Young Volcanism on the "Dead" Abyssal Plain: How Little we Really Know About Submarine Intraplate Volcanism

Abstract:

The Peru Basin is a site of Mn-nodule accumulation on 20Ma Nazca plate crust that was targetted, in 1989, for a large-scale disturbance experiment (the DISCOL experiment) to simulate the effects of seabed mining. A return trip in 2015 to assess recovery "accidentally" investigated a nearby seamount with a remotely-operated underwater vehicle (ROV). The ROV video records show the seamount to be generally heavily sedimented (fault-scarps expose up to 20m thick sequences of indurated sediments) but to have a small (100x150m) pillow mound and an area of indurated calcareous sediments cut by basaltic dykes near its summit. The lack of sediment cover on the pillows and the presence of small, white chimneys associated with the dykes suggest these features are very young. Acoustic data (especially multibeam backscatter) shows several other highly reflective, young seamounts in the region, although a linear volcanic chain is not evident. Strings of depressions in sediments along the tops of abyssal hills are also observed in the multibeam bathymetry data, which may result from venting of crustal fluids and dissolution of carbonates in the sedimentary sequence. Taken together, these observations suggest that the 20Ma Nazca Plate is both volcanically active and experiencing active fluid circulation on a regional scale. The consequences for plate alteration and bulk plate composition cannot presently be estimated.