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This study presents new petrological results obtained from high-grade metamorphic rocks of the Beit Bridge, Mahalapye and Phikwe Complexes, which constitute the Central Zone of the Limpopo Belt in southern Africa. These results provide detailed information about the prograde and retrograde pressure-temperature (P-T) evolution of the three investigated complexes and, in concert with geochronological data, form the basis for the development of a coherent geodynamic model for the evolution of the Limpopo’s Central Zone. The P-T paths were inferred by the thorough investigation of silica-saturated and silica- undersaturated metapelitic and metabasic rocks, comprising six sillimanite-garnet-cordierite gneisses, four (garnet)-biotite-plagioclase gneisses, two garnet-orthopyroxene-biotite-Kfeldspar-plagioclase gneisses, one garnet- cordierite-orthoamphibole fels, one garnet-biotite amphibolite, and one garnet-clinopyroxene amphibolite. P-T points and P-T evolutions were derived by the application of conventional geothermobarometers, and quantitative phase diagrams in the systems Na2O - CaO - K2O - FeO - MgO - Al2O3 - SiO2 - H2O - TiO2 - O (NCKFMASHTiO), and MnO - TiO2 - Na2O - CaO - K2O - FeO - MgO - Al2O3 - SiO2 - H2O (MnTiNCKFMASH) - using the computer software THERMOCALC and THERIAK-DOMINO. The petrological information, in particular those obtained by comparison between observed and thermodynamically calculated mineral assemblages, zonations and modes, in combination with new and existing geochronological data provide evidence that rocks from the three investigated complexes underwent slightly different P-T evolutions at different times. The samples from the Bulai Pluton area (Beit Bridge Complex) provide evidence for a Neoarchean high-grade metamorphic event at ~2.64 Ga (M2), with peak P-T conditions of ~850°C at 8-9 kbar, and a decompression-cooling path to ~750°C at 5-6 kbar. This metamorphic evolution perhaps took place in a magmatic arc setting. In contrast, samples from the Mahalapye and Phikwe Complex document a Palaeoproterozoic event at ~2.03-2.05 Ga (M3), and were subject to different styles of prograde metamorphism. Metamorphic rocks from the Mahalapye Complex experienced a high-temperature low-pressure (HT-LP) metamorphic overprint, accompanied by the emplacement of voluminous granite bodies between 2.06 and 2.02 Ga, and provide evidence for a slightly prograde decompression from ~650°C/7 kbar to ~800°C/5.5 kbar. In contrast, the metamorphic rocks from the Phikwe Complex provide evidence for a simultaneous pressure and temperature increase from ~600°C/6 kbar to ~750°C/8 kbar, in the absence of significant Palaeoproterozoic magmatism. The HT-LP metamorphic evolution of the Mahalapye Complex is interpreted to be initiated by the underplating of hot mafic melts, either formed in response to SE-subduction during the Kheis-Magondi orogeny, and/or by contemporaneous mantle plume activities related to the formation of the Bushveld Complex. In contrast, the prograde pressure and temperature increase reflected by the rocks from the Phikwe Complex rather reflects successive crustal stacking at ~2.03 Ga. This stacking, which is also reported from many other units throughout the Limpopo Belt, is interpreted to result from the final convergence between the Kaapvaal and Zimbabwe Cratons, perhaps caused by SE-directed compression in response to the Kheis-Magondi orogeny between ~2.06 and 1.90 Ga.
Ziel der vorliegenden Arbeit war es, anhand von aktuellen Hochwasserschadensdaten aus Telefonbefragungen in Privathaushalten in Deutschland und Österreich die Minderung von Hochwasserschäden durch Frühwarnung und privater Eigenvorsorge zu quantifizieren. Im ersten Schritt wurden die Datensätze aus den vier zugrunde liegenden Befragungen zu den Hochwasserereignissen der Jahre 2002, 2005 und 2006 zusammengeführt und die Hochwasserschäden auf das Referenzjahr 2007 angepasst. Um das Schadensminderungspotenzial von Frühwarnung und diversen Vorsorge-/ Notmaßnahmen beurteilen zu können, wurde der konsistente Datensatz nach verschiedenen schadensbestimmenden Faktoren (Wasserstand, Hochwassertyp, Kontaminationsart und Hochwassererfahrung) aufgeteilt. Dabei stellte sich heraus, dass eine Hochwasserwarnung z.B. durch Behörden den Schaden am Gebäude und Hausrat nur dann reduzieren kann, wenn der Frühwarnungsinhalt klar verständlich oder das Wissen der Betroffenen ausreichend ist, wie man sich und seinen Haushalt vor dem Hochwasser schützen kann (durch das Ergreifen von Notmaßnahmen). Der Nutzen einer langfristigen Vorsorge, insbesondere von baulichen Maßnahmen, wurde in dieser Studie sehr deutlich. Vor allem die geringwertige Nutzung der hochwassergefährdeten Stockwerke und die hochwasserangepasste Inneneinrichtung konnten die Schäden am Gebäude und Inventar erheblich reduzieren.
Glacier outlines during the ‘Little Ice Age’ maximum in Jotunheimen were mapped by using remote sensing techniques (vertical aerial photos and satellite imagery), glacier outlines from the 1980s and 2003, a digital terrain model (DTM), geomorphological maps of individual glaciers, and field-GPS measurements. The related inventory data (surface area, minimum and maximum altitude) and several other variables (e.g. slope, range) were calculated automatically by using a geographical information system. The length of the glacier flowline was mapped manually based on the glacier outlines at the maximum of the ‘Little Ice Age’ and the DTM. The glacier data during the maximum of the ‘Little Ice Age’ were compared with the Norwegian glacier inventory of 2003. Based on the glacier inventories during the maximum of the ‘Little Ice Age’, the 1980s and 2003, a simple parameterization after HAEBERLI & HOELZLE (1995) was performed to estimate unmeasured glacier variables, as e.g. surface velocity or mean net mass balance. Input data were composed of surface glacier area, minimum and maximum elevation, and glacier length. The results of the parameterization were compared with the results of previous parameterizations in the European Alps and the Southern Alps of New Zealand (HAEBERLI & HOELZLE 1995; HOELZLE et al. 2007). A relationship between these results of the inventories and of the parameterization and climate and climate changes was made.
The locality of Zwartbas is situated at the border of Namibia and South Africa about 15 km west of Noordoewer. The mapped area is confined by the Tandjieskoppe Mountains in the north and the Orange River in the south. Outcropping rocks are predominantly sediments of the Nama Group and of the Karoo Supergroup. During the compilation of this paper doubts arose about the correct classification of the Nama rocks as it is found in literature. Since no certain clues were found to revise the classification of the Nama rocks, the original classification remains still valid. Thus the Kuibis and Schwarzrand Subgroup constitute the Nama succession and date it to Vendian age. A glacial unconformity represents a hiatus for about 260 Ma. This is covered by sediments of the Karoo Supergroup. Late Carboniferous and early Permian glacial deposits of diamictitic shale of the Dwyka and shales of the Ecca Group overlie the unconformity. The shales of the Dwyka Group contain fossiliferous units and volcanic ash-layers. A sill of the Jurassic Tandjiesberg Dolerite Complex (also Karoo Supergroup) intruded rocks at the Dwyka-Ecca-boundary. Finally fluvial and aeolian deposits and calcretes of the Cretaceous to Tertiary Kalahari Group and recent depositionary events cover the older rocks occasionally.
At Zwartbas, about 10 km west of Vioolsdrif, southern Namibia, the Dwyka succession is composed of tillites and distal fossiliferous dropstone-bearing glacio-marine shales. The completely exposed Dwyka succession is interbedded with thin bentonites, altered distal pyroclastic deposits, which were derived from the magmatic arc at the southern rim of Gondwana. Dropstone-bearing and dropstonefree sequences intercalate with four diamictites, of which the two lowest were certainly recognised as tillites. Four events of deglaciation were proven at Zwartbas and thus consist with correlative deposits in southern Africa. Numerous fossilised fishes, trace fossils, and plant fragments appear frequently within the lower half of the Dwyka succession whereas trace fossils were principally found in the complete succession. Although the environmental determination is quite problematic, the fossil assemblage rather implies proximal, shallow water conditions with temporary restricted oxygenation. The hinterland was covered with considerable vegetation, which points to a moderate climate. Water salinity determinations based on shale geochemistry rectify contrary palaeontological results and point to rather brackish or non-marine conditions in comparison to present-day salinites. Geochemical analyses of the bentonites relate the pyroclastic deposits with acid to intermediate source magmas, as they are known from the magmatic arc in present-day Patagonia. Tectono-magmatic comparisons furthermore emphasise a syn-collision or volcanic-arc situation of the magma source. However, significant cyclicity in the production of the pyroclastic deposits was not observed. Radiometric age determinations of two tuff beds clearly date the onset of glacial activity into the Late Carboniferous.
Calc-silicate rocks occur as elliptical bands and boudins intimately interlayered with eclogites and high-pressure gneisses in the Munchberg gneiss complex of NE Bavaria. Core assemblages of the boudins consist of grossular-rich garnet, diopside, quartz, zoisite, clinozoisite, calcite, rutile and titanite. The polygonal granoblastic texture commonly displays mineral relics and reaction textures such as postkinematic grossular-rich garnet coronas. Reactions between these mineral phases have been modelled in the CaO-Al203-Si02-C02-H2 0 system with an internally consistent thermodynamic data base. High-pressure metamorphism in the calc-silicate rocks has been estimated at a minimum pressure of 31 kbar at a temperature of 630°C with X^oSQ.Gi. Small volumes of a C02-N2-rich fluid whose composition was buffered on a local scale were present at peak-metamorphic conditions. The P-T conditions for the onset of the amphibolite facies overprint are about 10 kbar at the same temperature. A'co., of the H20-rich fluid phase is regarded to have been <0.03 during amphibolite facies conditions. These P-T estimates are interpreted as representing different stages of recrystallization during isothermal decompression. The presence of multiple generations of mineral phases and the preservation of very high-pressure relics in single thin sections preclude pervasive post-peak metamorphic fluid flow as a cause of a re-equilibration within the calc-silicates. The preservation of eclogite facies, very high-pressure relics as well as amphibolite facies reactions textures in the presence of a fluid phase is in agreement with fast, tectonically driven unroofing of these rocks.
Various amphibolites, metagabbros and eclogitic relics of the Mariimske Lazne complex, and amphibolites from the Cerna Hora Massif exhibit an uniform geochemical character which compares well with modern mid-ocean ridge basalts. Geochemically these metabasites are similar to the amphibolites of the My to area and to schistose. partly striped amphibolites of the neighbouring Tirschenreuth-Mahring Zone and the Erbendorf-Vohenstrauss Zone (Bavaria). Greenschists and amphibolites from the Domailice metamorphic complex show an alkaline-basaltic tendency conforming to modern within-plate basalts or basalts from anomalous midocean ridge segments. In their chemical character, these metabasites compare well with the flaseramphibolites of the Erbendorf-Vohenstrauss Zone. Fine-grained amphibolites in the Warzenrieth area and gabbroic amphiboltes in the Blatterberg-Hoher Bogen area show normal MORB character. The metamorphosed gabbroic rocks in the southern part of the Neukirchen-Kdyne (meta-) igneous complex are subalkaline-tholeiitic and exhibit a magmatic differentiation trend. They differ from the neighbouring amphibolites by generally lower contents of incompatible elements.
The Upper Bajocian-Bathonian Kashafrud Formation is a thick package of siliciclastic sediments that crops out in NE Iran from the southeast, near the Afghanistan border, to north- northwestern areas around the city of Mashhad. The thickness ranges from less than 300 m in a deltaic succession (Kuh-e-Radar) to more than 2500 m in the Maiamay area, but the normal thickness in Ghal-e-Sangi, Kol-e-Malekabad, and Fraizi areas is about 1200-1300 m. It is the fill of an elongated basin, which extended for more than 200 km in NW-SE direction and a width of at least 50 km along the southern margin of the Koppeh Dagh. Prior to this study, little information existed about the sedimentary environments and other characters, especially the geometry of the basin. Exact biostratigraphic data from the top of the Kashafrud Formation were rare. Based on the macrofauna from the lower part of the overlying Chamanbid Formation the upper boundary of the Kashafrud Formation had been attributed to the Late Bathonian and/or Early Callovian, but now the upper limit of the Kashafrud Formation is defined as Late Bathonian in age, based on ammonite biostratigraphy. Except for chapter one, which deals with the introduction and related sub-titles, in the following chapters, step by step, field observations and data were surveyed according to the questions to solve. In order to reconstruct the facies architecture and the geometry of the basin, a number of sections have been logged in detail (see chapter 3, “The sections”). The exact biostratigraphic setting is discussed in chapter 4 (“Biostratigraphy”). Sedimentary environments range from non-marine alluvial fans and braided rivers in the basal part of the succession to deltas, storm-dominated shelf, slope and deep-marine basin. The latter comprises the largest part of the basin fill, consisting of monotonous mudstones, siltstones and proximal to distal turbidities. The only continuous carbonate unit (~30 m) locally formed at Tappenader. Other localities in which thin fossil-bearing carbonate strata occur are Torbat-e-Jam (benthic fauna) and, to a lesser extent, Ghal-e-Sangi. These rare shallow-water carbonates, which also contain corals, represent only short intervals (see chapter 5,” Facies association and sedimentary environments”). Relative changes in sea level were reconstructed on the basis of deepening- and shallowing-upward trends. Sequence boundaries and parasequences have been distinguished and analyzed in chapter 6 (“Sequence stratigraphy”). In most areas, the basin rapidly evolved from a shallow marine, transgressive succession to a deep-marine, basinal succession. The only area where shallow conditions persisted from the Late Bajocian to the Late Bathonian, and even into the Early Callovian is the Kuh-e-Radar area which corresponds to a fan-delta setting. A trace fossil analysis has been carried out to obtain additional evidence on the bathymetry of the basin (see chapter 7, “Ichnology”). Altogether 29 ichnospecies belonging to 15 ichnogenera have been identified, as well as 10 ichnogenera, which were determined only at genus level. They can be grouped in the well-known “Seilacherian ichnofacies”. Very high subsidence rates and strong lateral thickness variations suggest that the Kashafrud Formation is a rift related basin that formed as the eastern extension of the South Caspian Basin. The basin evolution is reviewed, the eastern and western continuations of the basin were checked in the field and also in the literature (see chapter 8, “Basin evolution”). In all, the present study provided new insights into the development of the Kashafrud Formation, e.g. more biostratigraphic data from the base and the top of the succession, a relatively complete picture of the trace fossil associations, a better recognition and reconstruction of the sedimentary environments in different parts of the basin. Finally this research project will be a good basis for further investigations, especially towards the west, as parts of the Kashafrud Formation are source rocks of a hydrocarbon reservoir in NE Iran.
Geochronologische Untersuchungen in der Oberpfalz: K/Ar Mineral- und Rb/Sr Gesamtgesteinsdatierungen
(1986)
No abstract available
No abstract available