Extended Data Fig. 6: Overview of the regional geodynamic setting in relation to the full set of metamorphic CO2 results from both the ‘iterate over samples’ and ‘iterate over endmembers’ model approaches.

a) and b) Colored circles and squares illustrate samples with non-zero yearly average HCO₃ from metamorphic carbon, scaled by the concentration. White, outlined circles and squares illustrate samples where HCO₃ from metamorphic CO₂ is zero (ref. ²¹). The purple line marks the boundary between low p-wave velocity (V_p) anomalies to the west and high V_p anomalies to the east at 52 km depth, and the dashed indentations in the line mark the locations of slab windows in the central (CAW) and southern Apennines (SAW). The orange overlay illustrates the spatial extent of measured CO₂ gas emissions, gray circles illustrate the locations and depth of seismicity deeper than 40 km and magnitude 3 or higher, and the black sawtoothed line marks the subduction front. b) illustrates an enlarged view of the results within the study area, including the locations of normal faults (black lines). Figure adapted with permission from refs. ^8,47,48 Elsevier.