Petrology of basalts from DSDP Hole 66-487

Basaltic rocks recovered at the Middle America Trench area off Mexico are typical plagioclase-olivine phyric abyssal tholeiites containing less than 0.2 wt.% K2O. Phenocrysts of plagioclase and olivine usually make up the aggregate. Plagioclase phenocrysts are Ca-rich and up to An90. Olivine phenocrysts, which are always attached to plagioclase phenocrysts, are magnesian, Fo88 to Fo89, and contain 0.2 to 0.3 wt. % of NiO. Plagioclase phenocrysts contain numerous glass inclusions with the Mg/Mg+Fe atomic ratio of 0.70 to 0.73, which is distinctly higher than the same ratio of the bulk rock (0.62-0.63). Olivine of Fo88 to Fo89 is equilibrated with the liquid with an Mg/Mg+Fe atomic ratio of about 0.7, assuming the KDMg-Fe between liquid and olivine of 0.3. Small droplets of glass within glass inclusions in plagioclase are more enriched in K2O and volatiles than the host glass. This enrichment may have been caused by the extraction of Al2O3 as plagioclase from the trapped liquid and implies its immiscibility. Aggregates of plagioclase with small amounts of olivine may have been floated from more primitive magma with an Mg/Mg+Fe atomic ratio of about 0.7, judging from the chemical characteristics mentioned above. Flotation must have occurred at relatively high pressure. Large crystals of plagioclase and smaller crystals of olivine are xenocryst rather than phenocryst. Parental magma of Leg 66 basalt was high-MgO olivine tholeiite.

Nd and Sr isotopic compositions and isotope dilution trace element concentrations from 7 sediment cores along the southeast Greenland margin

The Nd and Sr isotopic compositions of Quaternary glacial and glacimarine siliciclastic sediments deposited along the margin of southeast Greenland were determined to assess the roles of the Greenland, Iceland, and more distal ice sheets in delivering detritus to this portion of the northern North Atlantic. The isotopic compositions of detritus generated by portions of the southern Greenland Ice Sheet were defined through measurements of till and trough mouth fan sediments. Massive diamicts from the Scoresby Sund trough mouth fan show a restricted range of e-Nd (-11.8 to -16.6) and 87Sr/86Sr (0.7192-0.7246) consistent with their derivation from mixtures of sediments derived from Paleoproterozoic and/or Caledonian basement and Tertiary Greenland basalts. Further south at Kangerlussuaq, till isotopic compositions covary with the underlying basement type, with low e-Nd values in the inner fiord (-18.1) reflecting the erosion of the local Precambrian gneisses, but with higher e-Nd values (-2.3 to 2.5) found where the trough crosses East Greenland Tertiary basalts. Fine-grained (< 63 µm) sediments deposited along the southeast Greenland margin also show regular spatial isotopic variations. Ambient sediments and ice-rafted detritus in the southern Irminger Basin trend towards low e-Nd values (to ~ -28) and 87Sr/86Sr ratios (~ 0.711 to ~ 0.715) and are likely derived from proximal Archean gneisses of SE Greenland. Further north in the northern Irminger and Blosseville Basins, sediments trend toward much higher e-Nd (> -4) and low 87Sr/86Sr (< 0.709) reflecting a component derived from the local Iceland volcanic rocks and/or the East Greenland Tertiary basalts. In all three regions, the locally-derived detritus is intermixed with sediment with an intermediate e-Nd value (~ -10) and 87Sr/86Sr (~ 0.718) that was likely delivered by icebergs emanating from the Eurasian Ice Sheets and not from eastern Greenland. Deposition of glacial sediments from both proximal and distal (Eurasian) sources occurred adjacent to SE Greenland throughout the past 50 Ka, with periodic increases in IRD deposition at various times including those of Heinrich events 1, 2 and 4. These results suggest that at least the southern portions of the Greenland Ice Sheet experienced periodic instabilities during the Last Glacial period.

Petrology and origin of basalts at DSDP Hole 66-487

The volcanism of Central America, according to current theory (Pichler and Weyl, 1973; Stoiber and Carr, 1974; Hey, 1977), is related to the subduction of the Cocos Plate under the North American lithospheric plate and the melting of ocean crust material in the subduction zone (Green and Ringwood, 1968; Dickinson, 1970, Fitton, 1971). Since Cocos Plate subduction occurs at the rate of more than 7 cm/y. (Hey et al., 1977), basalts underlying upper Miocene sediments of the Middle America Trench outer slope, penetrated in Hole 487 (Fig. 1) during Leg 66 (Moore et al., 1979), should have formed far from their present position if current theory is accurate. Present manifestations of basaltic magmatism in adjacent areas of the Pacific derive from the axial part of the East Pacific Rise, the Galapagos spreading center, and transform fracture zones. The question arises: Are there analogs of the Middle America Trench basalts among magmatic cock associated with these modern features, or do the trench basalts have some other origin?

Zooplankton collected in the ice covered Chupa Inlet (White Sea) on 6-7 April 2002

Size-, species- and age composition of zooplankton was studied in the ice-covered Chupa Inlet (White Sea, Kandalksha Bay) in early April 2002. The species composition of zooplankton was poor and typical for the end of the winter season, and abundance and biomass were considerably lower than in summer. In terms of biomass two species of copepods (Calanus glacialis and Pseudocalanus minutus) prevailed. Both species were already feeding on ice algae available and began to reproduce. Such early reproduction of Calanus glacialis was noted in the White Sea for the first time. Obtained results show that secondary production in the White Sea starts well before thawing of the ice cover.