Mineral resorption triggers explosive mixed silicate–carbonatite eruptions
Abstract
Historic eruptions of Earth's only active carbonatite volcano, Oldoinyo Lengai (Tanzania), have repeatedly switched from low energy carbonatite lava extrusion to highly energetic explosive silicate volcanism, most recently in 1966–67 and 2007–08. The explosive eruptions produce strongly Si-undersaturated peralkaline silicate ashes with unusually high (Na + K)/Al of 3.4–6.3 when compared to the average peralkalinity of ∼0.8 in the East African Rift System. A series of experiments in the carbonatite–clinopyroxene system at 750–1150 °C, 0.1 GPa, reveal that augitic clinopyroxene breaks down peritectically at >900 °C yielding strongly peralkaline conjugated silicate- and carbonatite melts. The clinopyroxene-derived silicate melt dissolves (Na,K)_2O from the (Na,K)_2CO_3-component of the carbonatite leading to high peralkalinities and to liberation of excess CO_2, since the solubility of carbon dioxide in silicate liquids is ≪1 wt.% at subvolcanic pressures. Carbonatite injection into subvolcanic clinopyroxene-rich crystal mushes hence explains the occurrence of strongly peralkaline silicate melts and provides a mechanism for CO_2-driven explosive eruptions. The silicate melt compositions mostly depend on the (Na + K)/Ca ratio of the intruding carbonatite, the silicate ashes erupted in 1966–67 and 2007–08 require an interaction of a clinopyroxene-rich crystal mush with a slightly less evolved alkali-carbonatite than presently erupted at Oldoinyo Lengai. The mechanism identified here, where mineral breakdown induced melt hybridization triggers volatile saturation and highly explosive volcanism is generally applicable to igneous systems that involve carbonatites or other low-viscosity CO_2-bearing alkaline silicate melts.
Additional Information
© 2019 Elsevier B.V. Received 1 May 2018, Revised 27 December 2018, Accepted 3 January 2019, Available online 28 January 2019. This study was financed by ETH grant 34-11-1 and supported by SNSF grants P2EZP2_162274 and P300P2_177798. The authors acknowledge insightful comments from Tom Andersen and one anonymous reviewer, Mike Bickle is thanked for editorial handling.Attached Files
Supplemental Material - 1-s2.0-S0012821X19300135-mmc1.xlsx
Supplemental Material - 1-s2.0-S0012821X19300135-mmc2.pdf
Supplemental Material - 1-s2.0-S0012821X19300135-mmc3.pdf
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Additional details
- Eprint ID
- 92498
- DOI
- 10.1016/j.epsl.2019.01.003
- Resolver ID
- CaltechAUTHORS:20190128-144416116
- 34-11-1
- ETH Zurich
- P2EZP2_162274
- Swiss National Science Foundation (SNSF)
- P300P2_177798
- Swiss National Science Foundation (SNSF)
- Created
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2019-01-29Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field