This paper presents combined major element, trace element, and petrographic data on 108 samples from sites 332, 334, and 335 of DSDP (Deep‐Sea Drilling Project) leg 37. The 102 basalt samples have characteristics of midocean tholeiites but exhibit wide compositional variation ranging from ‘normally’ LREE (light rare earth element) depleted to ‘anomalous’ LREE enriched compositions. We have distinguished five basalt types on the basis of major elements. The olivine phyric basalts type IV (site 332) with characteristics (Mg/(Mg + Fe) ∼ 0.7, Ni ∼ 250 μg/g, and Sc ∼ 35 μg/g) indicative of primitive magmas can be related to plagioclase accumulative basalts (type II) and picrites (type III) by simple addition of plagioclase and olivine. Plagioclase phyric basalts (type I) characterized by lower Mg/(Mg + Fe) (≃0.50–0.65) at sites 332 and 335 are not related by fractional crystallization to a common parent or to each other. The plagioclase phyric type V basalts recovered from site 334 are not related to type I basalts or to a common parental magma by fractional crystallization processes. Several parental magmas derived from an inhomogeneous mantle are required.
Sulfide samples obtained from the U.S. Geological Survey's DSRV Alvin dives on the southern Juan de Fuca Ridge closely resemble those from the same area described by Koski et al. (1984). Major minerals include sphalerite, wurtzite, pyrite, marcasite, isocubanite, anhydrite, and chalcopyrite. Equilibrium, if attained at all, during deposition of most sulfides was a transient event over a few tens of micrometers at most and was perturbed by rapid temperature and compositional changes of the circulating fluid. Two new minerals were found: one, a hydrated Zn, Fe hydroxy-chlorosulfate, and the other, a (Mn, Mg, Fe) hydroxide or hydroxy-hydrate. Both were formed at relatively low temperatures. Lizardite, starkeyite, and anatase were found for the first time in such an environment. Sulfide geothermometry involving the system Cu-Fe-S indicates a vent temperature of <328 degrees C for one sample. Fluid inclusion studies on crystals from the same vicinity of the same sample give pressure-corrected homogenization temperatures of 268 degrees and 285 degrees C. Ice-melting temperatures on inclusions from the same sample are about -2.8 degrees C, indicating that the equivalent salinity of the trapped fluid is about 50% greater than that of seawater. Volatile concentrations from vesicle-free basalt glass from the vent field are about 0.013 wt% CO2 and 0.16 wt% H2O, CO2 contents in these samples yield an entrapment depth of 2200 m of seawater, which is the depth from which the samples were collected.
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