Fluid Geochemistry Contribution to the Interpretation of the 2011–2012 Unrest of Santorini, Greece, in the Frame of the Dynamics of the Aegean Volcanic Arc

Abstract

Tectonic and magmatic activity may couple at volcanic arcs, even though any relationship is less defined in smaller arcs, experiencing limited activity. Here we use gas geochemistry data collected during the 2011-2012 unrest at Santorini (Greece) to understand better the dynamics of the Aegean Volcanic Arc with regard to its tectonic setting. Since the most recent eruption in 1950 and before the unrest, minor seismicity and CO 2 degassing (mainly from the fumaroles of Nea Kameni islet) were observed at Santorini. On January 2011, anomalous seismicity along the NE-SW trending Kameni Line was accompanied by an inflation north of Nea Kameni. Fumarolic gas composition changed and gas release notably increased. We carried out geochemical study on both Kameni and Thera islands from January 2012 to June 2013. We repeated surveys of diffuse soil CO 2 degassing and of in-soil gas concentration, and we analyzed fumaroles and gas dissolved in thermal waters for chemical and isotopic composition. In agreement with previous studies, our geochemical data, particularly the diffuse soil CO 2 flux increase, the increase of H 2 content, and of CO 2 /CH 4 and 3 He/ 4 He ratios in fumarolic gases, support geophysical data in indicating that unrest was associated with the emplacement of new mafic magma. This unrest had limited effect on the regional setting, with gas emissions focusing along the regional NE-SW structures, without triggering by any seismic event, conversely to the 1950 eruption, which probably occurred in a frame of general tectonic reorganization of the Aegean microplate.

Shallow Sea Gas Manifestations in the Aegean Sea (Greece) as Natural Analogs to Study Ocean Acidification: First Catalog and Geochemical Characterization

“…This scarcity evidences the lack of underlying organic-rich source rocks in these areas. Few gases of Milos, Kos and Santorini are virtually enriched in CH 4 due to loss of CO 2 by dissolution as evidenced also in 2013), Rizzo et al (2016Rizzo et al ( , 2019, Daskalopoulou et al (2018aDaskalopoulou et al ( ,b, 2019bDaskalopoulou et al ( , 2021a, and Tarchini et al (2019). 2013), Rizzo et al (2016Rizzo et al ( , 2019, Daskalopoulou et al (2018a,b, 2019b, 2021a), and Tarchini et al (2019.…”

“…The outlet temperatures of the two points are 36 (Agios Nikolaos) and 40 • C (Agios Giorgios) (Böstrom and Widenfalk, 1984;Dotsika et al, 2009). On the other hand, Irinia shows a mixed CO 2 -N 2 composition (Daskalopoulou et al, 2018b;Tarchini et al, 2019). All three sites are in protected coves where the seawater is heavily stained by iron oxides due to the input of the hydrothermal fluids.…”

“…Lies and Katsouni are two gas manifestations rich in CO 2 (Supplementary Table 1). They are 2013), Rizzo et al (2016Rizzo et al ( , 2019, Daskalopoulou et al (2018a,b, 2019b, 2021a), and Tarchini et al (2019.…”

“…In the current study, a total of 122 data from submarine gas manifestations are presented. This dataset comprises both literature (Chiodini et al, 1998;Shimizu et al, 2005;Kyriakopoulos, 2010;Carey et al, 2013;Tassi et al, 2013;Rizzo et al, 2016Rizzo et al, , 2019Daskalopoulou et al, 2018aDaskalopoulou et al, ,b, 2019bDaskalopoulou et al, , 2021aTarchini et al, 2019) and 7 unpublished results from submarine degassing areas distributed in ten areas of the Aegean Sea; seven of which belong to the SAAVA. Gases were collected using the inverted funnel method (Figure 5).…”

“…Slopes of biogenic and abiogenic oxidation of CH 4 are also plotted. Literature data from Chiodini et al (1998), Shimizu et al (2005), Kyriakopoulos (2010), Carey et al (2013), Tassi et al (2013), Rizzo et al (2016Rizzo et al ( , 2019, Daskalopoulou et al (2018a,b, 2019b, 2021a), and Tarchini et al (2019.…”