Hydrothermal deposits sampled by diving saucer in transform fault "a" near 37°n on the mid-atlantic ridge, famous area

Deep-sea hydrothermal deposits were observed, mapped and sampled in situ with the submersible "Cyana" in the Famous area of the Mid-Atlantic Ridge.Two neighbouring fields, each covering an area of about 600 m2, are associated with low, E-W trending sediment-covered ridges that lie at a depth of about 2 700 m close to the axis of Transform Fault "A".In each field the deposits are thicker (up to about 1 m) close to the small, fissure-like vents through which they were evidently delivered. Despite their heterogeneous composition, their mineralogical and chemical variations have an orderly pattern.The principal constituents are a green clay-rich material, and Fe-Mn oxides in the form of black concretions. The relative abundances of these products vary with distance from the source-vent.The green clay-rich material, abundant near the vent, consists of hydromica, smectite and an amorphous Fe-Si compound.Further away, the Fe-Mn concretions, made up of rancieite and todorokite, are the dominant components. [NOT CONTROLLED OCR]