Annotated record of the detailed examination of Mn deposits from the Snellius II - Cruise 4 stations in the vicinity of the island of Misool, Eastern Indonesia

The chemical analyses of ferromanganese encrustations found on the seabed west of Misool, eastern Indonesia, indicate that these deposits formed in a way different from that of world-wide occurring manganese nodules. Ferromanganese coated pebbles and fragments that were found in the deeper parts of the study area probably originate from nearby ridges. The ferromanganese crust on the upper part of a dolomite fragment of ?30 kg is likely to be formed by hydrogenous processes, whereas that from the lower part seems to be formed by diagenetic processes mainly. These assumptions are supported by pore-water data from two box cores taken in the same area. The manganese and iron profiles versus depth in these cores indicate a high flux of these metals to the uppermost sediment layer, and possibly into the overlying bottom water. Factor analysis for the principal components of the microprobe analytical results of the mainly hydrogenous ferromanganese crust demonstrates a strong correlation of manganese with the trace metals, of iron with phosphorus and an antipathetic relationship between iron and manganese. Similar results have also been reported for abyssal manganese nodules in the world oceans. Factor analysis for the principal components of the analytical data obtained for the diagenetic ferromanganese crust results in a clear dolomite (Ca/Mg) dilution factor only.

Geochemistry of sheeted dike complex minerals of ODP Hole 140-504B

Diabases were recovered during Legs 137 and 140 at Hole 504B from depths between 1621.5 and 2000.4 meters below seafloor in the lower sheeted dike complex. The samples contain multiple generations of millimetric to centimetric veins. The orientation of the measured veins suggests that two main vein sets exist: one characterized by shallow dipping and the other by random trend. Thermal contraction during rock cooling is considered the main mechanism responsible for fracture formation. Vein infill is related to the circulation of hydrothermal fluids near the spreading axis. Some veins are surrounded by millimeter-sized alteration halos due to fluid percolation from the fractures through the host rock. Vein-filling minerals are essentially amphibole, chlorite, and zeolites. Amphibole composition is controlled by the microstructural site of the rock. Actinolite is the main amphibole occurring in the veins and also in the groundmass away from the halos. In the alteration halos, amphibole shows composition of actinolitic hornblende and Mg-hornblende. Late-stage tension gashes and interstitial spaces in some amphibole-bearing veins are filled with zeolites, suggesting that the veins likely suffered multiple opening stages that record the cooling history of the circulating fluids. Evidence of deformation recorded by the recovered samples seems to be restricted to veins that clearly represent elements of weakness of the rock. On the basis of vein geometry and microstructure we infer structural interpretations for the formation mechanism and for deformation of veins.