Hydrothermal Exploration of the Southern Chile Rise: Sediment‐Hosted Venting at the Chile Triple Junction. (10th March 2022) - German, C. R.
Abstract: We report results from a hydrothermal plume survey along the southernmost Chile Rise from the Guamblin Fracture Zone to the Chile Triple Junction (CTJ) encompassing two segments (93 km cumulative length) of intermediate spreading‐rate mid‐ocean ridge axis. Our approach used in situ water column sensing (CTD, optical clarity, redox disequilibrium) coupled with sampling for shipboard and shore based geochemical analyses (δ 3 He, CH4, total dissolvable iron (TDFe) and manganese, (TDMn)) to explore for evidence of seafloor hydrothermal venting. Across the entire survey, the only location at which evidence for submarine venting was detected was at the southernmost limit to the survey. There, the source of a dispersing hydrothermal plume was located at 46°16.5'S, 75°47.9'W, coincident with the CTJ itself. The plume exhibits anomalies in both δ 3 He and dissolved CH4 but no enrichments in TDFe or TDMn beyond what can be attributed to resuspension of sediments covering the seafloor where the ridge intersects the Chile margin. These results are indicative of sediment‐hosted venting at the CTJ. Plain Language Summary: Since their first discovery in the 1970s, submarine hot‐springs have now been located in every ocean basin on Earth. But vast tracts (at least 75%–80%) of the globe‐encircling mid‐ocean ridge volcanic chain remain completely unexplored which means that the majority of vents, and probably an increasing diversity of styles of submarine venting, remain to be discovered. The absence of discoveries is particularly acute in the southern hemisphere. Here we report results from the southern Chile Rise, close to the Chile Margin, where a segment of volcanic mid‐ocean ridge crust is actively being subducted beneath the over‐riding South American continental margin. The setting is unique in present‐day tectonics, giving rise to unusual hydrothermal signatures. But the same processes may have recurred consistently around the rim of the Pacific throughout its ∼200My history. Key Points: Hydrothermal exploration along the southernmost Chile Rise has revealed evidence for venting located at the Chile Triple Junction Hydrothermal plume signals include dissolved methane enrichments co‐registered with diagnostic mantle‐like Helium isotope signatures Seafloor morphology, turbidity and total dissolvable iron (TDFe), TDFe data all provide evidence that this is a sediment‐hosted hydrothermal vent‐field