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Tinderet volcano, Kenya: an altered natrocarbonatite locality?

Published online by Cambridge University Press:  05 July 2018

A. N. Zaitsev*
Affiliation:
Department of Mineralogy, Faculty of Geology, St Petersburg State University, University Emb. 7/9, St Petersburg 199034, Russia Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
T. Wenzel
Affiliation:
Fachbereich Geowissenschaften, Universität Tübingen, Wilhelmstr. 56, Tübingen 72074, Germany
T. Vennemann
Affiliation:
Institute of Earth Sciences, University of Lausanne, Géopolis, CH-1015 Lausanne, Switzerland
G. Markl
Affiliation:
Fachbereich Geowissenschaften, Universität Tübingen, Wilhelmstr. 56, Tübingen 72074, Germany

Abstract

The Tinderet volcano (19.9 to 5.5 Ma), located within the Kavirondo rift in Kenya, contains blocks of carbonatite lavas with calcite, minor apatite, fluorite, spinel-group minerals, accessory perovskite and 'plumbopyrochlore'; nyerereite is present as inclusions in the perovskite. At least four types of calcite are present in the carbonatite lavas; they differ in morphology, composition and origin. The dominant variety is secondary type-II calcite, which is enriched in sodium (up to 1.1 wt.% Na2O) and strontium (up to 1.3 wt.% SrO). The spinel-group minerals are manganese-bearing and include Mn-rich magnetite, magnesioferrite and jacobsite. Oxygen isotope data for bulk carbonatite samples (δ18O = +16.2 % to +22.6 % VSMOW) support a low crystallization temperature for the secondary calcite. Petrographic, mineralogical and isotopic data indicate that the Tinderet carbonatites are similar to natrocarbonatites from the Oldoinyo Lengai and Kerimasi volcanoes that have altered and recrystallized to form calcite carbonatites. These data support the hypothesis that some of the Tinderet carbonatites were originally alkali-rich rocks which contained primary nyerereite.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2013

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