 3.8h). The single Unit 14 basalt sample I examined has a 20% modal abundance of plagioclase. I did not measure olivine modal abundances in the Unit 14 sample and Tarduno et al. [128] did not note any olivine in this sample. Figure 3.7. In each basalt chosen for microanalysis large phenocrysts (i.e., population B crystals) are present as glomerocrysts and individual crystals that are commonly rounded or embayed. The field of view in each photomicrograph is 2 cm. Large plagioclase phenocrysts are a) 0.5-2 mm in Site 1203 Unit 3; b) 1-8 mm in Site 1203 Unit 14; c) 1-4 mm in Site 1203 Unit 31; d) up to 1.5 cm in the sample from the middle of Site 884 Unit 8; and e) up to 1.5 cm from the bottom of Site 884 Unit 8. 110
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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
Page 71 and 72: 58 TABLE 2.2 Continued Crystal Zone
Page 73 and 74: 60 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
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: ln (n) [mm -4 ] ln (n) [mm -4 ] 10
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 and 150: pressure, and growth of An-rich pla
Page 151 and 152: 138 TABLE 3.3 PLAGIOCLASE PHENOCRYS
Page 153 and 154: 140 TABLE 3.3 Continued Sample Zone
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160 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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