SPINEL, KALSILITE, CLINOPYROXENE AND OLIVINE by

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II. Geological background San Carlos Volcanic Field is comprised of several vents, one of which, on Peridot Mesa, has been studied the most. The vents erupted pyroclastic tephra and lava flows of basaltic composition. The age of the flows has been dated as 0.58 ± 0.21 Ma by the K-Ar method (Bernatowicz 1981). The flows are generally thin (less than 10 m) and overlie Tertiary lake beds. Xenoliths are found in the flows and bombs around the vent. In addition to the xenoliths, megacrysts of black clinopyroxene, spinel, magnetite, amphibole, and plagioclase are found around the vent area. Since Ross et al. (1954) first examined, in great detail, xenoliths in basaltic rocks from many localities, these xenoliths have been the subject of many studies. Wilshire and Shervais (1975) classified ultramafic xenoliths in basalts from the western United States into two groups: Cr-diopside group and Al-augite group. These groups correspond to Group I and II, respectively, in Frey and Prinz (1978), who reported the petrology and major- and trace-elemental chemistry of San Carlos (SC) samples. Group I xenoliths are characterized by high Mg content (Mg/(Mg + ∑Fe) = 0.86 to 0.91) while Group II xenoliths are more Fe rich (Mg/(Mg + ∑Fe) = 0.62 – 0.78). Olivine-rich peridotites classified as lherzolite and dunite, containing Cr-rich diopside and spinel, dominate Group I while clinopyroxene-rich peridotites such as olivine clinopyroxenite and wehrlite, containing Al- and Ti-rich augite and Al-rich spinel, dominate Group II (Frey and Prinz 1978). Group I xenoliths are reported to contain olivine, orthopyroxene, clinopyroxene and spinel, while those of Group II contain clinopyroxene, olivine, orthopyroxene, spinel, kaersutite, and plagioclase. Neither Group I nor II contains garnet, which sets an upper 20
limit of ~ 25 kbars in the equilibration pressure estimate for the source of both xenolith types and a lower limit of 9 kbar for Group I by the absence of plagioclase. On the basis of their petrographic study, Frey and Prinz (1978) suggest that SC Group I initially formed in equilibrium with silicate magma, which then underwent subsolidus recrystallization at the temperature between 1100 to 1300 º C. Equilibration conditions of the SC samples in this study are reported in APPENDIX D. Group I pyroxenites and wherlite occur as discrete inclusions and also as portions of composite inclusions where they have a sharp planar contact with lherzolite. The origin of those pyroxenite inclusions and their relation with lherzolite have not been established, but are postulated to be of a different origin based on major-elemental analyses. Of our samples, SC 8 and SC 10 are such clinopyroxene-rich inclusions in contact with lherzolite. In these samples, larger relic pyroxene grains up to a couple of centimeters and displaying coarse exsolution lamellae of clino- and orthopyroxene are often present. These relic unrecrystallized pyroxenes attest to an earlier high-temperature history and subsequent slow cooling. Spinel is present as an accessory mineral, often as subhedral to anhedral inclusions in olivine or is molded between other mineral grains. In general olivine-rich Group I xenoliths are interpreted as a residue, many of which have experienced solid deformation in variable degrees. San Carlos Group I samples appear to have undergone a lesser degree of metamorphism resulting from solid flow compared to those found in other localities (Wilshire and Shervais 1975). Group II xenoliths have been interpreted as high-pressure cumulates in numerous studies. From their chemical and textural studies on Group II xenoliths from different localities (e.g., 21
Page 1 and 2: CRYSTAL CHEMICAL AND STRUCTURAL ANA
Page 3 and 4: STATEMENT BY AUTHOR This dissertati
Page 5 and 6: DEDICATION This dissertation is ded
Page 7 and 8: TABLE OF CONTENTS - Continued APPEN
Page 9 and 10: ABSTRACT Natural and synthetic comm
Page 11 and 12: Explanation of the Problem and its
Page 13 and 14: (APPENDIX C), clinopyroxene (APPEND
Page 15 and 16: etween observed structure and the m
Page 17 and 18: close to 1.0 for Fa24 at room tempe
Page 19: crystallization can provide useful
Page 23 and 24: isotopes (Zartman and Tera 1973). F
Page 25 and 26: crystals are present (up to 1 cm) (
Page 27 and 28: Downs (2001). I examined packing di
Page 29 and 30: the substitution of Co for Mg resul
Page 31 and 32: Figure 2. Two melting indicators, A
Page 33 and 34: Fig. 3 cont. (b) (c) (d) 33
Page 35 and 36: Fig. 3 cont. (h) (i) 35
Page 37 and 38: REFERENCES Aoki, K. (1975) Origin o
Page 39 and 40: Princivalle, F., Della Giusta, A.,
Page 41 and 42: APPENDIX A: INVESTIGATION OF SYNTHE
Page 43 and 44: (XEDS) suggested that the Mg-rich i
Page 45 and 46: The presence of a small amount of c
Page 47 and 48: However, the inclusions were too sm
Page 49 and 50: Turner (1968). The refined paramete
Page 51 and 52: is occupied, the nearest octahedral
Page 53 and 54: the observed tetrahedral bond dista
Page 55 and 56: length because of its low abundance
Page 57 and 58: Devanathan, R., Yu, N., Sickafus, K
Page 59 and 60: Nowell, M.M. and Wright, S.I. (2004
Page 61 and 62: Figure 1. BSE images of (a) the sel
Page 63 and 64: Figure 2. XEDS maps and statistics.
Page 65 and 66: Figure 3. EBSD patterns of (a) spin
Page 67 and 68: Figure 5. Two possible structural i
Page 69 and 70: Table 1. Chemical composition of Mg
Page 71 and 72:
Table 3. Comparison of refinement r
Page 73 and 74:
APPENDIX B: AN APPARENT SYMMETRY P6
Page 75 and 76:
Additionally, the same crystal from
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displacive transformation between P
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1955) and later in most kalsilite (
Page 81 and 82:
temperatures on a Bruker X8 APEX si
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oxygen, O1, and assigning O1 off th
Page 85 and 86:
layers was on the 3-fold axis. This
Page 87 and 88:
ecame more perpendicular to the c a
Page 89 and 90:
Downs, R.T. (2000) Analysis of harm
Page 91 and 92:
Figure 1. Unit-cell volume changes
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c-c o 0.06 0.04 0.02 0.00 -0.02 -0.
Page 95 and 96:
Table 1. Chemical composition (wt%)
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Table 3. Summary of crystal data an
Page 99 and 100:
Table 4. Refinement results at room
Page 101 and 102:
Table 4. cont. ====================
Page 103 and 104:
Table 4. cont. ====================
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Single-crystal X-ray diffraction of
Page 107 and 108:
to the host basalt but rather they
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O and T-O bond distances (u = 0.262
Page 111 and 112:
temperature of TQ onto the equilibr
Page 113 and 114:
higher value of Rw, but it insures
Page 115 and 116:
would rigidly constrain the optimiz
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these three figures. In addition to
Page 119 and 120:
Closure temperatures, Tc, for our s
Page 121 and 122:
Bond distances, T-O vs. M-O, are pl
Page 123 and 124:
Finger, L.W. and Prince, E. (1975)
Page 125 and 126:
diffraction study of MgAl2O4 at tem
Page 127 and 128:
Figure 1. Chemistry of spinels from
Page 129 and 130:
129
Page 131 and 132:
131
Page 133 and 134:
Figure 4. Closure temperatures vers
Page 135 and 136:
Figure 6. Bond distances, M-O vs. T
Page 137 and 138:
Table 2. Structural refinement resu
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Table 2. cont. Sample SC 1 SC 11 SC
Page 141 and 142:
Table 4. Cation distribution, inver
Page 143 and 144:
Table 4. cont. Sample Occ T Occ M F
Page 145 and 146:
APPENDIX D: CRYSTAL CHEMISTRY OF CL
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effect on Ucp in case of clinopyrox
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Pyroxene is an important mineralogi
Page 151 and 152:
and M polyhedra (VT and VM, respect
Page 153 and 154:
Ganguly 2003). Liermann and Ganguly
Page 155 and 156:
crystal chemistry of those samples.
Page 157 and 158:
Experimental Crystals were selected
Page 159 and 160:
of both xenoliths types. The absenc
Page 161 and 162:
temperature and pressure for the sa
Page 163 and 164:
elationships among geometrical para
Page 165 and 166:
We examined the datasets to find th
Page 167 and 168:
Figure 6 shows a correlation betwee
Page 169 and 170:
References Basu, A.R. and MacGregor
Page 171 and 172:
Galer, S.J.G. and O’Nions, R.K. (
Page 173 and 174:
Princivalle, F., Salviulo, G., Fabr
Page 175 and 176:
Witt-Eickschen, G. and Seck, H.A. (
Page 177 and 178:
Figure 2. Estimated pressure and te
Page 179 and 180:
(b) 179
Page 181 and 182:
(b) 181
Page 183 and 184:
Figure 6. Correlation between Ucp (
Page 185 and 186:
Table 1. Chemical composition of th
Page 187 and 188:
Table 2. cont. SC19 SC1 SC11 a (Å)
Page 189 and 190:
Table 3. cont. SC19 SC1 SC11 M1 y 0
Page 191 and 192:
Table 5. Pressure and temperature e
Page 193 and 194:
Investigation of distortions from i
Page 195 and 196:
ideal geometry. For olivine, while
Page 197 and 198:
and shown to have a widely ranging
Page 199 and 200:
this viewpoint gave meaningful resu
Page 201 and 202:
201 After the X-ray data collection
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Discussion (1) Relationship between
Page 205 and 206:
NiMgSiO4 (Henderson et al. 2001), F
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increases. As Thompson and Downs (2
Page 209 and 210:
correlated with the average radii o
Page 211 and 212:
211 We have shown in Uchida et al.
Page 213 and 214:
Belokoneva, E.L., Ivanov, Y.A., Sim
Page 215 and 216:
Kimata, M. and Nishida, N. (1987) T
Page 217 and 218:
Smyth, J.R. (1975) High-temperature
Page 219 and 220:
Figure 2. x coordinate vs. y coordi
Page 221 and 222:
Figure 4. Ucp (Å 2 ) as a function
Page 223 and 224:
Ucp 0.075 0.070 0.065 (b) Ucp = 0.0
Page 225 and 226:
Figure 7. Changes in lengths of O-O
Page 227 and 228:
Table 1. Chemical composition of th
Page 229 and 230:
Table 2. cont. SC19 SC1-2 SC11-4 SC
Page 231 and 232:
Table 3.cont. SC8 SC2 SC19 SC1-2 SC
Page 233:
Table 4. Ucp of selected silicate a
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SPINEL, KALSILITE, CLINOPYROXENE AND OLIVINE by

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