Journal article
Timescales of magma degassing - Insights from U-series disequilibria, Mount Cameroon, West Africa
Journal of volcanology and geothermal research, Vol.262, pp.38-46
07/15/2013
DOI: 10.1016/j.jvolgeores.2013.06.003
Abstract
Short-lived uranium-series isotope data from rocks erupted under explosive and effusive regimes are presented and used to provide constraints on the timescales of magmatic degassing and volatile fluxing during the 1999 and 2000 AD eruption of Mt. Cameroon. In contrast to the relatively homogenous major and trace element data of the analysed rocks, volcanic rocks from Mt. Cameroon reveal a spread of Th-230-Ra-226 isotope data. Volcanic rocks erupted along the southwest rift in 1999 have (Ra-226/Th-230 11) ratios of similar to 1.25, whereas rocks erupted more axially in 2000 have relatively low (Ra-226/Th-230) ratios of 1.09-1.2 and concomitant low Ba/Th ratios. These differences imply separate magma chamber systems and probably reflect differences in the concentrations of water within the primary magmas, which led to different amounts of amphibole fractionation at depth. Variations in the ((210)p/Ra-226) ratios are used to track degassing or volatile accumulation within the magma system. The near equilibrium ((210)p/Ra-226) values for effusively erupted rocks from Mt. Cameroon suggest that this magma resided for more than several decades and less than a few thousand years before it erupted. The small excesses of Pb-210 over Ra-226 in some samples indicate that some of this magma was fluxed by a Rn-bearing gaseous phase for weeks to years before the eruption. In contrast, most explosively erupted rocks from Mt. Cameroon have deficits of Pb-210 relative to Ra-226 that require years to decades of degassing before eruption. We suggest that the magmas erupted as scoria at Mt. Cameroon degassed as they rose from lithospheric depths. Deep degassing was CO2-dominated, whereas shallower magma degassing involved more water and crystallisation of an anhydrous mineral assemblage. (C) 2013 Elsevier B.V. All rights reserved.
Details
- Title: Subtitle
- Timescales of magma degassing - Insights from U-series disequilibria, Mount Cameroon, West Africa
- Creators
- K. B Turner - Macquarie UniversityM. K Reagan - University of IowaS. P Turner - Macquarie UniversityR. S. J Sparks - University of BristolH. K Handley - Macquarie UniversityG Girard - University of IowaC. E Suh - University of Buea
- Resource Type
- Journal article
- Publication Details
- Journal of volcanology and geothermal research, Vol.262, pp.38-46
- Publisher
- ELSEVIER SCIENCE BV
- DOI
- 10.1016/j.jvolgeores.2013.06.003
- ISSN
- 0377-0273
- eISSN
- 1872-6097
- Number of pages
- 9
- Grant note
- New Zealand Foundation of Research in Science and Technology postdoctoral fellowship European research Council Grant (VOLDIES) DP0988658 / Australian Research Council Discovery Proposal ARC LIEF DEST systemic Infrastructure Grants, Macquarie University
- Language
- English
- Date published
- 07/15/2013
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240799202771
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