Submarine salt flows in the central Red Sea

Abstract

The central Red Sea, an oceanic basin floored by Miocene evaporites reaching kilometres in thickness in places, is at an early stage of development, where seafloor spreading has geologically only recently replaced continental rifting. Surveying with a high-resolution multibeam echo-sounder around Thetis Deep, a new spreading centre, has revealed a remarkable series of structures resembling viscous gravity flows, which are 2 here interpreted as originating from flowage of the evaporites laterally unloaded by axial rifting and other processes developing the relief of the deep. The flow margins are marked by stream-wise lineaments and some apparently rotated markers. Their fronts in the floor of the deep are rounded in plan view and profile. Their surfaces contain small closely spaced features resembling extensional faults. In one area below declining gradients, the surface contains along-slope ridges and valleys typical of compression folds (ogives). Flow-parallel lineaments and extensional faults lie, respectively, parallel and orthogonal to the direction of maximum seabed gradient. Movement is apparently heterogeneous, at least in part by varied blocking by relief of underlying basement observed protruding between flows. Flowage is currently transporting materials into the floor of the deep where it has the potential to become incorporated into the young oceanic crust by repeated eruption of axial lavas over them. In the light of these new data, we reexamine the possibility and implications of flowage in the South Atlantic marginal evaporites, in particular whether flowage contaminated early oceanic crust in such areas.

Hydrothermal activity at the ultraslow- to slow-spreading Red Sea Rift traced by chlorine in basalt

“…Pierret et al, 2001;Gurvich, 2006)), and thick evaporite sequences flanking the active rift (e.g. Whitmarsh et al, 1974;Mitchell et al, 2010). All of these have the potential to increase the Cl contents of circulating hydrothermal fluids and, potentially, their alteration products, thus increasing the amount of Cl that could contaminate a magma.…”

Red Sea isolation history suggested by Plio-Pleistocene seismic reflection sequences

“…Collectively, these data suggest that the accumulation of sediments is quasi-uniform pelagic-like, rather than spatially-varied as with gravity-driven deposition in depressions (Mitchell, 1995). Although the sediments were deposited on mobile evaporites (Mitchell et al, 2010), except in areas of slope steepening and around faults, the PP layer appears to be passively rafting towards the deep on the evaporites, i.e., tectonics do not complicate the interpretation of the reflections except locally around faults or superficial slumps, which we avoid.…”

“…6. Background is a map of the bathymetry of Thetis Deep(Mitchell et al, 2010). Also shown is the path of RV Conrad cruise RC0911 (white dashed line).…”

Comment on “Formation of Thetis Deep metal-rich sediments in the absence of brines, Red Sea” by

“…The oldest C14 date reported by Scholten et al was 18,000 y. Our study of the geology of Thetis Deep has only recently been published (Mitchell et al, 2010) and unfortunately would not have been available to Pierret et al The magnetic anomaly data from this area clearly show at least one or two field reversals (Chu and Gordon, 1998;Izzeldin, 1987) suggesting that sea-floor spreading has occurred here since at least the BrunhesMatuyama boundary at 0.78 Ma and the central Red Sea evaporites have been dated as Late Miocene or around 5 Ma. A sequence of core samples would need to be analysed including material extending to much older dates than currently available to demonstrate that brines have never existed here.…”