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Pérez-Gussinyé et al. 2023


Interactions between tectonic, magmatic, sedimentary and hydrothermal processes during rifting and break-up of continental lithosphere lead to a variety of rifted margin types. As potential reservoirs for mineral deposits and native hydrogen, and as sites for COstorage and generation of geothermal energy, rifted margins are likely to have a key role in the future transition to a carbon-neutral economy. In this Review, we discuss the wide variability of rifted margin anatomy in terms of the processes that shape them. We demonstrate that observations combined with models can provide a process-based understanding of margin evolution that allows any given region to be understood more holistically than with a static end-member type (magma-rich versus magma-poor) classification. Many margins show intermediate characteristics between those end-members. Even within end-member types, there are substantial structural variations, which are shaped by the feedbacks between inheritance, deformation, sedimentation, magmatism and fluid flow. A better understanding of these feedbacks is required to assess the potential of margins to support the carbon-neutral economy. Integration of observations and modelling will help to de-risk exploration of these environments. In particular, margins need to be characterized by integrated geophysical studies, including improved wide-angle seismic velocity models with closely spaced instruments together with advanced numerical modelling techniques.

Liu et al. 2023


Mantle serpentinization influences the rheology of altered peridotites and the global fluxes of energy and volatiles, the generation of seafloor and sub-seafloor chemolithotrophic life, and the carbon cycle. As a by-product of serpentinization, molecular hydrogen (H2) is generated, which supports chemosynthetic communities, and this mechanism may have driven the origin of life on early Earth. At continent-ocean transition zones (COTs) of magma-poor rifted margins, the mantle is exposed and hydrated over hundreds of kilometers across the rift, but the H2 fluxes associated with this process are poorly known. Here, we coupled a thermomechanical model with serpentinization reaction equations to estimate associated H2 release during mantle exhumation at COTs. This reproduced a tectonic structure similar to that of the West Iberia margin, one of the best-studied magma-poor margins. We estimated the rate of H2 production from mantle hydration at (7.5 ± 2.5) × 107 mol/(yr × km). By estimating the area of exhumed mantle from wide-angle seismic profiles at North Atlantic magma-poor margins, we calculated that the accumulated H2 production could have been as high as ∼4.3 × 1018 mol (∼8.6 × 1012 metric tons) prior to opening of the North Atlantic Ocean, at a rate of ∼1.4 × 1017 mol/m.y. This is one quarter of the total predicted flux produced by the global system of mid-ocean ridges, thus highlighting the significance of H2 generation at magma-poor margins in global H2 fluxes, to hydrogenothropic microbial life, and, perhaps, as a potential energy source.

Bradley et al. 2020


Microbial cells buried in subseafloor sediments comprise a substantial portion of Earth’s biosphere and control global biogeochemical cycles; however, the rate at which they use energy (i.e., power) is virtually unknown. Here, we quantify organic matter degradation and calculate the power utilization of microbial cells throughout Earth’s Quaternary-age subseafloor sediments. Aerobic respiration, sulfate reduction, and methanogenesis mediate 6.9, 64.5, and 28.6% of global subseafloor organic matter degradation, respectively. The total power utilization of the subseafloor sediment biosphere is 37.3 gigawatts, less than 0.1% of the power produced in the marine photic zone. Aerobic heterotrophs use the largest share of global power (54.5%) with a median power utilization of 2.23 × 10−18 watts per cell, while sulfate reducers and methanogens use 1.08 × 10−19 and 1.50 × 10−20 watts per cell, respectively. Most subseafloor cells subsist at energy fluxes lower than have previously been shown to support life, calling into question the power limit to life.