Young lava flows on 20 Ma crust in the North Atlantic

Abstract:

Submarine volcanism in the ocean basins is conventionally expected to occur along the mid-ocean ridges, at subduction zones and near hotspots. The vast areas of abyssal plain between these features are assumed to be volcanically inactive. Here we present acoustic backscatter data collected by R/V "Meteor" in 2016 on transit between Barbados and the Mid-Atlantic Ridge which shows indications of young volcanism on heavily sedimented 20 Ma-old crust. The site lies in 4000 m water depth, 2000 km away from the closest hotspot, 340 km west of the Mid-Atlantic Ridge, and 70 km south of the Kane Fracture Zone. Sedimentation rates in this region (≈1cm/kyr) mean the igneous crust should be covered with ca. 200 m of sediment. But over a 50 km-long section of the transect we recognize four lava flows covering a total of 224 km². The flows are characterized by bright lobate reflections with distinct boundaries and show varying backscatter intensities indicating differences in the sediment cover thickness, presumably related to differing ages of emplacement. They are apparently not associated with any major submarine volcanic cones and flow boundaries seem to be influenced by the regional N-S-striking fabric of the abyssal hills. Modelling of acoustic attenuation in sediments suggests a maximum of 2m of sediment covers the flows, suggesting they are of Holocene age.

Examination of a further 40,000 km of transit multibeam data collected by German Research Vessels over the last year and covering all seafloor ages in the Atlantic, shows no other similar features. Nevertheless, as this new coverage represents less than 1% of the North Atlantic abyssal seafloor now surveyed, we expect continued surveying to yield other interesting volcanic features on the old plates.