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Authors: Parks, M. M.* 
Caliro, S.* 
Chiodini, G.* 
Pyle, D. M.* 
Mather, T. A.* 
Berlo, K.* 
Edmonds, M.* 
Biggs, J.* 
Nomikou, P.* 
Raptakis, C.* 
Title: Distinguishing contributions to diffuse CO2 emissions in volcanic areas from magmatic degassing and thermal decarbonation using soil gas 222Rn–δ13 C systematics: Applicationto Santorini volcano,Greece
Issue Date: 2013
Series/Report no.: 377-378 (2013)
DOI: 10.1016/j.epsl.2013.06.046
Keywords: volcanic unrest
soil gas measurements
carbon isotopic analysis
magmatic degassing
Subject Classification03. Hydrosphere::03.02. Hydrology::03.02.04. Measurements and monitoring 
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry 
04. Solid Earth::04.08. Volcanology::04.08.01. Gases 
04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques 
Abstract: Between January 2011 and April 2012, Santorini volcano (Greece) experienced a period of unrest characterised by the onset of detectable seismicity and caldera-wide uplift. This episode of inflation represented the first sizeable intrusion of magma beneath Santorini in the past 50 years. We employ a new approach using 222 Rn– δ 13 C systematics to identify and quantify the source of diffuse degassing at Santorini during the period of renewed activity. Soil CO 2 flux measurements were made across a network of sites on Nea Kameni between September 2010 and January 2012. Gas samples were collected in April and September 2011 for isotopic analysis of CO 2 ( δ 13 C), and radon detectors were deployed during September 2011 to measure ( 222 Rn). Our results reveal a change in the pattern of degassing from the summit of the volcano (Nea Kameni) and suggest an increase in diffuse CO 2 emissions between September 2010 and January 2012. High-CO 2 -flux soil gas samples have δ 13 C ∼ 0 .Using this value and other evidence from the literature we conclude that these CO 2 emissions from Santorini were a mixture between CO 2 sourced from magma, and CO 2 released by the thermal or metamorphic breakdown of crustal limestone. We suggest that this mixing of magmatic and crustal carbonate sources may account more broadly for the typical range of δ 13 CvaluesofCO 2 (from ∼− 4 to ∼+ 1 )in diffuse volcanic and fumarole gas emissions around the Mediterranean, without the need to invoke unusual mantle source compositions. At Santorini a mixing model involving magmatic CO 2 (with δ 13 C of − 3 ± 2 and elevated ( 222 Rn)/CO 2 ratios ∼ 10 5 –10 6 Bqkg − 1 )andCO 2 released from decarbonation of crustal limestone (with ( 222 Rn)/CO 2 ∼ 30–300 Bqkg − 1 ,and δ 13 Cof + 5 ) can account for the δ 13 C and ( 222 Rn)/CO 2 characteristics of the ‘high flux’ gas source. This model suggests ∼ 60% of the carbon in the high flux deep CO 2 end member is of magmatic origin. This combination of δ 13 Cand( 222 Rn) measurements has potential to quantify magmatic and crustal contributions to the diffuse outgassing of CO 2 in volcanic areas, especially those where breakdown of crustal limestone is likely to contribute significantly to the CO 2 flux
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