Eoalpine tectonics of the Eastern Alps: implications from the evolution of monometamorphic Austroalpine units (Schneeberg and Radenthein Complex)

Monometamorphic metasediments of Paleozoic or Mesozoic age constituting Schneeberg and Radenthein Complex experienced coherent deformation and metamorphism during Late Cretaceous times. Both complexes are part of the Eoalpine high-pressure wedge that formed an intracontinental suture and occur between the polymetamorphosed Ötztal–Bundschuh nappe system on top and the Texel–Millstatt Complex below. During Eoalpine orogeny Schneeberg and Radenthein Complexes were south-dipping and they experienced a common tectonometamorphic history from ca. 115 Ma onwards until unroofing of the Tauern Window in Miocene times. This evolution is subdivided into four distinct tectonometamorphic phases. Deformation stage D1 is characterized by WNW-directed shearing at high temperature conditions (550–600°C) and related to the initial exhumation of the high-pressure wedge. D2 and D3 are largely coaxial and evolved during high- to medium-temperature conditions (ca. 450 to ≥550°C). These stages are related to advanced exhumation and associated with large-scale folding of the high-pressure wedge including the Ötztal-Bundschuh nappe system above and the Texel–Millstatt Complex below. For the area west of the Tauern Window, F2/F3 fold interference results in the formation of large-scale sheath-folds in the frontal part of the nappe stack (formerly called “Schlingentektonik” by previous authors). Earlier thrusts were reactivated during Late Cretaceous normal faulting at the base of the Ötztal–Bundschuh nappe system and its cover. Deformation stage D4 is of Oligo-Miocene age and accounted for tilting of individual basement blocks along large-scale strike-slip shear zones. This tilting phase resulted from indentation of the Southern Alps accompanied by the formation of the Tauern Window.     

Lithologic mapping of HED terrains on Vesta using Dawn Framing Camera color data

The surface composition of Vesta, the most massive intact basaltic object in the asteroid belt, is interesting because it provides us with an insight into magmatic differentiation of planetesimals that eventually coalesced to form the terrestrial planets. The distribution of lithologic and compositional units on the surface of Vesta provides important constraints on its petrologic evolution, impact history, and its relationship with vestoids and howardite‐eucrite‐diogenite (HED) meteorites. Using color parameters (band tilt and band curvature) originally developed for analyzing lunar data, we have identified and mapped HED terrains on Vesta in Dawn Framing Camera (FC) color data. The average color spectrum of Vesta is identical to that of howardite regions, suggesting an extensive mixing of surface regolith due to impact gardening over the course of solar system history. Our results confirm the hemispherical dichotomy (east‐west and north‐south) in albedo/color/composition that has been observed by earlier studies. The presence of diogenite‐rich material in the southern hemisphere suggests that it was excavated during the formation of the Rheasilvia and Veneneia basins. Our lithologic mapping of HED regions provides direct evidence for magmatic evolution of Vesta with diogenite units in Rheasilvia forming the lower crust of a differentiated object.     

The effect of titanium and phosphorus on ferric/ferrous ratio in silicate melts: an experimental study

The effect of TiO₂ and P₂O₅ on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts at air conditions in the temperature range 1,400–1,550 °C at 1-atm total pressure. The base composition of the anorthite–diopside eutectic composition was modified with 10 wt % Fe₂O₃ and variable amounts of TiO₂ (up to 30 wt %) or P₂O₅ (up to 20 wt %). Some compositions also contained higher SiO₂ concentrations to compare the role of SiO₂, TiO₂, and P₂O₅ on the Fe³⁺/Fe²⁺ ratio. The ferric/ferrous ratio in experimental glasses was analyzed using a wet chemical technique with colorimetric detection of ferrous iron. It is shown that at constant temperature, an increase in SiO₂, TiO₂, and P₂O₅ content results in a decrease in the ferric/ferrous ratio. The effects of TiO₂ and SiO₂ on the Fe³⁺/Fe²⁺ ratio was found to be almost identical. In contrast, adding P₂O₅ was found to decrease ferric/ferrous ratio much more effectively than adding silica. The results were compared with the predictions from the published empirical equations forecasting Fe³⁺/Fe²⁺ ratio. It was demonstrated that the effects of TiO₂ are minor but that the effects of P₂O₅ should be included in models to better describe ferric/ferrous ratio in phosphorus-bearing silicate melts. Based on our observations, the determination of the prevailing fO₂ in magmas from the Fe³⁺/Fe²⁺ ratio in natural glasses using empirical equations published so far is discussed critically.     

Regional sulfate–hematite–sulfide zoning in the auriferous Mariana anticline, Quadrilátero Ferrífero of Minas Gerais, Brazil

The distribution of mineral deposits, characterised as barite deposits, hematite-rich auriferous deposits and auriferous tourmaline–sulfide deposits, displays a regional sulfate–hematite–sulfide zoning along the thrust-delineated limbs of the Mariana anticline, in the south-eastern part of the Quadrilátero Ferrífero of Minas Gerais, Brazil. Cross-cut relationships of barite veins and sulfide lodes indicate that sulfidation occurred in a late-tectonic context, which is here attributed to the collapse of the ～0.6-Ga Brasiliano thrust front. Reconnaissance S-isotopic data from barite and pyrite (Antônio Pereira barite deposit and its adjacent gold deposit, respectively), and arsenopyrite (Passagem de Mariana gold deposit), suggest a new interpretation for the hydrothermal fluid overprint in the Mariana anticline. The Antônio Pereira barite has Δ³³S values that are near zero, constraining the sulfate source to rocks younger than 2.45 Ga. The barite-δ³⁴S values are between +19.6 and +20.8?‰. The Passagem arsenopyrite and tourmaline have Co/Ni ratios that define a positive linear trend with the Antônio Pereira pyrite. The latter has homogenous δ³⁴S values, between +8.8 and +8.9?‰, which are compatible with thermochemical reduction of aqueous sulfate with the S-isotopic composition of the Antônio Pereira barite.     

Earth's oldest preserved unconformity — Prospect of a beginning in the tectono-sedimentary continental cycle?

Earth's oldest preserved conglomerates and basaltic pillow lavas at Isua, Greenland, provide robust field evidence for deep- and shallow-water environments on our planet within the first billion years of its formation. The conglomerates represent the first Paleoarchaean archive of sub-aerial erosion and shallow water sedimentation. These ca. 3700 million year old sedimentary rocks, now metamorphosed at amphibolite grade, comprise units of rounded quartz pebbles set in a sandy to muddy matrix that unconformably overlie an ophiolite sequence. The pillow lavas of the ophiolite are variolitic and essentially vesicle-free, indicative of formation in a deep water environment. Locally, an unconformity separates the conglomerates from the deformed ophiolite-related rocks; elsewhere the contact between these units is tectonic. Such field relationship between deep and shallow water environments resemble those preserved in younger orogenic belts, where obducted oceanic crust has been tectonically emplaced across terrestrial platforms or subaerial parts of forearc and backarc basins.     

Joint clay–heavy–light mineral analysis: a tool to investigate the hydrographic–hydraulic regime of Late Cenozoic deltaic inland fans under changing climatic conditions (Cuvelai-Etosha Basin, Namibia)

An interdisciplinary study (major and minor elements, C and O isotopes, heavy and light minerals, phyllosilicates, wireline logs) in northern Namibia unraveled the hydrographic and hydraulic evolution of alluvial–fluvial sediments of the Kunene and Cubango megafans (Etosha-Cuvelai Basin). Three principal aquatic regimes were operative within the megafan complex: (1) the hydrographic regime, (2) the proximal hydraulic regime, (3) the distal hydraulic regime. The allogenic mineral assemblages mirror the hydrographic variation or drainage system and the lithological evolution of the fan sediments (alluvial–fluvial fan, lacustrine environment with evaporites, fan delta progradation). Authigenic heavy minerals are markers of the physical–chemical condition (Eh and pH values) of the hydraulic regime within the proximal fan at the basin margin. Authigenic heavy, light and clay minerals equally contribute to the determination of the fluid chemistry and temperature, as well as the source of chemical constituents of the former pore fluids percolating through the distal fan. Carbonatization was the most pronounced event in the distal hydraulic system and controlled by the presence of biogenic as well as atmospheric carbon. The isotope-based determination of the temperatures, albeit strongly fluctuating, do not exceed 40 °C. The overall pH values determined for the hydraulic regime within the distal fan range from slightly acidic to alkaline. The presence of zeolites attests to some short-lasting but strong deviations from the pH range, mainly towards more alkaline conditions. Heavy, light and clay mineral analyses proved to be a useful tool to determine the (paleo)hydrology of alluvial–fluvial fan systems in tropical arid to semiarid climates.     

Salt kinematics and regional tectonics across a Permian gas field: a case study from East Frisia, NW Germany

This study presents a reconstruction of the tectonic history of an Upper Rotliegend tight gas field in Northern Germany. Tectonism of the greater study area was influenced by multiple phases of salt movement, which produced a variety of salt-related structural features such as salt walls, salt diapirs as well as salt glaciers (namakiers). A sequential 2D retro-deformation and stratal backstripping methodology was used to differentiate mechanisms inducing salt movement and to discuss their relation to regional tectonics. The quantitative geometric restoration included sedimentary balancing, decompaction, fault-related deformation, salt movement, thermal subsidence, and isostasy to unravel the post-depositional tectonic overprint of the Rotliegend reservoir rock. The results of this study indicate that reactive salt diapirism started during an Early Triassic interval of thin-skinned extensional tectonics, followed by an active diapirism stage with an overburden salt piercement in the Late Triassic, and finally a period of intensive salt surface extrusion and the formation of salt glaciers (namakiers) in Late Triassic and Jurassic times. Since the Early Cretaceous, salt in the study area has been rising by passive diapirism.     

The Berchtesgaden National Park (Bavaria, Germany): a platform for interdisciplinary catchment research

The Berchtesgaden National Park (Bavaria, Germany), a study site of the UNESCO Man and the Biosphere program in the catchment of Berchtesgadener Ache, is introduced as a platform for interdisciplinary research. As the investigation of how human activities affect the natural resources in the park area, which has been defined a main aim of the program, naturally requires expertise from different scientific fields, interdisciplinary research has been fostered in the national park plan since the very beginning of the Man and the Biosphere program in 1981. To analyze the complex interactions and mutual dependencies between socio-economic and natural systems, a variety of monitoring programs have been initialized in different disciplines (e.g. climate sciences, zoology, botany) that are addressed in this paper. As a result of these research efforts, the park offers a profound data basis to be used in future studies (e.g. land cover classifications, maps of geological and soil conditions). Detailed information is provided on a climate monitoring network that has been installed in the park starting in the year 1993. The network has been continuously extended over the years and now provides extraordinary comprehensive information on meteorological conditions in the park, setting the basis for current as well as for potential future climate-related studies. A special characteristic of the station network is the fact that it covers a large range of elevations from 600 m a.s.l in the valleys to 2,600 m a.s.l in the summit regions and is therefore able to capture altitudinal gradients in meteorological variables as typical for Alpine regions. Due to the large number of stations in high elevations (15 stations are in elevations higher than 1,500 m a.s.l) the network provides information on the complex hydrometeorological conditions in summit regions which are often insufficiently represented in observation networks due to the increased costs for maintenance of climate stations in these locations. Beside the various monitoring programs, a variety of numerical models have been (further) developed for application in the park area that make extensive use of the different data collected and therefore largely benefit from the comprehensive data pool. The potential and necessity of the climate monitoring network for modelling studies is demonstrated by utilizing the meteorological recordings in the framework of a hydrometeorological simulation experiment. Further examples of environmental modelling efforts are shortly described together with preliminary model results.     

Impact of Poroelastic Response of Sandstones on Geothermal Power Production

During geothermal power production using a borehole doublet consisting of a production and injection well, the reservoir conditions such as permeability k, porosity φ and Skempton coefficient B at the geothermal research site Gross Schoenebeck/Germany will change. Besides a temperature decrease at the injection well and a change of the chemical equilibrium, also the pore pressure p _p will vary in a range of approximately 44 MPa ± 10 MPa in our reservoir at ?3850 to ?4258 m depth. This leads to a poroelastic response of the reservoir rocks depending on effective pressure p _eff (difference between mean stress and pore pressure), resulting in a change in permeability k, porosity φ and the poroelastic parameter Skempton coefficient B. Hence, we investigated the effective pressure dependency of Flechtinger sandstone, an outcropping equivalent of the reservoir rock via laboratory experiments. The permeability decreased by 21% at an effective pressure range from 3 to 30 MPa, the porosity decreased by 11% (p _eff = 6 to 65 MPa) and the Skempton coefficient decreased by 24% (p _eff = 4 to 25 MPa). We will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir. The most significant changes occur at low effective pressures until 15 to 20 MPa. For our in situ reservoir conditions p _eff = 43 MPa a change of 10 MPa effective pressure will result in a change in matrix permeability of less than 4% and in matrix porosity of less than 2%. Besides natural fracture systems, fault zones and induced hydraulic fractures, the rock matrix its only one part of geothermal systems. All components can be influenced by pressure, temperature and chemical reactions. Therefore, the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir.     

Labor Market Marginalization of Youth in San Antonio,Texas

Poverty among inner‐city residents is associated with their marginal status in the labor market. Marginalization in the labor market begins during youth when important educational and employment decisions are made. Analysis of 1990 U.S. Census tract data for San Antonio, Texas identifies the lack of a high school diploma, poverty, non‐employment, and non‐enrollment in school as conditions of marginality for youth. Spatial patterns of youth labor market marginalization show concentrations in the inner city and in sectors on the West, South, and Eastside. Regression analysis reveals that levels of youth marginalization are associated with neighborhood context represented by the employment, behavioral, and ethnic characteristics of the overall residential population of a census tract.