ALBERT

Description: In the summer of 1974, upon returning to Woods Hole from the Azores, the submersible Alvin had the opportunity to make brief dives on Corner Rise and the New England seamount chain. This was the first time man had directly viewed the expanse of the Earth between the Mid-Atlantic Ridge and the North of the American continent. Single dives were made on seven seamounts: Corner Rise and Nashville, Gilliss, Rehoboth, Manning, Balanus, and Mytilus.

Description: Unlike most previous Deep Sea Drilling Project cruises, Leg 39 was not scientifically planned as a "theme" cruise, on which a number of sites are drilled to address a single scientific problem area, namely, to improve our knowledge of paleocirculation changes and the overall geologic history of the South Atlantic Ocean. This would be done along more specific objectives: 1) collect a biostratigraphic section on the Ceará Rise (Site 354), determine the nature and age of a prominent reflector there, and determine the nature and age of basement; 2) date basement between magnetic anomalies 32 and 33 in the Argentine Basin (Site 358), and 33 and 34 in the Brazil Basin (Site 355); obtain as complete sedimentary sections as time would permit at the Ceará Rise, Brazil Basin, the Argentine Basin and Sào Paulo Plateau (Site 356).

Description: Quaternary sediments cored in the northeast Pacific nodule area (DOMES site C, 14°N, 126°W) contain a significant amount of hydrothermal metalliferous mud. Water content, color, mineralogy, and chemical composition are analogous to metalliferous sediments of the subequatorial East Pacific Rise. Correction for contribution of pelagic clay indicates the metalliferous fraction to be about 40% of the sediment. SiO2 and Mg are major components in the corrected composition, as they are for other metalliferous sediments similarly corrected from a variety of East Pacific Rise and DSDP metalliferous sediments. A correlation between Mg and SiO2 for these corrected sediments could indicate a hydrothermal origin for a significant portion of the SiO2. Results from DSDP in the nodule area suggest that metalliferous globules are a ubiquitous minor component of the Clipperton Oceanic Formation, which underlies much of the Pacific ferromanganese nodule belt. This indicates that deposition of hydrothermal precipitates is not confined to spreading centers.

Description: Two types of deep-sea dredges are currently under development for the mining of the manganese nodules, a deep-sea hydraulic dredge and a mechanical cable-bucket system. Both systems offer some advantages with the hydraulic system appearing to be advantageous in themining of a specific deposit for which it is designed while the cable-bucket system appears to be somewhat more flexible in working in a variety of deposits, topographic environments, and water depths. Environmental studies conducted in conjunction with deep-sea tests of the two types of mining systems currently indicate that substantially no environmental damage will be done in the mining of the deep-sea nodules. Because of the nature of the deposits and the way in which they can be mined, the manganese nodules appear to be a relatively pollution free and energy-saving source of a number of industrially important metals.

Description: Basalt samples obtained from the Siqueiros transform fault/fracture zone and the adjacent East Pacific Rise are mostly very fresh oceanic tholeiite and fractionated oceanic tholeiite with Fe+3/ Fe+2 ? 0.25; however, alkali basalts occur in the area as well. The rocks of the tholeiitic suite are ol + pl phyric and ol + pl + cpx phyric basalts, while the alkali basalts are ol and ol + pl phyric. Microprobe analyses of the tholeiitic suite phenocrysts indicate that they are Fo68-Fo86, An58-An75, and augite (Ca34Mg50Fe16). The range of olivine and plagioclase compositions represents the chemical variation of the phenocryst compositions with fractionation. The phenocyrsts in the alkali basalts are Fo81 and An69. The suite of tholeiites comprises a fractionation series characterized by relative enrichment of Fe, Ti, Mn, V, Na, K, and P and depletion of Ca, Al, Mg, Ni, and Cr. The fractionated tholeiites occur on the median ridge (which is a sliver of normal oceanic crust) of the double Siqueiros transform fault, on the western Siqueiros fracture zone, and on the adjoining East Pacific Rise, while the two transform fault troughs contain mostly unfractionated or only slightly fractionated tholeiite. We suggest that the fractionated tholeiites are produced by fractional crystallization of more 'primitive' tholeiitic liquid in a crustal magma chamber below the crest of the East Pacific Rise. This magma chamber may be disrupted by the transform fault troughs, thus explaining the paucity of fractionated tholeiites in the troughs. The alkali basalts are found only on the flanks of a topographic high near the intersection of the northern transform trough with the East Pacific Rise.

Description: Eighty-seven manganese nodules, representing 6 different locations at depths ranging from 2400 to 7400 m, from the eastern edge of the Blake Plateau were studied. Most of the nodules contained secondary structural textures resulting from the apparent burrowing of marine microfauna. This biogenic activity produced modification of the original growth patterns. In many cases the burrowed zones served as favored sites for redeposition of iron-manganese material. Transmitted light and scanning electron microscope analysis revealed the presence of 3 types of organic activity: (1) agglutinated foraminiferal tests; (2) pre-bored clay particles acting as nuclei or later included during nodule growth; and (3) younger burrows that cross-cut all older structures. In many instances this cross-cutting action resulted in almost total eradication of areas of the original growth patterns. The final texture may be mistaken for a similar growth texture previously classified as mottled, but a more specific genetic term might be 'disrupted'.