ALBERT

Description: A submersible study has been conducted in February - March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera - Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of giant size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.

Description: This paper reviews the state of the art in processing and extraction of ocean floor manganese nodules. It briefly reviews the mining sites where the abundant rich nodules occur and also discusses the metal distribution in nodules in view of economical processing and extraction of these metal values. The paper discloses in a detailed manner the physical and chemical characteristics of nodules, including porosity, surface area, water content and the effect of temperature on crystal structure of major constituents of nodules. In the extraction aspect of nodules, the paper reviews two different extraction schemes revealed in the literature, namely hydrometallurgical treatment and pyrometallurgical treatment. The hydrometallurgical treatments include acid leaching, ammonia leaching, leaching with reducing agents and leaching after high temperature pre-treatments such as in sulfating rousting, while the pyrometallurgical processes include smelting, chlorination-vaporization and segregation. The paper also covers metal recovery processes from leach liquor. An economic survey of processing nodules has been made in terms of problems associated with metal-marketing, and impact of metal production from nodules on mineral industries.

Description: During the period of 22-28 July, 1978, five dives were made in the manned submersible ALVIN into the Atlantic Ocean 3800 meter depth radioactive waste disposal site located in the Hudson Canyon channel approximately 320 kilometers from the Maryland-Delaware coast. A geological description of the site was made by direct examination of the bottom topography, bedrock exposures, sedimentary and erosional processes, and sediment cores collected from the dumpsite area. Observations within a depth range of 3985-3830 meters revealed angular blocks and piles of displaced channel wall rock, boulder and cobble olistoliths of Eocene-age chalks derived from higher elevations on the slope, and bedforms such as ripples and scour marks which imply the existence of periodic strong currents. Local benthic fauna were sparse. Three low-level radioactive waste drums were examined from the submersible, and one was subsequently recovered for corrosion, and concrete deterioration analyses. Photographic and visual evidence suggest that downslope transport of objects such as talus blocks, olistoliths, and radioactive waste drums has occurred in this area. These observations complement those made by G. Keller in earlier ALVIN dives performed in 1972 and by the AOML(MG&GL project. COMSED (Continental Margin Sedimentary Processes) cruise performed in 1974 by the R/V Researcher.

Description: Cosmogenic beryllium-10 activities have been measured in marine accumulations of up to about 6 m.y age by conventional beta counting technique and by accelerator mass spectrometry. The two sets of data at 10Be levels of 109-1010 atoms/g agree within the absolute errors of the two methods. The detection limit for 10Be by the accelerator mass spectrometry is about five orders of magnitude lower than that with the beta counting method.

Description: The D'Entrecasteaux Zone (Southwest Pacific) is an arched submarine horst- and graben structure, which extends from the northern end of the New Caledonia ridge to the western border of the New Hebrides island arc. A review of the bathymetry, seismic-reflection data, paleomagnetism, gravimetry, seismology and DSDP data available for this area is combined with a study of basaltic samples dredged along the horsts of this regional fracture zone. These basalts show strong petrographic and chemical affinities with MORB. Their fissiontrack ages range between 56 Ma (Paleocene-Eocene boundary) and 36 Ma (Eocene-Oligocene boundary). It is suggested that the D'Entrecasteaux Zone represents the northern arcuate extension of the northeast-dipping Eocene subduction/obduction zone, located along the New Caledonia/Loyalty Islands ridge, while its present morphology appeared from post-obduction extensional movements, resulting in a progressive uplift of basaltic ocean floor since Middle Miocene times.

Description: The sulfide deposit at Site 471 occurs between overlying pelagic sediment and underlying basalt. The deposit is vertically zoned and consists, from top to bottom, of the following mineral assemblages: (1) pyrite, chalcopyrite, and Zn-sulfide in chert and calcite gangue (~ 35 cm thick); (2) a 5-cm-thick metalliferous sediment layer and (3) a 4-cm-thick chert layer. The calcite gangue appears at a later stage than chert gangue in the sequence of deposition, also filling in voids and fractures. The manganese content of calcite is particularly high and varies systematically, reaching a maximum at the top of the massive sulfide portion of the deposit.

Description: The cores and dredges described at this site were taken on the DRAKAR cruise from 1 March until 1 April 1983 by the Muséum National d'Histoire Naturelle from the R/V Marion Dufresne. A total of 45 cores and dredges were recovered along with underwater camera runs. They are available at MNHN for sampling and study.

Description: The cores and dredges described at this site were taken on the SAFARI II cruise from 21 July until 1 September 1981 by the MusÈum National d'Histoire Naturelle from the R/V Marion Dufresne. A total of 65 cores, dredges and camera stations were recovered and are available at MNHN for sampling and study.