(Table 2) Concentrations of dissolved aluminum in interstitial water from sediments of the Indian Ocean

Results are presented of application of laser stepwise photoionization of atoms in combination with thermal atomization of matter in vacuum for direct determination of aluminum dissolved in sea and interstitial waters. Dry residue from evaporation of 40 ?l sea water was atomized in a crucible at 1800°C, and aluminum atoms in the beam thus formed were energized into Rydberg state in two steps by two tunable dye laser beams; the atoms were then ionized by an electric pulse and resulting ions were recorded by secondary emission electron multiplier (ion detector). Ionic signal dependence on sample vaporization time was studied. The procedure is suggested for separating out a selective signal in a single measurement. Dissolved aluminum concentrations in interstitial waters of the Indian Ocean and in waters of the river-sea zone were determined using preliminarily plotted calibration characteristics for aluminum solutions in deionized and sea waters. The minimum detectable Al concentration in seawater was 1 ?g/l that corresponds to 40 pg of Al in a sample.

Representative analyses of garnet, plagioclase, orthopyroxene, ilmenite, hornblende and biotite for pre-tectonic mafic and metapelitic rocks in Gjelsvikfjella

A metamorphic petrological study, in conjunction with recent precise geochronometric data, revealed a complex P-T-t path for high-grade gneisses in a hitherto poorly understood sector of the Mesoproterozoic Maud Belt in East Antarctica. The Maud Belt is an extensive high-grade, polydeformed, metamorphic belt, which records two significant tectono-thermal episodes, once towards the end of the Mesoproterozoic and again towards the late Neoproterozoic/Cambrian. In contrast to previous models, most of the metamorphic mineral assemblages are related to a Pan-African tectono-thermal overprint, with only very few relics of late Mesoproterozoic granulite-facies mineral assemblages (M1) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P-T-t path for the Pan-African orogeny. Peak metamorphic (M2b) conditions recorded by most rocks in the area (T = 709-785 °C and P = 7.0-9.5 kbar) during the Pan-African orogeny were attained subsequent to decompression from probably eclogite-facies metamorphic conditions (M2a). The new data acquired in this study, together with recent geochronological and geochemical data, permit the development of a geodynamic model for the Maud Belt that involves volcanic arc formation during the late Mesoproterozoic followed by extension at 1100 Ma and subsequent high-grade tectono-thermal reworking once during continent-continent collision at the end of the Mesoproterozoic (M1; 1090-1030 Ma) and again during the Pan-African orogeny (M2a, M2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.

Chemical and mineral composition of rocks from the Philippine Sea

The book is devoted to geology of the Philippine Sea floor. This region is studied most extensively among other marginal seas of the Pacific Ocean. Rocks of the sedimentary and basalt layers within this sea have been studied during five legs of D/S Glomar Challenger. International geological expedition on board R/V Dmitry Mendeleev carried out according to the Project ''Ophiolites of Continents and Comparable Rocks of the Ocean Floor''obtained unique collection of rocks from the second and third layers of the ocean crust in the Philippine Sea. The book provides detailed petrographic and geochemical description of igneous and sedimentary formations from the Philippine Sea and compares them with rocks of the continental ophiolite association. An analysis of structure and history of the ocean crust formation in the region is based on all known geological information. The main periods of tectonic movement activation and nature of their manifestations within the sea are shown.

Composition of bottom sediments from the Clarion Fracture Zone

New data on lithology and stratigraphy of Cenozoic sediments from the Clarion Transform Fault Zone (Pacific Ocean) have been obtained on the base of polygon studies. It has been established that on different blocks (uplifted and subsided) of the Clarion tectonic structure deposits of different age (Eocene to Quaternary) occur. Unconsolidated sediments have been deposited under pelagic conditions since Eocene (probably, since Early Cretaceous) until now. Their mineral composition and content of different ore components are given.

High-pressure experiments on a natural olivine gabbro from ODP Hole 176-735B

We have conducted high-pressure experiments on a natural oceanic gabbro composition (Gb108). Our aim was to test recent proposals that Sr-enrichment in rare primitive melt inclusions from Mauna Loa, Hawaii, may have resulted from melting of garnet pyroxenite formed in the magma source regions by reaction of peridotite with siliceous, Sr-enriched partial melts of eclogite of gabbroic composition. Gb108 is a natural, Sr-enriched olivine gabbro, which has a strong positive Sr anomaly superimposed on an overall depleted incompatible trace element pattern, reflecting its origin as a plagioclase-rich cumulate. At high pressures it crystallises as a coesite eclogite assemblage, with the solidus between 1,300 and 1,350°C at 3.5 GPa and 1,450 and 1,500°C at 4.5 GPa. Clinopyroxenes contain 4-9% Ca-eskolaite component, which varies systematically with pressure and temperature. Garnets are almandine and grossular-rich. Low degree partial melts are highly siliceous in composition, resembling dacites. Coesite is eliminated between 50 and 100°C above the solidus. The whole-rock Sr-enrichment is primarily hosted by clinopyroxene. This phase dominates the mode (>75 wt%) at all investigated PT conditions, and is the major contributor to partial melts of this eclogite composition. Hence the partial melts have trace element patterns sub-parallel to those of clinopyroxene with ~10* greater overall abundances and with strong positive Sr anomalies. Recent studies of primitive Hawaiian volcanics have suggested the incorporation into their source regions of eclogite, formerly gabbroic material recycled through the mantle at subduction zones. The models suggest that formerly gabbroic material, present as eclogite in the Hawaiian plume, partially melted earlier than surrounding peridotite (i.e. at higher pressure) because of the lower solidus temperature of eclogite compared with peridotite. This produced highly siliceous melts which reacted with surrounding peridotite producing hybrid pyroxene + garnet lithologies. The Sr-enriched nature of the formerly plagioclase-rich gabbro was present in the siliceous partial melts, as demonstrated by these experiments, and was transferred to the reactive pyroxenite. These in turn partially melted, producing Sr-enriched picritic liquids which mixed with normal picritic partial melts of peridotite before eruption. On rare occasions these mixed, relatively Sr-rich melts were trapped as melt inclusions in primitive olivine phenocrysts.Yaxley-Sobolev

Geochemistry of ODP Hole 108-658C sediments

During the African Humid Period (AHP), much of the modern hyperarid Saharan desert was vegetated and covered with numerous lakes. In marine sediments off northwestern Africa, the AHP is represented by markedly reduced siliciclastic sediment flux between ~ 12.3 and 5.5 ka. Changes in the origin of this terrigenous sediment fraction can be constrained by sediment chemistry and radiogenic isotope tracers. At Ocean Drilling Program (ODP) Site 658, Hole C (20°44.95'N, 18°34.85'W, 2263 mbsl), the neodymium (Nd) isotope composition of terrigenous detritus shows little variability throughout the last 25 kyr, indicating that the contributing geological terranes have not changed appreciably since the last glacial period. In contrast, there were large and abrupt changes in strontium (Sr) isotope ratios and chemical compositions associated with the AHP, during which 87Sr/86Sr ratios were markedly less radiogenic, and sediments show higher chemical indices of alteration. We show that sediment geochemical changes during the AHP cannot be attributed to changes in the source terranes, physical sorting, or intensity of chemical weathering. The low 87Sr/86Sr and high Sr concentrations of AHP-age samples also conflict with the interpretation of increased fine-grained, fluvially derived sediments. We propose that the most significant compositional changes at ODP 658C are due to the addition of an aluminosilicate component that has a highly altered major element signature but is enriched in soluble elements like Sr and magnesium (Mg) compared to aluminum (Al) and has low 87Sr/86Sr relative to local terrigenous source areas. We interpret these characteristics to reflect authigenic sediment supply from extensive North African paleolake basins that were prevalent during the AHP.