Major element oxides of minerals from a lava pond at ODP Site 206-1256

At Ocean Drilling Program Site 1256 (6°44.2'N, 91°56.1'W), during Leg 206, a thick massive unit was cored in two neighboring penetrations of the uppermost basement, Holes 1256C and 1256D. This thick massive lava flow, commonly referred to as the "Lava Pond," is identified as Unit 18 (>30 m thick) in Hole 1256C and Unit 1 (>74.2 m thick) in Hole 1256D (Wilson et al., 2003, doi:10.2973/odp.proc.ir.206.2003). In the coarse-grained basalt that comprises this lithological unit, low-temperature "background" alteration events are present. This report provides microprobe analyses of both primary and secondary minerals present in this massive lava pond. The analyses of typically magmatic minerals (titanomagnetite, plagioclase, and clinopyroxene) are given for comparison with secondary minerals.

Major and minor elements in hydrothermal and pelagic sediments at DSDP Leg 70 Holes

Interaction between young basaltic crust and seawater near the oceanic speading centers is one of the important processes affecting the chemical composition of the oceanic layer. The formation of metalliferous hydrothermal sediments results from this interaction. The importance of the interaction between seawater and basalt in determining the chemical composition of pore waters from sediments is well known. The influence of mineral solutions derived from this interaction on ocean water composition and the significant flux of some elements (e.g., Mn) are reported by Lyle (1976), Bogdanov et al. (1979), and others. Metal-rich sediments found in active zones of the ocean basins illustrate the influence of seawater-basalt interaction and its effect on the sedimentary cover in such areas. The role of hydrothermal activity and seawater circulation in basalts with regard to global geochemistry cycles has recently been demonstrated by Edmond, Measures, McDuff, McDuff et al. (1979), and Edmond, Measures, Mangum (1979). In the area of the Galapagos Spreading Center the interaction of sediments and solutions derived from interaction of seawater and basalt has resulted in the formation of hydrothermal mounds. The mounds are composed of manganese crusts and green clay interbedded and mixed with pelagic nannofossil ooze. These mounds are observed only in areas characterized by high heat flow (Honnorez, et al., 1981) and high hydrothermal activity.