| Библ. ссылка: | Yui T.-F., Chu H.-T., Hwang S.-L., Shen P., Wu T.-W., Liou J.G., Sobolev N.V. Geochemistry of garnetiferous Ti-clinohumite rock and talc-kyanite-phengite-almandine schist from the Kokchetav UHP terrane, Kazakhstan: An insight to possible origins of some chemically unusual UHP rocks // Lithos. - 2010. - Vol.118. - Iss. 1-2. - P.131-144. - ISSN 0024-4937. - EISSN 1872-6143. |
| Реферат: | eng: Major-element, trace-element and O-isotope analyses were carried out for garnetiferous Ti-clinohumite rocks and eclogites from the Kumdy Kol area, as well as talc-kyanite-phengite-almandine schists (previously named as whiteschists) and eclogites from the Kulet area of the Kokchetav ultrahigh-pressure (UHP) terrane, to explore their possible origins. Both garnetiferous Ti-clinohumite rocks and talc-kyanite-phengite-almandine schists are possibly genetically related to eclogites, as they occur in close association with eclogites enclosed within gneiss/metapelite in these two areas. Most eclogites from the Kumdy Kol and the Kulet areas exhibit chemical characteristics similar to that of ocean floor basalt, although a few show arc affinity with slight Ta and Nb depletions. Garnetiferous Ti-clinohumite rocks from the Kumdy Kol region are characterized by very high Mg, low Si, Ca, Na, and K contents compared with eclogites. They also exhibit LREE depleted patterns with negative Eu anomalies. Their O-isotope compositions are less than +. 5.6. On the other hand, the rocks show comparable Al, Ni, Cr, Co and HREE contents as eclogites. The Mg enrichment of these garnetiferous Ti-clinohumite rocks is suggested to have originated from their mafic protoliths that had been subjected to mafic rock-ultramafic rock-fluid interactions. Talc-kyanite-phengite-almandine schists from the Kulet area are typically low in Ca and Na, but high in Mg, K, Rb, Ba, Cs, Th, U and O-isotope compositions (+. 6 to +. 10) relative to eclogites. This peculiar chemical composition can be accounted for if the basaltic protoliths had been subjected to sequential high-temperature (enrichment of Mg) and low-temperature (enrichment of K, Rb, Ba, Cs, Th, U and O-isotope compositions) seawater-basalt interactions. One talc-kyanite-phengite-almandine schist sample KLW 7 is distinctly high in Si and K, but low in Mg and Fe, which can be attributed to more severe low-temperature hydrothermal alterations. However, except for Mg, the enrichment of Rb, Ba, Cs, Th, U and O-isotope compositions in these schist samples could also be enhanced by, or otherwise be interpreted as a result of, fluid influx sourced from enclosing metapelite during subduction. © 2010 Elsevier B.V.
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