TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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During core to rim line scans a point was measured every 6 µm using a 5 µm diameter beam. Microprobe data were corrected for matrix effects using a ZAF correction routine. Data points near Fe-rich phases such as melt inclusions and alteration-filled fractures were discarded. 4.3.3 Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP- MS) Scandium, Ti V, Rb, Sr, Y, Ba, La, Ce, Nd, Sm, Eu, and Pb were measured in plagioclase crystals using a New Wave UP-213 UV laser ablation system interfaced with a ThermoFinnigan Element 2 ICP-MS operated in fast magnet scanning mode at the University of Notre Dame. I used a laser frequency of 5 Hz, pulse energy of 0.02-0.03 mJ pulse −1 , 30 µm diameter pits, and helium as the carrier gas (∼ 0.7 l min −1 ) mixed with argon (∼ 1.0 l min −1 ) before introduction to the plasma. Due to the transient nature of the laser ablation signal, analyses were conducted in peak jumping mode with one point quantified per mass. The LA- ICP-MS spots were coincident with previous EPMA analyses, and Ca measured by EPMA was used as an internal standard for each spot analysis. The trace element glass NIST 612 was used as a calibration standard for all laser ablation analyses. Although heterogeneity for certain elements has been documented in the widely used NIST 612 glass i.e., [44], Eggins et al. [44] considered it a reliable calibration standard for the elements examined in this study. The analytical protocols of Longerich et al. [88] were used for LA-ICP-MS data reduction. 179
4.3.4 Major and Trace Element Data quality The quality of EPMA data were monitored by major element and cation totals. Data points where major element totals were greater than 101.5% or less than 98.5% are not used in further discussion nor are points with cation totals greater or less than 20 ± 0.1 cations (based on 32 O). All laser ablation analyses were collected in time-resolved mode so that signal from inclusions and alteration-filled fractures could be easily identified. Results from laser ablation spots close to fractures or that penetrated into underlying fractures were discarded. The rate of laser ablation was tested using a 100 µm thick plagioclase wafer prior to sampling, which allowed optimization of operating conditions to yield desired sensitivity and sampling depth (< 30 µm). 4.3.5 Microdrilling and Sr isotope microanalysis Microdrilling for Sr isotope microanalysis was performed using a Merchantek MicroMill at the University of Durham, UK after completion of EPMA and LA- ICP-MS work. We used a highly tapered tungsten carbide drill bit for all drilling, which provided < 50 µm diameter single drill pits. Microdrilling was performed by setting precision scans consisting of grids and lines of drill points, which allowed us to target zones of interest to maximize the amount of Sr recovered in order to ensure as accurate and precise 87 Sr/ 86 Sr measurements as possible (see Fig. 4.3). Prior to microdrilling, a square 4 cm x 4 cm piece of parafilm pre-cleaned in ultrapure water with a ∼ 2 cm center hole was adhered to the polished sample surface. A droplet of ultrapure water was then placed over the center hole and area to be drilled. The parafilm was used to minimize dispersion of the water droplet and to minimize sample loss. Microdrilling was then performed within the water 180
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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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Page 151 and 152: 138 TABLE 3.3 PLAGIOCLASE PHENOCRYS
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Page 191: flow [33]. I selected a single samp
Page 195 and 196: B) C) parafilm splash guard A) tape
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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 and 222: 4.5.0.2 Insights from Trace Element
Page 223 and 224: that other factors influenced the a
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
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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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