Chemical and isotope composition of carbonate nodules and host bottom sediments from Core DM9-666, Gulf of California

Results of mineralogical and isotopic analyzes of sulfur and carbon in carbonate nodules and host bottom sediments and results of 14C measurement in carbonate nodules are reported. It is proved that the carbonate nodules formed 11-22 thousand years ago in anaerobic diagenesis of bottom sediments rich in organic matter. Isotopic light metabolic carbon dioxide was a source of carbonate for nodules. It formed during microbial degradation of organic matter of bottom sediments.

Chemical and isotopic compositions of volcanics from ODP Hole 210-1276

Site 1276, Leg 210 of the Ocean Drilling Program, was located on the Newfoundland margin in a seismically-defined ~128 Ma "transitional" crust just west of the presumed oceanic crust, and the M3 magnetic anomaly. The goal of drilling on this non-volcanic margin was to study the rifting, nature of basement, and post-rift sedimentation in the Newfoundland-Iberia rift. Drilling of this 1739 m hole was terminated 90-160 m above basement, in the lower of a doublet of alkaline diabase sills. We have carried out geochemical studies of the sill complex, in the hopes that they will provide proxy information regarding the nature of the underlying basement. Excellent 40Ar/39Ar plateau ages were obtained for the two sills: upper sill ~105.3 Ma; lower sill ~97.8 Ma. Thus the sills are substantially younger than the presumed age of the seafloor at site 1276 (~128 Ma), and were intruded beneath substantial sediment overburden (250 m for the upper, older sill, and 575 m for the lower younger sill). While some of the geochemistry of the sills has been compromised by alteration, the "immobile" trace elements show these sills to be hawaiites, differentiated from an enriched alkaline or basanitic parentage. Sr, Nd and Pb isotopes are suggestive of an enriched hotspot/plume mantle source, with a possible "added" component of continental material. These sills unequivocally were not derived from typical MORB (asthenospheric) upper mantle.

Chemical and isotopic compositions and age of carbonates from the Lost City hydrothermal field, Mid-Atlantic Ridge

Two genetically different types of authigenic carbonate mounds are studied: (1) from an active hydrothermal field related to serpentinite protrusions in a zone of intersection of a transform fracture zone with the Mid-Atlantic Ridge, (2) from an active field of methane seepings in the Dnieper canyon of the Black sea. General geochemical conditions, under which authigenic carbonate formation occurs within these two fields, were found. They include: presence of reduced H2S, H2, and CH4 gases at absence of free oxygen; high alkalinity of waters participating in carbonate formation; similarity of textural and structural features of authigenic aragonite, which represents the initial carbonate mineral of the mounds; paragenesis of aragonite with sulfide minerals; close relation of carbonate mounds with communities of sulfate-reducing and methane-oxidizing microorganisms. A new mechanism of formation of hydrothermal authigenic carbonates is suggested. It implies their microbial sulfate reduction over hydrogen from fluid in the subsurface mixing zone of hydrothermal solution and adjacent seawater.

Chemical and isotope composition of rocks from the Omgon Range, Western Kamchatka coastal area

Hypabyssal rocks of the Omgon Range, Western Kamchatka that intrude Upper Albian-Lower Campanian deposits of the Eurasian continental margin belong to three coeval (62.5-63.0 Ma) associations: (1) ilmenite gabbro-dolerites, (2) titanomagnetite gabbro-dolerites and quartz microdiorites, and (3) porphyritic biotite granites and granite-aplites. Early Paleocene age of ilmenite gabbro-dolerites and biotite granites was confirmed by zircon and apatite fission-track dating. Ilmenite and titanomagnetite gabbro-dolerites were produced by multilevel fractional crystallization of basaltic melts with, respectively, moderate and high Fe-Ti contents and contamination of these melts with rhyolitic melts of different compositions. Moderate- and high-Fe-Ti basaltic melts were derived from mantle spinel peridotite variably depleted and metasomatized by slab-derived fluid prior to melting. The melts were generated at variable depths and different degrees of melting. Biotite granites and granite aplites were produced by combined fractional crystallization of a crustal rhyolitic melt and its contamination with terrigenous rocks of the Omgon Group. The rhyolitic melts were likely derived from metabasaltic rocks of suprasubduction nature. Early Paleocene hypabyssal rocks of the Omgon Range were demonstrated to have been formed in an extensional environment, which dominated in the margin of the Eurasian continent from Late Cretaceous throughout Early Paleocene. Extension in the Western Kamchatka segment preceded the origin of the Western Koryakian-Kamchatka (Kinkil') continental-margin volcanic belt in Eocene time. This research was conducted based on original geological, mineralogical, geochemical, and isotopic (Rb-Sr) data obtained by the authors.

Chemical and isotopic composition of interstitial waters and hydrocarbon composition at ODP Site 184-1146

Bottom-simulating reflectors were observed beneath the southeastern slope of the Dongsha Islands in the South China Sea, raising the potential for the presence of gas hydrate in the area. We have analyzed the chemical and isotopic compositions of interstitial water, headspace gas, and authigenic siderite concretions from Site 1146. Geochemical anomalies, including a slight decrease of chlorine concentration in interstitial water, substantial increase of methane concentration in headspace gas, and 18O enrichment in the authigenic siderite concretion below 400 meters below seafloor are probably caused by the decomposition of gas hydrate. The low-chlorine pore fluids contain higher molecular-weight hydrocarbons and probably migrate to Site 1146 along faults or bedded planes.

Chemical and isotopical analsyes of DSDP Hole 34-321 basalts

A blue-green smectite (iron-rich saponite) and green mica (celadonite) are the dominant sheet silicates in veins within the 10.5 m of basalt cored during DSDP Leg 34, Site 32l, in the Nazca plate. Oxygen isotopic analyses of these clays, and associated calcite, indicate a formation temperature of <25°C. Celadonite contains appreciable Fe2O3, K2O and SiO2, intermediate MgO, and very little Al2O3. Celadonite is commonly associated with goethite and hematite, which suggests that this phase formed by precipitation within a dominantly oxygenated environment of components leached from basalt and provided by seawater. A mass balance estimate indicates that celadonite formation can remove no more than 15% of the K annually transported to the oceans by rivers. In contrast, iron-rich saponite containing significant Al2O3 appears to have precipitated from a nonoxidizing, distinctly alkaline fluid containing a high Na/K ratio relative to unmodified seawater. Seawater-basalt interaction at low temperatures, resulting in the formation of celadonite and smectite may explain chemical gradients observed in interstitial waters of sediments overlying basalts.

Chemical and mineral composition of rocks and sediments from the Amirante Arc

New geological and geophysical data on the Amirante Arc, which locates to the south of the Seychelles Islands, are presented. These data were obtained by Pacific Oceanological Institute during the 33-rd cruise of R/V Professor Bogorov in 1990. The Amirante Arc represents a seamount chain, which has submeridional strike and total length about 400 km. To the west of the Amirante Arc there are a deep sea trench and a back-arc basin, i.e. this area is characterized by structural elements associated with the subduction zone of Western Pacific type. According to our data the Amirante Arc is composed by tholeiites of ocean plateau type. This facts are evidences that the Amirante Arc differs from typical Pacific island arcs. This gives an opportunity to distinguish a special type of oceanic structures, i.e. non-volcanic (amagmatic) ridges. The Amirante Ridge has been probably formed as a result of oceanic crust heaping due to horizontal displacements of its blocks in the process of spreding ridge formation in the Indian Ocean during Cretaceous-Paleogene.

Chemical and mineral compositions of sedimentary deposits and magmatic rocks from DSDP Legs 41, 45, 48, and 49

This collective monography by a group of lithologists from the Geological Institute of the USSR Academy of Sciences summarizes materials of the Deep-Sea Drilling Project from the Atlantic Ocean. It gives results of processing materials on the sequences drilled during DSDP Legs 41, 45, 48 and 49. These studies were based on lithological-facial analysis combined with detailed mineralogical-petrographic description. Its chapters give a number of ideas on formation of the Earth sedimentary cover, which can be used for compilation of regional and global schemes of ocean paleogeography, reconstruction of history of some structures in the World Ocean, correlation between sedimentary processes on continents and in oceans, estimation of perspectives for oil and gas fields and ore formation.

Chemical and Sr isotopic compositions and timing of carbonate mineral precipitation, ODP Leg 115

The strontium isotope ratios of authigenic carbonates from Indian Ocean sea-floor basalts have been used to determine the timing of carbonate mineral precipitation and fluid flow. The samples include calcites from 57.2 Ma crust from Ocean Drilling Project (ODP) Site 715, and calcites, aragonites, and siderites from 63.7 Ma crust from ODP Site 707. At Site 715, calcite precipitation may have begun at any time after the basalts cooled, and it continued until approximately 31 Ma, or 26 m.y. after basalt eruption. At Site 707, aragonite and siderite did not begin to precipitate until about 36 Ma, almost 30 m.y. after basalt eruption, and continued to precipitate until at least 30 and 28 Ma, respectively. Calcite precipitation began at approximately 32 Ma and continued until 22 Ma. These ages suggest that vein mineral deposition and low-temperature fluid circulation in the ocean crust may continue for much longer periods of time than previously observed.

Palaeomagnetic and physical properties records from Foulden Maar, New Zealand

This dataset includes palaeomagnetic inclination directions and density, reflectance (CIEL*a*b*) and red intensity (RGB) measurements from 100 metres of diatomaceous lake sediments from the Oligocene/Miocene Foulden Maar, New Zealand.