An unprecedented arctic ozone depletion event during spring 2020 and its impacts across Europe

The response of the ozone column across Europe to the extreme 2020 Arctic ozone depletion was examined by analyzing ground-based observations at 38 European stations. The ozone decrease at the northernmost site, Ny-Ålesund (79°N) was about 43% with respect to a climatology of more than 30 years. The magnitude of the decrease declined by about 0.7% deg−1 moving south to reach nearly 15% at 40°N. In addition, it was found that the variations of the ozone column at each of the selected stations in March-May were similar to those observed at Ny-Ålesund but with a delay increasing to about 20 days at mid-latitudes with a gradient of approximately 0.5 days deg−1. The distributions of reconstructed ozone column anomalies over a sector covering a large European area show decreasing ozone that started from the north at the beginning of April 2020 and spread south. Such behavior was shown to be similar to that observed after the Arctic ozone depletion in 2011. Stratospheric dynamical patterns in March–May 2011 and during 2020 suggested that the migration of ozone-poor air masses from polar areas to the south after the vortex breakup caused the observed ozone responses. A brief survey of the ozone mass mixing ratios at three stratospheric levels showed the exceptional strength of the 2020 episode. Despite the stronger and longer-lasting Arctic ozone loss in 2020, the analysis in this work indicates a similar ozone response at latitudes below 50°N to both 2011 and 2020 phenomena

A geophysically constrained litho-structural analysis of the Eburnean greenstone belts and associated granitoid domains, Burkina Faso, West Africa

Interpretation of airborne geophysical data integrated with field structural and lithological observation was successfully employed in the creation of the litho-structural framework in a poorly exposed Paleoproterozoic granite-greenstone terrain of the West African Craton. The geophysical data portray with sufficient detail all of the lithological units and structural features present. The results suggest that the granitoid domains are formed by numerous small to medium-sized plutons. The existence of several generations of magmatic episodes has a significant impact on the development of a regional tectonic model. The magnetic data provided a better definition of the actual pluton shapes and several highly magnetic late-orogenic plutons were reliably identified. Relic F1 fold hinges were recognized in the Hounde and Boromo greenstone belts. The D1 penetrative structures are generally affected by the D2 transcurrent shear zones, which often form as well the granite-greenstone belt boundaries. Previously unreported S2 shear zones including the Bossie shear zone, transecting the Sideradougou granitoid domain and abundant small-scale shear zones affecting all of the lithologies represent prospective areas for gold exploration. Airborne gamma-ray spectrometry data aided in the mapping process in areas with less regolith cover including erosional ridges and parts of the Banfora greenstone belt. The magnetic data revealed at least three generations of doleritic dykes crosscutting the western Burkina Faso

Tectonics, mineralisation and regolith evolution of the West African Craton

In situ and laboratory 0.35 mu m-2.5 mu m spectra of rocks from a Paleoproterozoic granite-greenstone terrain along with its Neoproterozoic sedimentary cover and derived regolith materials were examined in western Burkina Faso. The reflectance spectra show the influence of typical arid to semi-arid weathering with the formation of desert varnish, iron films, and dust coatings. Fe and Mg-OH absorption features related to chlorite, amphibole, pyroxene, epidote, and biotite are observable in the mafic and intermediate meta-volcanic rocks as well as in the granodiorites and tonalites. Al-OH absorption caused by kaolinite, smectite, illite/muscovite are typical for meta-volcano-sedimentary schists, Tarlcwaian-type detrital meta-sediments, sandstones of the Taoudeni basin, all of the weathered surfaces and regolith materials. Ferric and ferrous iron absorptions related to both primary rock-forming minerals and secondary weathering minerals (goethite, hematite) were observed in most of the sampled materials. The results show that although weathering alters the spectral signature of the fresh rock, indicative absorption features located in the short wave infrared region remain detectable. In addition, spectra of soils partially reflect the mineral composition of the weathered rock surfaces. The analysis of the hyperspectral data shows the potential of differentiating between the sampled surfaces. The library presents a primary database for the geological and regolith analysis of remote sensing data in West Africa

Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso, West Africa)

The regionally correlated and dated regolith–paleolandform sequence of Sub-Saharan West Africa offers a unique opportunity to constrain continental-scale regolith dynamics as the key part of the sediment routing system. In this study, a regolith mapping protocol is developed and applied at the scale of Southwestern Burkina Faso. Mapping combines field survey and remote sensing data to reconstruct the topography of the last pediplain that formed over West Africa in the Early and Mid-Miocene (24-11 Ma). The nature and preservation pattern of the pediplain are controlled by the spatial variation of bedrock lithology and are partitioned among large drainage basins. Quantification of pediplain dissection and drainage growth allows definition of a cratonic background denudation rate of 2 m/My and a minimum characteristic timescale of 20 Ma for shield resurfacing. These results may be used to simulate minimum export fluxes of drainage basins of constrained size over geological timescales. Background cratonic denudation results in a clastic export flux of ~ 4 t/km2/year, which is limited by low denudation efficiency of slope processes and correlatively high regolith storage capacity of tropical shields. These salient characteristics of shields' surface dynamics would tend to smooth the riverine export fluxes of shields through geological time

Object data model for urban drainage domain.

Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Juvenile paleoproterozoic crust evolution during the Eburnean orogeny (similar to 2.2-2.0 Ga), western Burkina Faso

We have investigated three greenstone belts (Boromo, Hounde, and Banfora) and associated granitoid terrains, which form part of the Eburnean orogen, situated in western Burkina Faso. These belts expose tholeiitic basalts (basal unit) followed by calc-alkaline intermediate predominantly effusive volcanic and sedimentary suites geochemically reminiscent of present-day volcanic island arc environments. The basal mafic unit probably corresponds to a juvenile arc crust or oceanic plateau. It contains unusual megacrystic tholeiitic basalts, allowing us to correlate the western margin of the Boromo belt with the eastern margin of the Hounde belt. These two N-S trending belt-parallel tholeiitic units are interpreted as limbs of a crustal scale anticline, intruded and partially obliterated by tonalite-trondhjemite-granodiorite (TTG) and granite intrusions. Three deformation events (D1-D3) can be distinguished in western Burkina Faso. The first deformation phase (D1) operated under an E-W to WNW-oriented compression. Regional greenschist to lower amphibolite facies metamorphism and intense folding characterize early-Eburnean deformation phases, during which time the crust was thickened by lateral shortening of volcanic island arcs and concomitant magma input. The crustal-scale antiform between the Boromo and Hounde belts is attributed to the D1 event. Shallow water detrital Tarkwaian-type sediments were deposited during the late D1 event within the Hounde belt, in a belt-parallel basin extending for 400 km. The subsequent D2 phase overprints the structural grain of the study area, and is best visible in airborne magnetic data. It is characterized by N to NE-trending transcurrent shear zones, which are considered preferred host structures for gold mineralization. We suggest that the newly formed and thickened crust reached the maximum thickness supportable by a weak and hot mantle during the D1 phase, and the pure shear dominated compressional regime switched to simple shear dominated transgression during the subsequent D2 phase. Granitoid diapirism played an important role at all stages of the Eburnean crustal growth processes in particular through early volume addition to the newly formed orogen and through later accommodating part of the lateral shortening. Pluton emplacement contributed to the greenstone belt structuration at local scales; however, the regional scale system geometry was controlled by coaxial shortening of the viscous volcanic units (basalts, gabbros, and andesites) of the greenstone belts, supported by coeval magma input. The last D3 deformation, which is either late-Eburnean or perhaps even Pan-African in age, is characterized by shallow N or S dipping minor thrust faults or an E-W trending steeply dipping spaced crenulation cleavage and kink folds, occurring mainly in highly anisotropic lithologies across the study region

Tectonics, mineralisation and regolith evolution of the West African Craton

Studies of mafic dyke swarms may simultaneously provide information on the mechanical, geochemical, geochronological and magnetic environments at the time of their formation. The mafic intrusive history of different cratons can also be potentially used to unravel their assembly into their current configuration. The identification and classification of dykes is a first step to all these studies. Fortunately, even in regions with poor outcrop, we can use the strong magnetic response of mafic dykes to identify and map their extent. In West Africa the first maps of mafic dyke distribution were made over 40 years ago, but there are still large areas where there are almost no published data. In this paper we present a significantly updated map of mafic dykes for the West Africa Craton based in large part on new interpretations of the regional airborne magnetic database. This map includes the locations of over three thousand dykes across the craton, which locally shows several orientation clusters that provide a minimum estimate for the total number of dyke swarms in this region. Whilst we will have to wait until systematic dating of the different swarms is completed, we can demonstrate that there is a long and complex history of mafic magmatism across the craton, with up to 26 distinct dyke swarms mapped based according to their orientation. The mapping and dating of these swarms will provide key constraints on the assembly of the fragments that make up the modern continents

Multicommodity mineral systems analysis highlighting mineral prospectivity in the Halls Creek Orogen

Understanding the regional context of mineral prospectivity is essential for opening areas to effective exploration. The Halls Creek Orogen in Western Australia, is one such region. Here we have completed a multi-commodity mineral systems analysis, which we have used as a basis for the production of semi-automated prospectivity models. Known mineral occurrences or deposits formed over a period dominated by the compressional 1865-1850. Ma Hooper and 1835-1805. Ma Halls Creek orogenies, either followed, or preceded by periods of extension. Prospectivity models were built on knowledge-based fuzzy inference networks for seven commodity groups. The work has demonstrated a link between key model components and the propensity of disparate styles of mineral deposits to occur in this region, which has not been documented before. Different tectonic terranes defined as 'zones' in the Halls Creek Orogen are prospective for different commodity groups. A link between major crustal-scale faults or shear zones and the location of known ore deposits and occurrences in the area has been established. Many structures are either newly discovered, or their extension through the upper crust and down to the Moho has just been established. The lithospheric scale of these structurally weak zones would allow fluid migration from within, or below the lower crust. Of these structures, orogen perpendicular (northwest trending) and orogen oblique (north trending) faults are the most influential structures with respect to ore deposition, especially in regions where they intersect each other. The orogen-parallel structures were found to be less important. The crustal-scale architecture of the region and its link to known mineral occurrences suggests that the mineral prospectivity of the Halls Creek Orogen for commodities such as Ni, Cu, PGEs, Au, Pb, Zn and diamonds could be extended beyond known occurrences into the new zones delineated by the prospectivity analysis

Vyhodnocení možnosti modelování klimatu v regionální oblasti za účelem zpřesnění scénářů klimatické změny a dlouhodobé předpovědi anomálií klimatu

Cílem projektu je vyhodnotit možnosti modelování klimatu na omezené oblasti pro region střední Evropy, adaptovat regionální předpovědní model atmosféry pro modelování klimatu a jeho změn v oblasti střední Evropy, verifikovat regionální klimatický model a připravit systém dynamického modelování klimatu a experimentálně ho otestovat. Řešení je rozděleno do pěti dílčích projektů: DP 01: Zprovoznění globálního klimatického modelu (GCM) APRÉGE a zpracování technologie navázání okrajových podmínek regionálního klimatického modelu (RCM) na výstupy GCM, DP 02: Optimalizace konfigurace RCM ALADIN-CLIMAT pro klimatologické simulace a provedení experimentální simulace pro 1 x CO2, DP 03: Porovnání výsledků kontrolního experimentu pro 1 x CO2 s dalšími metodami a výstupy, DP 04: Posouzení možnosti realizace ensemblových simulací a jejich experimentální validace, DP 05: Souhrnné zhodnocení, vypracování závěrečné zprávy projektu. Popis prací provedených v roce 2002

Tectonics, mineralisation and regolith evolution of the West African Craton

The interpretation of high-resolution airborne geophysical data integrated with field structural and lithological observations were employed in the creation of a litho-structural framework for the Gaoua region, Burkina Faso. The granite-greenstone domain of Paleoproterozoic age was affected by multiple deformation and mineralization events. The early tectonic phase is characterized by the emplacement of voluminous tholeiitic and calc-alkaline lavas, probably in a volcanic arc setting. The copper mineralization in Gongondy, Dienemera and Mt Biri is concentrated in a diorite/andesite breccia, and is interpreted as porphyry-copper style formed at an early stage of the evolution of the area. Evidence for the first deformation event D1(Ga) corresponding to N-S shortening was only found in the E-W trending mafic unit bordering the Gaoua batholith to the south. A second deformation phase D2(Ga) occurred under greenschist facies conditions and lead to a development of more or less penetrative metamorphic foliation and its subsequent folding under overall E-W compression. At later stages, the D2(Ga) switched to a transcurrent regime characterized by intense N-S to NW-trending steeply dipping shear zones. The first significant gold mineralization event is related to this transcurrent tectonic phase. During subsequent D3(Ga), intense network of brittle to brittle ductile NW and NE faults developed. Economic gold concentrations are attributed to the D3(Ga) event and are associated with the remobilization of early disseminated low grade gold concentrations. Significant deposits in the area are Nassara, Gomblora, Batie West and Kampti. The last deformation event D4(Ga) resulted in E-W trending thrust faults and crenulation cleavage planes, under overall N-S compression. No mineralization events related to this stage have been seen