The Structural and Geomorphological Setting of Hydrothermal Deposits on the Mid-Atlantic Ridge

摘要

Six large hydrothermal ore deposits (Fig. 1) were studied on the Mid-Atlantic Ridge (MAR). Two new fields (Lucky Strike and Lost City) have been discovered recently. All of them are confined to the 13°-37° N segment of the MAR rift zone. One may suggest that this segment is characterized by the most favorable conditions for hydrothermal ore deposition. The rift valley (RV) is a key morphostructure providing insights into the origin of hydrothermal fields and their evolution. Models of RV formation show that its existence is possible only under the steady reproduction realized by permanent uplift of marginal parts of the valley floor. Isostasy, viscous dynamic processes, and serpentini-zation of mantle material are responsible for such uplift. Isostatic uplift is related to the formation of a relatively light lithosphere in the axial zone of mid-ocean ridge. The thickening of the light lithosphere from 3-4 km near the spreading center to 10-14 km beneath the outer parts of valley can raise the oceanic floor and form the RV slopes. The axial channel in slow-spreading ridges is very narrow, and the magmatic melt adhering to its wall does not always attain the hydrostatic equilibrium level. This results in mass deficiency and driving up of the Earth's crust by buoyancy forces, Serpen-tinization of mantle rocks decreases their density and distorts the tectonic equilibrium of the RV floor.