Induced recharge at new dam sites—Sana’a Basin, Yemen

In approaching the task of developing recharge estimates for dam sites, several constraints are apparent, including the scarcity of site-specific data for the selected new sites and the availability of simple yet robust analysis techniques. Combined, these constraints require an approach which involves best use of available data, adoption of relatively simple analytical approximations of reality, and the adoption of several key assumptions. In arid country with limited resources, two simple techniques have been used for recharge estimation: (1) a simple water balance model in spreadsheet and (2) a more refined Darcian approach involving an analytical approximation of a flow-net solution. By applying the two models at three new dam sites, the amount of recharge rates calculated over the period 2007–2026 was close. This is because, despite Darcian approach that should have affected the recharge rate as other parameters were introduced in the calculation of q _t , e.g., groundwater table mound, reservoir water height, etc., the results show general agreement between the two methods which seem to validate the assumptions made in both methods. A general conclusion of this comparison is that the hydraulic conductivity (K) is the main determining factor in recharge calculations in these situations. The water balance model was used to estimate recharge at Wadi Bahaman, under gravity and cascade dams’ scenarios. Using gravity dam at Wadi Bahaman for groundwater recharge proved not suitable based on the relatively small predicted runoff from a small catchment area and geological concerns in the abutment areas. Instead, a series of three low check dams (2 to 4 m high) was proposed. These check dams will slow down the runoff flow, form small reservoirs, and enhance recharge along the valley, without requiring expensive foundations. Estimated groundwater recharge under cascade dams (141,407 m³/year) is greater than recharge estimated for gravity dam (103,853 m³/year) by at least 36%.     

A new exposure of Quaternary deposits at Poets’ Corner Yard,Westminster Abbey,Central London

Work prior to the construction of a tower for access to the triforium, Westminster Abbey, provided temporary exposures of Quaternary deposits. Two units were seen: the Shepperton Gravel Member, and overlying Poets’ Corner Sand (new name). Distinctive features of the Poets’ Corner Sand are described. The age of the base of the Poets’ Corner Sand by optical dating is 15 000?±?1000?years BP. The foundations of the Abbey are briefly described.     

Butchulla perspectives on dingo displacement and agency at K’gari-Fraser Island,Australia

There is a complex geography to Aboriginal-dingo-settler-dog relationships in Australia. This paper examines aspects of that geography in a world heritage area, heavily contested by multiple stakeholders for whom the dingo has come to represent resource and identity, as well as a powerful symbol of nature. The Butchulla people were recently recognised in Australian law as holding native title to world-heritage listed K’gari-Fraser Island, a decision that confers recognition and consultation rights; however, genuine ownership and control of the island is denied through a lack of joint management of the island. This paper reviews evidence from some Butchulla people who declare their ongoing dispossession through various discourses and actions that attempt to circumvent extinguishment of their title to territory. They implied that dingoes have equally endured dispossession and extinguishment of territory through common colonial discourses that subjugate the ‘other’, albeit Butchulla people and dingoes have different forms of resistance and agency. Butchulla people in our study parallel their treatment under colonial structures of governance with those of the dingo in that both have endured limited freedom of movement and expressions of sovereignty. We argue some Butchulla people liken notions of dingo agency and resistance with their own attempts to assert sovereignty and responses to displacement. Aligning with the dingo (and broader discourses and politics that surround the dingo) may afford Butchulla people a greater entitlement to be a major voice in dingo 'management' specifically, and management of the island more broadly, than their native title resolution confers.     

Peculiarities of ore formation at the N’yavlenga Au-Ag epithermal deposit,Northeast Russia

Thermobarogeochemical studies have revealed the relatively high-temperature ore-bearing fluid of the N’yavlenga deposit. The dependence between the homogenization temperatures of the fluid inclusions and salinity of the fluid and the bimodal distribution of salinity values indicates mixing of two different fluids in the ore-bearing system. These facts are related to the thermal metamorphism of ores from the N’yavlenga deposit and indicate the complex relations of the early Au-Ag epithermal and late Au-Cu-Mo porphyry mineral complexes in orebodies of the deposit.     

Age stages of metamorphism at the Kitoi Sillimanite schist deposit, southeastern Prisayan’e

The Irkut Block with dominant rocks of the Sharyzhalgai Series and Kitoi Block with prevalence of the Kitoi Series rocks are the main structures of the Presayanian basement elevation of the Siberian Craton. Two stages of metamorphism, Neoarchean (2.6–2.7 Ga) and Paleoproterozoic (1.85–1.87 Ga), were established for the granulitic complexes of these blocks. The rocks of the Kitoi sillimanite schist deposit composed of sillimanite, andalusite-sillimanite, and garnet-sillimanite schists and gneisses underwent by intense ultrametamorphic transformations which led to the formation of sillimanite- and garnet-bearing plagioclase and feldspar migmatites, and also granites, sienites, and granite-pegmatites. The geochronological study of melanocratic schists and leucocratic plagiogneisses-the typical rocks of the Kitoi deposit-showed the manifestation of metamorphism only at the Archean and Proterozoic boundary (2450–2550 Ma).     

The Fugløy Reef at 70°N; acoustic signature,geologic, geomorphologic and oceanographic setting

This is the first in-depth study of a cluster of cold-water coral reefs, the Fugløy Reefs, found at 70°N on the Norwegian margin. Combining high-resolution seismic reflection data, side-scan sonar, video-images, and oceanographic measurements reveals the geologic, geomorphologic and oceanographic setting in which the reefs occur. The reefs consist mainly of the scleractinian ahermatypic Lophelia pertusa, and exist below the thermocline at water depths between 140  m and 190 m. The reefs appear as cone-shaped, acoustically transparent features on seismic reflection data, consistently located in places characterized by the availability of hard substrate, high relief, and periodical exposure to high tidal currents (>30 cm/s). These currents transport water of the Norwegian Atlantic Current to the reefs from an area with fluid expulsion-related pockmarks. The spatial relationship between reef, pockmark locations, and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth. With a height of more than 40 m some of the Fugløy reefs are among the highest reported from the Norwegian Margin. This indicates highly favourable growth conditions, and conservative estimates indicate a net growth rate for the reefs of ~5 mm/year. We expect that cold-water reefs will be found further north along the Barents Sea margin as general awareness on the geophysical signature and appearance of the reefs increases, because all known factors involved in reef establishment and growth are within the required intervals also further north.     

Anticlockwise metamorphic paths at ca. 890–790 Ma from the NE Baidrag block,Mongolia, indicate back-arc compression at the Rodinia periphery

The processes leading to the assembly of the Rodinia supercontinent through Grenvillian collisional orogeny are relatively well known. In contrast, accretionary orogenic processes occurring at the supercontinent periphery following Rodinia assembly are poorly understood. To fill this gap, we have identified metamorphic rocks in the Mongolia collage of the Central Asian Orogenic Belt, where numerous data testify for Meso- to Neoproterozoic magmatic reworking. The tectono-metamorphic evolution of the peri-Siberian tract of the Central Asian Orogenic Belt is mainly characterized by the late Proterozoic–early Cambrian (Baikalian) cycle. However, we document here a Tonian age metamorphism at the northern part of the Precambrian Baidrag block, previously considered as a typical example of the Baikalian metamorphic belt. This study incorporates zircon and in-situ monazite geochronology linked to P-T modelling of Grt-Sil-Ky migmatite gneiss and Grt-St micaschist. Grt-Sil-Ky gneiss records initial burial to the sillimanite stability field at ～720 °C and 6.0 kbar followed by further burial to the kyanite stability field at ～750 °C and ～9 kbar and decompression to ～650 °C and ～8 kbar. The Grt-St schist records initial burial to the staurolite stability field at ～620 °C and 6 kbar, followed by further burial to ～590 °C and 8.5 kbar. The monazite data yield a continuum of ²⁰⁷Pb-corrected ²³⁸U/²⁰⁶Pb dates of ca. 926–768 Ma in the Grt-Sil-Ky gneiss, and ca. 937–754 Ma in the Grt-St schist. Based on monazite textural positon, internal zoning, and REE patterns, the time of prograde burial to 6.0 kbar under a thermal gradient of 27–32 °C/km is estimated at ca. 890–853 Ma. It is not clear whether such high-grade conditions prevailed until a phase of further burial under a geothermal gradient of 18–22 °C/km dated at ca. 835–815 Ma. The late monazite recrystallization at ca. 790 Ma is related to decompression. Additionally, monazite with dates of ca. 568–515 Ma occur as whole grains or as rims with sharp boundaries on Tonian monazite in Grt-St schist suggesting a minor Baikalian overprint. Metamorphic zircon rims with Th/U ratios of ～ 0.01–0.06 in Grt-Sil-Ky gneiss with 877 ± 7 Ma age, together with lower intercepts of detrital zircon discordia lines in both Grt-Sil-Ky gneiss and Grt-St schist further support the Tonian age of high-grade metamorphism. The anticlockwise P-T evolution is interpreted as a result of thickening of a supra-subduction extensional and hot edifice – probably of back-arc or arc type. This kind of prograde metamorphism has so far only been described on the northern part of the Tarim block and was interpreted to be a result of initiation of peri-Rodinian subduction of the Mirovoi Ocean. The geodynamic consequences of a unique discovery of Tonian metamorphism are discussed in terms of tectonic switch related to initiation of peri-Rodinian oceanic subduction during supercontinent assembly, followed by strong mechanical coupling potentially related to onset of Rodinia dispersal.     

New Data of Phosphatized Acritarchs from the Ediacaran Doushantuo Formation at Weng’an, Guizhou Province, Southwest China

1 Introduction The Ediacaran Doushantuo Formation at Weng’an, Guizhou Province, southwest China is famous for the well-preserved phosphatized Weng’an biota, including algae, large spinous acritarchs, filaceous and spherical Cyanobacteria, microtubular cnidarian, dubious sponges, resting eggs and embryos of animals, etc. Chen and Liu (1986) first reported a few phosphatized globular fossils and large spinous acritarchs after acetic acid maceration of the deposit. Since then, the phosphat…     

Griesbachian Cyclostratigraphy at MajiashanSection, Anhui Province, China

INTRODUCTIONAs a large regression continued over the world at the endof the Paleozoic, a new remarkable transgression was intrudinginto the Lower Yangtze located in the eastern Tethys duringthe Late Permian, resulting in many excellent continuous marine Permian-Triassic sequences in this region. But the middleTriassic indosinian movement transformed this region from marine to continental factes, resulting in the deposition of theLower Triassic in the marked regression setting prior to …     

Influence of temperature,composition, silica activity and oxygen fugacity on the H<Subscript>2</Subscript>O storage capacity of olivine at 8 GPa

Olivine crystals were grown in the presence of a hydrous silicate fluid during multi-anvil experiments at 8 GPa and 1,000–1,600°C. Experiments were conducted both in a simple system (FeO–MgO–SiO₂–H₂O) and in a more complex system containing additional elements (CaO–Na₂O–Al₂O₃–Cr₂O₃–TiO₂–FeO–MgO–SiO₂–H₂O). Silica activity was buffered by the presence of either pyroxene (high a _SiO2) or ferropericlase (low a _SiO2), and was buffered by the presence of Ni + NiO or Fe + FeO, or constrained by the presence of Fe₂O₃. Raman spectroscopy was used to identify pyroxene polymorphs in the run products. Clinoenstatite was present in the 1,000°C experiment, and enstatite in experiments at 1,400–1,520°C. The H₂O content of olivine was measured using secondary ion mass spectroscopy, and infrared spectroscopy was used to investigate the nature of hydrous defects. The H₂O storage capacity of olivine decreases with increasing temperature at 8 GPa. In contrast to previous experimental results at ≤2 GPa, no significant effect of varying oxygen fugacity is evident, but H₂O storage capacity is enhanced under conditions of low silica activity. No significant growth of low wavenumber (<3,400 cm⁻¹) peaks, generally associated with high at low pressure, was observed in the FTIR spectra of olivine from the high experiments. Our experiments show that previous high pressure H₂O storage capacity measurements for olivine synthesized under more oxidizing conditions than the Earth’s mantle are not likely to be compromised by the of the experiments. However, the considerable effect of temperature on H₂O storage capacity in olivine must be taken into account to avoid overestimation of the bulk upper mantle H₂O storage capacity.     

Solubility of columbite, (Mn,Fe)(Nb,Ta)<Subscript>2</Subscript>O<Subscript>6</Subscript>, in granitoid and alkaline melts at 650–850°C and 30–400 MPa: An experimental investigation

This paper reports experimental data on columbite solubility in model water-saturated Li- and F-rich silicic melts with different contents of alumina and alkalis. It was found that the columbite solubility is strongly affected by melt composition and is maximal in peralkaline melt. The maximum contents of Ta and Nb in subaluminous and peraluminous melts at the contact with columbite are lower by at least an order of magnitude. The peralkaline melt is relatively enriched in Nb, and the peraluminous melt is enriched in Ta. The temperature dependence of solubility is positive but less pronounced than the effect of melt composition. It is most distinct in the subaluminous melts. The Nb/Ta ratio of melt usually decreases with decreasing temperature. The effect of pressure is relatively small. It was shown that columbite cannot crystallize on the liquidus of both peralkaline and peraluminous magmas. Perhaps, columbite crystallization from a melt is possible only at final near-solidus stages at the high degrees of crystallization of strongly evolved low-temperature melts.     

‘Nation-states’, ‘quasi-states’, and ‘collapsed-states’ in contemporary Africa

The revival of ethnic identities and the search for historical roots have been significant factors in re-shaping the map of the world in the late twentieth century. Multi-ethnic states have come under increasing strain throughout the century and undermining the concept of the nation-state. However, the successor states to the colonial empires in Africa exhibit the same strains as the often highly fragile successors to the European continental empires earlier in the century. The survival of these quasi-states has been dependent upon the support of the international community for over thirty years as a reaction to the era of colonialism. Anti-colonialism offers little practical support for states in a post-colonial, post-Cold War era. In some cases the result has been disintegration and the emergence of the collapsed state. The revived political movements aimed at democratisation and self-determination have unleashed forces which may be incompatible with the survival of the current state system.     

Secondary quartzites and their relation to gold mineralization at the Svetloe deposit, Ul’ya Trough, Okhotsk-Chukotka volcanic belt

Hydrothermally altered rocks and their relation to gold mineralization at the Svetloe deposit in the Ul’ya Trough, western sector of the Okhotsk-Chukotka volcanic belt, are studied. The rock composition and style of mineralization are typical of acid-sulfate type deposits. The hydrothermally altered rocks of the deposit are medium-temperature secondary quartzites with developed alunite facies. The upper structural level in the massif of secondary quartzites is made up of a sheetlike body 30 km² in area and up to 300 m thick with gentle (5–10°) periclinal bedding relative to the arcuate axis of the volcanic range. Below the sheet, there are a number of local steep mostly carinate zones and small (a few hundreds of square meters) multilayered trough-shaped structures, the foot of which is located 100–150 m under the secondary quartzite sheet. All structures of the lower level are restricted to the volcanic range pericline, marked by elevated thicknesses of monoquartzites, and have a gradual transition to the sheetlike part of the massif. The massif of secondary quartzites shows symmetrical zoning. The central zone of the sheetlike body is composed of alunite quartzites framed by dickite varieties. Down the section, the latter grade into hydromica and hydromica-montmorillonite argillic rocks. Monoquartzites form axial zones in the structures of the lower level. In the blanketlike part of the deposit, monoquartzites occur as rare thin lenses and interlayers spatially related to local structures of the lower level. Gold mineralization at the deposit associates with porous monoquartzites. Gold precipitated after quartzite formation during infilling of pores and cavities with colloform silica with barite, and hypogene jarosite.     

The influence of the Jahn–Teller effect at Fe<Superscript>2+</Superscript> on the structure of chromite at high pressure

The crystal structure of chromite FeCr₂O₄ was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch–Murnaghan equation of state (EoS) based on the P–V data gives: K ₀ = 209 (13) GPa, K′ = 4.0 (fixed), and V ₀ = 588 (1) ų. The FeO₄ tetrahedra and CrO₆ octahedra are compressed isotropically with pressure with their Fe–O and Cr–O bond distances decreasing from 1.996 (6) to 1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe²⁺ cation is more compressible than the octahedral site occupied by the Cr³⁺ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K ₀ = 147 (9) GPa, K′ = 4.0 (fixed), V ₀ = 4.07 (1) ų and K ₀ = 275 (24) GPa, K′ = 4.0 (fixed), V ₀ = 10.42 (2) ų, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd-[`3]{\overline{3}} m) to a tetragonal structure (space group I4₁ /amd). At the phase transition boundary, the two Cr–O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr–O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5° to 106.6 (7)°, which generates a “stretched” tetrahedral geometry. It is proposed that the Jahn–Teller effect at the tetrahedrally coordinated Fe²⁺ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn–Teller effect observed in this structure and its role in the pressure-induced phase transition.     

Metallurgy at the Crossroads: New Analyses of Copper-based Objects at Tianshanbeilu, Eastern Xinjiang, China

Tianshanbeilu is the largest Bronze Age site in eastern Xinjiang, China. Stretching across the entire second millennium BC, it performed a prominent role in connecting the Hexi corridor, Central China and the steppe. A further insight into the metallurgical tradition and the metal supply network is of vital importance to improve our understanding of its multi-connected nature. This paper offers a new set of chemical and isotopic data on the copper-based objects at Tianshanbeilu, including alloying elements, trace elements (impurities) and lead isotopes. Combining the concentrations of arsenic and antimony reveals that arsenic was introduced to copper partially due to the use of specific minerals tethrahedrite-tennantite. Lead isotopes demonstrate that multiple sources of copper were employed at Tianshanbeilu and a majority of them are characterized by common lead, which appears rather different from those of the Central Plains and the Hexi corridor, but highly consistent with local ores. Surprisingly, one object at Tianshanbeilu contains the well-known highly radiogenic lead. This object undoubtedly marks the westernmost boundary of the distribution of the highly radiogenic lead. We also anticipate that more lead isotopic analyses in NW China will further contribute to the study of the highly radiogenic lead in Central China.     

Mineral Components, Texture, and Forming Conditions of Hydrothermal Chimney on the East Pacific Rise at 9°-10°N

To characterize the hydrothermal processes of East Pacific rise at 9°-10°N, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope,scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely：（i） anhydrite ＋ marcasite ＋ pyrite, （ii） pyrite ＋ sphalerite ＋ chalcopyrite, and （iii） chalcopyrite ＋ bornite ＋ digenite ＋ covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.     

The first finding of explosive alkaline picrites at Nadan’hada-Alin’ (China)

During joint Russian-Chinese investigations of contiguous territories in the Nadan’khada mountain range (China), explosive micaceous picrites earlier unknown here but widespread in adjacent regions of Primor’e, where small diamonds were found in them, were discovered. The described picrites are attributed to the Yurassic alkaline-ultrabasic volcano-plutonic formation consisting of alkaline basalts, meimechites, and concentric zoned sienite-peridotite intrusions. The discovered body (m-6m) is a diatreme, which was proved by ultrabasic inclusions and original (symplektitic) forms of chrome spinel disaggregations in them. As well as in Primor’e, the body is localized in Jurassic picrite-basalts in framing of large gabbro-peridotite in Zhaokheiskii massif. The rock is composed of large (up to 2 cm) megacrystals of kaersutite and titanphlogopite, sunk into a fine mass of microlites of the same minerals and ilmenite cemented by calcite. Grains of kaersutite have zoning with enrichment of the rims with Mg and Ti and depletion with K. Calcite is of two generations: (a) the initial magmatic in the main mass, enriched with Sr, and (b) the secondary, intersecting all the above-mentioned minerals and containing only insignificant additions of Mn. Phlogopite loses Ti (from 6 to 2% TiO₂) at the contact with this calcite. However, K-kaersutite transfers into glaucophane (up to 7% Na₂O) at the contact with magmatic calcite. Spinel can be found only in ultrabasic inclusions replaced by talc. In the core of the grains it is moderately chromous (39.45% Cr₂O₃), on the rims it is replaced by titanous-manganous-flinty (up to 2% SiO₂) ferrochromite. Ilmenite is highly manganous and does not contain Mg and Cr. Enrichment by both siderophile and lithophile microelements is characteristic of the entire rock. The examined picrites are fluidized explosive apophysis of large alkaline-ultrabasic intrusions in fact and deserve more detailed investigation because of small diamond findings in them.