Nature and timing of multiple metasomatic events in the sub-cratonic lithosphere beneath Labait, Tanzania

Koornneef, Janne M., Davies, Gareth R., Döpp, Sonja P., Vukmanovic, Zoja ORCID: https://orcid.org/0000-0001-7559-0023, Nikogosian, Igor K. and Mason, Paul R. D. (2009) Nature and timing of multiple metasomatic events in the sub-cratonic lithosphere beneath Labait, Tanzania. Lithos, 112 (S2). pp. 896-912. ISSN 0024-4937

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Abstract

Petrography, mineral major- and trace element analyses and Rb–Sr and Sm–Nd systematics of xenoliths from Labait volcano, north-central Tanzania, document multiple metasomatic events after initial depletion of the Archaean sub-lithospheric mantle. Four distinct metasomatic phases occurred during the 2.8–3.2 Ga history of the mantle section of the Tanzanian craton. 1) Garnet and Cr-diopside in two depleted lherzolites record LREE enrichment in an early cryptic metasomatic event (~ 2 Ga) resulting in unradiogenic εNd (− 6.6) and relatively radiogenic Sr signature (87Sr/86Sr = 0.7049); 2) Four texturally equilibrated peridotites contain phlogopite and Cr-diopside inferred to be introduced by a hydrous melt/fluid that produced LREE enrichment related to the subduction and collision during the 650 Ma Pan-African Orogeny; 3) Fe-enrichment is observed in many garnet-free wehrlites and dunites having low Mg# olivines. Timing of this enrichment event remains poorly defined; and 4) One spinel lherzolite records orthopyroxene replacing clinopyroxene due to recent infiltration of a rift-related H2O poor, K-alkaline silicate melt. This ongoing metasomatic reaction caused by rift-related magmatism would result in the conversion of lherzolite to orthopyroxene-rich harzburgite. The reaction possibly represents the mechanism involved in the formation of orthopyroxene-rich sub-continental lithospheric mantle below the Kaapvaal and Siberian cratons. Generally, the rift-related metasomatism beneath Tanzania has caused formation of interstitial clinopyroxene, melt veins and melt pockets and new rims of phlogopite, all of which are in chemical disequilibrium with the original xenolith mineralogy.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: LivePure Connector
Date Deposited: 14 Sep 2022 12:30
Last Modified: 30 Sep 2022 02:33
URI: https://ueaeprints.uea.ac.uk/id/eprint/88286
DOI: 10.1016/j.lithos.2009.04.039

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