1 Gas hydrate estimate in an area of deformation and 2 high heat flow at the Chile Triple Junction 3

Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, 16 near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is 17 converted to methane in a zone of very high heat flow and intense rock deformation above the 18 downgoing oceanic spreading ridge separating the Nazca and Antarctic plates. This regime enables 19 vigorous fluid migration. Here we present an analysis of the spatial distribution, concentration, 20 estimate of gas phases (gas hydrate and free gas) and geothermal gradients in the accretionary prism 21 and forearc sediments offshore Taitao (45.5° 47° S). Velocity analysis of Seismic Profile RC2901-751 22 indicates gas hydrate concentration values <10% of the total rock volume, and extremely high 23 geothermal gradients (<190 °Ckm-1). Gas hydrates are located in shallow sediments (90-280 meters 24 below the seafloor). The large amount of hydrate and free gas estimated (7.21x1011 m3 and 4.1x1010 25 m3, respectively), the high seismicity, the mechanically unstable nature of the sediments, and the 26 anomalous geothermal conditions, set the stage for potential massive releases of methane to the 27 ocean mainly through hydrate dissociation and/or migration directly to the seabed through faults. 28 We conclude that the Chile Triple Junction is an important methane seepage area and should be the 29 focus of novel geological and ecological research. 30