An oceanic core complex and its associated weathered hydrothermal deposit on a ridge-transform intersection zone at 23°S, Southern Mid-Atlantic Ridge

Abstract

Numerous investigations into the northern Mid-Atlantic Ridge (the NMAR), a typical slow-spreading mid-ocean ridge, have revealed that NMAR is favorable for the development of long-lived detachment faults and the formation of oceanic core complexes (OCCs). OCCs are often conducive to the development of ultramafic-hosted hydrothermal deposits with significant resource potential. However, as a counterpart of the NMAR on the Southern Hemisphere, the southern Mid-Atlantic Ridge (SMAR), also belonging to the class of slow-spreading ridges, has only received very limited investigation. This prompts the inquiry as to whether the SMAR, like the NMAR, can foster the development of OCC and associated hydrothermal deposit. To address this issue, we present the identification of an OCC (named as Kaifeng OCC) at the intersection of the SMAR and the Martin Vaz transform fault (∼23°S). This discovery is accompanied by evidence detailing a new detachment fault breakaway on an old detachment footwall. Collected samples reveal indications of hydrothermal activity, encompassing (1) residual sulfide containing chalcopyrite within honeycomb-like structures, (2) reddish-brown Fe oxides and atacamite, partially concretized by dolomite, and (3) a dark gray Mn-oxide crust. These mineralogical features indicate the presence of gossans, commonly iron oxide-dominated cover layers that envelope the outer surface of weathered seafloor sulfide deposits, which subsequently undergo modifications due to subsequent hydrothermal activities. Our work proves the existence of OCC and associated hydrothermal deposits at a ridge-transform intersection of the SMAR.