Physical properties, mineral and chemical compositions, and accumulation rates of Holocene and Upper Pleistocene bottom sediments from the Sea of Okhotsk

Mineral and chemical compositions and physical properties of diatomaceous clayey-siliceous sediments from the Sea of Okhotsk are studied. Accumulation rates of silica are determined. Their compositional model based on silica content is similar to that of Late Jurassic and Olenekian-Middle Anisian cherts from the Sikhote Alin region. Thickness of Holocene siliceous unit and accumulation rates of siliceous deposits depended on bioproductivity in the upper water layer and seafloor topography. Accumulation rates of amorphous SiO2 (0.05-5.7 g/cm**2/ka) and free SiO2 (0.5-11.6 g/cm**2/ka) are minimal on seamounts and maximal in depressions near foothills. These values match accumulation rates of free SiO2 in Triassic and Late Jurassic basins of the Sikhote Alin region (0.33-3 g/cm**2/ka). Comparison of composition and accumulation rates of silica shows that Triassic and Late Jurassic siliceous sequences of Sikhote Alin could accumulate in a marginal marine basin near a continent.

Mineral and chemical compositions of hydrothermal ores and sediments from the Menez Gwen Hydrothermal Field, Mid-Atlantic Ridge

Mineralogy and geochemistry of sulfide-bearing rocks and ores discovered within the Menez Gwen Hydrothermal Field are studied. Samples were taken during Cruise 49 of R/V Akademik Mstislav Keldysh of the p.p. Shirshov Institute of Oceanology. Mineral composition of rocks and ores were studied by traditional methods of optical microscopy, scanning electron microscopy (CAMSCAN), and microprobe analysis (EPMA SX-50). Contents of trace elements were determined by laser ablation inductively coupled plasma - mass spectrometry (LA-ICP-MS). Zn-Cu ore comprises zonal sulfide chimney intergrowths. Numerous Se-rich copper ore fragments occur in volcanomictic layered gritstones and/or barite slabs. Mineral composition, zonality and association of trace elements in ore are typical of black smokers formed at the basalt base near the Azores Triple Junction in the MAR. Obtained results make it possible to reconstruct formation history of the Menez Gwen Hydrothermal Field into the high-temperature (Cu-Se association in ore clasts), medium-temperature (Zn-Cu-As association in ore), and recent (Ba-SiO2 association) stages.

Main components and isotopic composition of gases from mineral waters of the Taman Peninsula and Caucasus

Helium isotope composition as an indicator of the mantle-derived component was studied in gases from mineral springs, stratal waters, and mud volcanoes developed west of the Teberda River valley (10 objects) and two springs in the central segment of the Greater Caucasus orogen between the active El'brus and Kazbek volcanoes. In the western segment of the orogen ratios of 3He/4He = R_corr vary from 46x10**-8 to 114x10**-8 (from 0.33 to 0.81 R_atm, where R_atm = 1.4x10**-6 is the atmospheric ratio). They are substantially lower relative to ratios in the vicinity of El'brus and Kazbek and close to those in samples from the central segment (from 70x10**-8 to 134x10**-8 (from 0.50 to 0.96 R_atm), as well as to ratios previously recorded in the Caucasian Mineral Waters (CMW) area. Moreover, concentration of 3He in them is notably higher than its crustal radiogenic level characteristic of mud volcanoes in the Taman Peninsula, where 3He/4He varies from 1.4x10**-8 to 2.8x10**-8 (from 0.01 to 0.02 R_atm). Nitrogen-methane gas from northern piedmonts of the western Caucasus also contains nonatmogenic components including radiogenic 40Ar (40Ar/36Ar = 900), excessive nitrogen (~87% of total N2 concentration in sample) and mantle He. These data specify distribution of mantle derivates along the orogen strike and age of intrusive magmatic activity in its different segments.