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Magma Evolution at La Fossa Volcano (Vulcano Island, Italy)

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Magma Evolution at La Fossa Volcano (Vulcano Island, Italy) Magma evolution at La Fossa volcano (Vulcano Island, Italy) in the last 1000 years: evidence from eruptive products and temperature gradient experiments Delphine Bosch, Simone Costa, M. Masotta, A. Gioncada, M. Pistolesi, P. Scarlato To cite this version: Delphine Bosch, Simone Costa, M. Masotta, A. Gioncada, M. Pistolesi, et al.. Magma evolution at La Fossa volcano (Vulcano Island, Italy) in the last 1000 years: evidence from eruptive products and temperature gradient experiments. Contributions to Mineralogy and Petrology, Springer Verlag, 2020, 175 (4), 10.1007/s00410-020-1669-0. hal-03013250 HAL Id: hal-03013250 https://hal.archives-ouvertes.fr/hal-03013250 Submitted on 21 Nov 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Contributions to Mineralogy and Petrology (2020) 175:31 https://doi.org/10.1007/s00410-020-1669-0 ORIGINAL PAPER Magma evolution at La Fossa volcano (Vulcano Island, Italy) in the last 1000 years: evidence from eruptive products and temperature gradient experiments S. Costa1,2 · M. Masotta2 · A. Gioncada2 · M. Pistolesi2 · D. Bosch3 · P. Scarlato4 Received: 31 July 2019 / Accepted: 28 February 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract The intense explosive and effusive volcanic activity of the last 1000 years at La Fossa volcano (Vulcano Island, Italy) was characterized by the eruption of magmas ranging in composition from latites to trachytes and rhyolites, as well as K-rich trachytes. Evidence of syn-eruptive mixing among these magmas is frequently observed in the form of magmatic enclaves and bands in lava flows and pyroclastic products. The petrological and volcanological diversity of the erupted materials suggests that complex differentiation processes occurred in the shallow part of the plumbing system. With the aim to reconstruct the magmatic feeding system and to identify the differentiation processes behind such a petrologic complexity, we analysed lavas and pyroclastic products representative of the recent eruptive sequences at La Fossa and combined the petro-chemical features with thermo-barometric calculations, geochemical modelling and temperature gradient experiments. Thermo-barometric calculations indicate that the K-rich trachytic magma crystallized at lower pressure (160 ± 54 MPa) compared to the latitic (307 ± 47 MPa) and trachytic (208 ± 30 MPa) magmas. Differentiation modelling suggests that both trachytic and rhyolitic compositions can be obtained through differentiation of a common latitic magma, essentially by varying the plagioclase/ sanidine ratio. Temperature gradient experiments, performed at the conditions inferred for the shallow plumbing system of La Fossa volcano (150 MPa and 1050–900 °C), indicate different paths of melt differentiation that overall produce an increase of the SiO2/K2O ratio with the increasing H2O in the system (from 0 to 4 wt.%). This is consistent with the origin of K-rich trachytes at lower pressure and lower H 2O content. In turn, the formation of crystal-poor rhyolites is explained by the segregation of the interstitial melt formed in a latitic–trachytic crystal mush, favoured by the second boiling of the melt and consequent exsolution of a fluid phase. Keywords Vulcano Island · Trachyte · Crystal-poor rhyolite · Crystal mush · Temperature gradient experiments Introduction Communicated by Gordon Moore. The physico-chemical characterization of the plumbing Electronic supplementary material The online version of this system of frequently active arc volcanoes is one of the article (https ://doi.org/10.1007/s0041 0-020-1669-0) contains supplementary material, which is available to authorized users. main challenges in volcanology, as it constitutes a ground element for the assessment of the pre-eruptive conditions * S. Costa of magmas and for the definition of future eruptive sce- simone.costa@unifi.it narios. On the one hand, the estimate of the intensive vari- 1 Dipartimento Di Scienze Della Terra, Università Di Firenze, ables of the magma is possible either through the thermo- via La Pira, 4 50121 Florence, Italy barometric calculations based on the phase compositions 2 Dipartimento Di Scienze Della Terra, Università Di Pisa, via of eruptive products (Putirka 2008), or via direct compari- S. Maria, 53 56126 Pisa, Italy son of the natural products with laboratory experiments 3 Géosciences Montpellier, Université de Montpellier, Place performed under constrained physical conditions (Scaillet E. Bataillon, 34095 Montpellier, France et al. 2008). On the other hand, clues on the chemical com- 4 Istituto Nazionale Di Geofisica E Vulcanologia, Via di Vigna position of magmas feeding the eruptions can be obtained Murata 605, 00191 Rome, Italy through the petrologic study of the eruptive products of the Vol.:(0123456789)1 3 31 Page 2 of 22 Contributions to Mineralogy and Petrology (2020) 175:31 recent volcanic activity (Cioni et al. 1998). Such informa- of the plumbing system and to place constraints on magma tion, combined with data obtained from the geochemical dynamics and evolution in small arc volcanoes. and geophysical monitoring, is critical for determining the In this study, we took in exam the last 1000 years activ- variations of the physico-chemical parameters of magmas ity of La Fossa volcano, with the aim of reconstructing the and, ultimately, for the volcanic hazard assessment and physical conditions at which magmas evolved, interacted for designing risk mitigation plans (Neri et al. 2008). In and erupted. For this purpose, we selected representative this context, the active volcanic system of La Fossa (Vul- rock samples encompassing the entire compositional range cano Island, Italy), with its recurrent historic activity and of erupted magmas, and combined new whole rock and well-known stratigraphy (De Astis et al. 2013), represents micro-chemical analyses of natural samples with tempera- an ideal study case for the investigation of magmatic pro- ture gradient experiments that emulate the crystallization cesses and eruptive dynamics. and differentiation processes occurring in a shallow and The eruptive products of La Fossa encompass a broad temperature-zoned magma reservoir. The results obtained in range of magma compositions, ranging from latite to tra- this work contribute to envisage the complexity of the poly- chyte and rhyolite. The heterogeneous composition of mag- baric storage system of La Fossa volcano, where the role of mas erupted even within single eruptions, testifies to syn- shallow crystal mushes is determinant for the production of eruptive mixing and or mingling processes (De Astis et al. small volumes of rhyolitic magmas at rather short timescale, 2013). Latitic to trachytic magmatic enclaves in rhyolitic through repeated episodes of melt extraction. lavas and compositionally heterogeneous (banded) pumices are, in fact, common in the recent activity of La Fossa vol- cano (e.g. Piochi et al. 2009; Rossi et al. 2019). Significant Geological background and stratigraphy variations of magma chemistry at a same SiO2 content are of the last 1000 years of La Fossa also observed, as in the case of the fallout products emplaced during the Palizzi–Commenda eruptive cluster (Di Traglia Vulcano is the southernmost island of the Aeolian archi- et al. 2013), whose trachytic composition has the highest pelago, a volcanic arc located in southern Tyrrhenian sea concentration in K2O of the entire eruptive history of La (Fig. 1). La Fossa cone, located in the northern sector of the Fossa volcano (up to 7.5 wt.%; Fulignati et al. 2018). island and active since 6 ka, last erupted in AD 1888–1890 The petrological complexity of the plumbing system of (Keller 1980). The stratigraphy of La Fossa cone has been La Fossa has been the object of many studies in the past 2 described in detail in many studies and consists mainly of decades, aimed at defining (i) the intensive variables and pyroclastic fallout deposits (ash, pumiceous lapilli, blocks the magmatic processes governing the evolution of paren- and bread crust bombs) and lava flows (Clocchiatti et al. tal magmas (Clocchiatti et al. 1994; De Astis et al. 1997; 1994; Piochi et al. 2009; Di Traglia et al. 2013; De Astis Del Moro et al. 1998; Gioncada et al. 1998; Pinarelli et al. et al. 2013). Following the stratigraphic reconstruction pro- 2019); (ii) the pre- and syn-eruptive interaction of magmas posed by Di Traglia et al. (2013), the eruptive history of the at different degrees of evolution (Piochi et al. 2009; Bullock last 1000 years can be summarized in two eruptive clusters: et al. 2019); (iii) the dynamics and timescales of pre-erup- the Palizzi–Commenda eruptive cluster (PCEC), developed tive magma ascent, mixing and eruption (Vetere et al. 2015; during the thirteenth century, and the Gran Cratere eruptive Nicotra et al. 2018; Rossi et al. 2019). Although there is a cluster (GCEC, fifteenth century-1890 AD) (Fig. 2a). The general consensus for the pre-eruptive temperature estimates stratigraphic sequence of PCEC displays a large variety of and mixing processes of the latitic, trachytic
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