Isotope composition of sulfur, oxygen and carbon in Black Sea sediments

Inversion of isotopic composition in the SO4(2-)-H2S system is shown to be universal in Neoeuxine sediments and an explanation of its occurrence is proposed. Change in isotopic composition of sulfate sulfur in Black Sea waters over last 10-15 thousand years is reconstructed. Periods of alteration between aerobic and anaerobic situations are identified, the beginning of entry of Mediterranean waters into the basin is dated, presence of authigenic carbonates in sediments of the sea is established and amounts are determined. Methane generation from carbon dioxide is shown to have been replaced by its generation from acetate in the paleo-Black Sea period.

Chemical composition of basalts and basaltic glasses from the Sierra Leone Fracture Zone region

Major and trace element (including REE) geochemistry of basalts and chilled basaltic glasses from the MAR axial zone in the vicinity of the Sierra Leone FZ (5-7°10'N) has been studied. Associations of basalts of various compositions with particular ocean-floor geological structural features have been analyzed as well. Three basaltic varieties have been discriminated. Almost ubiquitous are high-Mg basalts (Variety 1) that are derivatives of N-MORB tholeiitic melts and that are produced in the axial zone of spreading. Variety 2 is alkaline basalts widespread on the southwestern flank of the MAR crest zone in the Sierra Leone region, likely generated through deep mantle melting under plume impact. Variety 3 is basalts derivative from T- and P-MORB-like tholeiitic melts and originating through addition of deeper mantle material to depleted upper mantle melts. Magma generation parameters, as calculated from chilled glass compositions, are different for depleted tholeiites (44-55 km, 1320-1370°C) and enriched tholeiites (45-78 km, 1330-1450°C). Mantle plume impact is shown to affect not only tholeiitic basalt compositions but also magma generation conditions in the axial spreading zone, resulting in higher Ti and Na concentrations in melts parental to rift-related basalts occurring near the plume. T- and P-MORBs are also developed near areas where mantle plumes are localized. High-Mg basalts are shown to come in several types with distinctive Ti and Na contents. Nearly every single MAR segment (bounded by sinistral strike slips and the Bogdanov Fracture Zone) is featured by its own basalt type suggesting that it has formed above an asthenospheric diapir with its unique magma generation conditions. These conditions are time variable. Likely causes of temporal and spatial instability of the mantle upwelling beneath this portion of the MAR are singular tectonic processes and plume activity. In sulfide-bearing rift morphostructures (so-called "Ore area'' and the Markov Basin), basalts make up highly evolved suites generated through olivine and plagioclase fractionation, which is suggestive of relatively long-lived magma chambers beneath the sulfide-bearing rift morphostructures. Functioning of these chambers is a combined effect of singular geodynamic regime and plume activity. In these chambers melts undergo deep differentiation leading to progressively increasing concentration of sulfide phase, eventually to be supplied to the hydrothermal plumbing system.

Trace element geochemistry of zircons frim in situ ocean lithoshere

We characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite, evolved gabbro, and metamorphosed ultramafic host-rocks collected along present-day slow and ultraslow spreading mid-ocean ridges (MORs). The geochemistry of 267 zircon grains was measured by sensitive high-resolution ion microprobe-reverse geometry at the USGS-Stanford Ion Microprobe facility. Three types of zircon are recognized based on texture and geochemistry. Most ocean crustal zircons resemble young magmatic zircon from other crustal settings, occurring as pristine, colorless euhedral (Type 1) or subhedral to anhedral (Type 2) grains. In these grains, Hf and most trace elements vary systematically with Ti, typically becoming enriched with falling Ti-in-zircon temperature. Ti-in-zircon temperatures range from 1,040 to 660°C (corrected for a TiO2 ~ 0.7, a SiO2 ~ 1.0, pressure ~ 2 kbar); intra-sample variation is typically ~60-15°C. Decreasing Ti correlates with enrichment in Hf to ~2 wt%, while additional Hf-enrichment occurs at relatively constant temperature. Trends between Ti and U, Y, REE, and Eu/Eu* exhibit a similar inflection, which may denote the onset of eutectic crystallization; the inflection is well-defined by zircons from plagiogranite and implies solidus temperatures of ~680-740°C. A third type of zircon is defined as being porous and colored with chaotic CL zoning, and occurs in ~25% of rock samples studied. These features, along with high measured La, Cl, S, Ca, and Fe, and low (Sm/La)N ratios are suggestive of interaction with aqueous fluids. Non-porous, luminescent CL overgrowth rims on porous grains record uniform temperatures averaging 615 ± 26°C (2SD, n = 7), implying zircon formation below the wet-granite solidus and under water-saturated conditions. Zircon geochemistry reflects, in part, source region; elevated HREE coupled with low U concentrations allow effective discrimination of ~80% of zircon formed at modern MORs from zircon in continental crust. The geochemistry and textural observations reported here serve as an important database for comparison with detrital, xenocrystic, and metamorphosed mafic rock-hosted zircon populations to evaluate provenance.

Composition of Fe-Mn nodules from the radiolarian belt of the Pacific Ocean

Typomorphic features of the main morphogenetic types of Fe-Mn nodules from the radiolarian belt have been considered on materials from polygons in the Clarion-Clipperton ore province and in the Central Basin of the Pacific Ocean. By character of surfaces, features of internal structure, mineral and chemical compositions, behavior of trace elements at selective leaching three genetic types of nodules have been divided: predominantly sedimentary, diagenetic, and sedimentary diagenetic. Their formation results from mechanism of growth.

Composition of bottom sediments from the Central Basin of the Indian Ocean

A study of petrographic and mineral compositions of 26 sediment cores from the western part of the Central Basin of the Indian Ocean has identified biogenic, terrigenous, volcanogenic, and authigenic sediment types formed in certain facies conditions. On the basis of bio- and paleomagnetic stratigraphy data from the cores sedimentation rates of different sediment types have been calculated. Modern and Pliocene-Pleistocene positions of the main facies boundaries (the critical depth of carbonate accumulation, the geochemical boundary between hemi- and miopelagic zones, the frontal boundaries of the equatorial belt of biogenic silica accumulation) have been determined. It has been shown that the sedimentary process during Pliocene-Quaternary had cycle variations characterized by successive changes of different sedimentation types - hemipelagic, miopelagic, and biogenic.

(Table 1) Chemical compositions of iron-manganese phosphate crusts, phosphorites, volcanic products, and phosphate limestones from ocean seamounts

New data on phosphorites of Atlantic seamounts are presented and used in combination with published data to analyze sources of phosphorus in them.

Geology, geochemistry, and mineralogy of sediments from the Trans Indian Ocean Geotraverse

The monograph is devoted to the main results of research on the Trans Indian Ocean Geotraverse from the Maskarene Basin to the north-western margin of Australia. These results were obtained by Russian specialists and together with Indian specialists during 15 years of cooperation in investigation of geological structure and mineral resources of the Indian Ocean. The monograph includes materials on information support of marine geological and geophysical studies, composition and structure of information resources on the Indian Ocean, bathymetry and geomorphology, structure and geological nature of the magnetic field, gravity field, plate tectonics, crustal structure and sedimentary cover, seismic stratigraphy, perspectives for detecting oil and gas, solid minerals, sediment composition, composition and properties of clay minerals, stratigraphy and sediment age, chemical composition of sediments, composition of and prospects for solid minerals.