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Mineral resorption triggers explosive mixed silicate–carbonatite eruptions

Weidendorfer, Daniel and Schmidt, Max W. and Mattsson, Hannes B. (2019) Mineral resorption triggers explosive mixed silicate–carbonatite eruptions. Earth and Planetary Science Letters, 510 . pp. 219-230. ISSN 0012-821X.

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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.

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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.
Funding AgencyGrant Number
ETH Zurich34-11-1
Swiss National Science Foundation (SNSF)P2EZP2_162274
Swiss National Science Foundation (SNSF)P300P2_177798
Subject Keywords:silicate–carbonatite volcanism; mineral resorption; melt hybridization; peralkaline magmatism; element partitioning
Record Number:CaltechAUTHORS:20190128-144416116
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Official Citation:Daniel Weidendorfer, Max W. Schmidt, Hannes B. Mattsson, Mineral resorption triggers explosive mixed silicate–carbonatite eruptions, Earth and Planetary Science Letters, Volume 510, 2019, Pages 219-230, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92498
Deposited By: Tony Diaz
Deposited On:29 Jan 2019 16:14
Last Modified:03 Oct 2019 20:45

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