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Volcanism and Chemogenic Sedimentation

Margaret Leinen

Seawater interactions with volcanic rocks in mid-ocean-ridge crest environments produce various chemogenic sediments. These sediments range from particulate sulfide precipitated at the exit point of high-temperature hydrothermal vents (black smoke), to mixed sulfides, sulfates, and amorphous silica precipitated at lower temperature vents (white smoke), to amorphous iron oxides and silica precipitated at oxide vents. Sulfide edifices at the vents and dispersed sulfide particulate around the vents are oxidized rapidly after vent activity ceases. Vent particulate injected into the water column moves away from the ridge crest as a diffused plume in which material oxidizes and incorporates transition metals from the seawater. This material is incorporated into the sedimentary ecord to form the familiar red-brown metalliferous sediments above basalts in the deep sea. Studies comparing past accumulation rates for these sediments with ridge crest processes suggest that the rate of seafloor spreading does not control the amount of chemogenic sedimentation with time. The times of greatest accumulation of such sediment are associated with major reorganizations of the spreading system, such as ridge-crest jumps and changes in spreading direction.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.