Age determination of ODP Leg 120 samples

Conventional K-Ar and 40Ar/39Ar analyses on whole-rock samples are reported for basaltic samples retrieved on the Central and Southern Kerguelen plateaus during Ocean Drilling Program Leg 120. Sites 747, 749, and 750 recovered basalts from the plateau basement, whereas Site 748 drilled a lava flow interbedded with sediments of probable Albian age. The freshest core basalts from the basement yielded dates falling in the 110-100 m.y. interval. Sample 120-749C-15R-3 (26-31 cm) gave conventional K-Ar, total fusion, and plateau 40Ar/39Ar ages that are closely concordant: 111.5 ± 3.2 m.y., 109.9 ± 1.2 m.y., and 109.6 ± 0.7 m.y., respectively. Sample 120-750B-15R-5 (54-60 cm), when taking into account the analytical uncertainties, yields conventional K-Ar and 40Ar/39Ar plateau ages that can be considered similar: 101.2 ± 7.5 and 118.2 ± 5 m.y., respectively. Inspection of the 39Ar/40Ar vs. 36Ar/40Ar diagram does not reveal the occurrence of an initial argon component of radiogenic composition in the two samples. Accordingly, our results suggest that the formation of the basement of the Central Kerguelen Plateau was closed at 110 m.y.. Furthermore, these results are in agreement with a K-Ar age of 114 ± 1 m.y. mentioned in the literature for a basalt dredged in the 77°E Graben. The still scant amount of data indicates that the outpourings of the Central Kerguelen Plateau correspond rather well with widespread continental magmatism in Gondwanaland that is believed to mark the incipient opening of the eastern Indian Ocean. This implies a huge head for the mantle plume at the source of these liquids. Nevertheless, on land and at sea the exact duration of magmatism remains unknown. Therefore, a catastrophic pattern similar to that currently invoked for the Deccan Traps at the end of the Cretaceous, though possible, is not yet required by present geochronologic data.

Mineral composition of 0.1-0.05 mm grain size fraction from the surface layer of bottom sediments in the West European province of the Atlantic Ocean

Rock material sampled from the Mir manned deep-sea submersibles and by dradges, grabs, and sediment cores over a vast area of the North Atlantic was analyzed to show that this material is of continental origin, unlike original rocks of the ocean floor. It is proved to be related to iceberg rafting during Quaternary glaciations. Independent data on distribution and composition of sandy and silty grains in sediment cores also support this relation to the recent glaciation. New criteria for identification of iceberg rock matter in pelagic sediments are presented on the base of analysis of all available data.

Analysis of Manganese nodules from Sonne cruises SO06/1 and /2, "Hawaii-Tahiti-Transect", Teilprojekt ICIME

Manganese nodules research has focused on the area between the Clarion Fracture Zone to the North and the Clipperton Fracture Zone to the South where significant concentrations were found ni Ni-Cu. During the CCOP/SOPAC-IOC/IDOE International workshop on the "Geology Mineral Resources and Geophysics of the South Pacific" held in Fiji in September 1975, a working group on manganese nodules was formed by scientists from: CNEXO, Brest, the Institute of Oceanography, New Zealand, Imperial College, London and the Technical University of Aachen. A draft project was presented in July 1976 by J. Andrews, University of Hawaii and G. Pautot, Cnexo on a joint survey under the name of: "Hawaii-Tahiti Transect program". Further details were worked on in September 1976 during the International Geological Congress in Sydney with the participation of D. Cronan, Imperial College, Glasby, New Zealand Geological Survey and G. Friedrich, Aachen TU. The scientific final program was established in July 1977, planning on the participation of three research vessels: the Suroit (CNEXO), the Kana Keoki (U. of Hawaii) and the Sonne (Aachen TU). Several survey areas were selected across the Pacific Ocean (Areas A, B, C, D, E, F, G and H) with about the same crustal age (about 40 million years) and a similar water depths. Being near large fault zones, the ares would be adequate to study the influences of biological productivity, sedimentation rate and possibly volcanic activity on the formation and growth of manganese nodules. The influnece of volcanic activity study would particularly apply to area G being situated near the Marquesas Fracture Zone. The cruise from R/V Sonne started in August 1978 over areas C, D, F, G K. The R/V suroit conducted a similar expedition in 1979 over areas A, B, C, D, E, H and I. Others cruises were planned during the 1979-1980 for the R/V Kana Keoki. The present text relates the R/V Sonne Cruises SO-06/1 and SO-06/2 held within the frame work of this international cooperative project.