Search

Copyright of Virtual Archaeology Review is the property of Virtual Archaeology Review and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Volcanic rocks erupted during the January 2011 - April 2013 paroxysmal sequence at Mt. Etna volcano have been investigated through in situ microanalysis of mineral phases and whole rock geochemistry. These products have been also considered within the framework of the post-2001 record, evidencing that magmas feeding the 2011-2013 paroxysmal activity inherited deep signature comparable to that of the 2007-2009 volcanic rocks for what concerns their trace element concentration. Analysis performed on plagioclase, clinopyroxene and olivine, which are sensitive to differentiation processes, show respectively fluctuations of the An, Mg# and Fo contents during the considered period. Also major and trace elements measured on the whole rock provide evidence of the evolutionary degree variations through time. Simulations by MELTS at fixed chemical-physical parameters allowed the definition of feeding system dynamics controlling the geochemical variability of magmas during the 2011-2013 period. Specifically, compositional changes have been interpreted as due to superimposition of fractional crystallization and mixing in variable proportions with more basic magma ascending from intermediate to shallower levels of the plumbing system. Composition of the recharging end-member is compatible with that of the most basic magmas emitted during the 2007 and the early paroxysmal eruptions of 2012. Analysis of the erupted volumes of magma combined with its petrologic evolution through time support the idea that large volumes of magma are continuously intruded and stored in the intermediate plumbing system after major recharging phases in the deepest levels of it. Transient recharge from the intermediate to the shallow levels is then responsible for the paroxysmal eruptions. [ABSTRACT FROM AUTHOR]

Abstract: Since January 2011, Mt. Etna volcano has been affected by more than forty paroxysmal eruptions at the summit (New South East Crater; NSEC). On the basis of their very variable duration, seven eruptions have been selected among the twenty-five of 2011–2012 in order to decipher potential differences in their triggering mechanism. Paroxysms have been investigated through a multidisciplinary approach that integrates data from volcanic tremor and petrology (textures and micro-analysis on plagioclase crystals). Our results lead to the conclusion that close relationships exist between the duration of the eruptions and the temporal evolution of the volcanic tremor amplitude, especially during the Strombolian phase preceding the paroxysmal activity. In this regard, we distinguished: 1) paroxysms preceded by long-lasting initial Strombolian phases, characterized by low rate of volcanic tremor amplitude increase; and 2) eruptions preceded by short initial Strombolian phases, showing high rate of volcanic tremor amplitude increase. Based on the pattern of volcanic tremor amplitude increase, the former mainly showed a ramp-shaped morphology, while the latter a bell-shaped trend. Location of the volcanic tremor centroid during the quiescent intervals between the paroxysmal eruptions has highlighted the presence of a magmatic volume at 1–2kma.s.l. beneath the North East Crater (NEC). During the syn-eruptive Strombolian and lava fountaining phases, the centroid of volcanic tremor migrates below the NSEC. This leads to the consideration that the magma batch residing beneath NEC played an important role in the volcanic activity at NSEC during the considered period. Also the textures and compositional zoning (anorthite and iron variations) in selected plagioclase crystals of the analyzed lavas suggest relations between duration of the paroxysms and dynamics of pre-eruptive magmatic processes at depth. Particularly, two mechanisms have been accounted for triggering of eruptions at the NSEC on the basis of the concordant or discordant behavior of anorthite and iron in plagioclase coupled with disequilibrium textures at the rim. Concordant anorthite and iron increases in plagioclase crystals with sieve-textured rims indicate recharge by more mafic, gas-rich magma. This textural-compositional behavior has been related to long-lasting eruptions, whose volcanic tremor amplitude evolution produced ramp-shaped increase of the volcanic tremor amplitude before the paroxysmal phase. On the contrary, crystals with sieve-textures at the rim, characterized by increasing iron at rather constant or decreasing anorthite, suggest the prominent role of gas injections into the residing system. In this instance, the compositional behavior has been linked with short-lasting eruptions, whose volcanic tremor amplitude evolution led to a sudden increase of the seismic amplitude before the climax of the eruption. Thus, our work put forward the idea that the evolution and duration of the Strombolian phase preceding the paroxysmal eruptions of 2011–2012 at Mt. Etna are strongly controlled by the eruption triggering mechanism, which can be either gas burst or gas-rich magma recharge. [Copyright &y& Elsevier]