Concentrations of Fe, Mn, Cu, Zn, Co, Ni, Pb, Cd, B, and SiO2 in interstitial waters from bottom sediments of the Atlantis II and Discovery Deeps, Red Sea rift zone

Chemical analyzes show that interstitial waters from ore-bearing bottom sediments of the Atlantis II and Discovery Deeps are enriched in Fe, Mn, Cu, Ni, Co, Zn, Pb, and Cd compared to sea water. Enrichment factors of these trace elements in the interstitial waters of the Atlantis II Deep relative to the sea water vary within the following ranges: for Fe from 100 to 7000, for Mn from 19047 to 32738, for Zn from 500 to 1600, for Pb from 78333 to 190000, for Cu from 107 to 654. Comparison of average weighted concentrations of Fe, Mn, Zn, Pb, Cu, Ni in the bottom sediments and the interstitial waters of the Atlantis II Deep indicates common regularities and good relationship in distribution of these elements along sediment cores. Differences in concentrations and distribution of the studied trace elements in the interstitial waters of the Atlantis II and Discovery Deeps result from different chemical compositions of hydrothermal fluids entering these deeps.

Elemental and isotopic compositions of metalliferous and pelagic sediments from the Galapagos mounds area, data of DSDP Leg 70

Nontronite, the main metalliferous phase of the Galapagos mounds, occurs at a subsurface depth of ~2-20 m; Mn-oxide material is limited to the upper 2 m of these mounds. The nontronite forms intervals of up to a few metres thickness, consisting essentially of 100% nontronite granules, which alternate with intervals of normal pelagic sediment. The metalliferous phases represent essentially authigenic precipitates, apparently formed in the presence of upwelling basement-derived hydrothermal solutions which dissolved pre-existent pelagic sediment. Electron microprobe analyses of nontronite granules from different core samples indicate that: (1) there is little difference in major-element composition between nontronitic material from varying locations within the mounds; and (2) adjacent granules from a given sample have very similar compositions and are internally homogeneous. This indicates that the granules are composed of a single mineral of essentially constant composition, consistent with relatively uniform conditions of solution Eh and composition during nontronite formation. The Pb-isotopic composition of the nontronite and Mn-oxide sediments indicates that they were formed from solutions which contained variable proportions of basaltic Pb, introduced into pore waters by basement-derived solutions, and of normal-seawater Pb. However, the Sr-isotopic composition of these sediments is essentially indistinguishable from the value for modern seawater. On the basis of 18O/16O ratios, formation temperatures of ~20-30°C have been estimated for the nontronites. By comparison, temperatures of up to 11.5°C at 9 m depth have been directly measured within the mounds and heat flow data suggest present basement-sediment interface temperatures of 15-25°C.

Chemical and isotopic compositions of zircons from amphibolites of the Kamchatksky Cape Peninsula

The paper reports the first data on geochemistry and U-Pb SHRIMP geochronology of zircons from garnet amphibolites whose fragments are hosted by the sole of the ophiolite complex of the Kamchatsky Cape, eastern Kamchatka. The zircons compose homogeneous sampling, have relatively small sizes, are anhedral, have no oscillatory zoning, and possess practically no inclusions. Chemical and photoluminescent characteristics of the zircons testify to their metamorphic genesis. U-Pb SHRIMP dates of the zircons (81.4+/-9.6 Ma) indicate that metamorphism of the amphibolite complex took place in Campanian, Late Cretaceous. These dates seem to correspond to the peak of high-pressure metamorphism, which is thought to be related to origin of an ophiolite complex of the suprasubduction type and its uplift within the Kronotsky Island arc.

Chemical and isotopic compositions of Archean magmatic and metasedimentary rocks and minerals from the Podolia domain, Ukrainian Shield

Zircons from the oldest magmatic and metasedimentary rocks in the Podolia domain of the Ukrainian shield were studied and dated by the U-Pb method on a NORDSIM secondary-ion mass spectrometer. Age of zircon cores in enderbite gneisses sampled in the Kazachii Yar and Odessa quarries on the opposite banks of the Yuzhnyi Bug River reaches 3790 Ma. Cores of terrigenous zircons in quartzites from the Odessa quarry as well as in garnet gneisses from the Zaval'e graphite quarry have age within 3650-3750 Ma. Zircon rims record two metamorphic events around 2750-2850 Ma and 1900-2000 Ma. Extremely low U content in zircons of the second age group indicates conditions of the granulite facies metamorphism in Paleoproterozoic within the Podolia domain. Measured data on orthorocks (enderbite-gneiss) and metasedimentary rocks unambiguously suggest existence of the ancient Paleoarchean crust in the Podolia (Dniester-Bug) domain of the Ukrainian shield. They contribute in our knowledge of scales of formation and geochemical features of the primordial crust.