FIRST INVESTIGATIONS OF MASSIVE FERROMANGANESE CRUSTS IN THE NE ATLANTIC IN COMPARISON WITH HYDROGENETIC PACIFIC OCCURRENCES

Ferromanganese crusts comparable with central Pacific occurrences with respect to thickness and extension have been discovered at the Tropic Seamount in the subtropical NE Atlantic. A comparison with typical hy drogenetic crusts from a central Pacific seamount revealed lower conce ntration of the Mn phase with Mn, Co, Ni, Zn, and Cu but a strongly in creased terrigenous input of Fe, Pb, Al and Si in the Atlantic crusts. Growth rates are increased compared with the Pacific crusts, and crus t ages average at 10 My. The old phosphatized crust generation that st arted to grow about 20 My ago on the Pacific seamounts is not pronounc ed at the Tropic Seamount. The typical hydrographic and morphological parameters for hydrogenetic crust growth have also been found at the T ropic Seamount, which implies that the Tropic Seamount crusts have dev eloped according to the hydrogenetic growth model. There are no indica tions of hydrothermal influence.