Geophysical and geomorphological approach for locating groundwater potential zones in Sukinda chromite mining area

The impact of mining causes deterioration of environment and decline of groundwater level in the adjoining mining areas, which influences groundwater source for domestic and agriculture purposes. This necessitated locating and exploiting of new groundwater source. A fast, cost-effective and economical way of locating and exploration is to study and analyze remote sensing data. Interpreted remote sensing data were used to select sites for carrying out surface geophysical investigations. Various geomorphologic units were demarcated, and the lineaments were identified by interpretation of false color composite satellite imageries. The potential for occurrence of groundwater in the Sukinda Valley was classified as very good, good, moderate and poor by interpreting the images. Sub-surface geophysical investigations, namely vertical electrical soundings, were carried out to delineate and demarcate potential water-bearing zones. Integrated studies of interpretation of geomorphologic, lineaments and geophysical data (aquifer thickness) were used to prepare groundwater potential map. The studies reveal that the groundwater potential of shallow aquifers is due to geomorphologic features, and the potential of deeper aquifers is determined by lineaments and degree of weathering.     

The Strel’tsovka uranium district: Isotopic geochronological (U-Pb,Rb-Sr,Sm-Nd) characterization of granitoids and their place in the formation history of uranium deposits

An isotopic geochronological study of Russia’s largest Strel’tsovka uranium district has been carried out. Polychronous granite generation, which determined the structure of the pre-Mesozoic basement, had important implications for the formation of volcanotectonic structural elements bearing economic uranium mineralization. The study of U-Pb, Rb-Sr, and Sm-Nd isotopic systems of whole-rock samples and minerals of granitic rocks allowed us to estimate the deportment of these systems in spatially conjugated granite-forming and hydrothermal processes differing in age and gave grounds for revising the age of granites pertaining to the Urulyungui Complex and refining the age of the Unda Complex.     

Formation of orange hibonite,as inferred from some Allende inclusions

Abstract— We studied three fluffy Type A refractory inclusions from Allende that contain orange hibonite. The melilite in the present samples is very Al‐rich, averaging Åk₆, Åk₁₄, and Åk₁₂ in the three samples studied. Hibonite in two inclusions, unlike that in Murchison, has low rare earth element abundances of <10 × CI; in the other inclusion, the hibonite, melilite and perovskite have Group II‐like patterns. The hibonite and melilite in all three inclusions studied have excess ²⁶Mg consistent with (²⁶Al/²⁷Al)_I = 5 × 10^?5. Much of the hibonite and some of the spinel in these inclusions is corroded. These phases are found enclosed in melilite, but based on bulk compositions and phase equilibria, hibonite should not be an early‐crystallizing phase in these inclusions. We conclude that the hibonite and probably some of the spinel is relic. Reversely zoned melilite, rounded spinel and isotopically heavy Mg in the inclusions probably reflect reheating events that involved melting and evaporation. Alteration of the gehlenitic melilite gave rise to some rare phases, including corundum and nearly pure CaTs pyroxene. Studies have shown that blue hibonite contains Ti³⁺ while orange hibonite does not (Ihinger and Stolper, 1986; Beckett et al., 1988). Orange hibonite formed either under oxidizing conditions (such as at oxygen fugacities at least seven orders of magnitude greater than that of a solar gas at 1700 K), or under conditions reducing enough (e.g., solar) that it contained Ti³⁺, which was later oxidized in situ. Although V and Ce oxides are volatile at the temperature and range of oxygen fugacities at which orange hibonite is known to be stable, we find that (a) the hibonite is V‐rich (～1 wt% V₂O₃) and (b) there are no negative Ce anomalies in Allende hibonite. This indicates that the hibonite did not form by condensation under oxidizing conditions. In addition, there are slight excesses of Ti + Si cations relative to Mg + Fe cations (up to 0.1 of 0.8 cations per 19 oxygen anions), probably reflecting the original presence of Ti³⁺. The results of this study strongly support the suggestion (Ihinger and Stolper, 1986) that Allende hibonite originally formed under reducing conditions and was later oxidized. Oxygen fugacities within ～2–3 orders of magnitude of that of a solar gas are implied; otherwise, strong Ce and V depletions would be observed.     

The Eastern Congo—a beauty spot,rediscovered from a geological point of view

In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, ‘Riftlink’. The group's focus is the Albertine Rift, the northern part of the western branch of the East African Rift System, and in particular the rising Rwenzori Mountains that stretch along the border of the D.R. Congo and Uganda. Major questions relate to the timing of the formation of the Rwenzori Mountains, and whether the height of these mountains (> 5000 m) relates to rift movements in Neogene times, or represents an old basement block that formed a topographic high long before. Though, at first, research concentrated on the eastern (Ugandan) part of the Albertine Rift and Rwenzori Mountains, it has now moved further to the west to the D.R. Congo. A first field‐campaign, covering the area from northern Lake Edward along the rift shoulder up to the Blue Mountains at Lake Albert, was conducted in summer 2009, in cooperation with the Ruwenzori State University of Butembo. Here, we present a brief overview of the field‐campaign, with impressions gathered on the morphology and geology of the study area.     

Estimation of unrecorded groundwater abstractions in Jordan through regional groundwater modelling

Jordan suffers from water scarcity and groundwater covers the majority of Jordan’s water supply. Therefore, there is an urgent need to manage this resource conscientiously. A regional numerical groundwater flow model, developed as part of a decision support system for the country of Jordan, allows for quantification of the overexploitation of groundwater resources and enables determination of the extent of unrecorded agricultural groundwater abstraction. Groundwater in Jordan is abstracted from three main aquifers partly separated by aquitards. With updated geological, structural, and hydrogeological data available in the country, a regional numerical groundwater flow model for the whole of Jordan and the southernmost part of Syria was developed using MODFLOW. It was first calibrated for a steady-state condition using data from the 1960s, when groundwater abstraction was negligible. After transient calibration using groundwater level measurements from all aquifers, model results reproduce the large groundwater-level declines experienced in the last decades, which have led to the drying out of numerous springs. They show a reversal of groundwater flow directions in some regions, due to over-abstraction, and demonstrate that documented abstractions are not sufficient to cause the observed groundwater-level decline. Only after considering irrigation water demand derived from remote sensing data, the model is able to simulate these declines. Illegal abstractions can be quantified and predictive scenarios show the potential impact of different management strategies on future groundwater resources.

     

Radon volumetric activity and ion production in the undisturbed lower atmosphere: Ground-based observations and numerical modeling

The results of in situ ground-based observations of radon volumetric activity carried out at the Borok Geophysical Observatory of Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (58°04′ N; 38°14′ E) are presented. Modeling the characteristic diurnal variation in the ion production rate in the undisturbed midlatitude lower atmosphere above land is carried out. The Lagrangian stochastic model of turbulent transport is developed in application to determining the vertical profiles of radon activity for 222Rn and 220Rn isotopes and their radioactive decay products. The results calculated by the Lagrangian stochastic model are matched with the analytical solution for the free atmosphere. Based on the model, the estimate is obtained for the rate of radon outflow from the convective boundary layer to the free clear sky atmosphere. The implications of temperature stratification of the atmosphere for the vertical distribution of the ion production rate at the different radon emission rate are explored.     

The Petrology and Origin of the Tertiary Lundy Granite (Bristol Channel, UK)

The British Tertiary Volcanic Province (BTVP) comprises within-platecentral igneous complexes associated with plateau lavas andregional dyke swarms. Lundy is the southernmost complex of theBTVP and comprises granite ({small tilde}90%) emplaced intodeformed Devonian sedimentary rocks within the Hercynian Cornubiangranite province of southwest England. The complex is intrudedby a northwest-southeast trending dyke swarm. In common withother BTVP igneous complexes, Lundy is associated with positivegravity and magnetic anomalies which are interpreted in termsof the presena of an underlying basic intrusion at shallow depth,with a volume exceeding that of the overlying granite. The Lundy intrusion is a coarse-grained megacrystic granitecontaining up to 20% alkali feldspar megacrysts in a coarse-grainedgroundmass composed of alkali feldspar, quartz, lithium-bearingmuscovite, and ‘biotite’ (lithian siderophyllite),with a range of aaxssory minerals. The main granite has a coarse-grained(locally miarolitic) pegmatitic facies and is intruded by thinsheets and veins of fine-grained aplite and microgranite. Themineralogy indicates crystallization of the Lundy granite froma highly fractionated H₂O- and halogen-rich magma at a relativelyshallow crustal level. The main Lundy granite is a peraluminous leucogranite with Na₂O=3–4%,K₂O{small tilde}5%, low TiO₂, MeO, CaO, Zr, and Sr, and highRb and Rb/Sr in comparison with many other peralurninous granites,including those from the Cornubian batholith and the BTVP. Anew Rb-Sr whole-rock isochron for the granite yields an ageof 58?7?1?6 Ma with an initial ⁸⁷Sr/86Sr of 0?715?0?006. _Ndvalues for the granite (–0?9 to –1?9) plot betweencontemporaneous mantle (positive _Nd and Cornubian granites (_Nd=ca.–11). The trace element data (Rb, Y, Nb) show affinities with syn-collisionand within-plate granites. As the Sr isotope data indicate amajor crustal component, and the Nd isotope data suggest bothmantle and crustal components, we propose that the Lundy graniteis derived from a parental magma comprising crustal components(derived from a similar source to that of the Cornubian granitebatholith) and a mantle-derived component (derived from a differentiateof contemporaneous basaltic magma This magma experienced fractionalcrystallization of plagioclase, alkai feldspar, Fe-Mg minerals,and REE-bearing accessory minerals before emplacement, and theLundy granite experienced further in situ fractional crystallization,associateded with crustal contamination by the Devonian shaleafter emplacement.     

Magmatic Evolution of the La Pacana Caldera System, Central Andes, Chile: Compositional Variation of Two Cogenetic, Large-Volume Felsic Ignimbrites

La Pacana is one of the largest known calderas on Earth, andis the source of at least two major ignimbrite eruptions witha combined volume of some 2700 km³. These ignimbrites have stronglycontrasting compositions, raising the question of whether theyare genetically related. The Toconao ignimbrite is crystal poor,and contains rhyolitic (76–77 wt % SiO₂) tube pumices.The overlying Atana ignimbrite is a homogeneous tuff whose pumiceis dacitic (66–70 wt % SiO₂), dense (40–60% vesicularity)and crystal rich (30–40 % crystals). Phase equilibriaindicate that the Atana magma equilibrated at temperatures of770–790°C with melt water contents of 3·1–4·4wt %. The pre-eruptive Toconao magma was cooler (730–750°C)and its melt more water rich (6·3–6·8 wt% H₂O). A pressure of 200 MPa is inferred from mineral barometryfor the Atana magma chamber. Isotope compositions are variablebut overlapping for both units (⁸⁷Sr/⁸⁶Sr_i 0·7094–0·7131;¹⁴³Nd/¹⁴⁴Nd 0·51222–0·51230) and are consistentwith a dominantly crustal origin. Glass analyses from Atanapumices are similar in composition to those in Toconao tubepumices, demonstrating that the Toconao magma could representa differentiated melt of the Atana magma. Fractional crystallizationmodelling suggests that the Toconao magma can be produced by30% crystallization of the observed Atana mineral phases. Toconaomelt characteristics and intensive parameters are consistentwith a volatile oversaturation-driven eruption. However, thelow H₂O content, high viscosity and high crystal content ofthe Atana magma imply an external eruption trigger. KEY WORDS: Central Andes; crystal-rich dacite; eruption trigger; high-silica rhyolite; zoned magma chamber     

Seasonal climate patterns and their influence on calibration of the Hargreaves-Samani equation

Abstract

Annual patterns in climate parameters were studied to evaluate how these influence the quality of reference evapotranspiration (ETo) estimates obtained from the Hargreaves-Samani (HS) equation, since the method only uses the measured temperature directly. The work evaluates how these patterns can be used to improve the HS ETo estimates. Ten-year moving averages from a set of California Irrigation Management Information System (CIMIS) stations were used to evaluate the relationships between solar radiation (R_s), temperature (T) and ETo. The results indicate that T treads behind solar radiation and its value peaks some 25 days later. Thus, the main irrigation season in the Mediterranean climate (1 May–30 September) can be divided into three phases: increasing R_s and T; decreasing R_s with increasing T; and decreasing R_s and T. Non-univocal annual cycles were observed between R_s and T, ETo and R_s, and ETo and T. These annual patterns result in important seasonal changes in the ratio between the HS and Penman-Monteith (FAO PM) ETo estimates. The changes are particularly important during the irrigation season, where the FAO PM initially calculates greater ETo values than the HS methodology, and from the end of May to early September, where the HS equation overestimates the ETo values (by 17 mm, or 3%). These patterns obtained from 2000–2009 data were used to calibrate and improve HS ETo estimates at new sites for the 2010–2011 period. Calibration based on the proposed seasonal region-wide FAO PM/HS ETo ratios improved both the bias (decreased from 0.40 to 0.36 mm d^-1) and r² (increased from 0.67 to 0.87) of the ETo estimates for the irrigation season. The proposed methodology can be easily applied to other regions, even when the existing weather stations are sparse.

Editor Z.W. Kundzewicz     

Harmonic sources of the main geomagnetic field in the Earth’s core

The large-scale harmonic magnetic-convective sources of the main geomagnetic field in the Earth’s core have been determined for the first time. The determination is based on a complete system of eigenfunctions of the magnetic diffusion equation in a homogeneously conducting sphere, which is surrounded by an insulator. The sources of the main geomagnetic field observed, which is responsible for the distribution of the electric currents generating this field in the core, are expressed in terms of large-scale eigenfunctions. In this case, the dipole sources are directly related to the observed geomagnetic dipole, whereas the quadrupole sources are related to the quadrupole, etc. The time variations in the obtained sources are responsible for individual spatiotemporal features in the generation or suppression of each Gaussian component of the observed geomagnetic field. When the commonly accepted observational international geomagnetic reference field (IGRF) models were used to partially reveal these time variations, it became possible to specify the estimate of the Earth’s core conductivity and determine the minimum period that can separate us from the commencement of further inversion or excursion.