Geochemistry of secondary carbonates in Leg 115 basalts: tracers of basalt/seawater interaction

Abstract

This report presents the results of a study of the stable isotopic and chemical composition of secondary carbonate minerals precipitated within basalts at Ocean Drilling Program Sites 707 and 715. The geochemistry of Site 715 samples indicates that they precipitated from seawater-dominated fluids, at low temperatures, as is typical of secondary carbonates from most Deep Sea Drilling Project sites. Site 707 carbonates precipitated at low temperatures in a fairly closed system, in which basalt-seawater interaction has greatly influenced the chemistry of the pore fluids. The reactions occurring within the system before and in conjunction with secondary carbonate precipitation include oxidation of isotopically light methane, derived from fluids circulating within the basalts, and reduction of substantial amounts of iron and manganese oxides from the basalts. -from Authors