TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

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trivalent REE diffuse slower that the more abundant divalent cations (i.e., Sr and Ba). This indicates that investigation of REE diffusion in plagioclase may provide a more extensive time record of magmatic residence. Although plagioclase trace element studies have proven to be useful, perhaps the most robust future petrologic insights will come from intramineral isotope studies beyond Sr (including Pb, Sm-Nd for example). Mineral scale isotope studies are limited by the amount of the element of interest in the mineral. For example, the greater abundance of Sr in plagioclase versus clinopyroxene makes Sr isotope microanalysis of plagioclase much less difficult. Improvement of ion- ization efficiency in TIMS analysis can help alleviate some of this problem (e.g., discussion in [40]), as can instrumentation advances that improve signal intensity at a given concentration (e.g., guard electrodes). One of the difficulties faced with a microdrill-TIMS approach is the high incidence of fracturing, flaking, and inadvertent sampling of undesired zones. Perhaps one of the surest ways to improve the controlled removal of mineral material for isotopic analysis is through the use of laser ablation [40]. Laser ablation based isotopic studies generally requires interfacing the LA system with a multicollector ICP-MS. The use of a Ar based plasma introduces a host of issues and interferences not encountered with TIMS. For example Ar used in ICP-MS commonly contains trace Kr, of which 86 Kr (17.37% abundance) represents a particularly problematic polybaric interference. At present a variety of corrections are necessary to obtain close to meanigful 87 Sr/ 86 Srm by MC-LA-ICP-MS. If mineral standards were available for isotopic analyses, quality control of MC-LA-ICP-MS work would be more straightforward. 221
BIBLIOGRAPHY 1. C. Allegre, A. Provost and C. Jaupart, Oscillatory zoning: a pathological case of crystal growth. Nature, 294: 223–228 (1981). 2. P. Asimow and M. Ghiorso, Algorithmic modifications extending MELTS to calculate subsolidus phase relations. American Mineralogist, 83(1127-1131) (1998). 3. K. Bartels, R. Kinzler and T. G. and, High pressure phase relations of primitive high-alumina basalts from Medicine Lake volcano, northern California. Contributions to Mineralogy and Petrology, 108: 253–270 (1991). 4. G. Bergantz, Melt fraction diagrams: the link between chemical and transport models. In J. Nicholls and J. Russell, editors, Modern methods of igneous petrology: Understanding magmatic processes, volume 24 of Reviews in Mineralogy, pages 239–258, Mineralogical Society of America (1990). 5. I. Bindeman and J. Bailey, Trace elements in anorthite megacrysts from the Kurile Island Arc: A window to across-arc geochemical variations in magma compositions. Earth and Planetary Science Letters, 169: 209–226 (1999). 6. I. Bindeman and A. Davis, Trace element partitioning between plagioclase and melt: Investigation of dopant influence on partition behavior. Geochimica et Cosmochimica Acta, 63: 2863–2878 (2000). 7. I. Bindeman, A. Davis and M. Drake, Ion microprobe study of plagioclasebasalt partition experiments at natural concentration levels in trace elements. Geochimica et Cosmochimica Acta, 62(7): 1175–1193 (1998). 8. I. Bindeman, A. Davis and S. Wickham, 400 m.y. of basic magmatism in a single lithospheric block during cratonization: ion microprobe study of plagioclase megacrysts in mafic rocks from transbaikalia, russia. Journal of Petrology, 40: 807–830 (1999). 9. J. Blundy, Experimental study of a Kiglapait marginal rock and implications for trace element partitioning in layered intrusions. Chemical Geology, 141: 73–92 (1997). 222
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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 183 and 184: 170 TABLE 3.4 Continued Sample Zone
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Page 193 and 194: 4.3.4 Major and Trace Element Data
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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
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Page 209 and 210: 87 86 Sr/ SrI = 0.705722(8) Ba/Sr =
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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
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Page 225 and 226: C A/B / D A/B C A/B / D A/B Unit 4
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Page 229 and 230: whole-rock basalt data. Cumulate xe
Page 231 and 232: over short time spans but may be ea
Page 233: lowing initial Elan Bank magma empl
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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