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<journal-meta>
<journal-id journal-id-type="archive">gsminmag</journal-id>
<journal-title>Mineralogical Magazine</journal-title>
<abbrev-journal-title abbrev-type="full">Mineralogical Magazine</abbrev-journal-title>
<issn pub-type="ppub">0026-461X</issn>
<publisher>
<publisher-name>Mineralogical Society</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.1180/minmag.1982.045.337.14</article-id>
<title-group>
<article-title>Cr-rich Spinel and Garnet in Two Peridotite Xenoliths from the Frank Smith Mine South Africa: Significance of Al and Cr Distribution Between Spinel and Garnet</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Exley</surname>
<given-names>R. A.</given-names>
</name></contrib>
<contrib contrib-type="author">
<name>
<surname>Smith</surname>
<given-names>J. V.</given-names>
</name></contrib>
<contrib contrib-type="author">
<name>
<surname>Hervig</surname>
<given-names>R. L.</given-names>
</name>
<xref ref-type="author-notes" rid="FN1">*</xref></contrib>
<aff>Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637 USA</aff></contrib-group>
<author-notes>
<fn fn-type="present-address" id="FN1"><label>*</label><p>Present address: Department of Chemistry, Arizona State University, Tempe, Arizona 85281 USA.</p></fn></author-notes>
<pub-date pub-type="ppub">
<year>1982</year>
</pub-date>
<volume>45</volume>
<issue>337</issue>
<fpage>129</fpage>
<lpage>134</lpage>
<copyright-statement>Copyright &#x00A9; 1982, The Mineralogical Society</copyright-statement>
<copyright-year>1982</copyright-year>
<abstract>
<title>Abstract</title>
<p>Peridotite xenoliths 73&#x2013;106 and 73&#x2013;109 have coarse textures. All minerals in 73&#x2013;106 are very Ti-rich, and include olivine (Fo 87.6), orthopyroxene (En 90.0), garnet (core TiO<sub>2</sub> 0.8, Cr<sub>2</sub>O<sub>3</sub> 7; rim 1.4, 4 wt. %), spinel (TiO<sub>2</sub> 5, Cr<sub>2</sub>O<sub>3</sub> 38), clinopyroxene (A1<sub>2</sub>O<sub>3</sub> 1&#x2013;8) secondary mica (TiO<sub>2</sub> 6, Cr<sub>2</sub>O<sub>3</sub> 2.5 near garnet 0.5 away from garnet), and serpentine (FeO 5&#x2013;12) enclosing perovskite-rimmed ilmenite and minute apatites. All minerals in peridotite 73&#x2013;109 are Ti-poor, and include olivine (Fo 92.6), orthopyroxene (En 93.6), garnet (Cr<sub>2</sub>O<sub>3</sub> 3.1&#x2013;3.8), spinel (55), ureyitic diopside, primary mica (TiO<sub>2</sub> 0.06, Cr<sub>2</sub>O<sub>3</sub> 1.0, BaO 0.5, Cl 0.04), and serpentine (FeO 2&#x2013;23). Various thermometers indicate &#x223C; 1350K (73&#x2013;106) and 1100K (73&#x2013;109). The low Al<sub>2</sub>O<sub>3</sub> in the orthopyroxenes gives 39&#x2013;47 kb for 73&#x2013;109 from the Wood-Banno barometer. In 73&#x2013;106, the spinel lies in secondary mica next to the garnet rim, whereas the spinel of 73&#x2013;109 occurs in grains enclosed by garnet. The former assemblage indicates diffusion-dependent disequilibrium, whereas the latter is attributed to simultaneous growth of spinel and garnet, perhaps consequent upon exsolution from orthopyroxene. Complex behaviour was found for the Cr/Al distribution in published analyses of garnet and spinel. The 73&#x2013;109 pair lies near the Thaba Putsoa trend, and the 73&#x2013;106 assemblages are displaced towards the kely-phite region in which garnet and spinel have similar Cr/Al. Spinel and garnet may coexist over a 30 kb pressure interval ranging from &#x223C; 16 kb for low bulk Cr to &#x223C; 40 kb for high Cr.</p></abstract>
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