The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

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Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.

     

Deforestation in the Buea-Limbe and Bertoua regions in southern Cameroon (1984–2000): modernization,world-systems,and neo-Malthusian outlook

This paper characterizes changes in land use and forest cover in southern Cameroon. In doing so, we use remotely sensed data to define the rates and area of forest loss and cover change in two reference areas over a period of 16 years (from 1984 to 2000)—the Buea-Limbe area in the southwest province and the Bertoua area in the east province. We relate socio-economic data of these study areas with results from the empirical spatial analysis to explain causes of deforestation. A second set of explanations, which we call the theoretical perspective, attributes deforestation in southern Cameroon to the intricacies of modernization, world-systems, and neo-Malthusian theories.     

(Re)constructing rural–urban spaces: gendered livelihoods,migration, and natural resources in South Africa

Critical approaches to development theory and practice provide alternative perspectives that focus on counterhegemonic and discursive dimensions of the development process. Feminist development is one such approach that opens up new spaces and opportunities to promote socially progressive and sustainable economic strategies. This paper uses feminist development geography as a framework to highlight the intersection of diverse spaces and economic strategies at the household and community levels. The analysis focuses on gendered livelihoods that are linked to circular migration and use of natural resources as a way to understand the integration of rural and urban spaces of development. The empirical section of this paper examines demographic patterns and socio-economic trends in Limpopo Province, South Africa as a context for the case study of two community-based women’s producer groups. These examples illustrate how economic strategies and social identities are embedded in and integrate both rural and urban spaces. This analysis contributes to feminist and post-structural development theory and practice by highlighting the potential for progressive forms of economic and social empowerment.     

Fe–Mg Interdiffusion in (Mg,Fe)O

We have performed a series of interdiffusion experiments on magnesiowüstite samples at room pressure, temperatures from 1,320° to 1,400°C, and oxygen fugacities from 10^?1.0 Pa to 10^?4.3 Pa, using mixed CO/CO₂ or H₂/CO₂ gases. The interdiffusion couples were composed of a single-crystal of MgO lightly pressed against a single-crystal of (Mg_1-x Fe _x )_1-δO with 0.07<x<0.27. The interdiffusion coefficient was calculated using the Boltzmann–Matano analysis as a function of iron content, oxygen fugacity, temperature, and water fugacity. For the entire range of conditions tested and for compositions with 0.01<x<0.27, the interdiffusion coefficient varies as $$\tilde D\, =\,2.9\times10^{ - 6}\,f_{{\text{O}}_2 }^{0.19}\,x^{0.73}\,{\text{e}}^{ - (209,000\, -\,96,000\,x)/RT}\,\,{\text{m}}^{\text{2}} {\text{s}}^{ -1} $$ These dependencies on oxygen fugacity and composition are reasonably consistent with interdiffusion mediated by unassociated cation vacancies. For the limited range of water activity that could be investigated using mixed gases at room pressure, no effect of water on interdiffusion could be observed. The dependence of the interdiffusion coefficient on iron content decreased with increasing iron concentration at constant oxygen fugacity and temperature. There is a close agreement between our activation energy for interdiffusion extrapolated to zero iron content (x=0) and that of previous researchers who used electrical conductivity experiments to determine vacancy diffusivities in lightly doped MgO.     

Paleo water–rock interaction determined through isotopic tracing (Sr,O, C,U) in fracture-fill minerals: Evidence from the Vienne granitoids (France)

Based on the concepts (a) that the stable C and O isotopes combined with the Sr isotope ratios of fracture fills should reflect the source groundwater from which the solid phases precipitated and (b) that U-series disequilibria (USD) enable the calculation of residence time for the U by using Fe oxides as the best candidate, an “isotopic toolbox” was applied to fracture fill from the crystalline basement of the Vienne district. The fracture fills are formed mainly of carbonates, clays and Fe oxides. The isotope data indicate two main generations of carbonate that originated from hydrothermal circulation and equilibrium with present-day groundwaters but the Sr isotope ratios highlight another component with a higher ⁸⁷Sr/⁸⁶Sr ratio reflecting the complexity of the water–rock interactions.For the USD, the Fe-hydroxides located at 207 m depth yield an age of 102 ± 5 ka (St. Germain I interglacial stage), whereas those located at 277 m and 300 m yield respective ages of 173 ± 15 ka and 181 ± 10 ka. These corresponding to the transition between the penultimate glacial period (isotopic stage 6) and the end of the preceding interglacial stage (isotopic sub-stage 7a). Investigating water–rock interaction (⁸⁷Sr/⁸⁶Sr, ¹⁸O, ¹³C, USD) in the fracture-fill minerals from the crystalline basement has shown that such an approach is relevant to developing an understanding of how the groundwater system has changed over time.     

Reply to Comment on “Hydrodynamics of karst aquifers in metamorphic carbonate rocks: results from spring monitoring in the Apuan Alps (Tuscany,Italy)”: report published in Hydrogeology Journal (2023) 31:241–255, by Leonardo Piccini,Alessia Nannoni,and Emilio Poggetti

Hydrogeology Journal -     

Loess in Britain and Ireland: Formation,modification and environmental significance,a review in memory of John Catt (1937–2017)

Loess was first identified in England as early as the mid-19th century, although these deposits were later mapped as ‘brickearth’ or ‘head-brickearth’ by the British Geological Survey. Much of this material was subsequently recognised and named as loess again by soil scientists, most notably by J.A. Catt. The early reports of loess were mostly located in southeast England, however, more recently loessic deposits have also been reported from the north of England, possibly in Scotland, and as far west as western Ireland. Catt also appreciated that these deposits are the western limits of a broad cover of loess stretching across Eurasia. Here, contrasting models for the possible origin, transport pathways and reworking of these deposits are presented. While some of these British deposits are primary in situ loess, a range of processes has likely affected many of them, including periglaciation, Holocene climatic, and human impacts. Luminescence dating has confirmed British loess to be primarily of late Pleistocene age, however, examples of older loess are also reviewed. Deposits in southeast England are the thickest and best expressed today, and these have yielded significant insight into both the mechanism of the hydroconsolidation (collapse) of loess and landscape evolution in northwest Europe during the Last Glacial Period. The thin and regional nature of British and Irish loess may make it an excellent material for studying loess formation, with advantages over the thicker deposits of typical loess of central Europe, where the impact of smaller scale landscape processes may be less obvious.     

Water soluble components of PM_(10) in Chongqing, China

1Introduction Particleswithanaerodynamicdiameterof< 10μmarerecognizedasinhalabaleparticlesandhave beenfoundtobewidelyassociatedwithhealthprob lems(Chapmanetal.,1997).Theywouldalsoinflu enceclimateandvisibilitythroughanumberofimpor tantatmosphericprocesses(Horvath,1993). Rapiddevelopmentofurbanconstructionandrap idgrowthofpopulationhaveexacerbatedChongqing’s pollution.Althoughsulfurdioxidehasbeenreducedby morethan60%incontrasttothevaluein1991,the concentrationsofparticulatematterarestil…     

Flexible–inflexible: socio-demographic,spatial and temporal dimensions of flat sharing in Leipzig (Germany)

Flat sharers are one of the most distinct representatives of the ‘new’ household types, but have received only very limited attention from researchers. Back in the 1960s shared flats were usually founded with a strong ideological impetus, whereas flat sharing nowadays is just one household type among many others. Typically, this housing arrangement consists of at least two young adult individuals without children. Sharing the flat and the housing costs is the basis of their relationship but living with others is an additional motive. As a rule, flat sharing bridges two distinct events in the course of one’s life: the leaving of the parental home and the foundation of the first independent household. Thus for a restricted period in time, it is a flexible household type adapted to the situational needs of its members. Germany has one of the strongest and longest traditions of flat sharing in Europe, especially among university students. An explorative study was conducted in Leipzig to come to a deeper understanding of what flat sharing means in its ambivalence of being both an economic unit and a social arrangement. Based on qualitative and quantitative evidence from group discussions and Internet adverts, we shed light on the highly under-researched social practice of flat sharing. We will show that despite the structural flexibility of this household type, there is also evidence for its socio-demographic selectivity, spatial concentration and temporal limitation over the individual life courses.     

Timimoun’s foggara (Algeria): an heritage in danger

Timimoun is located in the hyper-arid zone of the Sahara, with an annual rainfall not exceeding 100 mm/year. To fill the shortage of rainfall, the oasis has developed a traditional means for mobilization of the groundwater. In the foggara with this hydraulic system, oases have been developed throughout the region of Timimoun over ten centuries. Today, we witness the gradual disappearance of foggaras; we lose about one to two foggaras per year for over half a century. The discharge of the 250 functional foggaras shows a significant drop: 850 l/s in 1960 and 355 l/s in 2001, enough to irrigate 350 ha. The causes of declining foggaras are technical, social, and environmental. The surveys that we have led nearly with the population in the ksour during two missions in 2007 and 2008 in the oasis of Timimoun reveal that socio-economic problems (Heritage and depopulation) are common to both types of foggara (foggara of the Erg and foggara Albian). Environmental problems (silting and flooding of the galleries by wild plants) are the main causes of the disappearance of foggaras of Erg. Technical problems (collapse of tunnels) are mainly the causes of degradation to Albian’s foggaras. Attempts to introduce changes to foggaras are temporary solutions. The modern collection of water (pump and drilling) is gradually replacing the traditional hydraulic system.     

Quaternary bimodal volcanism in the Niğde Volcanic Complex (Cappadocia,central Anatolia,Turkey): age,petrogenesis and geodynamic implications

The late Neogene to Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia is one of the most impressive volcanic fields of Turkey because of its extent and spectacular erosionally sculptured landscape. The late Neogene evolution of the CVP started with the eruption of extensive andesitic-dacitic lavas and ignimbrites with minor basaltic lavas. This stage was followed by Quaternary bimodal volcanism. Here, we present geochemical, isotopic (Sr–Nd–Pb and δ¹⁸O isotopes) and geochronological (U–Pb zircon and Ar–Ar amphibole and whole-rock ages) data for bimodal volcanic rocks of the Ni?de Volcanic Complex (NVC) in the western part of the CVP to determine mantle melting dynamics and magmatic processes within the overlying continental crust during the Quaternary. Geochronological data suggest that the bimodal volcanic activity in the study area occurred between ca. 1.1 and ca. 0.2 Ma (Pleistocene) and comprises (1) mafic lavas consisting of basalts, trachybasalts, basaltic andesites and scoria lapilli fallout deposits with mainly basaltic composition, (2) felsic lavas consisting of mostly rhyolites and pumice lapilli fall-out and surge deposits with dacitic to rhyolitic composition. The most mafic sample is basalt from a monogenetic cone, which is characterized by ⁸⁷Sr/⁸⁶Sr = 0.7038, ¹⁴³Nd/¹⁴⁴Nd = 0.5128, ²⁰⁶Pb/²⁰⁴Pb = 18.80, ²⁰⁷Pb/²⁰⁴Pb = 15.60 and ²⁰⁸Pb/²⁰⁴Pb = 38.68, suggesting a moderately depleted signature of the mantle source. Felsic volcanic rocks define a narrow range of ¹⁴³Nd/¹⁴⁴Nd isotope ratios (0.5126–0.5128) and are homogeneous in Pb isotope composition (²⁰⁶Pb/²⁰⁴Pb = 18.84–18.87, ²⁰⁷Pb/²⁰⁴Pb = 15.64–15.67 and ²⁰⁸Pb/²⁰⁴Pb = 38.93–38.99). ⁸⁷Sr/⁸⁶Sr isotopic compositions of mafic (0.7038–0.7053) and felsic (0.7040–0.7052) samples are similar, reflecting a common mantle source. The felsic rocks have relatively low zircon δ¹⁸O values (5.6 ± 0.6 ‰) overlapping mantle values (5.3 ± 0.3 %), consistent with an origin by fractional crystallization from a mafic melt with very minor continental crustal contamination. The geochronological and geochemical data suggest that mafic and felsic volcanic rocks of the NVC are genetically closely related to each other. Mafic rocks show a positive trend between ⁸⁷Sr/⁸⁶Sr and Th, suggesting simultaneous assimilation and fractional crystallization, whereas the felsic rocks are characterized by a flat or slightly negative variation. High ⁸⁷Sr/⁸⁶Sr gneisses are a potential crustal contaminant of the mafic magmas, but the comparatively low and invariant ⁸⁷Sr/⁸⁶Sr in the felsic volcanics suggests that these evolved dominantly by fractional crystallization. Mantle-derived basaltic melts, which experienced low degree of crustal assimilation, are proposed to be the parent melt of the felsic volcanics. Geochronological and geochemical results combined with regional geological and geophysical data suggest that bimodal volcanism of the NVC and the CVP, in general, developed in a post-collisional extensional tectonic regime that is caused by ascending asthenosphere, which played a key role during magma genesis.     

Rare earth elements (REE)—Minerals in the Silius fluorite vein system (Sardinia,Italy)

The Silius vein system, located in SE Sardinia (Italy) is analogous to other late- to post-Hercynian mineral systems of this type in Europe. The Silius system consists of two main veins, characterized by several generations of fluorite, calcite and quartz, with initial ribbon-like geometries, followed by breccias and cockade-like textures. In this study, aimed at investigating the REE concentrations in the Silius vein system, a REE average of ~ 800 ppm (locally ΣREE > 1500 ppm) has been observed in the carbonate gangue of the fluorite orebody. These amounts are related to the presence of the REE-bearing minerals synchysite-(Ce) and xenotime-(Y). The chemical composition of synchysite-(Ce) has been obtained by wavelength dispersive spectrometry (WDS). The average synchysite-(Ce) formula, built on the basis of (CO₃)₂F and 5 negative charges, is Ca_1.07(La_0.19,Ce_0.36,Pr_0.04,Nd_0.15,Sm_0.03,Gd_0.03,Y_0.13)(CO₃)₂F. From their geochemical characteristics, and their textural relationships with other gangue phases, it is likely that synchysite-(Ce) and xenotime-(Y) formed at the same P-T-X conditions as the other minerals of the Silius fluorite mineralization. Synchysite-(Ce) and xenotime-(Y) at Silius could be related to a local circulation phenomenon, where the REE are derived from a REE-bearing source rock in the basement of southeastern Sardinia, which has been leached by the same fluids precipitating the fluorite/calcite mineralization. REE concentrations contained in the carbonate gangue of still unexploited parts of the Silius vein deposit, as well as in dumps and tailings accumulated during past fluorite processing, could possibly represent a sub-economic by-product of the fluorite exploitation.     

Mercury in the Tinto-Odiel Estuarine System (Gulf of Cádiz, Spain): Sources and Dispersion

The Tinto and Odiel are small rivers draining one of the largest sulphide deposits in the world. As a result of these deposits and a large industrial complex, the adjacent marine area receives a high amount of metal input. Mercury distribution in the Tinto-Odiel estuary, the Huelva Ría and the Gulf of Cádiz was assessed in water and suspended particulatematter (SPM) and sediments. In the rivers and estuaries, dissolved (HgD)and particulate (HgP) mercury showed wide variations (13 to 200 pM and0.3 to 330 nmol g^-1 respectively) depending on the presence or notof sulphidic waters, phosphogypsum deposits, detrital pyrite and oxyhydroxides.In the Ría, concentrations were lower than 10 pM and 4.5 nmol g^-1 for HgD and HgP respectively. In surface waters of the Gulf of Cádiz, the average HgD concentration (pm standard deviation) was 2.9 pm 0.9 pM, which is similar to that of North Atlantic Central Waters. The surface sediments collected in the rivers, the Ría and the Gulf showed systematically enriched mercury compared to pre-industrial levels. Vertical mercury profiles in dated sediment cores were typical of anthropogenically influenced environments starting in the early Roman age. These distribution features suggest that most of the Hg discharged by the Huelva Ría is trapped in the sediments of the Gulf of Cádiz.     

Hydrogen bonding in goldichite,KFe(SO4)2⋅4H2O: structure refinement

Mineralogy and Petrology - The crystal structure of goldichite KFe(SO4)2⋅4H2O was determined on a single crystal from the Baiyinchang copper deposit, Gansu, China. [P121/c1, a = 10.395(2), b...     

Abtragung,Transport und Sedimentation in der östlichen Beltsee (Ostsee)

Ohne ZusammenfassungEine ausführliche Darstellung erscheint in Die Küste, Bd. 3, 1955.     

Dynamic compaction evaluation using in situ tests in Sagunto’s Harbor,Valencia (Spain)

This paper presents an assessment on the use of dynamic compaction as a ground improvement technique in a port’s hydraulic fill in the new southern dock of Sagunto’s Harbor near Valencia (Spain). Soil behavior improvement was monitored by several in situ techniques such as boreholes with SPTs, DPSH, CPTU and CSWS geophysical tests. A total energy between 2188 and 3125 kN/m² (depending the area) was applied to the hydraulic fill by the dynamic compaction procedure. In situ techniques led to evaluate dynamic compaction efficiency, as well as controlling ground modifications that might cause potential damages to adjacent buildings. The dynamic compaction carried out was capable of fulfilling requirements established to use the area, that is, an average deformability modulus (E′) of 30 MPa with a minimum of 20 MPa, in a depth of 10 m. Moreover, dynamic compaction increased hydraulic fill relative density by about 75%.     

Coping with uncertainty: Neolithic life in the Dhar Tichitt-Walata,Mauritania, (ca. 4000–2300 BP)

The sandstone escarpment of the Dhar Tichitt in South-Central Mauritania was inhabited by Neolithic agropastoral communities for approximately one and half millennium during the Late Holocene, from ca. 4000 to 2300 BP. The absence of prior evidence of human settlement points to the influx of mobile herders moving away from the “drying” Sahara towards more humid lower latitudes. These herders took advantage of the peculiarities of the local geology and environment and succeeded in domesticating bulrush millet – Pennisetum sp. The emerging agropastoral subsistence complex had conflicting and/or complementary requirements depending on circumstances. In the long run, the social adjustment to the new subsistence complex, shifting site location strategies, nested settlement patterns and the rise of more encompassing polities appear to have been used to cope with climatic hazards in this relatively circumscribed area. An intense arid spell in the middle of the first millennium BC triggered the collapse of the whole Neolithic agropastoral system and the abandonment of the areas. These regions, resettled by sparse oasis-dwellers populations and iron-using communities starting from the first half of the first millennium AD, became part of the famous Ghana “empire”, the earliest state in West African history.