This book gives an eye-opening account of the ways various political and intellectual projects have appropriated the medieval past for their own ends, grounded in an analysis of contemporary ...struggles over power and identity in the Eastern Alps.
Detrital geochronology studies require a careful quantification of hydraulic sorting effects and of the variable abundance (fertility) of datable minerals in different parent rocks. Because the ...physical processes of settling and selective entrainment are well known, their effects in sediments can be easily detected and modeled mathematically. By contrast, mineral fertility in parent rocks depends on their full geological history. As a consequence, the relationships between bedrock geology and mineral fertility are hardly predictable, and a direct measurement of this latter parameter is thus required. In this review article, we describe the basic principles of hydraulic sorting, and illustrate a quantitative approach for mineral fertility determination that applies these basic principles to the analysis of modern sediments. Its application to the European Alps shows that apatite and zircon fertility values may range over three orders of magnitude. Variable mineral fertility in parent rocks thus represents, by far, the largest source of bias in detrital geochronology studies. Our study highlights an evident relationship between bedrock geology and mineral fertility, which confirms that the mineral concentration in modern sediments, in the lack of hydraulic sorting effects, is a good proxy of the mineral abundance in bedrock. Mineral fertility maps of the European Alps unravel that metamorphic and plutonic rocks generally have higher apatite and zircon fertility values than sedimentary rocks, but major variations are also observed between different tectonic units within the same paleogeographic domain. The impact of mineral fertility in detrital studies is eventually illustrated with examples from the Alpine region, based on alternative sampling strategies (i.e., the confluence sampling and the along-trunk sampling approaches). We show that geological interpretations are strongly improved when mineral fertility is properly taken into account, not only in modern settings, but also in ancient sedimentary successions.
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•Basic principles to test hydraulic sorting effects in detrital geochronology studies•A quantitative approach for routine mineral fertility determination in source rocks•Variable mineral fertility is the major source of bias in detrital geochronology.
Though the Alps may appear to be a peaceful place, the famed mountains once provided the backdrop for a political, environmental, and cultural battle as Germany and Austria struggled to modernize. ...Tait Keller examines the mountains' threefold role in transforming the two countries, as people sought respite in the mountains, transformed and shaped them according to their needs, and over time began to view them as national symbols and icons of individualism. In the mid-nineteenth century, the Alps were regarded as a place of solace from industrial development and the stresses of urban life. Soon, however, mountaineers, or the so-called apostles of the Alps, began carving the crags to suit their whims, altering the natural landscape with trails and lodges, and seeking to modernize and nationalize the high frontier. Disagreements over the meaning of modernization opened the mountains to competing agendas and hostile ambitions. Keller examines the ways in which these opposing approaches corresponded to the political battles, social conflicts, culture wars, and environmental crusades that shaped modern Germany and Austria, placing the Alpine borderlands at the heart of the German question of nationhood.
Indices of connectivity are critical means for moving from qualitative to (semi-)quantitative evaluations of material (e.g., water, sediment and nutrients) transfer across the building blocks of a ...terrestrial system. In geomorphology, compared to closely related disciplines like ecology and hydrology, the development of indices has only recently started and as such presents opportunities and challenges that merit attention. In this paper, we review existing indices of sediment connectivity and suggest potential avenues of development for meeting current basic and applied research needs. Specifically, we focus on terrestrial geomorphic systems dominated by processes that are driven by hydro-meteorological forcing, neglecting seismically triggered events, karstic systems and environments controlled by eolian processes.
We begin by setting a conceptual framework that combines external forcings (drivers) and system (intrinsic) structural and functional properties relevant to sediment connectivity. This framework guides our review of response variables suitable for sediment connectivity indices. In particular, we consider three sample applications concerned with sediment connectivity in: (i) soil studies at the plot scale, (ii) bedload transport at the reach scale, and (iii) sediment budgets at the catchment scale. In relation to the set of response variables identified, we consider data availability and issues of data acquisition for use in indices of sediment connectivity. We classify currently available indices in raster based, object or network based, and indices based on effective catchment area. Virtually all existing indices address the degree of static, structural connectivity only, with limited attention for process-based, functional connectivity counterparts. Most recent developments in indices of sediment connectivity deal, to some extent, with different styles of anthropogenic and hydro-meteorological forcings and with the temporal variability of sediment connectivity, by incorporating additional variables and parameters in existing indices. We believe that, in order to use structural connectivity as explanatory or predictive tool, indices need to be interpretable in relation to geomorphic processes, material properties, and forcing styles and magnitude-frequency spectra. Improvements in this direction can be made through studies shaped to constrain structural-functional correlations across a range of hydro-meteorological scenarios, for example employing field-based techniques such as particle tracking and sediment provenance analysis, as well as numerical simulations.
We further consider existing indices in relation to spatial and temporal scales. The latter have immediate implications on the distinction and application between indices and models of sediment connectivity. In this context, we suggest that sediment connectivity over millennial or longer time scales should be dealt with models, as opposed to indices.
•Elevated pH promoted colloid formation in calcareous soils.•Ca acted as the bridging agent for colloidal formation.•Colloids in mineral soil layers originated from surface organic layers.•Retention ...of dissolved P accounted for P accumulation in deeper soil layers.•Colloids were more responsible than soil electrolytes for P loss to deeper soil horizons.
Dissolved and colloidal phosphorus (P) represent the mobile P fractions in soils, but their role in P cycling in forests is still largely unclear. In this study of four calcareous forest soil profiles, the elemental compositions of different size fractions of water dispersible colloids (WDC) were investigated by asymmetric field flow fractionation. Nuclear magnetic resonance spectroscopy (NMR) was applied to identify the organic P compounds in soils, WDC, and soil solutions. Carbon was the dominant element in WDC of all soil horizons, including mineral soils that were rich in Ca or Si. Although chemical composition of P varied dramatically with increasing depth, the colloidal P composition remained unchanged. This contrasting difference between mineral soil and its WDC fraction indicated that the colloids were not locally generated but originated from the overlying organic soil horizons. Carbonate minerals were unlikely involved in colloid formation under acidic condition. Instead, Ca2+ probably drove colloid formation by bridging organic matter, including P-containing compounds released from litter degradation. Colloid formation was influenced by climate, vegetation, and soil characteristics. No dissolved P was detected in deeper mineral soil horizons due to efficient retention by Ca minerals. Colloidal P was still present in deeper soil layers and thus of significance for potential P vertical transfer.
The Pennine domain of the Central and Western (PCW) Alps, including the Dora‐Maira, Monte Rosa, Gran Paradiso, Adula/Cima Lunga nappes and the Zermatt‐Saas zone underwent ultrahigh‐ or high‐pressure ...(U)HP >1.5 GPa metamorphism during the Alpine orogeny. We review structural, petrological and geochronological data for the (U)HP units in the PCW Alps (i) to clarify the relationship between (U)HP metamorphism and deformation, (ii) to confront published exhumation models for the (U)HP units with the reviewed data and (iii) to evaluate consequences of different pre‐Alpine paleogeographic settings (Penrose‐type ocean v. hyperextended margins) on the Alpine orogeny. The review indicates that (i) peak pressures are recorded only in minor volumes of the corresponding tectonic nappes; (ii) (U)HP rocks occur within coherent and imbricate thrust sheets which show substantial pressure jumps; (iii) peak pressures are mostly associated with a top‐to‐the‐foreland kinematics; (iv) decompression from (U)HP (4 to >1.5 GPa) to greenschist or amphibolite facies (~1 GPa) metamorphic conditions was fast (< c. 2 Ma); and (v) accreted fragments of the Alpine–Tethyan basins reflect Mesozoic hyperextended margins rather than mature Penrose‐type oceans. The comparison of these characteristics with numerical exhumation models suggests that exhumation of (U)HP rocks by buoyancy‐driven return flow within a subduction channel under near‐lithostatic pressure is unlikely because (i) models predict volumes of (U)HP rocks that are more than an order of magnitude larger as observed in the PCW Alps and (ii) the required top‐to‐the‐hinterland (U)HP kinematics in the hangingwall of (U)HP units has not been observed until now. Also, the buoyancy‐driven exhumation of the individual crustal (U)HP units within weak (≤1019 Pa s) and denser (> ~3180 kg m−3) rocks is questionable, because there is no evidence of such rocks around the (U)HP units. An alternative model, which could explain the main characteristics of the (U)HP units in the PCW Alps, is an orogenic wedge model that (i) involves dynamic stresses deviating from lithostatic pressure and (ii) is formed during the convergence of hyperextended margins. Deviations of dynamic stresses from the lithostatic pressure and local pressure variations cannot be excluded during the Alpine orogeny, but these deviations and variations have not been clearly identified until now.
We investigated complex tectonic structures within a km-scale shear zone (Cima Lunga unit), which is traditionally interpreted as generated by multiple, distinct deformation phases, despite showing ...unique schistosity and lineation. Based on structural analyses we discovered sheath folds developed in relatively weak gneissic/schistose rocks, enveloping inclusions of stronger ultramafics. The internal layering of inclusions experienced superimposed folding, boudinage and folding, attesting to layer-parallel shortening followed by stretching and further again shortening. Using 3D numerical modelling, we explored the structure evolution within and around deformable viscous inclusions under far-field simple shear. The numerical results showed that the internal deformation of ellipsoidal inclusions and the fold development around the inclusions are both dependent on the viscosity ratio, shear strain and the inclusion aspect ratio. The Cima Lunga structural patterns were reproduced for finite strains exceeding 7.5 and viscosity ratio between 2.8 and 9. Inclusions are characterized by persistent rotation of the internal layering, resulting in super-simple shear regime, with kinematic vorticity number >1. An important corollary is that ultramafics and host rocks experienced coupled deformation since the prograde metamorphic evolution. Finally, we emphasise that progressive deformation in shear zones may offer sufficient explanation for complex structural patterns, without invoking unjustified polyphase deformation.
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•We study 3D deformation pattern within and around deformable inclusion in simple shear.•Sheath folds can develop around deformable inclusions.•Super-simple shear deformation develop within deformable inclusions.•Cima Lunga structures are likely formed during single, progressive deformation phase.•Backward modelling supplies constraints on the rock rheology and shear strain.
We report fault slip data from exhumed fault surfaces along the NNE trending Alpenrhein valley and its intersection with the WNW striking Bodensee Graben near the Alpine thrust front of the Central ...Alps in the Swiss‐Austrian‐German border region. This conjugated graben system straddles the boundary between the Alps and its foreland and allows comparing the kinematics of graben formation between the two different tectonic domains. Our data show sinistral transtension along the Alpenrhein Graben and dextral transtension along the Bodensee Graben. Both transtensional graben systems resulted from the same kinematic regime of NW directed shortening and NE oriented extension. The graben faults are not older than NW striking tear faults associated with NW directed Oligocene nappe emplacement in the Helvetics starting at 35–30 Ma and ending by 25–20 Ma. Compatible with this are six U‐Pb ages of calcite fibers from four samples yielding consistent ages ranging from 25.3 ± 5.6 Ma to 21.8 ± 3.4 Ma (2σ errors). Earthquake data since 1996 show that kinematic directions persisted until the Recent. Our data broadly fit with the kinematic evolution of the Oberrhein Graben, which shows significant E‐W extension in the Oligocene. We suggest that Oligocene extension in the Alps and its foreland resulted from the increased curvature of the Western Alps arc and associated moderate tangential stretching in the internal parts of the Central Alps. We discuss a tectonic model of eastward rollback of the west Mediterranean subduction zone associated with counterclockwise rotation of Adria, the latter of which aided the formation of the Western Alps arc.
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Transtensional graben system at transition between Central Alps and its foreland studied for first time
Links graben kinematics to formation of Western Alps arc and rollback of west Mediterranean slab
Application of novel dating technique of fibers on fault planes
The estimation of the peak metamorphic temperature by Raman spectroscopy of carbonaceous material (RSCM) is influenced by several bias sources grouped in measuring conditions, spectral processing and ...sample heterogeneity. The measuring conditions (selected excitation wavelength) and the operator bias during spectral processing have a pronounced impact on the temperature estimate and thus on the comparability and portability of thermometric data obtained by RSCM. Several calibration lines of RSCM geothermometers are published already, but no standardised approach exists. Samples of carbonaceous material bearing metasediments with well‐established metamorphic conditions of the central and western Alps compile a reference series. By applying an automated, iterative and randomised curve‐fitting approach, a consistent and user input‐independent RSCM geothermometer is presented, which covers peak metamorphic temperatures from ca. 160 to 600 °C. The method is hardware independent because the measuring conditions bias is excluded by the use of the reference series and the automated curve‐fitting approach reduces the spectral processing bias effectively, increasing the method's comparability and portability. By distributing the reference series and the automated curve‐fitting software, a laboratory will be able to derive a laboratory specific calibration line for the RSCM geothermometer.
Key Points
Based on a novel evaluation scheme and a reference series a standardized methodology to RSCM geothermometry is presented.
The Scaled Total Area (STA)‐RSCM approach will increase the comparability of RSCM geothermometric data.
The STA‐RSCM approach provides a continuous geothermometer from ca. 160 to 600 °C
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