Non-volcanic degassing along fault zones in the southern Apennines (Italy) Assessing mantle versus crustal sources for non-volcanic degassing along fault zones in the actively extending southern Apennines mountain belt (Italy) Alessandra Ascione1,†, Giancarlo Ciotoli2,3, Sabina Bigi4, Jamie Buscher5,6, Stefano Mazzoli1, Livio Ruggiero4, Alessandra Sciarra3, Maria Chiara Tartarello4, and Ettore Valente1 1Department of Earth, Environmental and Resources Science (DiSTAR), University of Naples “Federico II,” 80126 Naples, Italy 2National Research Council of Italy, Institute of Environmental Geology and Geoengineering (IGAG), 00015 Monterotondo, Rome, Italy 3Istituto Nazionale di Geofisica e Vulcanologia (INGV), 00143 Rome, Italy 4Department of Earth Sciences, University of Rome Sapienza, 00185 Rome, Italy 5Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, 8370450 Santiago, Chile 6Department of Geology, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile 8370450 Santiago, Chile ABSTRACT Matese Ridge area is the result of both the morphic decarbonation of marine limestones presence of a dense network of active fault (Chiodini et al., 1999, 2004; Italiano et al., 2000, The actively extending axial zone of the strands, which provides efficient pathways 2008; Minissale, 2004; Caracausi et al., 2013). southern Apennine mountain belt of Italy is for fluid flow toward the surface, and the dra- Current models of degassing in non-volcanic characterized by a substantial flow of non- matically reduced thickness of the clay-rich areas of the Apennines imply that the process volcanic gas to the surface. In this study, we mélange zone acting elsewhere in the south- occurs from a deep hot source (“mantle wedge”) have analyzed the correlation between the ac- ern Apennines as a top seal overlying the bur- and by the progressive dehydration of the sub- tive tectonic framework of the Matese Ridge ied Apulian Platform carbonates. ducted Adriatic-Apulian plate (Chiodini et al., area and the high gas emissions found to the 2004, 2013; Frezzotti et al., 2009; Chiarabba southwest, which includes large amounts of INTRODUCTION and Chiodini, 2013). Also, mechanical energy CO2 (up to 99 vol%), CH4 (up to 0.55 vol%), released during seismic events has been recently and He (up to 52 ppmv). We measured CO2 Natural degassing of massive amounts proposed as a possible additional source of CO2 –1 and CH4 fluxes of up to 34000 g d and of CO2 occurs along the entire Apennines (through friction-related heating and associated 2000 g d–1, respectively, from zones of focused mountain belt of Italy (Chiodini et al., 2004; decarbonation processes; e.g., De Paola et al., degassing (gas vents and associated strong Minissale, 2004; Frezzotti et al., 2009; Burton 2011) for areas in the Apennines where the con- diffuse emission). This anomalously high flux et al., 2013). Very high fluxes of geogenic CO2 tribution of CO2 degassing from the mantle is 11 –1 of CO2 (advective plus diffusive) indicates (up to 1–2 × 10 mol y ; Chiodini et al., 2013) low (Italiano et al., 2008). that the study area has one of the largest non- are measured along the southwestern part of Non-volcanic gas emissions are mostly lo- volcanic natural emissions of CO2 ever mea- the Apennines, particularly in the central- calized within Quaternary continental grabens sured on Earth. The isotope composition of southern segment of the Tyrrhenian back-arc that punctuate areas along the axis of the cen- C in CO2 and CH4 shows there is a dominant basin margin, where there is evidence for tral and southern Apennines mountain belt. crustal contribution of emissions (as opposed Quaternary and active volcanism. In this area, This axial region is currently affected by ex- to a source from the mantle), indicating that the presence of thinned crust and mature sets tensional processes, which control the moder- thermometamorphism of the buried Apulian of extensional faults and fracture systems al- ate to strong seismicity that affects the Italian Platform carbonates is probably the main lows crustal and/or mantle fluids feeding the peninsula (e.g., Rovida et al., 2016). Addition- cause of CO2 production. This process has volcanic systems to migrate toward the sur- ally, there is evidence for both CO2 and CH4 likely been enhanced by Quaternary mag- face ( Chiodini et al., 1999, 2000, 2004, 2013; emissions occurring at the surface along active matism, which provides an additional local Chiodini and Frondini, 2001; Mörner and fault systems (Chiodini et al., 2004; Ciotoli source of heat triggering decarbonation of Etiope, 2002; Gambardella et al., 2004; Burton et al., 2007; Ciotoli et al., 2014; Caracausi and Apulian Platform limestones and dolostones et al., 2013; Etiope, 2015). Paternoster, 2015). at depth. The advective flux is concentrated at Natural CO2-dominant gas manifestations In the southern Apennines, CO2 emissions are gas vents located along active fault segments also occur in areas of the Apennines not affected widespread, but we have focused this study on located at the western tip of a major crustal by volcanic activity (i.e., non-volcanic areas). the high gas emissions occurring in areas sur- structure, the South Matese fault zone. We The isotopic signature (i.e., 13C and 3He/4He) of rounding the Ciorlano and Ailano villages lo- believe that the very high gas emission in the the majority of non-volcanic gas emissions sug- cated southwest of Matese Ridge (Fig. 1). In the gests that the gas is primarily produced by a com- Ailano area, we have identified a very high den- †alessandra .ascione@ unina.it. bination of upper mantle degassing and/or meta- sity of gas vents (~200 in ~2 km2) that to date GSA Bulletin; September/October 2018; v. 130; no. 9/10; p. 1697–1722; https://doi .org /10 .1130 /B31869 .1 ; 16 figures; 2 tables; Data Repository item 2018150 ; published online 30 April 2018 . For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 130, no. 9/10 1697 © 2018 Geological Society of America Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/130/9-10/1697/4315819/1697.pdf by Univ de Chile user on 26 August 2019 Ascione et al. Aquae Iuliae Middle Pleistocene A E14°00′ E15°00′ E16°00′ to Present volcanics fault Northern Matese Venafro Matese Ridge fault system Adriatic lower Middle Pleistocene Ciorlano (c. 0.6 Ma) to Present deposits Lete sea * Lower Pleistocene to lower *Ailano* basiAlifne South Matese Middle Pleistocene wedge-top fault zone and foreland basin deposits Roccamonfina volcano Telese late Lower Pliocene to Lower Bari Pleistocene wedge-top and Campania Plai A foreland basin deposits Sineussiane olturno R. p u l i a ′ V Mt.Forcuso Miocene wedge-top and Mefite foreland basin deposits d’Ansanto Maschito N41°00 Phlaegrean n Mt. Vulture basinal successions Fields I r p i n i a volcano X′ (Mesozoic-Tertiary) Naples Vesuvius a r e a Apennine Platform carbonates San Sisto Capasso (Mesozoic-Tertiary) Rosapepe Lagonegro - Molise basin strata (Mesozoic-Tertiary) E10° E15° tectonic mélange (cross section) N45° north Adriatic se ern Apennine Val d’Agri Apulian Platform carbonates central (Mesozoic-Tertiary) a s Permian-Triassic deposits southern Tyrrhenian (cross section) ′ basement N40° sea X Tyrrhenian (cross section) 0 50km N40°00 sea cinder cone / isolated lava flow main high-angle upper boundary buried thrust X′ trace of cross trace of swath * non-volcanic gas thrust fault fault to Lagonegro front X section in B profile in C emission area (undifferentiated) basin strata B X X′ km SW NE km 0 0 10 10 0 20 km 20 20 C SSW Matese ridge NNE 2 Matese Lake fault northern Matese South Matese fault system fault zone 1 Alife Campania Plain Plain elevation (km) 0 0 20 40 60 80 distance (km) Figure 1. (A) Geological map of the southern Apennines (modified from Ascione et al., 2013) indicating the main non-volcanic gas emission areas. (B) Geological cross section of the southern Apennines (after Mazzoli et al., 2014). (C) Topographic swath profile (10 km in width) of the southern Apennines spanning across the Matese area. The white box in diagram A indicates the location of the study area, shown in Figure 3. 3 4 represents a unique location for gas emissions the southern mountain front of Matese Ridge and CO2 and CH4, and the He isotopic ratio ( He/ He) relative to other areas in Italy. the topographic lows to the west where no strong to constrain the gas source at depth. In the Matese Ridge area, we have carried out historical earthquake has been localized. Second, Based on the inferred gas source from the a multidisciplinary study aimed at characterizing we conducted extensive and detailed-scale soil isotope analyses, the spatial distribution of the the spatial relationship between the active fault gas and gas flux surveys to examine the chemical continuous leakage and diffuse degassing, and framework and the network of gas emissions. composition of the gases emitted from both vents the reconstruction of the active tectonics frame- First, we carried out a tectonic geomorphology and diffuse emissions, and preliminarily quanti- work, we propose a new interpretation for the investigation to search for indicators of late Qua- fied the total geogenic CO2 from the investigated generation and complex migration of fluids ternary tectonic activity in the region, including area. In addition, we analyzed isotope δ13C in through the southern Apennines thrust belt. 1698 Geological Society of America Bulletin, v. 130, no. 9/10 Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/130/9-10/1697/4315819/1697.pdf by Univ de Chile user on 26 August 2019 Non-volcanic degassing along fault zones in the southern Apennines (Italy) TECTONIC FRAMEWORK posed in the foreland to the northeast (Shiner et al., 2006; Maggi et al., 2009; Frepoli et al., et al., 2004, and references therein; Fig.