A cold seep triggered by a hot ridge subduction

Abstract

The Chile Triple Junction, where the hot active spreading centre of the Chile Rise system subducts beneath the South American plate, offers a unique opportunity to understand the influence of the anomalous thermal regime on an otherwise cold continental margin. Integrated analysis of various geophysical and geological datasets, such as bathymetry, heat flow measured directly by thermal probes and calculated from gas hydrate distribution limits, thermal conductivities, and piston cores, have improved the knowledge about the hydrogeological system. In addition, rock dredging has evidenced the volcanism associated with ridge subduction. Here, we argue that the localized high heat flow over the toe of the accretionary prism results from fluid advection promoted by pressure-driven discharge (i.e., dewatering/discharge caused by horizontal compression of accreted sediments) as reported previously. However, by computing the new heat flow values with legacy data in the study area, we raise the assumption that these anomalous heat flow values are also promoted by the eastern flank of the currently subducting Chile Rise. Part of the rift axis is located just below the toe of the wedge, where active deformation and vigorous fluid advection are most intense, enhanced by the proximity of the young volcanic chain. Our results provide valuable information to current and future studies related to hydrothermal circulation, seismicity, volcanism, gas hydrate stability, and fluid venting in this natural laboratory.

Ridge Subduction: Unraveling the Consequences Linked to a Slab Window Development Beneath South America at the Chile Triple Junction

“…In Figure 7c, modeled heat flow values consistently underestimate the observed data. Comparatively higher values in observed heat flow can be also attributed to the advection of heat by the circulation of hydrothermal fluids, hypothesis which is consistent with the presence of hydrothermal activity suggested by previous studies (S. C. Cande et al, 1987;Villar-Muñoz et al, 2021).…”

“…We compiled the BSR data gathered on two R/V Conrad expeditions (RC2304 and RC2901) and one cruise of the R/V Mirai (MR1806). The studies developed in these expeditions (Bangs & Cande, 1997; K. Brown et al., 1996; S. C. Cande et al., 1987; Villar‐Muñoz et al., 2013, 2021) allowed a detailed characterization of the heat flow through the BSR in the vicinity of the CTJ from values that continuously decrease from ∼280 to ∼50 mW/m 2 in the first 50 km from the trench.…”

Links between spatially heterogeneous pore water geochemistry, fluid migration, and methane hydrate near a seafloor mound venting structure on the south Chilean Margin (41°S)

“…Seepage of methane-rich fluids typically cluster near these faults and support robust chemosynthetic communities near the seafloor [Munoz et al, 2016;Sellanes et al, 2008]. It has been suggested that onset of seepage in this region may be linked to the tectonic history of the margin, potentially as recent as the 2010 Maule earthquake in some sectors of the margin [Geersen et al, 2016;Villar-Muñoz et al, 2021]. Low pore water chloride concentrations in a small set of multicores near the CMSA were interpreted to reflect freshening from deep fluids released during clay dehydration processes at depth, potentially providing a mechanism for vertical migration of gas saturated fluids at these seeps [Scholz et al, 2013].…”

“…Despite these advances, the south Chilean Margin-a 1500 km convergent plate boundary and one of the most tectonically-active regions on Earth [Melnick et al, 2006;Völker et al, 2013]remains one such setting where cold seeps and mud volcanoes have only been documented within a limited sector of the margin near the Concepción Methane Seep Area (36°S) [Sellanes et al, 2004;Vargas-Cordero et al, 2020]. Recently, cold seeps have also been observed near the Chile Triple Junction in the south (46°S) [Villar-Muñoz et al, 2021]. The scarcity of documented venting systems is in stark contrast with fluid budget estimates in the forearc complex, which remain unbalanced and require transfer of fluid and volatiles from subducted sediments back to the ocean [Volker et al, 2014].…”