Central Andean magmatism can be constrained by three ubiquitous end‐members

The geochemical character of primary magmas and the nature of crustal melts remain poorly constrained at the active continental margin of the Central Andes, where the crustal thickness is >70 km. We identify three end‐members and constrain their full major and trace element compositions by polytopic vector analysis (PVA). The end‐members include two mafic parent magmas: (1) a slightly evolved calcalkaline basaltic andesite derived from the fluid‐fluxed mantle wedge that is typical of the Andes in general and (2) a strongly LREE‐enriched basalt akin in its trace element pattern to back‐arc shoshonites. (3) The third end‐member is a variably HREE‐depleted rhyodacite representing partial melts of lower to middle crustal lithologies. We propose that these end‐members are ubiquitous and typical of such thick‐crust settings, and can explain – in highly variable mixing proportions – the entire compositional range of Central Andean magmatism.     

Expected changes in agroclimatic conditions in Central Europe

During the past few decades, the basic assumption of agroclimatic zoning, i.e., that agroclimatic conditions remain relatively stable, has been shattered by ongoing climate change. The first aim of this study was to develop a tool that would allow for effective analysis of various agroclimatic indicators and their dynamics under climate change conditions for a particular region. The results of this effort were summarized in the AgriClim software package, which provides users with a wide range of parameters essential for the evaluation of climate-related stress factors in agricultural crop production. The software was then tested over an area of 114,000 km² in Central Europe. We have found that by 2020, the combination of increased air temperature and changes in the amount and distribution of precipitation will lead to a prolonged growing season and significant shifts in the agroclimatic zones in Central Europe; in particular, the areas that are currently most productive will be reduced and replaced by warmer but drier conditions in the same time the higher elevations will most likely experience improvement in their agroclimatic conditions. This positive effect might be short-lived, as by 2050, even these areas might experience much drier conditions than observed currently. Both the rate and the scale of the shift are amazing as by 2020 (assuming upper range of the climate change projections) only 20?C38% of agriculture land in the evaluated region will remain in the same agroclimatic and by 2050 it might be less than 2%. On the other hand farmers will be able to take advantage of an earlier start to the growing season, at least in the lowland areas, as the proportion of days suitable for sowing increases. As all of these changes might occur within less than four decades, these issues could pose serious adaptation challenges for farmers and governmental policies. The presented results also suggest that the rate of change might be so rapid that the concept of static agroclimatic zoning itself might lose relevance due to perpetual change.     

Mineral chemical study of U-bearing minerals from the Dominion Reefs,South Africa

The Neo-Archean Dominion Reefs (~3.06 Ga) are thin meta-conglomerate layers with concentrations of U- and Th-bearing heavy minerals higher than in the overlying Witwatersrand Reefs. Ore samples from Uranium One Africa’s Rietkuil and Dominion exploration areas near Klerksdorp, South Africa, were investigated for their mineral paragenesis, texture and mineral chemical composition. The ore and heavy mineral assemblages consist of uraninite, other uraniferous minerals, Fe sulphides, Ni–Co sulfarsenides, garnet, pyrite, pyrrhotite, monazite, zircon, chromite, magnetite and minor gold. Sub-rounded uraninite grains occur associated with the primary detrital heavy mineral paragenesis. U–Ti, U–Th minerals, pitchblende (colloform uraninite) and coffinite are of secondary, re-mobilised origin as evidenced by crystal shape and texture. Most of the uranium mineralisation is represented by detrital uraninite with up to 70.2 wt.% UO₂ and up to 9.3 wt.% ThO₂. Re-crystallised phases such as secondary pitchblende (without Th), coffinite, U–Ti and U–Th phases are related to hydrothermal overprint during low-grade metamorphism and are of minor abundance.     

Retrograde formation of NaCl-scapolite in high pressure metaevaporites from the Cordilleras Béticas (Spain)

A Permo-Triassic pelite-carbonate rock series (with interacalated metabasitic rocks) in the Cordilleras Béticas, Spain, was metamorphosed during the Alpine metamorphism at high pressures (P _min near 18 kbar). The rocks show well preserved sedimentary features of evaporites such as pseudomorphs of talc, of kyanite-phengitetalc-biotite, and of quartz after sulfate minerals, and relicts of baryte, anhydrite, NaCl, and KCl, indicating a salt-clay mixture of illite, chlorite, talc, and halite as the original rock. The evaporitic metapelites have a whole rock composition characterized by high Mg/(Mg+Ca) ratios>0.7, variable alkaline and Sr, Ba, contents, but are mostly K₂O rich (<8.8 wt%). The F (<2600 ppm), Cl (<3600 ppm), and P₂O₅ (<0.24 wt%) contents are also high. The pelitic member of this series is a fine grained biotite rock. Kyanite-phengite-talc-biotite aggregates in pseudomorphs developed in the high pressure stage. Albite-rich plagioclase was formed when the rocks crossed the albite stability curve in the early stages of the uplift. Scapolite, rich in NaCl (Ca/(Ca+Na) mol% 24–40) and poor in SO₄, with Cl/(Cl+CO₃) ratios between 0.6 and 0.8, formed as porphyroblasts, sometimes replacing up to 60% of the rock in a late stage of metamorphism (between 10 and 5 kbar, near 600°C). No reaction with albite is observed, and the scapolite formed from biotite by: $$\begin{gathered} Al - biotite + CaCO_3 + NaCl + SiO_2 \hfill \\ = Al - poor biotite + scapolite + MgCO_3 + KCl \hfill \\ + MgCl_2 + H_2 O \hfill \\ \end{gathered}$$ Calculated fluid composition in equilibrium with scapolite indicates varying salt concentrations in the fluid. Distribution of Cl and F in biotite and apatite also indicates varying fluid compositions.     

Carbonatite magmatism and fenitization of the epiclastic caldera-fill at Gross Brukkaros (Namibia)

The Gross Brukkaros inselberg is a dome structure with a crater-shaped central depression within Precambrian/Cambrian country rocks which was active as a depocenter during the Late Cretaceous. The formation of the structure was due to the intrusion and subsequent intermittent depletion of a shallow magma reservoir. Juvenile material has not been recognized hitherto. This is the first account of juvenile lapilli from within the epiclastic fill of the caldera structure. The lapilli are calciocarbonatites and magnesiocarbonatites in composition, but are characteristically low in elements such as P, Nb, Ba and Sr, otherwise typical of carbonatites. This signature, however, is also characteristic of carbonatites from surrounding volcanic centers and necks. The Brukkaros sediments suffered strong metasomatic-hydrothermal alteration, which introduced in a first stage fluids rich in Fe, Ti, Na, Nb, V, K (Ca?, CO₂?), and in a second stage the Brukkaros sediments were silicified on a large scale and locally enriched in P, Th and Cr. Si is derived from desilication of the wall rocks (basement?, Nama sediments) of the magma reservoir. Cr was probably mobilized during alteration of the abundant doleritic detritus within the Brukkaros depocenter.     

Rural-urban migration and the problem of town planning —

The conurbation of Khartoum has been long the main destination area of the rural-urban migration in the Sudan. The town-planning office has become unable to provide the inmigrant masses with the least required housing infrastructure. The result is that the inmigrants have been living for some decades now in squatter areas without any right of residence. The way from the formation of a squatter settlement which is officially non-existent and illegal to a demarcated residential area is long and tedious. The author describes this process using the example of Um Badda which is a traditional destination area of inmigrants. The analysis shows that the officials of the town-planning treat the ethnic groups on unequal basis with a strong bias against southern Sudanese.     

New aspects on the chemistry of aluminum in soils

Dissolution kinetics of minerals can be significantly inhibited by re-adsorbed aluminum. As a consequence of neutralization, polynuclear Al species may be formed in soil solutions. While re-acidification leads to decomposition of the polymers, further neutralization induces the formation of aggregates. The complexation of heavy metal ions with dissolved and aggregated Al polymers is illustrated as a potential factor influencing the chemical speciation of heavy metals in soils.     

CODE’s five-system orbit and clock solution—the challenges of multi-GNSS data analysis

This article describes the processing strategy and the validation results of CODE’s MGEX (COM) orbit and satellite clock solution, including the satellite systems GPS, GLONASS, Galileo, BeiDou, and QZSS. The validation with orbit misclosures and SLR residuals shows that the orbits of the new systems Galileo, BeiDou, and QZSS are affected by modelling deficiencies with impact on the orbit scale (e.g., antenna calibration, Earth albedo, and transmitter antenna thrust). Another weakness is the attitude and solar radiation pressure (SRP) modelling of satellites moving in the orbit normal mode—which is not yet correctly considered in the COM solution. Due to these issues, we consider the current state COM solution as preliminary. We, however, use the long-time series of COM products for identifying the challenges and for the assessment of model-improvements. The latter is demonstrated on the example of the solar radiation pressure (SRP) model, which has been replaced by a more generalized model. The SLR validation shows that the new SRP model significantly improves the orbit determination of Galileo and QZSS satellites at times when the satellite’s attitude is maintained by yaw-steering. The impact of this orbit improvement is also visible in the estimated satellite clocks—demonstrating the potential use of the new generation satellite clocks for orbit validation. Finally, we point out further challenges and open issues affecting multi-GNSS data processing that deserves dedicated studies.