Tab. 1: Mineralogical composition and chemical analyses of major and trace elements of Ameghino Formation rocks

As a result of a petrographical, mineralogical and geochemical characterization of the Ameghino Formation mudstones (Upper Jurassic- Lower Cretaceous, Antarctic Peninsula), "epiclastic" radiolaria-rich and mixed (radiolaria-rich + tuff) mudstone types were recognized. Contents of clastic material in the mudstones generally increase with younger paleontological age, but local exceptions to this trend have been found. The anoxic environment of the lower part of the sequence changes to more oxidizing conditions towards the top, in transition to the Hauterivian - Barrêmian conglomerates. Element to element correlations show good agreement with the normal differentiation trends of volcanic (andesite-rhyolite) rocks, suggesting that the overall sequence is mainly volcanic in origin with various grade of reworking. For example, the radiolaria-rich mudstone matrix could have been originated from very fine touffaceous suspensions deposited very slowly after the main fall of the tuffs. However, in the upper part of the sequence, some epiclastic supply is revealed by petrographic evidence and illite crystallinity index. The clay mineral association (illite, chlorite and illite-smectite mixed layers) is mainly of diagenetic origin in the stratigraphically lower sections. Low percentages of expandable layers in the illite-smectite mixed layers, as well as the general mineralogical association, suggest a late mesodiagenetic stage, and together with geological evidence, a relatively deep burial (> 1000 m - probably > 2500 m) and temperatures exceeding 100°C.

Composition of bottom sediments, rocks, and ores from the Tropical Atlantic

Geological features of some areas of the Tropical Atlantic (stratigraphy, tectonic structure, lithology, distribution of ore components in bottom sediments, petrography of bedrocks, etc.) are under consideration in the book. Regularities of concentration of trace elements in iron-manganese nodules, features of these nodules in bottom sediments, distribution of phosphorite nodules and other phosphorites have been studied. Much attention is paid to rocks of the ocean crust. A wide range of mineralization represented by magnetite, chromite, chalcopyrite, pyrite, pentlandite, and other minerals has been found.

Chemistry of the massive sulfide deposit at DSDP Hole 63-471

We report here chemical analyses of sulfide and other minerals occurring in the massive sulfide deposit cored at Site 471. Details of the mineralogy and inferred paragenesis of the deposit will be reported elsewhere. 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 (about 35 cm thick); (2) a 5-cm-thick metalliferous sediment layer described in detail by Leinen (this volume); and (3) a 4-cm-thick chert layer. The overlying sediment is a calcareous silty claystone that contains middle Miocene coccoliths (Bukry, this volume). The underlying basalt has been extensively chloritized and veined with calcite. In places feldspars are albitized, and calcite occurs as pseudomorphs after olivine. Relict textures suggest that the basalt grades into diabase and gabbro with increasing depth. Neither stock work nor disseminated sulfides was observed in the altered rocks.

Geochemical composition and atomic formulas of saponites, celadonites and clays from ODP Leg 168 sites

A drilling transect across the sedimented eastern flank of the Juan de Fuca Ridge, conducted during Leg 168 of the Ocean Drilling Program, resulted in the recovery of samples of volcanic basement rocks (pillow basalts, massive basalts, and volcanic glass breccias) that exhibit the effects of low-temperature hydrothermal alteration. Secondary clays are ubiquitous, with Mg-rich and Fe-rich saponite and celadonitic clays commonly accounting for several percent, and up to 10%-20% by volume. Present-day temperatures of the basement sites vary from 15° to 64°C, with the coolest site being about 0.8 Ma, and the warmest site being about 3.5 Ma. Whereas clays are abundant at sites that have been heated to present temperatures of 23°C and higher, the youngest site at 15°C has only a small trace of secondary clay alteration. Alteration increases as temperatures increase and as the volcanic basement ages. The chemical compositions of secondary clays were determined by electron microprobe, and additional trace element data were determined by both conventional nebulization inductively coupled plasma-mass spectroscopy (ICP-MS) and laser-ablation ICP-MS. Trioctahedral saponite and pyrite are characteristic of the interior of altered rock pieces, forming under conditions of low-oxygen fugacity. Dioctahedral celadonite-like clays along with iron oxyhydroxide and Mg-saponite are characteristic of oxidized haloes surrounding the nonoxidized rock interiors. Chemical compositions of the clays are very similar to those determined from other deep-sea basalts altered at low temperature. The variable Mg:Fe of saponite appears to be a systematic function both of the Mg:Fe of the host rock and the oxidation state during water-rock interaction.

Composition of hydrothermal manifestations in the World Ocean

The monograph summarizes results of studies of hydrothermal fields on the ocean floor, hydrothermal plumes and metalliferous sediments. Hydrothermal ore manifestations formed in different geodynamic settings, with different character of volcanism in different facial conditions of deposition are described. Causes of non-uniformity of hydrothermal system functioning in different parts of the ocean and therefore variability of hydrothermal deposits are under consideration. On the base of found relationships of these irregularities with geodynamics, volcanism and sedimentation a new classification of hydrothermal processes and genetic models of hydrothermal ore formation in the ocean have been created. Regularities of hydrothermal sedimentary material dispersion in bottom waters are discussed.

Boron contents and boron, carbon, and oxygen isotope data for ODP Sites 160-970 and 160-971

Products of two mud volcanoes from the distal part of the Mediterranean Ridge accretionary complex have been investigated regarding their B, C, and O stable isotope signatures. The mud breccias have been divided into mud matrix, lithified clasts, biogenic deposits, and authigenic cements and crusts related to fluid flow and cementation. Isotope geochemistry is used to evaluate the depth of mobilization of each phase in the subduction zone. B contents and isotope ratios of the mud and mud clasts show a general trend of B enrichment and decreasing d11B values with increasing consolidation (i.e., depth). However, the majority of the clast and matrix samples relate to moderate depths of mobilization within the wedge (1-2 km below seafloor). The carbonate cements of most of these clasts as well as the authigenic crusts, however, provide evidence for a deep fluid influence, probably associated with the décollement at 5-6 km depth. This interpretation is supported by d13C ratios of the crust, which indicate precipitation of C from thermogenic methane, and by the d11B ratios of pore-water samples of mud-breccia drill cores. Clams (Vesicomya sp.) living adjacent to fluid vents have d11B and d18O values corresponding to brines known in the area, which acted as the parent solution for shell precipitation. Such brines are most likely Miocene pore waters trapped at deep levels within the backstop to the accretionary prism, probably prior to desiccation of the Mediterranean in the Messinian (6-5 Ma). Combining all results, deep fluid circulation and expulsion are identified as the main processes triggering mud liquefaction and extrusion, whereas brines contribute only locally. Given the high B contents, mud extrusion has to be considered a major backflux mechanism of B into the hydrosphere.

Sulphur isotope composition in the Gulf of California and the Eastern Pacific

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.

Petrology and geochemistry of altered ocenaic crust of ODP Hole 140-504B

Altered basalt dikes from Hole 504B were partially melted at 1150°C and 1180°C to determine the composition of the first melts as oceanic Layer 2C is assimilated by a magma chamber. The partial melts are chemically similar to actinolite, the most abundant secondary mineral, but the melts are not simply melted actinolite. High TiO2, P2O5, and K2O abundances of the melts indicate that minor secondary minerals that are enriched in these elements also contribute to the melt. The incorporation of partial melts into a ridge-crest magma chamber may explain the local variability that is sometimes found in ocean ridge basalts that are not readily explained fractional crystallization or partial melting.

Geochemistry of pore fluids from ODP Leg 134 sites

Depending on the temperature and the extent of diagenetic alteration of fluid chemistry, fluid flow at convergent margins may transfer important quantities of heat and mass between the crust and seawater, thereby influencing global mass, isotopic and heat budgets. In the North Aoba Basin, an intra-arc basin located at the New Hebrides Island Arc, alteration of volcanic ash to clay minerals and zeolites forms a CaCl2 brine, perhaps in less than 1 to 3 m.y. The brine results from an exchange of Ca for Na, K, and Mg, and an increase in Cl concentrations to a maximum of 1241 mM. The Cl increase is partly due to the transfer of H2O from the pore fluid into authigenic minerals, but water mass balances, d18O-Cl correlations, and Br/Cl ratios suggest that there is a source of Cl in the sediments. Concentration profiles indicate that Li is transferred from the fluid to solid phase at depths <300 meters below seafloor (mbsf), but at greater depths it is transferred from the solid to fluid phase, at temperatures possibly as low as 25°C. In the accretionary wedge extensive fluid flow appears to be confined to highly faulted regions. Although Cl concentrations less than seawater value are common at convergent margins, the New Hebrides margin contains little low-Cl fluid. Br/Cl ratios suggest the low-Cl fluid is from dilution, and d18O values indicate the water may be derived from mineral dehydration and mixing with meteoric water. The New Hebrides margin exhibits few surface manifestations of venting (e.g., sulfide-oxidizing benthic biological communities, carbonate crusts, mud volcanoes) and thus fluid fluxes may be smaller than at many other margins.