Tracking changes of magma transfer beneath Mt. Etna: Evidence from crystal zonation and real-time gas monitoring
Abstract
The ability to anticipate the interval between pre-eruptive magma storage and magma ascent beneath highly active volcanoes, such as Mt. Etna is one of the major objectives of volcanology. So far, much of the information about magma emplacement and migration has been obtained by applying high-resolution geodetic, seismic and gas monitoring techniques. However, it has not been possible to relate such surface expressions of magma migration at depths to specific magmatic processes that generates them. Here we show an integrated methodology linking compositional and temporal information recorded in chemically zoned olivines with real-time variations (CO2/SO2) in gas emanations in order to monitor the intermittent input of new magma into sections of Mt. Etna's plumbing system. We have used data on compositional zoning of olivine in combination with real-time degassing data obtained during the period January 2005 - December 2006 [1] to show how variations in the monitoring signals can be related to changes occurring within the plumbing system at depth. The investigated eruptive products (July & October 2006) contain olivines with different populations of core and rim compositions (Fo70-72; Fo79-82; Fo73-75) and zoning patterns. We explain the diverging compositional and zoning record as the product of magma evolution in at least three distinct reservoirs (labeled M0, containing olivine of Fo79-82; M2 with Fo70-72 and mm1 with Fo73-75) with melt transfer and mixing between them. Further, consideration of the zoning data in a Systems analysis approach allowed us to decipher that at least two prominent magma passageways [(M0)-M2-mm1 and M0-M2] were activated during the course of the 2006 summit eruptive period at Mt. Etna. Modeling the diffusive relaxation of the compositional zoning profiles preserved in the olivines enabled us to constrain the time the crystals (+ their associated melts) spent in transit between these reservoirs. Based on this we found that the plumbing system of Etna underwent at least two major recharge events during the 2006 eruptive period. The first recharge beginning in late-May 2006 and culminating a few days before the onset of the first eruption-cycle in July. The second input of mafic magma could be detected from mid-June and very likely reactivated the eruptive activity in late-August. Correlating our results to the observed degassing record [1] we found that periods and timescales of magma input identified on the basis of zoning in olivine coincide with major changes in the measured CO2/SO2 signal [1]. We can therefore show that the observed systematic rise of the CO2/SO2 [1] signal before and during the eruptive sequences can be directly related to the gradual supply of batches of mafic magma, into different segments of the plumbing system, where mixing with residing (more evolved) magma is promoted. The method developed by us allows monitoring signals such as seismicity, ground deformation and gas monitoring to be associated with specific petrogenetic processes (e.g. magma mixing) within a continually evolving plumbing system that generates these signals [2], and has been adapted for other volcanoes [3, 4]. [1] Aiuppa et al. 2007, Geology 35, 1115-1118 [2] Kahl et al. 2011, EPSL 308, 11-22 [3] Druitt et al. 2012, Nature 482, 77-80 [4] Saunders et al. 2012, Science 336, 1023-1027
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V43F..03K
- Keywords:
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- 8410 VOLCANOLOGY / Geochemical modeling;
- 8419 VOLCANOLOGY / Volcano monitoring;
- 8425 VOLCANOLOGY / Effusive volcanism;
- 8430 VOLCANOLOGY / Volcanic gases