Evolution of the Lithospheric Mantle beneath the Marsabit Volcanic Field (Northern Kenya): Constraints from Textural, P-T and Geochemical Studies on Xenoliths |
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| Authors: | KAESER BENJAMIN; KALT ANGELIKA; PETTKE THOMAS |
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| Institution: | 1 INSTITUT DE GÉOLOGIE ET D'HYDROGÉOLOGIE, UNIVERSITÉ DE NEUCHÂTEL RUE EMILE-ARGAND 11, CASE POSTALE 158, CH-2009 NEUCHÂTEL, SWITZERLAND
2 ISOTOPE GEOCHEMISTRY AND MINERAL RESOURCES, DEPARTMENT OF EARTH SCIENCES, FEDERAL INSTITUTE OF TECHNOLOGY ETH ZENTRUM NO, CH-8092 ZÜRICH, SWITZERLAND |
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| Abstract: | Xenoliths hosted by Quaternary basanites and alkali basaltsfrom Marsabit (northern Kenya) represent fragments of Proterozoiclithospheric mantle thinned and chemically modified during riftingin the Mesozoic (Anza Graben) and in the Tertiary–Quaternary(Kenya rift). Four types of peridotite xenoliths were investigatedto constrain the thermal and chemical evolution of the lithosphericmantle. Group I, III and IV peridotites provide evidence ofa cold, highly deformed and heterogeneous upper mantle. Textures,thermobarometry and trace element characteristics of mineralsindicate that low temperatures in the spinel stability field( 750–800°C at <1·5 GPa) were attained bydecompression and cooling from initially high pressures andtemperatures in the garnet stability field (970–1080°Cat 2·3–2·9 GPa). Cooling, decompressionand penetrative deformation are consistent with lithosphericthinning, probably related to the development of the Mesozoicto Paleogene Anza Graben. Re-equilibrated and recrystallizedperidotite xenoliths (Group II) record heating (from 800°Cto 1100°C). Mineral trace element signatures indicate enrichmentby mafic silicate melts, parental to the Quaternary host basanitesand alkali basalts. Relationships between mineral textures,P–T conditions of equilibration, and geochemistry canbe explained by metasomatism and heating of the lithosphererelated to the formation of the Kenya rift, above a zone ofhot upwelling mantle. KEY WORDS: East African Rift System; Anza Graben; in situ LA-ICPMS; peridotite xenoliths; thermobarometry |
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| Keywords: | : East African Rift System Anza Graben in situ LA-ICPMS peridotite xenoliths thermobarometry |
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