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Fragmentation, eruption dynamics and depositional processes in mixed carbonatite - silicate volcanic eruptions

Applicant Mattsson Bjoern Hannes
Number 129985
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.08.2010 - 30.09.2012
Approved amount 128'242.00
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All Disciplines (4)

Discipline
Geochemistry
Mineralogy
Other disciplines of Earth Sciences
Geology

Keywords (11)

carbonatite; nephelinite; magma mixing; explosive volcanic eruptions; pyroclastic deposits; lithofacies analyses; Kerimasi; Oldoinyo Lengai; Fragmentation; East African Rift; volcanic hazards

Lay Summary (English)

Lead
Lay summary
Volcanic eruptions involving mixing of two magmas of widely different characteristics have been occurring on numerous occasions at the Kerimasi and Oldoinyo Lengai volcanoes in northern Tanzania, including a recent eruptive episode in 2007-2008. The contemporaneous eruptions of these mixed magmas have resulted in surprisingly vigorous explosions that predominantly produce fine ash. One goal of this project is to investigate the processes involved in the fragmentation of the magmas, i.e., is the fragmentation process driven by exsolution of volatiles from the magmas themselves, due to thermal decomposition of the carbonatite magma, or by explosive interactions with an external water source? This project is based on extensive fieldwork, sampling and mapping of volcanic deposits to detect spatial and temporal variations in magma fragmentation and deposition occurring during the eruptions. The collected material will be subject to laboratory-based analyses in order to characterize their chemistry and mineralogy. The samples will be subject to mechanical sieving to retrieve grain-size distributions, and a variety of imaging techniques will be applied to quantify the shapes of the resulting pyroclasts. In combination, these techniques will allow to constrain the physical mixing, eruption, and depositional processes involving two magmas of distinctively different chemistry and subsequently also different physical properties.Special emphasis will be placed on the deposits generated in the recent eruption of Oldoinyo Lengai, as this volcano is currently active and understanding the past behavior is an integral part of building a realistic hazard assessment for future eruptions.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
4th International Maar Conference 20.02.2012 Auckland, New Zealand
Nordic Geological Winter Meeting 09.01.2012 Reykjavik, Iceland
AGU Fall Meeting 2011 05.12.2011 San Francisco, USA


Communication with the public

Communication Title Media Place Year
Media relations: print media, online media Oldoinyo Lengai - Der berg Gottes Geosciences Actuel German-speaking Switzerland 16.01.2012

Associated projects

Number Title Start Funding scheme
140560 Eruptive history of the Oldoinyo Lengai volcano: Constraints on the stratigraphic record in northern Tanzania with implications for volcanological and anthropological research 01.01.2013 Project funding (Div. I-III)
144421 Fragmentation, eruption dynamics and depositional processes in mixed carbonatite - silicate volcanic eruptions 01.10.2012 Project funding (Div. I-III)

Abstract

In order to understand carbonatite volcanism, and the genesis of carbonatitic magmas, a wide spectrum of complementary studies needs to be conducted. By combining information retrieved from mineralogy, petrology, isotope geochemistry, with extensive field studies a more genuine understanding of how carbonatitic volcanoes work, and how the carbonatitic magmas are linked to the silicate rocks, will emerge. This project is focused on pyroclastic deposits generated by explosive mixed carbonatite-silicate eruptions of the Kerimasi and Oldoinyo Lengai volcanoes in northern Tanzania. The volcanoes are chosen for the present project because their close vicinity to each other, and the fact that they cover mixed eruptions of both calciocarbonatitic-nephelinitic (Kerimasi) and natrocarbonatitic-nephelinitic (Oldoinyo Lengai) compositions, and there exists an abundance of petrological, mineralogical and isotopic data in the published literature. However, detailed and systematic studies of the pyroclastic deposits and their field relations are lacking for both volcanoes. Therefore, the present project aims to close this informational gap by providing detailed field data that can be easily integrated with the existing studies to better understand carbonatite volcanism and to add constraints on the petrogenesis of the carbonatitic magmas. The project will give insights into the mixing, eruption, and depositional process involving two magmas of widely different chemical compositions and subsequently also very different physical properties. The project will also provide data on how natrocarbonatites, calciocarbonatites and nephelinites occur within the natural deposits at the Kerimasi and Oldoinyo Lengai volcanoes. These depositional relations and their characteristics, in combination with geochemical equilibrium/disequilibrium studies of the mineral phases involved will shed light on the genetic relationships between the different types of magmas.Pyroclastic deposits generated during the recent mixed eruption of Oldoinyo Lengai in 2007-2008 will be studied in detail, and the eruption dynamics will be established based on the measured spatial and temporal variations within the deposits in combination with studies of photographs and video clips from the same eruption. The results from Oldoinyo Lengai will then serve as a basis for interpreting similar, but predominately calciocarbonatitic, deposits of the adjacent Kerimasi volcano.This proposal seeks funding for a PhD student to perform extensive field-based stratigraphic logging of the pyroclastic deposits, which will be subject to subsequent laboratory-based granulometric, petrographic, textural and geochemical studies. By combining the results from the field with the laboratory analyzes interpretations of eruption dynamics and fragmentation modes, as well as different emplacement mechanisms can be made. Understanding the past eruptive behavior is an integral part in building a realistic hazard assessment for any volcano.
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