Basalt — Seawater Exchange: A Perspective from an Experimental Viewpoint

Abstract

The hydrothermal circulation of seawater through the ocean crust near spreading centers is not only responsible for dissipating about 30% of the heat generated by the emplacement of new crustal material (Sclater et al., 1981), but also for substantial chemical exchanges between the crust and the ocean. It has even been suggested that basalt-seawater interactions “buffer” the composition of the ocean with respect to certain elements. Submarine hot springs appear to discharge into the ocean quantities of manganese, rubidium and lithium equivalent to three, seven, and ten times the river fluxes of these three elements (see Table 1; also G. Thompson, this volume). Hydrothermal inputs in calcium and silica amount to 1/3 and 1/2, respectively, of the river fluxes whereas those in barium and potassium are of about the same order of magnitude as the river fluxes (see Table 1). On the other hand, quantities of magnesium of about the same order of magnitude as the river input seem to be taken up by the altered crust. The actual amounts of most of the various elements remobilized from crustal rocks by hydrothermal circulation are probably higher than those measured in the hot springs debouching on the sea floor because substantial quantities are left behind in the crust when secondary minerals precipitate in the cracks to form veins and cement of breccias. This is particularly true for calcium and silica which form the abundant veins of calcite, quartz, prehnite and various zeolites found in dredged and cored samples.