Growth rates of ferromanganese encrustations on rocks from the Romanche Fracture Zone, Equatorial Atlantic

Abstract

Based on radiochemical techniques, ferromanganese oxide crusts from the Romanche Fracture Zone (RFZ) have accretion rates ranging between 1.4 and 2.8 mm/10 years. In comparison with other ferromanganese deposits, the accretion rates for the RFZ crusts are close to the growth rates for typical hydrogenetic deposits formed on elevations and exposed rock surfaces in the Pacific Ocean. This would suggest that the RFZ crusts are formed by slow accumulation of metal hydroxides from the water column. probably in a manner analogous to the Pacific seamount crusts.