Unlocking the groundwater potential in the Indus Basin

This database allows the simulated vertical profile of the salt concentration (mg TDS/L) to be extracted for any location within the Chaj doab, Indus basin, Pakistan.

Physiography of the Ampère Seamount in the Horseshoe Seamount chain off Gibraltar

The Ampère Seamount, 600 km west of Gibraltar, is one of nine inactive volcanoes along a bent chain, the so called Horseshoe Seamounts. All of them ascend from an abyssal plain of 4000 to 4800 m depth up to a few hundred meters below the sea surface, except two, which nearly reach the surface: the Ampère massif on the southern flank of the group and the summit of the Gorringe bank in the north. The horseshoe, serrated like a crown, opens towards Gibraltar and stands in the way of its outflow. These seamounts are part of the Azores-Gibraltar structure, which marks the boundary between two major tectonic plates: the Eurasian and the African plate. The submarine volcanism which formed the Horseshoe Seamounts belongs to the sea floor spread area of the Mid-Atlantic Ridge. The maximum activity was between 17 and 10 Million years ago and terminated thereafter. The volcanoes consist of basalts and tuffs. Most of their flanks and the abyssal plain around are covered by sediments of micro-organic origin. These sediments, in particular their partial absence on the upper flanks are a circumstantial proof and a kind of diary of the initial rise and subsequent subsidence of about 6oo m of these seamounts. The horizons of erosion where the basalt substrate is laid bare indicate the rise above sea level in the past. Since the Ampère summit is 60 m deep today, this volcano must have been an island 500 m high. The stratification of the sediments covering the surrounding abyssal plain reveals discrete events of downslope suspension flows, called turbidites, separated by tens of thousands of years and perhaps induced by changes in climate conditions. The Ampère sea mount of 4800 m height and a base diameter of 50 km exceeds the size of the Mont Blanc massif. Its southern and eastern flanks are steep with basalts cropping out, in parts with nearly vertical walls of some hundred meters. The west and north sides consist of terraces and plateaus covered with sediments at 140 m, 400 m, 2000 m, and 3500 m. The Horseshoe Seamount area is also remarkable as a kind of disturbed crossing of three major oceanic flow systems at different depths and directions with forced upwelling and partial mixing of the water masses. Most prominent is the Mediterranean Outflow Water (MOW) with its higher temperature and salinity between 900 to 1500 m depth. It enters the horseshoe unimpaired from the open eastern side but penetrates the seamount chain through its valleys on the west, thereafter diverging and crossing the entire Atlantic Ocean. Below the MOW is the North Atlantic Deep Water (NADW) between 2000 m to 3000 m depth flowing southward and finally there is the Antarctic Bottom Water (AABW) flowing northward below the two other systems.

Tab. 2: U-Pb ion-microprobe ages from Taymyr peninsula

We present the initial results of a U-Th-Pb zircon ion-microprobe investigation on samples from the Central Belt of Taimyr, in order to constrain its tectono-magmatic evolution. The zircon samples are from a deformed twomica granite (Faddey Massif), deformed metamorphosed gabbroic dike entrained as pods and lenses within metamorphosed tholeiitic basalts of the Kunar-Mod volcanic suite (Klyaz'ma River region), a metamorphosed rhyolite of the same volcanic suite overlying the basic metavolcanic rocks, as well as an undeformed dolerite dike which intrudes the metamorphosed Kunar-Mod basic volcanic rocks. Preliminary results on zircons from the two-mica granite suggest a crystallization age of ~630 Ma for this rock, with inheritance from assimilated crust 840 Ma to 1.1 Ga in age. In the Klyaz'ma River region, zircons from the meta-rhyolite yield a concordant age of -630 Ma. Zircons from the entrained metagabbroic dikes have so far yielded an age of -615 Ma (1 grain), as well as Archean ages (5 grains, concordant at 2.6-2.8 Ga). It seems likely that the Archean grains represent assimilation of older crustal material. Zircons from the post-tectonic dolerite dike have a bimodal age distribution. A well-defined younger age of 281 ±9 Ma is interpreted to represent the crystallization age of the dike, while older, concordant ages of 2.6-2.9 Ga likely represent assimilation of Archean crust (Siberian craton at depth). Several important conclusions can be drawn from the data. (1) The mafic and felsic lithologies of the Kunar-Mod volcanic suite are genetically related and should be the same age. Ages of-630 Ma (meta-rhyolite) and -615 Ma (metagabbroic dikes representing the latest stage of mafic magmatism associated the Kunar-Mod suite) suggest that these lithologies may be the same age, but more data are required to confirm this hypothesis. (2) The 630 Ma two-mica granite is similar in age to the time of high-grade metamorphism, suggesting that syntectonic granite emplacement accompanied obduction of the accretionary Central Belt to the Siberian craton. (3) An Early Permian age is well defined for the undeformed dolerite dike. Dolerite dikes occur across the whole of Taimyr, but are deformed to the south. If related, this single magmatic event pre-dates Permo-Triassic Siberian trap magmatism. Furthermore, it suggests that deformation was localized to southeastern Taimyr.

Analysis and compound of carbon sequestration and serpentinization from the Iberian Margin and the Northern Apennine

Fluid circulation in peridotite-hosted hydrothermal systems influences the incorporation of carbon into the oceanic crust and its long-term storage. At low to moderate temperatures, serpentinization of peridotite produces alkaline fluids that are rich in CH4 and H2. Upon mixing with seawater, these fluids precipitate carbonate, forming an extensive network of calcite veins in the basement rocks, while H2 and CH4 serve as an energy source for microorganisms. Here, we analyzed the carbon geochemistry of two ancient peridotite-hosted hydrothermal systems: 1) ophiolites cropping out in the Northern Apennines, and 2) calcite-veined serpentinites from the Iberian Margin (Ocean Drilling Program (ODP) Legs 149 and 173), and compare them to active peridotite-hosted hydrothermal systems such as the Lost City hydrothermal field (LCHF) on the Atlantis Massif near the Mid-Atlantic Ridge (MAR). Our results show that large amounts of carbonate are formed during serpentinization of mantle rocks exposed on the seafloor (up to 9.6 wt.% C in ophicalcites) and that carbon incorporation decreases with depth. In the Northern Apennine serpentinites, serpentinization temperatures decrease from 240 °C to < 150 °C, while carbonates are formed at temperatures decreasing from ~ 150 °C to < 50 °C. At the Iberian Margin both carbonate formation and serpentinization temperatures are lower than in the Northern Apennines with serpentinization starting at ~ 150 °C, followed by clay alteration at < 100 °C and carbonate formation at < 19-44 °C. Comparison with various active peridotite-hosted hydrothermal systems on the MAR shows that the serpentinites from the Northern Apennines record a thermal evolution similar to that of the basement of the LCHF and that tectonic activity on the Jurassic seafloor, comparable to the present-day processes leading to oceanic core complexes, probably led to formation of fractures and faults, which promoted fluid circulation to greater depth and cooling of the mantle rocks. Thus, our study provides further evidence that the Northern Apennine serpentinites host a paleo-stockwork of a hydrothermal system similar to the basement of the LCHF. Furthermore, we argue that the extent of carbonate uptake is mainly controlled by the presence of fluid pathways. Low serpentinization temperatures promote microbial activity, which leads to enhanced biomass formation and the storage of organic carbon. Organic carbon becomes dominant with increasing depth and is the principal carbon phase at more than 50-100 m depth of the serpentinite basement at the Iberian Margin. We estimate that annually 1.1 to 2.7 × 1012 g C is stored within peridotites exposed to seawater, of which 30-40% is fixed within the uppermost 20-50 m mainly as carbonate. Additionally, we conclude that alteration of oceanic lithosphere is an important factor in the long-term global carbon cycle, having the potential to store carbon for millions of years.

Chemial and isotope compositions of rocks from the West Antarctic

The paper is devoted to a marine geophysical-geological research in the West Antarctic. This researche contributed to establishing the base geodesic network of the West Antarctic and supplemented geokinematic monitoring based on this network with geophysical and geologic information on structure and features of geomorphological and tectonic development of the South Ocean floor. Collected materials allow to conclude about the inhomogeneity of the Scotia Sea floor and about combination of fragments of a continental massif with young rift structures in conditions of the upwelling mantle. The ancient continental bridge, faunal connections between the South America and the West Antarctic has been destroyed by processes of destruction, taphrogeny and sea floor spreading. Structures of the Scotia and Caribbean Seas, North Fiji and Arctic Basins are similar.

Sediment investigations in the Kara Sea

AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the siliclastic and organic carbon fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyrs. BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge due to the final stage of mountain deglaciation of the Putoran Massif. Increased supply of Yenisei-derived material indicated by peak magnetic susceptibility values probably occurred in climate-related pulses culminating near 11, 10, and 9 Cal. kyrs. BP. As sea level rose, the main Holocene depocenter migrated southward. Based on hydrogen index values and n-alkanes, the organic matter is predominantly of terrigenous origin. Maximum accumulation rates of 1.5 to more than 6 g/cm**2/y occurred in the early Holocene sediments, suggesting more humid climatic conditions with an increased vegetation cover in the source area at that time. In general, high organic carbon accumulation rates characterize the estuaries and the inner Kara Sea as important sink for terrigenous organic carbon. A high-resolution record of Holocene variability of magnetic susceptibility (MS) in an AMS14C-dated sediment core from the northern Yenisei estuary may indicate natural variability of Arctic climate change and river discharge on a centennial to millenial time scale. Short-term maxima in MS probably related to warmer climate, enhanced precipitation, intensified weathering/erosion and increased river discharge, display a frequency of about 300 to 700 years.

Petrology and geochemistry of peridotites from IODP Site 304-U1309

Peridotite samples recovered from IODP Site U1309 at the Atlantis Massif in the Mid-Atlantic Ridge were examined to understand magmatic processes for the oceanic core complex formation. Original peridotite was fragmented, and the limited short peridotite intervals are now surrounded by a huge gabbro body probably formed by late-stage melt injections. Each peridotite interval has various petrographical and geochemical features. A spinel harzburgite in contact with gabbro shows evidence of limited melt penetrations causing gradual compositional change, in terms of trace-element compositions of pyroxenes, as well as modal change near the boundary. Geochemistry of clinopyroxenes with least melt effects indicates that the harzburgite is originally mantle residue formed by partial melting under polybaric conditions, and that such a depleted peridotite is one of the components of the oceanic core complex. Some of plagioclase-bearing peridotites, on the other hand, have more complicated origin. Although their original features were partly overprinted by the injected melt, the original peridotites, both residual and non-residual materials, were possibly derived from the upper mantle. This suggests that the melt injected around an upper mantle region or into mantle material fragments. The injected melt was possibly generated at the ridge-segment center and, then, moved and evolved toward the segment end beneath the oceanic core complex.

Geochemistry of carbonate cements of ODP Leg 112 samples

The evolution of pore fluids migrating through the forearc basins, continental massif, and accretionary prism of the Peru margin is recorded in the sequence of carbonate cements filling intergranular and fracture porosities. Petrographic, mineralogic, and isotopic analyses were obtained from cemented clastic sediments and tectonic breccias recovered during Leg 112 drilling. Microbial decomposition of the organic-rich upwelling facies occurs during early marine diagenesis, initially by sulfate-reduction mechanisms in the shallow subsurface, succeeded by carbonate reduction at depth. Microcrystalline, authigenic cements formed in the sulfate-reduction zone are 13C-depleted (to -20.1 per mil PDB), and those formed in the carbonate-reduction zone are 13C-enriched (to +19.0 per mil PDB). Calcium-rich dolomites and near-stoichiometric dolomites having uniformly heavy d18O values (+2.7 to +6.6 per mil PDB) are typical organic decomposition products. Quaternary marine dolomites from continental-shelf environments exhibit the strongest sulfate-reduction signatures, suggesting that Pleistocene sea-level fluctuations created a more oxygenated water column, caused periodic winnowing of the sediment floor, and expanded the subsurface penetration of marine sulfate. We have tentatively identified four exotic cement types precipitated from advected fluids and derived from the following diagenetic environments: (1) meteoric recharge, (2) basalt alteration, (3) seafloor venting and (4) hypersaline concentration. Coarsely crystalline, low-magnesium (Lo-Mg) calcite cements having pendant and blocky-spar morphologies, extremely negative d18O values (to -7.5 per mil PDB), and intermediate d13C values (-0.4 per mil to +4.6 per mil PDB) are found in shallow-marine Eocene strata. These cements are evidently products of meteoric diagenesis following subaerial emergence during late Eocene orogenic movements, although the strata have since subsided to greater than 4,000 m below sea level. Lo-Mg calcite cements filling scaly fabrics in the late Miocene accretionary prism sediments are apparently derived from fluids having lowered magnesium/calcium (Mg/Ca) and 18O/16O ratios; such fluids may have reacted with the subducting oceanic crust and ascended through the forearc along shallow-dipping thrust faults. Micritic, high-magnesium (Hi-Mg) calcite cements having extremely depleted d13C values (to -37.3%c PDB), and a benthic fauna of giant clams (Calyptogena sp.) supported by a symbiotic, chemoautotrophic metabolism, provide evidence for venting of methane-charged waters at the seafloor. Enriched d18O values (to +6.6%c PDB) in micritic dolomites from the continental shelf may be derived from hypersaline fluids that were concentrated in restricted lagoons behind an outer-shelf basement ridge, reactivated during late Miocene orogenesis.