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Magnetic mineralogy and rock magnetic properties of silicate and carbonatite rocks from Oldoinyo Lengai volcano (Tanzania)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Institute of Geochemistry and Petrology, Department of Earth Sciences, Swiss Federal Institute of Technology (ETH Zürich), Zürich, Switzerland.
Institute of Geochemistry and Petrology, Department of Earth Sciences, Swiss Federal Institute of Technology (ETH Zürich), Zürich, Switzerland.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.ORCID iD: 0000-0002-9385-7614
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2018 (English)In: Journal of African Earth Sciences, ISSN 0899-5362, Vol. 142, p. 193-206Article in journal (Refereed) Published
Abstract [en]

Oldoinyo Lengai, a stratovolcano in northern Tanzania, is most famous for being the only currently active carbonatite volcano on Earth. The bulk of the volcanic edifice is dominated by eruptive products produced by silica-undersaturated, peralkaline, silicate magmas (effusive, explosive and/or as cumulates at depth). The recent (2007–2008) explosive eruption produced the first ever recorded pyroclastic flows at this volcano and the accidental lithics incorporated into the pyroclastic flows represent a broad variety of different rock types, comprising both extrusive and intrusive varieties, in addition to various types of cumulates. This mix of different accidental lithics provides a unique insight into the inner workings of the world's only active carbonatite volcano.

Here, we focus on the magnetic mineralogy and the rock magnetic properties of a wide selection of samples spanning the spectrum of Oldoinyo Lengai rock types compositionally, as well from a textural point of view. Here we show that the magnetic properties of most extrusive silicate rocks are dominated by magnetite-ulvöspinel solid solutions, and that pyrrhotite plays a larger role in the magnetic properties of the intrusive silicate rocks. The natrocarbonatitic lavas, for which the volcano is best known for, show distinctly different magnetic properties in comparison with the silicate rocks. This discrepancy may be explained by abundant alabandite crystals/blebs in the groundmass of the natrocarbonatitic lavas.

A detailed combination of petrological/mineralogical studies with geophysical investigations is an absolute necessity in order to understand, and to better constrain, the overall architecture and inner workings of the subvolcanic plumbing system. The results presented here may also have implications for the quest in order to explain the genesis of the uniquely natrocarbonatitic magmas characteristic of Oldoinyo Lengai.

Place, publisher, year, edition, pages
2018. Vol. 142, p. 193-206
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-343161DOI: 10.1016/j.jafrearsci.2018.02.018ISI: 000430521700014OAI: oai:DiVA.org:uu-343161DiVA, id: diva2:1185613
Funder
The Crafoord FoundationAvailable from: 2018-02-26 Created: 2018-02-26 Last updated: 2018-08-02Bibliographically approved

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Publisher's full texthttps://www.sciencedirect.com/science/article/pii/S1464343X18300505

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Almqvist, Bjarne

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