TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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Ba/Sr Ba/Sr La/Sm 1.20 1.00 0.80 0.60 0.40 0.20 1.20 1.00 0.80 0.60 0.40 0.20 7.00 6.00 5.00 4.00 3.00 2.00 1.00 Unit 4 cores Unit 4 interm. zones Unit 4 rims Unit 10 cores Unit 10 interm. zones Unit 10 rims Site 1137 LG basalts Site 1137 UG basalts 20 40 60 80 100 120 Rb Unit 4 cores Unit 4 interm. zones Unit 4 rims Unit 10 cores Unit 10 interm. zones Unit 10 rims Site 1137 LG basalts Site 1137 UG basalts 0.7045 0.705 0.7055 0.706 0.7065 Unit 4 cores Unit 4 interm. zones Unit 4 rims Unit 10 cores Unit 10 interm. zones Unit 10 rims Site 1137 LG basalts Site 1137 UG basalts 87 Sr/ 86 SrI 0.7045 0.705 0.7055 0.706 0.7065 87 Sr/ 86 SrI Figure 4.14. A) Inverted Unit 4 and 10 plagioclase parent magmas of overlap fields defined by whole-rock data for Site 1137 upper and lower group basalts. B) Inverted Unit 4 and 10 plagioclase parent magma Ba/Sr versus 87 Sr/ 86 SrI and Site 1137 basalt fields drawn using whole-rock data. C) Inverted Unit 4 and 10 plagioclase parent magma La/Sm versus 87 Sr/ 86 SrI and Site 1137 basalt fields drawn using whole-rock data reported by [74]. Plagioclase parent magma compositions overlap whole-rock basalt field well in terms of 87 Sr/ 86 SrI but below or above whole-rock fields. The origin of this anomaly is discussed in the text. 209
that other factors influenced the accuracy of calculated D values. For example, Ba and Sr D values are probably the best constrained because they have been the focus of more partitioning studies than lower abundance elements like the REE (e.g., [7, 10]. My estimate of the trivalent strain-free partition coefficient (D +3 0 ; c.f., [11]) is poorly constrained. A D +3 0 that is too low would lead to systematically low estimates of Y and the REE (i.e., Table 4.4 and Table 4.5; Fig. 4.14c). Trace element diffusion may have also played a role in generating the impres- sion of low trace element and REE abundances in plagioclase parent magmas. This possibility is explored in the next section. 4.5.0.3 Diffusive Redistribution of Trace Elements Cherniak [27] and Cherniak and Watson [24] noted that at magmatic tem- peratures divalent cations diffuse faster through the plagioclase structure than trivalent cations. They also noted that diffusion occurs slower in An-richer plagioclase. Given the intermediate An contents (∼ An54−71) of crystals examined in this study, the possibility of trace element re-distribution via diffusion is rela- tively high. Zellmer et al. [145] presented a test for diffusive equilibrium, which as they noted does not lead to a flat compositional profile, but rather a profile that mirrors the variation in trace element D values most heavily influenced by An content. Equation 4.3 is a adaption of equation 2 of Zellmer et al. [145] that describes partitioning of a trace element (n) between plagioclase compositions A and B. D A/B n = CA n /CB n = DA n /DB n (4.3) 210
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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 [
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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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Page 171 and 172: 158 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
Page 201 and 202: 4.4.2 Electron Probe Microanalysis
Page 203 and 204: An (mol %) An (mol %) An (mol %) An
Page 205 and 206: study exhibit their highest An at t
Page 207 and 208: 4.4.3 LA-ICP-MS - Trace Elements An
Page 209 and 210: 87 86 Sr/ SrI = 0.705722(8) Ba/Sr =
Page 211 and 212: and Rb (Fig. 4.11d,e). 4.4.3.3 Yttr
Page 213 and 214: Sr (ppm) Y (ppm) La (ppm) Ce (ppm)
Page 215 and 216: Unit 4 plagioclase rims plagioclase
Page 217 and 218: 204 TABLE 4.4 UNIT 4 PLAGIOCLASE PA
Page 219 and 220: 4.5 Discussion 4.5.0.1 Origin of Ma
Page 221: 4.5.0.2 Insights from Trace Element
Page 225 and 226: C A/B / D A/B C A/B / D A/B Unit 4
Page 227 and 228: Magma chambers tend to form at hori
Page 229 and 230: whole-rock basalt data. Cumulate xe
Page 231 and 232: over short time spans but may be ea
Page 233 and 234: lowing initial Elan Bank magma empl
Page 235 and 236: BIBLIOGRAPHY 1. C. Allegre, A. Prov
Page 237 and 238: 22. B. Charlier, J. Davidson, O. Ba
Page 239 and 240: 46. J. Fitton and M. Godard, Origin
Page 241 and 242: 68. M. Higgins, Measurement of crys
Page 243 and 244: 89. J. Longhi, D. Walker and J. Hay
Page 245 and 246: 100 of Geophysical Monograph, pages
Page 247 and 248: 129. J. Tarduno, W. Sliter, L. Kroe
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