Exotic origin of the ruby deposits of the Mangari area in SE Kenya
Identifieur interne : 001F52 ( Istex/Corpus ); précédent : 001F51; suivant : 001F53Exotic origin of the ruby deposits of the Mangari area in SE Kenya
Auteurs : A. Mercier ; P. Debat ; John M. SaulSource :
- Ore Geology Reviews [ 0169-1368 ] ; 1999.
Abstract
The Proterozoic Mozambique Belt contains numerous primary deposits of gem-corundum (i.e., ruby and sapphire). The ruby deposits in the Mangari area of SE Kenya, are among the most productive and best known. Enclosed within a metasedimentary sequence dominated by sillimanite-graphitic gneisses, the Mangari deposits are associated with rootless ultrabasic bodies. Ruby occurs (1) in lenses on the inner side of the contacts between the ultrabasites and the surrounding metasediments and (2) in veins within the ultrabasic bodies or forming their margins. Field relationships reveal that the corundum-bearing rocks are genetically related to the ultrabasic bodies but not to the surrounding gneisses. Laboratory studies and petrographic comparisons indicate that the ruby-bearing rocks crystallized under granulite facies conditions of 700–750°C and 8–10.5 kbar. By contrast, the surrounding gneisses show only amphibolite facies metamorphism with maximum temperatures around 650°C and pressures which did not exceed 7 kbar. At Mangari, the ruby-bearing rocks, as their associated ultrabasites, appear to be exotic with respect to the surrounding metasedimentary rocks. We interpret them as fragments of a deeper crust brought up to their present-day exposure level by the ultrabasic bodies during their emplacement as thrust sheets. Similar reasoning may account for the presence of charnockitic gneisses nearby. By contrast, granulite facies metamorphism characterizes all rock types genetically relatable to the Tanzanian ruby deposits at Longido and Lossogonoi, both also situated in the Mozambique Belt. This suggests that, if associated with ultrabasites, primary deposits of rubies (and of subgem red corundum) formed only under granulite facies conditions in the Mozambique Belt. Some of these deposits were subsequently tectonically inserted into country rocks of lower metamorphic grade. This apparently occurred without the total fracturing of all crystalline gems.
Url:
DOI: 10.1016/S0169-1368(99)00002-5
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<record><TEI wicri:istexFullTextTei="biblStruct"><teiHeader><fileDesc><titleStmt><title>Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title><author><name sortKey="Mercier, A" sort="Mercier, A" uniqKey="Mercier A" first="A." last="Mercier">A. Mercier</name><affiliation><mods:affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</mods:affiliation></affiliation></author><author><name sortKey="Debat, P" sort="Debat, P" uniqKey="Debat P" first="P." last="Debat">P. Debat</name><affiliation><mods:affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</mods:affiliation></affiliation></author><author><name sortKey="Saul, John M" sort="Saul, John M" uniqKey="Saul J" first="John M." last="Saul">John M. Saul</name><affiliation><mods:affiliation>ORYX, 3 rue Bourdaloue, 75009 Paris, France</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:A62D09A532A7DF0643392A40396CD45BB3AED48C</idno><date when="1999" year="1999">1999</date><idno type="doi">10.1016/S0169-1368(99)00002-5</idno><idno type="url">https://api.istex.fr/document/A62D09A532A7DF0643392A40396CD45BB3AED48C/fulltext/pdf</idno><idno type="wicri:Area/Istex/Corpus">001F52</idno><idno type="wicri:explorRef" wicri:stream="Istex" wicri:step="Corpus" wicri:corpus="ISTEX">001F52</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a">Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title><author><name sortKey="Mercier, A" sort="Mercier, A" uniqKey="Mercier A" first="A." last="Mercier">A. Mercier</name><affiliation><mods:affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</mods:affiliation></affiliation></author><author><name sortKey="Debat, P" sort="Debat, P" uniqKey="Debat P" first="P." last="Debat">P. Debat</name><affiliation><mods:affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</mods:affiliation></affiliation></author><author><name sortKey="Saul, John M" sort="Saul, John M" uniqKey="Saul J" first="John M." last="Saul">John M. Saul</name><affiliation><mods:affiliation>ORYX, 3 rue Bourdaloue, 75009 Paris, France</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Ore Geology Reviews</title><title level="j" type="abbrev">OREGEO</title><idno type="ISSN">0169-1368</idno><imprint><publisher>ELSEVIER</publisher><date type="published" when="1999">1999</date><biblScope unit="volume">14</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="83">83</biblScope><biblScope unit="page" to="104">104</biblScope></imprint><idno type="ISSN">0169-1368</idno></series><idno type="istex">A62D09A532A7DF0643392A40396CD45BB3AED48C</idno><idno type="DOI">10.1016/S0169-1368(99)00002-5</idno><idno type="PII">S0169-1368(99)00002-5</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0169-1368</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">The Proterozoic Mozambique Belt contains numerous primary deposits of gem-corundum (i.e., ruby and sapphire). The ruby deposits in the Mangari area of SE Kenya, are among the most productive and best known. Enclosed within a metasedimentary sequence dominated by sillimanite-graphitic gneisses, the Mangari deposits are associated with rootless ultrabasic bodies. Ruby occurs (1) in lenses on the inner side of the contacts between the ultrabasites and the surrounding metasediments and (2) in veins within the ultrabasic bodies or forming their margins. Field relationships reveal that the corundum-bearing rocks are genetically related to the ultrabasic bodies but not to the surrounding gneisses. Laboratory studies and petrographic comparisons indicate that the ruby-bearing rocks crystallized under granulite facies conditions of 700–750°C and 8–10.5 kbar. By contrast, the surrounding gneisses show only amphibolite facies metamorphism with maximum temperatures around 650°C and pressures which did not exceed 7 kbar. At Mangari, the ruby-bearing rocks, as their associated ultrabasites, appear to be exotic with respect to the surrounding metasedimentary rocks. We interpret them as fragments of a deeper crust brought up to their present-day exposure level by the ultrabasic bodies during their emplacement as thrust sheets. Similar reasoning may account for the presence of charnockitic gneisses nearby. By contrast, granulite facies metamorphism characterizes all rock types genetically relatable to the Tanzanian ruby deposits at Longido and Lossogonoi, both also situated in the Mozambique Belt. This suggests that, if associated with ultrabasites, primary deposits of rubies (and of subgem red corundum) formed only under granulite facies conditions in the Mozambique Belt. Some of these deposits were subsequently tectonically inserted into country rocks of lower metamorphic grade. This apparently occurred without the total fracturing of all crystalline gems.</div></front></TEI><istex><corpusName>elsevier</corpusName><author><json:item><name>A. Mercier</name><affiliations><json:string>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</json:string></affiliations></json:item><json:item><name>P. Debat</name><affiliations><json:string>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</json:string></affiliations></json:item><json:item><name>John M. Saul</name><affiliations><json:string>ORYX, 3 rue Bourdaloue, 75009 Paris, France</json:string></affiliations></json:item></author><subject><json:item><lang><json:string>eng</json:string></lang><value>ruby deposits</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>Mozambique Belt</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>Kenya</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>ultrabasites</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>granulite facies</value></json:item></subject><language><json:string>eng</json:string></language><originalGenre><json:string>Full-length article</json:string></originalGenre><abstract>The Proterozoic Mozambique Belt contains numerous primary deposits of gem-corundum (i.e., ruby and sapphire). The ruby deposits in the Mangari area of SE Kenya, are among the most productive and best known. Enclosed within a metasedimentary sequence dominated by sillimanite-graphitic gneisses, the Mangari deposits are associated with rootless ultrabasic bodies. Ruby occurs (1) in lenses on the inner side of the contacts between the ultrabasites and the surrounding metasediments and (2) in veins within the ultrabasic bodies or forming their margins. Field relationships reveal that the corundum-bearing rocks are genetically related to the ultrabasic bodies but not to the surrounding gneisses. Laboratory studies and petrographic comparisons indicate that the ruby-bearing rocks crystallized under granulite facies conditions of 700–750°C and 8–10.5 kbar. By contrast, the surrounding gneisses show only amphibolite facies metamorphism with maximum temperatures around 650°C and pressures which did not exceed 7 kbar. At Mangari, the ruby-bearing rocks, as their associated ultrabasites, appear to be exotic with respect to the surrounding metasedimentary rocks. We interpret them as fragments of a deeper crust brought up to their present-day exposure level by the ultrabasic bodies during their emplacement as thrust sheets. Similar reasoning may account for the presence of charnockitic gneisses nearby. By contrast, granulite facies metamorphism characterizes all rock types genetically relatable to the Tanzanian ruby deposits at Longido and Lossogonoi, both also situated in the Mozambique Belt. This suggests that, if associated with ultrabasites, primary deposits of rubies (and of subgem red corundum) formed only under granulite facies conditions in the Mozambique Belt. Some of these deposits were subsequently tectonically inserted into country rocks of lower metamorphic grade. This apparently occurred without the total fracturing of all crystalline gems.</abstract><qualityIndicators><score>8</score><pdfVersion>1.2</pdfVersion><pdfPageSize>540 x 712 pts</pdfPageSize><refBibsNative>true</refBibsNative><keywordCount>5</keywordCount><abstractCharCount>1975</abstractCharCount><pdfWordCount>8029</pdfWordCount><pdfCharCount>51842</pdfCharCount><pdfPageCount>22</pdfPageCount><abstractWordCount>280</abstractWordCount></qualityIndicators><title>Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title><pii><json:string>S0169-1368(99)00002-5</json:string></pii><refBibs><json:item><author><json:item><name>D. Ackermand</name></json:item><json:item><name>F. Seifert</name></json:item><json:item><name>W. Schreyer</name></json:item></author><host><volume>12</volume><pages><last>12</last><first>1</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Instability of sapphirine at high pressure</title></json:item><json:item><author><json:item><name>J.M. Allen</name></json:item><json:item><name>J.J. Fawcett</name></json:item></author><host><volume>23</volume><pages><last>239</last><first>215</first></pages><author></author><title>J. Petrol.</title></host><title>Zoisite–anorthite–calcite stability relations in H2O–CO2 fluids at 5000 bars: an experimental and SEM study</title></json:item><json:item><author><json:item><name>R. Altherr</name></json:item><json:item><name>M. Okrusch</name></json:item><json:item><name>H. Bank</name></json:item></author><host><volume>15</volume><pages><last>197</last><first>191</first></pages><author></author><title>Lithos</title></host><title>Corundum and kyanite-bearing anatexites from the Precambrian of Tanzania</title></json:item><json:item><author><json:item><name>M.A.G. Andreoli</name></json:item></author><host><volume>25</volume><pages><last>186</last><first>161</first></pages><author></author><title>Precambrian Res.</title></host><title>Petrochemistry, tectonic evolution and metasomatic mineralisations of Mozambique Belt granulites from S. Malawi and Tete (Mozambique)</title></json:item><json:item><author><json:item><name>L. Aranovitch</name></json:item><json:item><name>K.K. Podlesskii</name></json:item></author><host><volume>251</volume><pages><last>1219</last><first>1216</first></pages><author></author><title>Acad. Nauk. USSR Dokl.</title></host><title>Garnet–plagioclase geobarometer</title></json:item><json:item><author><json:item><name>J.D. Arneth</name></json:item><json:item><name>M. Schidlowski</name></json:item><json:item><name>B. Sarbas</name></json:item><json:item><name>V. Goerg</name></json:item><json:item><name>G.C. Amstutz</name></json:item></author><host><volume>49</volume><pages><last>1560</last><first>1553</first></pages><author></author><title>Geochim. Cosmochim. Acta</title></host><title>Graphite content and isotopic fractionation between calcite–graphite pairs in metasediments from the Mgama Hills, southern Kenya</title></json:item><json:item><author><json:item><name>S.M. Berhe</name></json:item></author><host><volume>147</volume><pages><last>57</last><first>41</first></pages><author></author><title>J. Geol. Soc. London</title></host><title>Ophiolites in Northeast and East Africa: implications for Proterozoic crustal growth</title></json:item><json:item><author><json:item><name>R.G. Berman</name></json:item></author><host><volume>29</volume><pages><last>522</last><first>445</first></pages><author></author><title>J. Petrol.</title></host><title>Internally-consistent thermodynamic data for minerals in the system Na2O–K2O–CaO–MgO–FeO–Fe2O3–Al2O3–SiO2–TiO2–H2O–CO2</title></json:item><json:item><author><json:item><name>R.G. Berman</name></json:item></author><host><volume>75</volume><pages><last>344</last><first>328</first></pages><author></author><title>Am. Mineral.</title></host><title>Mixing properties of Ca–Mg–Fe–Mn garnets</title></json:item><json:item><author><json:item><name>R.G. Berman</name></json:item></author><host><volume>29</volume><pages><last>855</last><first>833</first></pages><author></author><title>Can. Mineral.</title></host><title>Thermobarometry using multi-equilibrium calculations: a new technique with petrological applications</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>K. Burke</name></json:item><json:item><name>A.M.C. Sengor</name></json:item></author><host><volume>14</volume><pages><last>53</last><first>41</first></pages><author></author><title>Am. Geophys. Union Geodyn. Ser.</title></host><title>Tectonic escape in the evolution of the continental crust</title></json:item><json:item><author><json:item><name>I. Cartwright</name></json:item><json:item><name>A.C. Barnicoat</name></json:item></author><host><volume>3</volume><pages><last>99</last><first>79</first></pages><author></author><title>J. Metamorph. Geol.</title></host><title>The generation of quartz-normative melts and corundum-bearing restites by crustal anatexis: petrogenetic modelling based on an example from the Lewisian of northwest Scotland</title></json:item><json:item><author><json:item><name>S.V. Chernosky</name></json:item><json:item><name>H.W. Day</name></json:item><json:item><name>L.S. Caruso</name></json:item></author><host><volume>70</volume><pages><last>236</last><first>223</first></pages><author></author><title>Am. Mineral.</title></host><title>Equilibria in the system MgO–SiO2–H2O. An experimental determination of the stability of Mg-anthophyllite</title></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>J.M. Ferry</name></json:item><json:item><name>F.S. Spear</name></json:item></author><host><volume>66</volume><pages><last>117</last><first>113</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Experimental calibration of the partitioning of Fe and Mg between biotite and garnet</title></json:item><json:item><author><json:item><name>W. Frisch</name></json:item><json:item><name>W. Pohl</name></json:item></author><host><volume>78</volume><pages><last>114</last><first>97</first></pages><author></author><title>Mitt. Österr. Geol. Ges.</title></host><title>Petrochemistry of some mafic and ultramafic rocks from the Mozambique Belt, SE Kenya</title></json:item><json:item><author><json:item><name>M.L. Furhman</name></json:item><json:item><name>D.H. Lindsley</name></json:item></author><host><volume>73</volume><pages><last>215</last><first>201</first></pages><author></author><title>Am. Mineral.</title></host><title>Ternary-feldspar modelling and thermometry</title></json:item><json:item><author><json:item><name>J.A. Grant</name></json:item></author><host><volume>285</volume><pages><last>435</last><first>409</first></pages><author></author><title>Am. J. Sci.</title></host><title>Phase equilibria in low-pressure partial melting of pelitic rocks</title></json:item><json:item><author><json:item><name>R.H. Grapes</name></json:item><json:item><name>K. Palmer</name></json:item></author><host><volume>37</volume><pages><last>315</last><first>293</first></pages><author></author><title>J. Petrol.</title></host><title>(Ruby–sapphire)–chromian mica–tourmaline rocks from Westland, New Zealand</title></json:item><json:item><author><json:item><name>H.J. Greenwood</name></json:item></author><host><volume>4</volume><pages><last>351</last><first>317</first></pages><author></author><title>J. Petrol.</title></host><title>The `synthesis and stability of anthophyllite'</title></json:item><json:item><author><json:item><name>J. Guo</name></json:item><json:item><name>S.Y. O'Reilly</name></json:item><json:item><name>W.L. Griffin</name></json:item></author><host><volume>122</volume><pages><last>386</last><first>368</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Corundum from basaltic terrains: a mineral inclusion approach to the enigma</title></json:item><json:item><author><json:item><name>D.L. Hall</name></json:item><json:item><name>R.J. Bodnar</name></json:item><json:item><name>J.R. Craig</name></json:item></author><host><volume>76</volume><pages><last>1355</last><first>1344</first></pages><author></author><title>Am. Mineral.</title></host><title>Evidence for postentrapment diffusion of hydrogen into peak metamorphic fluid inclusions from the massive sulfide deposits at Ducktown, Tennessee</title></json:item><json:item><author><json:item><name>M.H. Hey</name></json:item></author><host><volume>30</volume><pages><last>292</last><first>277</first></pages><author></author><title>Mineral. Mag.</title></host><title>A new review of chlorites</title></json:item><json:item><author><json:item><name>K.V. Hodges</name></json:item><json:item><name>F.S. Spear</name></json:item></author><host><volume>67</volume><pages><last>1134</last><first>1118</first></pages><author></author><title>Am. Mineral.</title></host><title>Geothermometry, geobaromatry and the Al2SiO5 triple point at Mt. Moosilanke, New Hampshire</title></json:item><json:item><author><json:item><name>M.J. Holdaway</name></json:item></author><host><volume>271</volume><pages><last>131</last><first>97</first></pages><author></author><title>Am. J. Sci.</title></host><title>Stability of andalusite and of alumino-silicate phases diagram</title></json:item><json:item><author><json:item><name>T. Holland</name></json:item><json:item><name>J. Blundy</name></json:item></author><host><volume>116</volume><pages><last>447</last><first>433</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Non-ideal interactions in calcic amphiboles and their bearing on amphibole–plagioclase thermometry</title></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>R. Kerrich</name></json:item><json:item><name>W.S. Fyfe</name></json:item><json:item><name>R.L. Barnett</name></json:item><json:item><name>B.B. Blair</name></json:item><json:item><name>L.M. Willmore</name></json:item></author><host><volume>95</volume><pages><last>498</last><first>481</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Corundum, Cr-muscovite rocks at O'Brians, Zimbabwe: the conjunction of hydrothermal desilicification and LIL-element enrichment—geochemical and isotope evidence</title></json:item><json:item><author><json:item><name>D.M. Kerrick</name></json:item></author><host><volume>272</volume><pages><last>958</last><first>946</first></pages><author></author><title>Am. J. Sci.</title></host><title>Experimental determination of muscovite+quartz stability with PH2O>PTotal</title></json:item><json:item><author><json:item><name>R.M. Key</name></json:item><json:item><name>J.O. Ochieng</name></json:item></author><host><volume>22</volume><pages><last>496</last><first>484</first></pages><author></author><title>J. Gemmol.</title></host><title>The growth of rubies in southeast Kenya</title></json:item><json:item><author><json:item><name>R.M. Key</name></json:item><json:item><name>T.J. Charsley</name></json:item><json:item><name>B.D. Hackman</name></json:item><json:item><name>A.F. Wilkinson</name></json:item><json:item><name>C.G. Rundle</name></json:item></author><host><volume>44</volume><pages><last>225</last><first>197</first></pages><author></author><title>Precambrian Res.</title></host><title>Superimposed Upper Proterzoic collision-controlled orogenies in the Mozambique Orogenic Belt of Kenya</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>R. Kretz</name></json:item></author><host><volume>68</volume><pages><last>279</last><first>277</first></pages><author></author><title>Am. Mineral.</title></host><title>Symbols for rock-forming minerals</title></json:item><json:item><author><json:item><name>A.A. Levinson</name></json:item><json:item><name>F.A. Cook</name></json:item></author><host><volume>30</volume><pages><last>262</last><first>253</first></pages><author></author><title>Gems Gemol.</title></host><title>Gem corundum in alkali basalt: origin and occurrence</title></json:item><json:item><author><json:item><name>E. Malisa</name></json:item><json:item><name>S. Muhongo</name></json:item></author><host><volume>46</volume><pages><last>176</last><first>167</first></pages><author></author><title>Precambrian Res.</title></host><title>Tectonic setting of gemstone mineralisation in the Proterozoic metamorphic terrane of the Mozambique Belt in Tanzania</title></json:item><json:item><author><json:item><name>J.E. Martelat</name></json:item><json:item><name>C. Nicollet</name></json:item><json:item><name>J.M. Lardeaux</name></json:item><json:item><name>G. Vidal</name></json:item><json:item><name>R. Rakotondrazafy</name></json:item></author><host><volume>10</volume><pages><last>114</last><first>94</first></pages><author></author><title>Geodin. Acta</title></host><title>Lithospheric tectonic structures developed under high-grade metamorphism in the southern part of Madagascar</title></json:item><json:item><author><json:item><name>D.W.A. McMullin</name></json:item><json:item><name>R.G. Berman</name></json:item><json:item><name>H.J. Greenwood</name></json:item></author><host><volume>29</volume><pages><last>908</last><first>889</first></pages><author></author><title>Can. Mineral.</title></host><title>Calibration of the SGAM thermobarometer for pelitic rocks using data from phase-equilibrium experiments and natural assemblages</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>D.P. Moecher</name></json:item><json:item><name>E.J. Essene</name></json:item><json:item><name>L.M. Anovitz</name></json:item></author><host><volume>100</volume><pages><last>106</last><first>92</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Calculation and application of clinopyroxene–garnet–plagioclase–quartz geobarometers</title></json:item><json:item><author><json:item><name>P.N. Mosley</name></json:item></author><host><volume>221</volume><pages><last>250</last><first>223</first></pages><author></author><title>Tectonophysics</title></host><title>Geological evolution of the late Proterozoic `Mozambique Belt' of Kenya</title></json:item><json:item><author><json:item><name>S. Muhongo</name></json:item><json:item><name>P. Tuisku</name></json:item></author><host><volume>23</volume><pages><last>463</last><first>443</first></pages><author></author><title>J. Afr. Earth Sci.</title></host><title>Pan-African high pressure isobaric cooling: evidence from the mineralogy and thermobarometry of the granulite-facies rocks from the Uluguru Mountains, eastern Tanzania</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>R.C. Newton</name></json:item><json:item><name>D. Perkins, III</name></json:item></author><host><volume>67</volume><pages><last>222</last><first>203</first></pages><author></author><title>Am. Mineral.</title></host><title>Thermodynamic calibration of geobarometers based on the assemblages garnet–plagioclase–orthopyroxene (clinopyroxene)–quartz</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>H. Ohmoto</name></json:item><json:item><name>D. Kerrick</name></json:item></author><host><volume>277</volume><pages><last>1044</last><first>1013</first></pages><author></author><title>Am. J. Sci.</title></host><title>Devolatilization equilibria in graphitic systems</title></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>P. Pinna</name></json:item><json:item><name>G. Jourde</name></json:item><json:item><name>J.Y. Calvez</name></json:item><json:item><name>J.P. Mroz</name></json:item><json:item><name>J.M. Marques</name></json:item></author><host><volume>62</volume><pages><last>59</last><first>1</first></pages><author></author><title>Precambrian Res.</title></host><title>The Mozambique Belt in northern Mozambique: neoproterozoic (1100–850 Ma) crustal growth and tectonogenesis, and superimposed Pan-African (800–550 Ma) tectonism</title></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>W. Pohl</name></json:item><json:item><name>A. Horkel</name></json:item></author><host><volume>73</volume><pages><last>152</last><first>135</first></pages><author></author><title>Mitt. Österr. Geol. Ges.</title></host><title>Notes on the geology and mineral resources of the Mtito Andei–Taita area (southern Kenya)</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>W. Prochaska</name></json:item><json:item><name>W. Pohl</name></json:item></author><host><volume>1</volume><pages><last>191</last><first>183</first></pages><author></author><title>J. Afr. Earth Sci.</title></host><title>Petrochemistry of some mafic and ultramafic rocks from the Mozambique Belt, Northern Tanzania</title></json:item><json:item><author><json:item><name>M. Raith</name></json:item><json:item><name>S. Karmakar</name></json:item><json:item><name>M. Brown</name></json:item></author><host><volume>15</volume><pages><last>399</last><first>379</first></pages><author></author><title>J. Metamorph. Geol.</title></host><title>Ultra-high-temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the Palni Hill Ranges, southern India</title></json:item><json:item><author><json:item><name>A.C. Ries</name></json:item><json:item><name>J.R. Vearncombe</name></json:item><json:item><name>R.C. Price</name></json:item><json:item><name>R.M. Shackleton</name></json:item></author><host><volume>14</volume><pages><last>36</last><first>25</first></pages><author></author><title>J. Afr. Earth Sci.</title></host><title>Geochronology and geochemistry of the rocks associated with a Late Proterozoic ophiolite in West Pokot, NW Kenya</title></json:item><json:item><author><json:item><name>S.G. Rivalenti</name></json:item></author><host><volume>93</volume><pages><last>32</last><first>23</first></pages><author></author><title>Bull. Soc. Geol. It.</title></host><title>A ruby corundum pegmatoid in an area near Fiskenaesset, Southwest Greenland</title></json:item><json:item><author><json:item><name>L.N. Rossovskiy</name></json:item><json:item><name>S.I. Konovalenko</name></json:item><json:item><name>Y.P. Bovin</name></json:item></author><host><volume>23</volume><pages><last>382</last><first>371</first></pages><author></author><title>Int. Geol. Rev.</title></host><title>Desilicified pegmatites with dravite and corundum (Southwestern Pamir)</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>E.S. Schandl</name></json:item><json:item><name>A.J. Naldrett</name></json:item></author><host><volume>30</volume><pages><last>108</last><first>93</first></pages><author></author><title>Can. Mineral.</title></host><title>CO2 metasomatism of serpentinites, south of Timmins, Ontario</title></json:item><json:item><author><json:item><name>F. Seifert</name></json:item></author><host><volume>82</volume><pages><last>204</last><first>173</first></pages><author></author><title>J. Geol.</title></host><title>Stability of sapphirine: a study of the aluminous part of the system MgO–Al2O3–SiO2–H2O</title></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>R.M. Shackleton</name></json:item></author><host><volume>23</volume><pages><last>287</last><first>271</first></pages><author></author><title>J. Afr. Earth Sci.</title></host><title>The final collision zone between East and West Gondwana: where is it?</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>M. Smith</name></json:item><json:item><name>P. Mosley</name></json:item></author><host><volume>12</volume><pages><last>606</last><first>591</first></pages><author></author><title>Tectonics</title></host><title>Crustal heterogeneity and basement influence on the development of the Kenya Rift, East Africa</title></json:item><json:item><author><json:item><name>F.W. Solesbury</name></json:item></author><host><volume>62</volume><pages><last>991</last><first>983</first></pages><author></author><title>Econ. Geol.</title></host><title>Gem corundum pegmatite in N.E. Tanganyika</title></json:item><json:item><author><json:item><name>F.L. Sutherland</name></json:item><json:item><name>R.R. Coenraads</name></json:item></author><host><volume>60</volume><pages><last>638</last><first>623</first></pages><author></author><title>Mineral. Mag.</title></host><title>An unusual ruby–sapphire–sapphirine–spinel assemblage from the Tertiary Barrington volcanic province, New South Wales, Australia</title></json:item><json:item><author><json:item><name>A.B. Thompson</name></json:item></author><host><volume>276</volume><pages><last>454</last><first>425</first></pages><author></author><title>Am. J. Sci.</title></host><title>Mineral Reactions in Pelitic Rocks: II. Calculation of some P–T–X (Fe–Mg). Phase relations</title></json:item><json:item><author><json:item><name>A.B. Thompson</name></json:item></author><host><volume>282</volume><pages><last>1595</last><first>1567</first></pages><author></author><title>Am. J. Sci.</title></host><title>Dehydration melting of pelitic rocks and the generation of H2O undersaturated granitic liquids</title></json:item><json:item><host><author></author></host></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>D. Vielzeuf</name></json:item><json:item><name>J. Kornprobst</name></json:item></author><host><volume>67</volume><pages><last>96</last><first>87</first></pages><author></author><title>Earth Planet. Sci. Lett.</title></host><title>Crustal splitting and the emplacement of Pyrenean lherzolites and granulites</title></json:item><json:item><author><json:item><name>D. Vielzeuf</name></json:item><json:item><name>J.R. Holloway</name></json:item></author><host><volume>98</volume><pages><last>276</last><first>257</first></pages><author></author><title>Contrib. Mineral. Petrol.</title></host><title>Experimental determinations of the fluid-absent melting relations in the pelitic system, consequences for crustal differentiation</title></json:item><json:item><host><author></author></host></json:item><json:item><author><json:item><name>A.J. Warden</name></json:item><json:item><name>D. Horkel</name></json:item></author><host><volume>77</volume><pages><last>184</last><first>161</first></pages><author></author><title>Mitt. Österr. Geol. Ges.</title></host><title>The geological evolution of the NE-branch of the Mozambique Belt (Kenya, Somalia, Ethiopia)</title></json:item></refBibs><genre><json:string>research-article</json:string></genre><host><volume>14</volume><pii><json:string>S0169-1368(00)X0018-2</json:string></pii><pages><last>104</last><first>83</first></pages><issn><json:string>0169-1368</json:string></issn><issue>2</issue><genre><json:string>journal</json:string></genre><language><json:string>unknown</json:string></language><title>Ore Geology Reviews</title><publicationDate>1999</publicationDate></host><categories><wos><json:string>science</json:string><json:string>mining & mineral processing</json:string><json:string>mineralogy</json:string><json:string>geology</json:string></wos><scienceMetrix><json:string>natural sciences</json:string><json:string>earth & environmental sciences</json:string><json:string>geology</json:string></scienceMetrix></categories><publicationDate>1999</publicationDate><copyrightDate>1999</copyrightDate><doi><json:string>10.1016/S0169-1368(99)00002-5</json:string></doi><id>A62D09A532A7DF0643392A40396CD45BB3AED48C</id><score>0.13736913</score><fulltext><json:item><extension>pdf</extension><original>true</original><mimetype>application/pdf</mimetype><uri>https://api.istex.fr/document/A62D09A532A7DF0643392A40396CD45BB3AED48C/fulltext/pdf</uri></json:item><json:item><extension>zip</extension><original>false</original><mimetype>application/zip</mimetype><uri>https://api.istex.fr/document/A62D09A532A7DF0643392A40396CD45BB3AED48C/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/A62D09A532A7DF0643392A40396CD45BB3AED48C/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a">Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>ELSEVIER</publisher><availability><p>©1999 Elsevier Science B.V.</p></availability><date>1999</date></publicationStmt><notesStmt><note type="content">Fig. 1: Simplified geological map of SE Kenya showing the distribution of the different types of the ultrabasic bodies and the location of some associated gem-corundum deposits, including those of the Mangari area (grouped together as one because the map scale) (modified from Frisch and Pohl, 1986).</note><note type="content">Fig. 2: Simplified geological map of the Mangari area, in SE Kenya (for location see Fig. 1) with the ruby deposits of JSM, PLM and HRM. Note how the regional foliation is deflected around the ultrabasic bodies associated with those deposits. The small box indicates the location of Fig. 3.</note><note type="content">Fig. 3: Geological map of the HRM deposit showing the two types of corundum occurrences closely associated with the ultrabasites. The positions of the cross-sections given in Fig. 4 are also indicated.</note><note type="content">Fig. 4: Cross-sections showing the structural relationships between the HRM ultrabasic body and the country rocks (for location, see Fig. 3). (a–b) The foliation of the graphitic gneisses is parallel to the eastern contact of the ultrabasic body but unconformable with its western contact. (c) The northern contact of the body dips in the opposite direction to the foliation of the surrounding rocks. (a) and (b) also show ruby-bearing rocks forming a vein within the ultrabasites and a lens along their contact with the country rocks. Neither the corundum-bearing vein nor the lens cut across the surrounding gneisses.</note><note type="content">Fig. 5: Field photograph and its schematic representation showing the WSW contact of the HRM ultrabasic body with the graphitic gneisses, and the setting of the corundum-bearing lens (see location in Fig. 4b). The contact of the ultrabasites and the corundum-bearing lens cut the foliation of the surrounding gneisses.</note><note type="content">Fig. 6: Field photograph showing the similar structural configuration of the corundum-bearing vein and the contact zone of the HRM ultrabasic body. The corundum-bearing vein crosscuts the ultrabasites but not the surrounding gneisses.</note><note type="content">Fig. 7: Field relationship between the corundum-bearing vein and the ultrabasites at the HRM (see location in Fig. 4a). The vein is confined within the ultrabasites and never crosscuts the contact with the surrounding gneisses.</note><note type="content">Fig. 8: Pressure–Log a(quartz β) diagram in the CaO–Al2O3–SiO2–H2O system, showing the a(quartz β) dependency of the reaction (5) 4An+W=Crn+2Qtz+2Zo established with the TWEEQU software of Berman (1991)for T=725°C, aAn=0.97, aZo=1 and aH2O=1 (mineral abbreviations after Kretz, 1983). The dashed part of the curve represents the P–a(quartz β) range defined from reaction (5) (see details in the text).</note><note type="content">Fig. 9: Summary P–T grid illustrating the contrasting P–T conditions recorded by the corundum-bearing rocks and the surrounding metasedimentary rocks in the ruby deposits of the Mangari area. For the country rocks: (1) kyanite/sillimanite stability fields from Holdaway (1971)and reaction (2) from Vielzeuf (1984)with the slope of Grant (1985). For the ultrabasites: reaction (3) from Greenwood (1963). For the corundum-bearing rocks: reactions (4) from Seifert (1974)and (5) from the TWEEQU program of Berman (1991)(Fig. 8). The `Granite melting' curve is from Kerrick (1972). Mineral abbreviations after Kretz (1983).</note><note type="content">Fig. 10: Geological location of the primary gem-corundum deposits (mostly ruby deposits) in East Africa and in Madagascar, especially in relation to the Proterozoic granulite terrains. Compiled and modified from: Hottin (1976), Andreoli (1984), Shackleton (1986), Malisa and Muhongo (1990), Pinna et al. (1993), Muhongo and Tuisku (1996), Shackleton (1996). Corundum deposits: in East Africa: 1=Mangari, 2=Kinyiki Hill, 3=Umba, 4=Longido, 5=Lossogonoi, 6=Morogoro in the Uluguru mountains, 7=Mahenge in the Furua Complex (the deposit at Chimwadzulu Hill in S Malawi is also indicated). In Madagascar: 8=Ejeda–Fotadrevo.</note><note type="content">Table 1: Representative compositions of the characteristic minerals of the corundum-bearing rocks from the HRM deposit</note><note type="content">Table 2: Representative compositions of the characteristic minerals of the sillimanite gneisses country rocks</note></notesStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title><author xml:id="author-1"><persName><forename type="first">A.</forename><surname>Mercier</surname></persName><note type="correspondence"><p>Corresponding author. Fax: +33-561-558250</p></note><affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</affiliation></author><author xml:id="author-2"><persName><forename type="first">P.</forename><surname>Debat</surname></persName><affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</affiliation></author><author xml:id="author-3"><persName><forename type="first">John M.</forename><surname>Saul</surname></persName><affiliation>ORYX, 3 rue Bourdaloue, 75009 Paris, France</affiliation></author></analytic><monogr><title level="j">Ore Geology Reviews</title><title level="j" type="abbrev">OREGEO</title><idno type="pISSN">0169-1368</idno><idno type="PII">S0169-1368(00)X0018-2</idno><imprint><publisher>ELSEVIER</publisher><date type="published" when="1999"></date><biblScope unit="volume">14</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="83">83</biblScope><biblScope unit="page" to="104">104</biblScope></imprint></monogr><idno type="istex">A62D09A532A7DF0643392A40396CD45BB3AED48C</idno><idno type="DOI">10.1016/S0169-1368(99)00002-5</idno><idno type="PII">S0169-1368(99)00002-5</idno></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>1999</date></creation><langUsage><language ident="en">en</language></langUsage><abstract xml:lang="en"><p>The Proterozoic Mozambique Belt contains numerous primary deposits of gem-corundum (i.e., ruby and sapphire). The ruby deposits in the Mangari area of SE Kenya, are among the most productive and best known. Enclosed within a metasedimentary sequence dominated by sillimanite-graphitic gneisses, the Mangari deposits are associated with rootless ultrabasic bodies. Ruby occurs (1) in lenses on the inner side of the contacts between the ultrabasites and the surrounding metasediments and (2) in veins within the ultrabasic bodies or forming their margins. Field relationships reveal that the corundum-bearing rocks are genetically related to the ultrabasic bodies but not to the surrounding gneisses. Laboratory studies and petrographic comparisons indicate that the ruby-bearing rocks crystallized under granulite facies conditions of 700–750°C and 8–10.5 kbar. By contrast, the surrounding gneisses show only amphibolite facies metamorphism with maximum temperatures around 650°C and pressures which did not exceed 7 kbar. At Mangari, the ruby-bearing rocks, as their associated ultrabasites, appear to be exotic with respect to the surrounding metasedimentary rocks. We interpret them as fragments of a deeper crust brought up to their present-day exposure level by the ultrabasic bodies during their emplacement as thrust sheets. Similar reasoning may account for the presence of charnockitic gneisses nearby. By contrast, granulite facies metamorphism characterizes all rock types genetically relatable to the Tanzanian ruby deposits at Longido and Lossogonoi, both also situated in the Mozambique Belt. This suggests that, if associated with ultrabasites, primary deposits of rubies (and of subgem red corundum) formed only under granulite facies conditions in the Mozambique Belt. Some of these deposits were subsequently tectonically inserted into country rocks of lower metamorphic grade. This apparently occurred without the total fracturing of all crystalline gems.</p></abstract><textClass><keywords scheme="keyword"><list><head>Keywords</head><item><term>ruby deposits</term></item><item><term>Mozambique Belt</term></item><item><term>Kenya</term></item><item><term>ultrabasites</term></item><item><term>granulite facies</term></item></list></keywords></textClass></profileDesc><revisionDesc><change when="1999">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/document/A62D09A532A7DF0643392A40396CD45BB3AED48C/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="Elsevier, elements deleted: ce:floats; body; tail"><istex:xmlDeclaration>version="1.0" encoding="utf-8"</istex:xmlDeclaration><istex:docType PUBLIC="-//ES//DTD journal article DTD version 4.5.2//EN//XML" URI="art452.dtd" name="istex:docType"><istex:entity SYSTEM="gr1" NDATA="IMAGE" name="gr1"></istex:entity><istex:entity SYSTEM="gr2" NDATA="IMAGE" name="gr2"></istex:entity><istex:entity SYSTEM="gr3" NDATA="IMAGE" name="gr3"></istex:entity><istex:entity SYSTEM="gr4" NDATA="IMAGE" name="gr4"></istex:entity><istex:entity SYSTEM="gr5" NDATA="IMAGE" name="gr5"></istex:entity><istex:entity SYSTEM="gr6" NDATA="IMAGE" name="gr6"></istex:entity><istex:entity SYSTEM="gr7" NDATA="IMAGE" name="gr7"></istex:entity><istex:entity SYSTEM="gr8" NDATA="IMAGE" name="gr8"></istex:entity><istex:entity SYSTEM="gr9" NDATA="IMAGE" name="gr9"></istex:entity><istex:entity SYSTEM="gr10" NDATA="IMAGE" name="gr10"></istex:entity></istex:docType><istex:document><converted-article version="4.5.2" docsubtype="fla"><item-info><jid>OREGEO</jid><aid>345</aid><ce:pii>S0169-1368(99)00002-5</ce:pii><ce:doi>10.1016/S0169-1368(99)00002-5</ce:doi><ce:copyright year="1999" type="full-transfer">Elsevier Science B.V.</ce:copyright></item-info><head><ce:title>Exotic origin of the ruby deposits of the Mangari area in SE Kenya</ce:title><ce:author-group><ce:author><ce:given-name>A.</ce:given-name><ce:surname>Mercier</ce:surname><ce:cross-ref refid="AFF1">a</ce:cross-ref><ce:cross-ref refid="CORR1">*</ce:cross-ref></ce:author><ce:author><ce:given-name>P.</ce:given-name><ce:surname>Debat</ce:surname><ce:cross-ref refid="AFF1">a</ce:cross-ref></ce:author><ce:author><ce:given-name>John M.</ce:given-name><ce:surname>Saul</ce:surname><ce:cross-ref refid="AFF2">b</ce:cross-ref></ce:author><ce:affiliation id="AFF1"><ce:label>a</ce:label><ce:textfn>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</ce:textfn></ce:affiliation><ce:affiliation id="AFF2"><ce:label>b</ce:label><ce:textfn>ORYX, 3 rue Bourdaloue, 75009 Paris, France</ce:textfn></ce:affiliation><ce:correspondence id="CORR1"><ce:label>*</ce:label><ce:text>Corresponding author. Fax: +33-561-558250</ce:text></ce:correspondence></ce:author-group><ce:date-received day="22" month="6" year="1998"></ce:date-received><ce:date-accepted day="11" month="1" year="1999"></ce:date-accepted><ce:abstract><ce:section-title>Abstract</ce:section-title><ce:abstract-sec><ce:simple-para>The Proterozoic Mozambique Belt contains numerous primary deposits of gem-corundum (i.e., ruby and sapphire). The ruby deposits in the Mangari area of SE Kenya, are among the most productive and best known. Enclosed within a metasedimentary sequence dominated by sillimanite-graphitic gneisses, the Mangari deposits are associated with rootless ultrabasic bodies. Ruby occurs (1) in lenses on the inner side of the contacts between the ultrabasites and the surrounding metasediments and (2) in veins within the ultrabasic bodies or forming their margins. Field relationships reveal that the corundum-bearing rocks are genetically related to the ultrabasic bodies but not to the surrounding gneisses. Laboratory studies and petrographic comparisons indicate that the ruby-bearing rocks crystallized under granulite facies conditions of 700–750°C and 8–10.5 kbar. By contrast, the surrounding gneisses show only amphibolite facies metamorphism with maximum temperatures around 650°C and pressures which did not exceed 7 kbar. At Mangari, the ruby-bearing rocks, as their associated ultrabasites, appear to be exotic with respect to the surrounding metasedimentary rocks. We interpret them as fragments of a deeper crust brought up to their present-day exposure level by the ultrabasic bodies during their emplacement as thrust sheets. Similar reasoning may account for the presence of charnockitic gneisses nearby. By contrast, granulite facies metamorphism characterizes all rock types genetically relatable to the Tanzanian ruby deposits at Longido and Lossogonoi, both also situated in the Mozambique Belt. This suggests that, if associated with ultrabasites, primary deposits of rubies (and of subgem red corundum) formed only under granulite facies conditions in the Mozambique Belt. Some of these deposits were subsequently tectonically inserted into country rocks of lower metamorphic grade. This apparently occurred without the total fracturing of all crystalline gems.</ce:simple-para></ce:abstract-sec></ce:abstract><ce:keywords class="keyword"><ce:section-title>Keywords</ce:section-title><ce:keyword><ce:text>ruby deposits</ce:text></ce:keyword><ce:keyword><ce:text>Mozambique Belt</ce:text></ce:keyword><ce:keyword><ce:text>Kenya</ce:text></ce:keyword><ce:keyword><ce:text>ultrabasites</ce:text></ce:keyword><ce:keyword><ce:text>granulite facies</ce:text></ce:keyword></ce:keywords></head></converted-article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>Exotic origin of the ruby deposits of the Mangari area in SE Kenya</title></titleInfo><name type="personal"><namePart type="given">A.</namePart><namePart type="family">Mercier</namePart><affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</affiliation><description>Corresponding author. Fax: +33-561-558250</description><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">P.</namePart><namePart type="family">Debat</namePart><affiliation>Laboratoire de Minéralogie UMR 5563 UPS-CNRS, 38 Rue des 36-Ponts, F-31400 Toulouse, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">John M.</namePart><namePart type="family">Saul</namePart><affiliation>ORYX, 3 rue Bourdaloue, 75009 Paris, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="Full-length article"></genre><originInfo><publisher>ELSEVIER</publisher><dateIssued encoding="w3cdtf">1999</dateIssued><copyrightDate encoding="w3cdtf">1999</copyrightDate></originInfo><language><languageTerm type="code" authority="iso639-2b">eng</languageTerm><languageTerm type="code" authority="rfc3066">en</languageTerm></language><physicalDescription><internetMediaType>text/html</internetMediaType></physicalDescription><abstract lang="en">The Proterozoic Mozambique Belt contains numerous primary deposits of gem-corundum (i.e., ruby and sapphire). The ruby deposits in the Mangari area of SE Kenya, are among the most productive and best known. Enclosed within a metasedimentary sequence dominated by sillimanite-graphitic gneisses, the Mangari deposits are associated with rootless ultrabasic bodies. Ruby occurs (1) in lenses on the inner side of the contacts between the ultrabasites and the surrounding metasediments and (2) in veins within the ultrabasic bodies or forming their margins. Field relationships reveal that the corundum-bearing rocks are genetically related to the ultrabasic bodies but not to the surrounding gneisses. Laboratory studies and petrographic comparisons indicate that the ruby-bearing rocks crystallized under granulite facies conditions of 700–750°C and 8–10.5 kbar. By contrast, the surrounding gneisses show only amphibolite facies metamorphism with maximum temperatures around 650°C and pressures which did not exceed 7 kbar. At Mangari, the ruby-bearing rocks, as their associated ultrabasites, appear to be exotic with respect to the surrounding metasedimentary rocks. We interpret them as fragments of a deeper crust brought up to their present-day exposure level by the ultrabasic bodies during their emplacement as thrust sheets. Similar reasoning may account for the presence of charnockitic gneisses nearby. By contrast, granulite facies metamorphism characterizes all rock types genetically relatable to the Tanzanian ruby deposits at Longido and Lossogonoi, both also situated in the Mozambique Belt. This suggests that, if associated with ultrabasites, primary deposits of rubies (and of subgem red corundum) formed only under granulite facies conditions in the Mozambique Belt. Some of these deposits were subsequently tectonically inserted into country rocks of lower metamorphic grade. This apparently occurred without the total fracturing of all crystalline gems.</abstract><note type="content">Fig. 1: Simplified geological map of SE Kenya showing the distribution of the different types of the ultrabasic bodies and the location of some associated gem-corundum deposits, including those of the Mangari area (grouped together as one because the map scale) (modified from Frisch and Pohl, 1986).</note><note type="content">Fig. 2: Simplified geological map of the Mangari area, in SE Kenya (for location see Fig. 1) with the ruby deposits of JSM, PLM and HRM. Note how the regional foliation is deflected around the ultrabasic bodies associated with those deposits. The small box indicates the location of Fig. 3.</note><note type="content">Fig. 3: Geological map of the HRM deposit showing the two types of corundum occurrences closely associated with the ultrabasites. The positions of the cross-sections given in Fig. 4 are also indicated.</note><note type="content">Fig. 4: Cross-sections showing the structural relationships between the HRM ultrabasic body and the country rocks (for location, see Fig. 3). (a–b) The foliation of the graphitic gneisses is parallel to the eastern contact of the ultrabasic body but unconformable with its western contact. (c) The northern contact of the body dips in the opposite direction to the foliation of the surrounding rocks. (a) and (b) also show ruby-bearing rocks forming a vein within the ultrabasites and a lens along their contact with the country rocks. Neither the corundum-bearing vein nor the lens cut across the surrounding gneisses.</note><note type="content">Fig. 5: Field photograph and its schematic representation showing the WSW contact of the HRM ultrabasic body with the graphitic gneisses, and the setting of the corundum-bearing lens (see location in Fig. 4b). The contact of the ultrabasites and the corundum-bearing lens cut the foliation of the surrounding gneisses.</note><note type="content">Fig. 6: Field photograph showing the similar structural configuration of the corundum-bearing vein and the contact zone of the HRM ultrabasic body. The corundum-bearing vein crosscuts the ultrabasites but not the surrounding gneisses.</note><note type="content">Fig. 7: Field relationship between the corundum-bearing vein and the ultrabasites at the HRM (see location in Fig. 4a). The vein is confined within the ultrabasites and never crosscuts the contact with the surrounding gneisses.</note><note type="content">Fig. 8: Pressure–Log a(quartz β) diagram in the CaO–Al2O3–SiO2–H2O system, showing the a(quartz β) dependency of the reaction (5) 4An+W=Crn+2Qtz+2Zo established with the TWEEQU software of Berman (1991)for T=725°C, aAn=0.97, aZo=1 and aH2O=1 (mineral abbreviations after Kretz, 1983). The dashed part of the curve represents the P–a(quartz β) range defined from reaction (5) (see details in the text).</note><note type="content">Fig. 9: Summary P–T grid illustrating the contrasting P–T conditions recorded by the corundum-bearing rocks and the surrounding metasedimentary rocks in the ruby deposits of the Mangari area. For the country rocks: (1) kyanite/sillimanite stability fields from Holdaway (1971)and reaction (2) from Vielzeuf (1984)with the slope of Grant (1985). For the ultrabasites: reaction (3) from Greenwood (1963). For the corundum-bearing rocks: reactions (4) from Seifert (1974)and (5) from the TWEEQU program of Berman (1991)(Fig. 8). The `Granite melting' curve is from Kerrick (1972). Mineral abbreviations after Kretz (1983).</note><note type="content">Fig. 10: Geological location of the primary gem-corundum deposits (mostly ruby deposits) in East Africa and in Madagascar, especially in relation to the Proterozoic granulite terrains. Compiled and modified from: Hottin (1976), Andreoli (1984), Shackleton (1986), Malisa and Muhongo (1990), Pinna et al. (1993), Muhongo and Tuisku (1996), Shackleton (1996). Corundum deposits: in East Africa: 1=Mangari, 2=Kinyiki Hill, 3=Umba, 4=Longido, 5=Lossogonoi, 6=Morogoro in the Uluguru mountains, 7=Mahenge in the Furua Complex (the deposit at Chimwadzulu Hill in S Malawi is also indicated). In Madagascar: 8=Ejeda–Fotadrevo.</note><note type="content">Table 1: Representative compositions of the characteristic minerals of the corundum-bearing rocks from the HRM deposit</note><note type="content">Table 2: Representative compositions of the characteristic minerals of the sillimanite gneisses country rocks</note><subject><genre>Keywords</genre><topic>ruby deposits</topic><topic>Mozambique Belt</topic><topic>Kenya</topic><topic>ultrabasites</topic><topic>granulite facies</topic></subject><relatedItem type="host"><titleInfo><title>Ore Geology Reviews</title></titleInfo><titleInfo type="abbreviated"><title>OREGEO</title></titleInfo><genre type="journal">journal</genre><originInfo><dateIssued encoding="w3cdtf">199903</dateIssued></originInfo><identifier type="ISSN">0169-1368</identifier><identifier type="PII">S0169-1368(00)X0018-2</identifier><part><date>199903</date><detail type="volume"><number>14</number><caption>vol.</caption></detail><detail type="issue"><number>2</number><caption>no.</caption></detail><extent unit="issue pages"><start>83</start><end>155</end></extent><extent unit="pages"><start>83</start><end>104</end></extent></part></relatedItem><identifier type="istex">A62D09A532A7DF0643392A40396CD45BB3AED48C</identifier><identifier type="DOI">10.1016/S0169-1368(99)00002-5</identifier><identifier type="PII">S0169-1368(99)00002-5</identifier><accessCondition type="use and reproduction" contentType="copyright">©1999 Elsevier Science B.V.</accessCondition><recordInfo><recordContentSource>ELSEVIER</recordContentSource><recordOrigin>Elsevier Science B.V., ©1999</recordOrigin></recordInfo></mods></metadata><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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