Manifestations of Degassing in Sedimentary Cover of the Southeastern Flank of the Knipovich Ridge (North Atlantic)

Abstract

The paper analyzes the “bright spot” and “flat spot” anomalies of seismic data on the southeastern flank of the Knipovich Ridge associated with the accumulation of free gas in the sedimentary cover above the oceanic basement. The identified anomalies are associated spatially with negative values of the residual Bouguer anomaly and positive magnetic field (ΔТа) anomalies. This fact indicates the existence of decompaction zones in the crust and upper mantle related to serpentinization that can also provoke the superimposed, probably modern, chemogenic magnetization and distortion of the primary linear pattern of magnetic anomalies in the oceanic basement in the study area. Serpentinization was also responsible for vertical displacements of the crustal and upper mantle blocks on the flanks, leading to deformations of the sedimentary cover with the rock dilation. Off-axis seismicity indicates tectonic disruptions on flanks of the ridge with a higher access of water necessary for the serpentinization and the subsequent change in the physical properties of rocks reflected in geophysical fields. The eastern flank of the Knipovich Ridge underwent tectonic activation along the basement structures representing the northern extension of the Senja fracture zone, resulting in accumulations of free gas in the sedimentary cover.