## 1 Introduction
### Geochemistry of CAVA and Aims of This Study  
CAVA shows significant along-arc geochemical variations in rock composition and age, and in volcanic activity [3; 4; 20; 21; 22; 23], which mostly result from the variations in subduction parameters, such as dip-angle, crustal thickness, extent of sediment underplating, faulting style and subduction erosion [16; 20; 24]. These parameters control the degree of source melting and determine a variable sedimentary fluid influx from the subducting Cocos plate. Some of the most evident variations in rock geochemistry are represented by trace element proxies for slab fluids (such as Ba/La, U/Th, Ba/Th, and Sr/Ce ratios) being highest in Nicaragua, and lowest in Costa Rica [20; 23; 25]. The same geochemical tracers indicate that melts beneath Guatem are generated by the mixing of a Costa Rica MORB-like melt component with Nicaragua-like slab fluid-rich melts [25], while the Quaternary volcanic arc in Panama shows an adakitic composition of still debated origin [26]. It must be mentioned that the Central Costa Rica (i.e., Platanar, Poas, Barva, and Irazu volcanoes) and Panama (i.e., Baru) magmas show an OIB signature that contrasts with that usually observed in the rest of CAVA, which has been attributed to the subduction of the Galapagos seamounts originating along the Galapagos hot-spot track [3; 4; 21; 22]. In terms of volatile geochemistry, most of the studies along CAVA have focused on the composition and fluxes of magmatic gases emitted from the most active volcanoes, such as Turrialba and Poas in Costa Rica [27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39], Cerro Negro, Masaya, Momotombo and San Cristobal in Nicaragua [35; 40; 41; 42; 43; 44], Pacaya in Guatem [27; 45; 46]. Several studies have also focused on the composition of noble gases, especially on the \({}^{3}\)He/\({}^{4}\)He ratio that is considered a powerful tracer of mantle vs. subducting slab contributions (e.g., [44; 47; 48]), and of crustal and/or hydrothermal interactions (e.g., [49; 50; 51; 52; 53]). Present knowledge on the \({}^{3}\)He/\({}^{4}\)He signature along CAVA has been mostly achieved through measurements in fumarole and spring gases [27; 28; 29; 30; 34; 42; 45; 54; 55; 56; 57; 58; 59; 60; 61], while much less information is available on fluid inclusions (FI) in olivine (OI) and pyroxene (Px) crystals [38; 44; 46; 62; 63]. Irrespective of the huge information available for CAVA, which is probably one of the best studied arcs on Earth, the \({}^{3}\)He/\({}^{4}\)He signature of the magmatic source remains unconstrained for many volcanic systems, and its along-arc variations are not well understood. One special concern is that the available \({}^{3}\)He/\({}^{4}\)He CAVA dataset is dominated by peripheral gas manifestations and cold springs, in which inferring the mantle source signature is complicated by shallow processes and fluid sources. Figure 1: (**A**) Map of the geodynamics of the Central American Volcanic Arc (CAVA), indicating arc-segments from Guatem to Panama. The white line with the transparent arrows indicates the subduction front direction, while its prolongation to the East indicates the oblique subduction beneath Panama and to the south-east, the Panama fracture Zone (PFZ). The orange dotted line indicates the Galapagos mantle influx inferred by [61]. The white dotted line reports the main location of the volcanic arc front from Guatem to Panama. The volcanoes mentioned in the text are also reported. (**B**) Inset of map A on Telica volcano (Nicaragua), where our sample location (in yellow) is reported together with the spring gases (in white) studied by [42] with the maximum air-corrected \({}^{3}\)He/\({}^{4}\)He (Rc/Ra). (**C**) Inset of map A on Baru volcano (Panama), where our sample location (in yellow) is reported together with the neighboring spring gases (in white) studied by [61] with the maximum air-corrected \({}^{3}\)He/\({}^{4}\)He (Rc/Ra).