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Control of the stress field and rift structures on the distribution and morphology of explosive volcanic craters in the Manyara and Albertine rifts
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2019 (English)In: Journal of African Earth Sciences, ISSN 1464-343X, E-ISSN 1879-1956Article in journal (Refereed) Accepted
Abstract [en]

Monogenetic volcanoes are widespread in the East African Rift. Their morphologies are diverse with positive(scoria and tuff cones) and negative reliefs (tuff rings and maars). The Manyara Rift (Tanzania) and AlbertineRift (Uganda) are characterised by a singular abundance of negative volcanic reliefs with about 300 and 350maars and tuff rings, respectively, covering a surface of about ∼3000 km2 in each country. Such high density ofexplosive craters is not observed elsewhere in the East African Rift.We perform spatial distribution and alignment analyses using two different approaches (Two Point Analysisand Point Alignments) to study the link between the distribution of the monogenetic volcanic vents, the riftstructures, and the stress field. Both methods give similar results although the Point Alignments perform betterfor large radius of investigations. Volcanic alignments in the Manyara rift suggest a dominant control of the oldbasement and rift structures on dyke emplacement and distribution of volcanic vents, under an oblique rifting.However, data further suggest that this influence is reducing, and the rift is entering a more mature phase withorthogonal rifting. On the other hand, volcanic alignments in the Albertine rift imply a dominant control of thestress field on dyke emplacement and on the distribution of volcanic vents under orthogonal rifting. This suggeststhat the Albertine rift is a mature rift since at least the past 50 000 yrs.We further tested the influence of rift structures and stress field on maar and tuff ring morphologies. Most ofthe craters are near-circular, or a least not strongly elongated, and show minor complexities in shape which weattribute to lateral migration of explosions. Few maars and tuff rings in Manyara show that lateral migrationhave followed pre-existing faults. In general, we advise not to fit an ellipse to individual maars and tuff rings toassess the orientation of the feeder intrusions.

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2019.
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Geology
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URN: urn:nbn:se:uu:diva-375188DOI: 10.1016/j.jafrearsci.2018.09.012OAI: oai:DiVA.org:uu-375188DiVA, id: diva2:1283115
Available from: 2019-01-28 Created: 2019-01-28 Last updated: 2019-01-28

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