Constraints on eruption dynamics of basaltic explosive activity derived from chemical and microtextural study: The example of the Fontana Lapilli Plinian eruption,Nicaragua |
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| Authors: | L Costantini BF Houghton C Bonadonna |
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| Institution: | 1. Department of Geology, Faculty of Sciences, University of Salamanca, Spain;2. Division of Earth and Planetary Materials Science, Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, Miyagi, Japan;3. School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK;4. Department of Physics, Engineering and Medical Radiology, University of Salamanca, Spain;5. Department of Earth and Environmental Sciences, Yamagata University, Japan;6. Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA;7. Division of GeoEnvironmental Science, Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, Miyagi, Japan;1. School of Geography, Environment and Earth Sciences, Victoria University, PO Box 600, Wellington 6140, New Zealand;2. Institut des Sciences de la Terre (ISTO), Centre National de la Recherche Scientifique (CNRS), l''Université d''Orléans, 1a rue de la Férollerie, Orléans Cedex 2, 45071, France;3. Institute of Geosciences, University of Mainz, Mainz, Germany;4. Lancaster Environment Centre, Lancaster University, UK;1. Lamont Doherty Earth Observatory, Columbia Univ., NY, USA;2. Carnegie Instit. of Washington, DC, USA;3. Michigan Tech Univ., Houghton, MI, USA;4. Rice Univ., Houston, TX, USA;1. Department of Earth Sciences, University of Geneva, 13 Rue des Maraîchers, 1205 Genève, Switzerland;2. Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Piazza Roma 2, 95125 Catania, Italy;1. School of Geography, Earth and Environmental Science, University of Plymouth, Plymouth, UK;2. Geology Department, University of Otago, PO Box 56, Dunedin 9054, New Zealand;1. School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia;2. School of the Environment, Washington State University, Pullman, WA 99164, USA;3. School of Physical Sciences, CODES, University of Tasmania, Hobart 7001, Australia;4. Institute of Earth Sciences ‘Jaume Almera’, CSIC, Lluis Sole Sabaris s/n, 08028 Barcelona, Spain |
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| Abstract: | The Fontana Lapilli deposit is one of very few examples of basaltic Plinian eruptions discovered so far. Juvenile clasts have uniform chemical composition and moderate ranges of density and bulk vesicularity. However, clast populations include two textural varieties which are microlite-poor and microlite-rich respectively. These two clast types have the same clast density range, making a distinction impossible on that base alone. The high bubble number density (～ 107 cm? 3) and small bubble population of the Fontana clasts suggest that the magma underwent coupled degassing following rapid decompression and fast ascent rate, leading to non-equilibrium degassing with continuous nucleation as it is common for silicic analogues. The Fontana products have lower microlite contents (10–60 vol.%) with respect to the other documented basaltic Plinian eruptions suggesting that the brittle fragmentation, implied for the other basaltic Plinian deposits, does not apply to the Fontana products and another fragmentation mechanism led the basaltic magma to erupt in a Plinian fashion. |
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