. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 668 RONA AND OTHERS Metallic sulfides have not been sampled from the TAG Hydrothermal Field, but their presence is suspected from geochemi- cal considerations and analogy with ophio- lites. Disseminated pyrite occurs in green- stone dredged from a transverse ridge in the study area (Table 2, station TAG 1972-15), and metallic sulfides are common in altered oceanic rocks (Dmitriev and others, 1970; Bonatti, 1975). Certain ophiolites, includ- ing thos
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 668 RONA AND OTHERS Metallic sulfides have not been sampled from the TAG Hydrothermal Field, but their presence is suspected from geochemi- cal considerations and analogy with ophio- lites. Disseminated pyrite occurs in green- stone dredged from a transverse ridge in the study area (Table 2, station TAG 1972-15), and metallic sulfides are common in altered oceanic rocks (Dmitriev and others, 1970; Bonatti, 1975). Certain ophiolites, includ- ing those of Newfoundland (Upadhyay and Strong, 1973) and the Troodos Massif of Cyprus (Constantinou and Govett, 1973; Hutchinson, 1973; Robertson and Hudson, 1973), exhibit an association of cupreous pyrite bodies, altered pillow lava, and over- lying manganiferous oxides attributed to hydrothermal processes similar to those in- ferred to be operating on the Mid-Atlantic Ridge at lat 26°N. Troodos-type massive stratiform cupreous sulfide bodies may be forming in pillow lava under the manganese oxide deposits at the TAG Hydrothermal Field (Fig. 10; Rona, 1973b; Scott, R. B., and others, 1974). It is infeasible to test this hypothesis by deep-sea drilling at this time because techniques constrain drilling to areas of sediment accumulation that, as topographic lows, are the inferred inflow areas of sub-sea-floor hydrothermal con- vection systems, and hydrothermal deposits would be absent. The massive stratiform sulfides would be expected to underlie hy- drothermal discharge areas at topographic highs expressed as transverse ridges. Development of Tectonic Fabric Why is a crustal layer of uniform thick- ness not generated about the rift valley in- stead of a layer of varying thickness that forms topographic highs (transverse ridges) and lows (intervening transverse valleys)? Why is the tectonic fabric not symmetric about the rift valley? How can the asym- metry of the tectonic fabric be
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