Potential serpentinization, degassing, and gas hydrate formation at a young (<20 Ma) sedimented ocean crust of the Arctic Ocean ridge system

摘要

Global assessment of methane must consider the role of mid-ocean ridges.Fluids from serpentinized mantle and gabbro material are noteworthy on ocean ridges,although they are not very well understood. Only a few sedimented ocean ridges exist worldwide,and they may document past and ongoing serpentinization-driven migration of gas-rich fluids.This study is based on two multichannel reflection seismic profiles acquired across a sedimented segment of the ultraslow spreading Knipovich Ridge offshore NW Svalbard.Seismic data allow suggesting a potential link between inferred areas of serpentinization, transfer of carbon from the deep-seated host rocks through the sediments above by diapirism,and methane capture within the gas hydrate stability zone at the eastern flank of the Knipovich Ridge.The origin of sediment remobilization features can be related to intrusions and the degassing process from mantle serpentinization.These disturbances in sediments overlying the oceanic crust can be observed in seismic data and are interpreted as diapirs.In shallower sediments,at the predicted base of the gas hydrate stability zone,the seismic data show a bright spot with all the characteristics of a gas hydrate related bottom-simulating reflector (BSR),such as enhanced reflection amplitude,phase reversal relative to the seabed reflection,and crosscutting of sedimentary strata.The BSR occurs at about 200 ms two-way time within a sequence of marine sediments.Two-dimensional concentration models of methane hydrate using the differential effective medium theory predict saturations of up to 26% of methane hydrate in the pore space of sediments in the gas hydrate reservoir.