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Ion microprobe U-Pb age and Zr-in-rutile thermometry of rutiles from the daixian rutile deposit in the Hengshan mountains, Shanxi province, China / Guanghai Shi in Economic geology, Vol. 107 N° 3 (Mai 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 525-535 Titre : Ion microprobe U-Pb age and Zr-in-rutile thermometry of rutiles from the daixian rutile deposit in the Hengshan mountains, Shanxi province, China Type de document : texte imprimé Auteurs : Guanghai Shi, Auteur ; Xianhua Li, Auteur ; Qiuli Li, Auteur Année de publication : 2012 Article en page(s) : pp. 525-535 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Dixian  rutile  deposit  Magnetite-ilmenite  ore  U-Pb  age  Zr-in  rutile  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Daixian rutile deposit is located in the Hengshan Mountains in the Trans-North China Orogen; it is considered to be one of the largest rutile deposits in China, with 6 million metric tons (Mt) of contained titanium. Most of the rutile ores are hosted in garnet-free anthophyllite gneiss with minor Mg hornblende, feldspar, quartz, phlogopite, rutile, zircon, and titanite. Rutile grains are euhedral, 0.02 to 0.50 mm in size, contain 98.649 to 99.784 wt % TiO2, and form chains, thin layers along the foliation, and dense aggregates. Rutiles are compositionally homogeneous and contain no detectable mineral inclusions except local ilmenite lamellae and zircon. Crystallization temperatures of the rutile are estimated at ~640°C at 0.7 GPa, and ~647°C without pressure calibration according to the Zr-in-rutile thermometer, recording amphibolite facies metamorphism of an intermediate P/T ratio series. Variations in Nb versus Cr in rutiles indicate a connection of the ores to mafic protolith; not a pelitic rock derived from aluminous sedimentary rocks. SIMS U-Pb analyses of rutiles from the deposit yield a mean 207Pb/207Pb age of 1780.2 ± 9.6 Ma. Considering the closure temperature (up to ~650°C), grain sizes and recrystallization of the rutile, this age is more likely to represent closure and/or recrystallization time rather than peak metamorphism period, so the rutile deposit formed not younger than ~1780 Ma. This unique garnet-free rutile deposit was metamorphosed from mafic rocks in amphibolite facies during the Paleoproterozoic or Archean, being distinct from any other metamorphic rutile deposits, such as the known eclogite-related types. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/525.short [article] Ion microprobe U-Pb age and Zr-in-rutile thermometry of rutiles from the daixian rutile deposit in the Hengshan mountains, Shanxi province, China [texte imprimé] / Guanghai Shi, Auteur ; Xianhua Li, Auteur ; Qiuli Li, Auteur . - 2012 . - pp. 525-535. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 3 (Mai 2012) . - pp. 525-535 Mots-clés : Dixian  rutile  deposit  Magnetite-ilmenite  ore  U-Pb  age  Zr-in  rutile  China Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Daixian rutile deposit is located in the Hengshan Mountains in the Trans-North China Orogen; it is considered to be one of the largest rutile deposits in China, with 6 million metric tons (Mt) of contained titanium. Most of the rutile ores are hosted in garnet-free anthophyllite gneiss with minor Mg hornblende, feldspar, quartz, phlogopite, rutile, zircon, and titanite. Rutile grains are euhedral, 0.02 to 0.50 mm in size, contain 98.649 to 99.784 wt % TiO2, and form chains, thin layers along the foliation, and dense aggregates. Rutiles are compositionally homogeneous and contain no detectable mineral inclusions except local ilmenite lamellae and zircon. Crystallization temperatures of the rutile are estimated at ~640°C at 0.7 GPa, and ~647°C without pressure calibration according to the Zr-in-rutile thermometer, recording amphibolite facies metamorphism of an intermediate P/T ratio series. Variations in Nb versus Cr in rutiles indicate a connection of the ores to mafic protolith; not a pelitic rock derived from aluminous sedimentary rocks. SIMS U-Pb analyses of rutiles from the deposit yield a mean 207Pb/207Pb age of 1780.2 ± 9.6 Ma. Considering the closure temperature (up to ~650°C), grain sizes and recrystallization of the rutile, this age is more likely to represent closure and/or recrystallization time rather than peak metamorphism period, so the rutile deposit formed not younger than ~1780 Ma. This unique garnet-free rutile deposit was metamorphosed from mafic rocks in amphibolite facies during the Paleoproterozoic or Archean, being distinct from any other metamorphic rutile deposits, such as the known eclogite-related types. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/3/525.short