This innermost zone is surrounded by an aureole with numerous, almost completely eroded smoker relicts. The relatively fast disintegration of the massive sulfide smokers is due to an originally high content of anhydrite, which is unstable under ambient cold seawater conditions. Manganese crusts observed and sampled from the periphery of the mineralized site represent low-temperature distal precipitates. Euhedral to subhedral pyrite crystals are intimately intergrown with younger marcasite. Minor sulfides include sphalerite and chalcopyrite, locally hosted by pyrite.
Massive chalcopyrite is the principal ore mineral, hosting older euhedral to subhedral pyrite.
A CIR origin by means of tectonic uplift in transform portions of the spreading center appears the most plausible mechanism for the emplacement of the mantle restites. The magma reservoir acts as heat source, driving the hydrothermal convection of sea water penetrating the crust along major faults and fractures, and leaching metals in considerable quantities from the basaltic crustal succession. Lack of a neovolcanic zone in the tectonic trough and a thick sediment cover are evidence for an amagmatic period of crustal evolution at the easternmost portion of the SWIR, with virtually no magmatic accre tion taking place at present. The multidisciplinary program will address topics related to geochemistry, petrology and geophysics of crustal accretion processes at mid-ocean ridges and associated hydrothermalism. Both the SO 92 and ME 33 projects are also regarded as pre-site surveys for a possible ODP Leg to the triple junction region.