Styles of Alteration of Ti Oxides of the Kimberlite Groundmass: Implications on the Petrogenesis and Classification of Kimberlites and Similar Rocks
The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlit...
| Autores: | , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | Varias* (Consorci de Biblioteques Universitáries de Catalunya, Centre de Serveis Científics i Acadèmics de Catalunya) |
| Repositorio: | Recercat. Dipósit de la Recerca de Catalunya |
| OAI Identifier: | oai:recercat.cat:2445/121012 |
| Acceso en línea: | https://hdl.handle.net/2445/121012 |
| Access Level: | acceso abierto |
| Palabra clave: | Òxids metàl·lics Petrogènesi Kimberlita Metallic oxides Petrogenesis Kimberlite |
| Sumario: | The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlite magma, it is light rare-earth elements (LREE)-rich and Fe-poor and its ΔNNO calculated value is from −3.82 to −0.73. The second generation of perovskite (type 2 perovskite) is found replacing groundmass atoll spinel, it was formed from hydrothermal fluids, it is LREE-free and Fe-rich and has very high ΔNNO value (from 1.03 to 10.52). Type 1 groundmass perovskite may be either replaced by anatase or kassite along with aeschynite-(Ce). These differences in the alteration are related to different f(CO2) and f(H2O) conditions. Furthermore, primary perovskite may be strongly altered to secondary minerals, resulting in redistribution of rare-earth elements (REE) and, potentially, U, Pb and Th. Therefore, accurate petrographic and chemical analyses are necessary in order to demonstrate that perovskite is magmatic before proceeding to sort geochronological data by using perovskite. Ti-rich hydrogarnets (12.9 wt %-26.3 wt % TiO2) were produced during spinel replacement by late hydrothermal processes. Therefore, attention must be paid to the position of Ca-Ti-garnets in the mineral sequence and their water content before using them to classify the rock based on their occurrence. |
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