Geologic Processes of the Mid-Ocean Ridge and their Relation to Sulfide Deposition

Abstract

Enough detailed data has been obtained along the axis of the Mid-Ocean Ridge to construct a kinematic model which attempts to describe observed variations in time, space, and spreading rate of volcanic, tectonic, and hydrothermal processes and their relationship to the deposition of massive sulfide deposits. Each accretionary segment or accretionary cell bounded by two transform faults is underlain by a unique magma reservoir. Because of cooling at the tranform fault edges, the magma reservoir pinches out and is most developed at a location away from the transform faults. Where the reservoir reaches its fullest development, there is a higher heat flux into the overlying crustal lid. The shallow region where the magma reservoir is most developed and where the crustal lid is thinnest should correspond to the most vigorous hydrothermal activity because of the higher energy content in the system at shallow depths. Because the crustal lid, at the high, is at its minimum thickness, rifting of the lid should result in lava flows having the most direct and shortest path from the magma reservoir to the young seafloor along the rifting axis. At least in the case of moderate to fast spreading segments, the flows nearest the topographic high should be copious surface-fed fluid lavas with the ratio of fluid to pillow flows decreasing down the topographic gradient above a domain of lid thickening. The farther from the topographic high, the more distal and channelized the flows would be resulting in more tube-fed pillow flows. We propose that areas of shallow sea floor at the axis of the Mid-Ocean Ridge are used as a prospecting tool in the search for active sulfide deposition along any given accretion segment. The model draws upon submersible and towed camera mapping programs in the FAMOUS area of the Mid-Atlantic Ridge where the spreading rate is approximately 2 cm/yr. In addition, recent efforts along various segments of the East Pacific Rise and Galapagos Rift have the most profound impact on the model as they involve spreading rates ranging from 6.0 to 10.2 cm/yr where hydrothermal circulation and associated massive sulfide deposition is well developed.