Hydrodynamic modeling for groundwater assessment in Sana’a Basin, Yemen

Yemen is a semi-arid country with very limited water resources. Sana’a Basin is located in the central part of Yemen and is the major source of water for drinking and irrigation. High abstraction rates in Sana’a Basin rising from 21.1 million (M) m³ in 1972 to 227.7?Mm³ in 2006, have led to a major decline in water levels and deterioration in groundwater quality. Effective management of groundwater resources in Sana’a Basin can be aided by modelling. FEFLOW was used to build a groundwater flow model for the basin and the model was calibrated under transient conditions for the period 1972–2006. The water balance for transient conditions of the Sana’a Basin in 2006 indicated that the total annual inflow was 116.9?Mm³, and the total annual outflow was 245.8?Mm³. Three scenarios for potential groundwater extraction for the period 2006–2020 are presented. The first represents the present status based on the 2006 extraction rates without introducing any management measures. The second is based on maximum domestic, agricultural and industrial consumption of water resources. The third simulates the effect of water-resource augmentation, i.e. the increase of groundwater recharge, and maximizes sustainability by reducing water consumption. Identified areas of the basin require prompt management action.     

Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U–Pb geochronology of its Ordovician protolith

For the first time, an albite orthogneiss has been recognised and dated within the HP–LT blueschist facies metabasites and metapelites of the Ile de Groix. It is characterised by a peraluminous composition, high LILE, Th and U contents, MORB-like HREE abundances and moderate Nb and Y values. A U–Pb age of 480.8?±?4.8?Ma was obtained by LA-ICP-MS dating of zircon and titanite. It is interpreted as the age of the magmatic emplacement during the Early Ordovician. Morphologically different zircon grains yield late Neoproterozoic ages of 546.6–647.4?Ma. Zircon and titanite U–Pb ages indicate that the felsic magmatism from the Ile de Groix is contemporaneous with the acid, pre-orogenic magmatism widely recognised in the internal zones of the Variscan belt, related to the Cambro-Ordovician continental rifting. The magmatic protolith probably inherited a specific chemical composition from a combination of orogenic, back-arc and anorogenic signatures because of partial melting of the Cadomian basement during magma emplacement. Besides, the late Devonian U–Pb age of 366?±?33?Ma obtained for titanite from a blueschist facies metapelite corresponds to the age of the HP–LT peak metamorphism.     

Nursery Habitat Shifts in an Estuarine Ecosystem<Emphasis Type="Bold">:</Emphasis> Patterns of Use by Sympatric Catfish Species

The seasonal and spatial distribution (density and biomass) of five size classes of two catfish species (Cathorops spixii and Cathorops agassizii) were studied along an estuarine ecocline to test the relative importance of the nursery function of each habitat. Seasonal vs. area interactions were significant for all size classes of both species. During the early rainy season, the middle estuary is an important nursery habitat for juveniles of both species. When environmental conditions change during the late rainy season, the C. spixii primary nursery habitat shifts to the lower estuary. During this period, juveniles of C. agassizii remain in the middle estuary. Another important ecological area is the upper estuary, which becomes a breeding, spawning and hatchery area during the late dry season for both species. The nursery function of habitats shifts according to the seasonal fluctuation of salinity and dissolved oxygen, and each species responds differently to this change.     

Mapping spatial disparity of canal water distribution under irrigated cropping environment using satellite imageries

In this study, a great variation in crop yield, which affects the socio-economic and physical environment of the area, is observed along the irrigation channels in Pakistan. This is mainly due to inequitable distribution of canal water causing spatial variations along the system. Assessing the performance of irrigation system can help to find any disparity which should be rectified to achieve the desired objectives of irrigation. Due to lack of real-time data, performance of an irrigation system cannot be readily determined particularly in developing countries. Remote sensing and geographic information system are the best tools to overcome this difficulty. Normalized difference vegetation index indirectly indicates the presence of water in plants. Biomass production and evapotranspiration are crucial indicators for describing the spatial variation of irrigation water. In this study, infrared bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer sensor were used to determine surface temperatures and various components of the energy balance equation. The spatial disparity in evapotranspiration was found from head to tail of the system. Classification of evapotranspiration into different groups revealed that the area under higher evapotranspiration range is more at the head of the system than its tail, which indicates that more canal water is supplied at the head of the system. These results clearly testify the disparity of canal water distribution along the system leading to reduced income and environmental degradation of the downstream water users.     

Origin and evolution of post-collisional volcanism: an example from Neoproterozoic Dokhan volcanics at Gabal Nugara area, Northeastern Desert, Egypt

Nugara volcanics are one of the northernmost outcrops of the Arabian?CNubian Shield. Two distinct volcanic successions are found in the Nugara basin: (1) old volcanic sequence composed of voluminous medium- to high-K calc-alkaline lavas and minor alkali basalt and (2) young volcanic sequence composed of subordinate tholeiitic mafic lavas. Their eruptions were punctuated by occasional volcaniclastic deposits that generated fall, flow, or reworked suites compositionally identical to the lava flows. These volcanics are a part of a post-subduction and extensional-related magmatic event in Northeastern Desert of Egypt. The volcanic rocks of the Nugara basin are characterized by strong enrichment in LILE relative to HESF, high LILE/HFSE ratios, and depletions of Nb on MORB-normalized multi-element diagrams. The geochemical features of the volcanic rocks suggest that they experienced fractional crystallization, along with mixing processes. Crustal contributions to the magma sources may also have occurred during magmatic evolution. These processes have resulted in scattered major and trace element variations with respect to increasing silica contents. The model proposed for their origin involves contrasting ascent paths and differentiation histories through crustal columns with different thermal and density gradients. The geochemical features of the most mafic samples suggest that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the East and West Gondwanaland. The volcanic activity in the region is best explained by the delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction-related processes.     

Grouting Rock Fractures with Cement Grout

The radial flow rate of a cement grout in a rock fracture is obtained from Bingham’s relation and the fact that the power expended by the injection mechanism is the energy dissipated by viscous effects. The energy balance reveals that the advance ratio is of fundamental importance in the grouting process and is inherently related to the rest and advance phases of a cement grout. This allows giving a precise definition of the zero flow path that divides the energy diagram into two distinct domains for advancing and non-advancing grout. The advance ratio and the zero flow path are used to explore the grouting of one or more fractures, analyze the GIN model in the context of the SL dispute, draw a terminal sequence considering the energy interval alternative, and reformulate the refusal criterion of the North American grouting method. Secondary grouting effects are also investigated.     

Strain analysis and microstructural evolution characteristic of neoproterozoic rocks associations of Wadi El Falek,centre Eastern Desert,Egypt

The estimation of finite strain in rocks is fundamental to a meaningful understanding of deformational processes and products on all scales from microscopic fabric development to regional structural analyses. The R_f/φ and Fry methods on feldspar porphyroclasts and mafic grains from 5 granite, 1 metavolcanic, 3 metasedimentary and 1 granodiorite samples were used in Wadi El Falek region. Finite-strain data shows that a high to moderate range of deformation of the granitic to metavolcano-sedimentary samples and axial ratios in the XZ section range from 1.60 to 4.10 for the R_f/φ method and from 2.80 to 4.90 for the Fry method. Furthermore, the short axes are subvertical associated with a subhorizontal foliation. We conclude that finite strain in the deformed granite rocks is of the same order of magnitude as that from metavolcano-sedimentary rocks. Furthermore, contacts formed during intrusion of plutons with some faults in the Wadi El Falek area under brittle to semi-ductile deformation conditions. In this case, finite strain accumulated during superimposed deformation on the already assembled nappe structure. It indicates that the nappe contacts formed during the accumulation of finite strain.     

Occurrence of Sn-Bearing colusite in the ore-body “T” of the Bor copper deposit, Serbia

The ore body “T” is the newly discovered massive-pyrite type one which is located in the central part of the Bor copper mine. The main copper minerals are chalcocite-digenite, covellite and enargite. Small amounts of colusite are frequently present in the ore-body. It mostly occurs as the distinct exsolutions in digenite and, associating with enargite and covellite. Composition of the studied colusite shows enriched Sn content, giving an empirical formula from Cu_24.7V_1.8Fe_0.2As_5.1Sb_0.2Sn_0.8S₃₂ to Cu_26.7V_2.0Fe_0.3A_s3.0Sb_0.3Sn_3.5S₃₂. This colusite represents a solid solution between colusite and nekrasovite within a range of 14–54 mol % nekrasovite. Most of the analyses show content of <50 mol % nekrasovite corresponding to the Sn-bearing colusite variety, while one analysis shows content of 54 mol % nekrasovite corresponding to the As-bearing nekrasovite.     

Coupes équilibrees crustales : méthodologie et application aux Alpes occidentales

Résumé

La construction de coupes équilibrées à l’échelle de la croûte ainsi que leur remise à l’état avant déformation suivent les règles générales de construction des coupes équilibrées (conservation des longueurs et des surfaces entre l’état avant déformation et l’état actuel), mais présentent des caractères qui leur sont propres (nécessité de connaître les mouvements verticaux importants qui accompagnent les déformations à cette échelle ainsi que le mode de déformation de la croûte).

Un exemple de construction de telles coupes est proposé pour les Alpes occidentales. Ces coupes, équilibrées pour le chevauchement crustal des massifs cristallins externes (Burdigalien-Actuel), traduisent un raccourcissement crustal variant de 10 km environ au niveau du Vercors à 55 km environ au niveau des Préalpes. Elles permettent d’intégrer dans un modèle unique un certain nombre de phénomènes comme le raccourcissement crustal, le raccourcissement dans la couverture, la subsidence du bassin molassique, la surrection des massifs cristallins externes, le rétrodéversement des structures en arrière de ces massifs.