TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

More documents

Recommendations

Info

origins via accumulation or magma mixing. Unit 3 population A and B crystal cores have overlapping An content, which suggests the two crystal populations could have formed under similar conditions. There are, however, two groups of Unit 3 population A crystals in terms of core An content. This grouping may be an artifact of limited sampling, as the population A crystals from Units 14 and 31 span a similar range of An content. Experimental studies have shown that in low H2O magmas relatively albite-rich plagioclase crystallizes at elevated pressure, and growth of An-rich plagioclase is favored in high temperature magmas at lower pressures [3, 61, 137]. Based strictly upon An content, this suggests that population B crystals from Units 14 and 31 formed at lower mean pressures in shallower magma chambers relative to population B crystals from Unit 3 and all population A crystals. The lack of variation in Mg# [Mg/(Mg+total Fe)] between crystal populations is likely related to the poorly constrained manner in which Fe and Mg partition into plagioclase (i.e., partitioning into more than one site under different conditions; [7, 117]; Fig. 3.9d). The negative correlation of Ti abundance with An content is undoubtedly related to enhanced Ti partitioning into the more elastic structure of lower An plagioclase [11] (Fig. 3.9e). However, if each unit is consid- ered individually, there is minimal correlation of Ti abundance with An content at An > 70. Based upon this observation, I suggest Unit 3 population B crystals grew from a magma that was slightly more Ti-rich than parent magmas of population B crystals from Units 14 and 31 and much more Ti-rich than Site 884 Unit 8 population B parent magmas. A working hypothesis based upon CSD results, mineral zoning, and major element compositions is that the Site 884 Unit 8 and 10 magmas and Site 1203 125
Unit 14 and 31 magmas accumulated older plagioclase crystals. Based strictly upon CSD results, petrography, plagioclase An variations, and the conclusions of Huang et al. [72], I suggest that accumulation was the dominant mechanism for generation of non-linear CSDs. Magmas ascending from depth accumulated crystals from the margins of shallow magma chambers and/or conduits. This magma experienced minor partial crystallization in a a deeper magma chamber and/or partial crystallization related to cooling during ascent to form the population A crystals. As the population B crystals were stirred up and accumulated they were partially resorbed, which is consistent with my petrographic observations and the whole-rock results reported by Huang et al. [72]. The Unit 3 magma experienced minor plagioclase accumulation that was accentuated by flow sorting or plagioclase flotation. Unit 3 population A and B crystals appear to share a common parent magma. At least two different parent magma compositions are recorded in Units 14 and 31 each, which I suggest were from the same source but had experienced different degrees of plagioclase-dominated partial (fractional, equilibrium, or in-situ) crystallization. My limited sampling of Site 884 Unit 8 reflects only one unique parent magma composition (i.e., that of the population B crystals). Mea- sured trace element abundances and inferred parent magma compositions allow us to test this working hypothesis and constrain the parent magma compositions of each crystal population as well as assess potential differences in source affinity for each parent magma. 126
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 and 46:
Figure 2.2. Hand sample and thin se
Page 47 and 48:
2.3.1 A Cogenetic Relationship Betw
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 59 and 60:
Page 61 and 62:
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 71 and 72:
Page 73 and 74:
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 and 122: ln (n) [mm -4 ] ln (n) [mm -4 ] 10
Page 123 and 124: ulation A crystals are unzoned (An6
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: etween the different crystal popula
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
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 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
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
show all

TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?