Episodic shear zone associated fluid flow in the Curnamona Province, South Australia

Two distinct generations of fluid flow associated with shear zone activity have been identified in Willyama Supergroup rocks of the southern Curnamona Province in northeastern South Australia. Fluids in the first event are inferred to have been sourced from the devolatilisation of Willyama Supergroup metasedimentary rocks during prograde metamorphism associated with the (1.61–1.58 Ga) Mesoproterozoic Olarian Orogeny. The second episode of fluid flow occurred during the (c. 500 Ma) Cambrian Delamerian Orogeny and resulted in localised rehydration of the Willyama Supergroup. Fluids were isotopically light and most likely sourced from prograde Delamerian metamorphism and dehydration of fault rocks and entrained meteoric waters that originally were involved in (c. 700 Ma) Neoproterozoic Adelaidean rifting. A key outcome of this study is the identification of this previously unrecognised fluid flow system that was active during the Delamerian Orogeny.     

Complex systems in aeolian geomorphology

Aeolian geomorphology provides a rich ground for investigating Earth surface processes and landforms as complex systems. Sand transport by wind is a classic dissipative process with non-linear dynamics, while dune field evolution is a prototypical self-organisation phenomenon. Both of these broad areas of aeolian geomorphology are discussed and analysed in the context of complexity and a systems approach. A feedback loop analysis of the aeolian boundary-layer-flow/sediment-transport/bedform interactions, based on contemporary physical models, reveals that the system is fundamentally unstable (or at most meta-stable) and likely to exhibit chaotic behaviour. Recent field-experimental research on aeolian streamers and spatio-temporal transport patterns, however, indicates that sand transport by wind may be wholly controlled by a self-similar turbulence cascade in the boundary layer flow, and that key aspects of transport event time-series can be fully reproduced from a combination of (self-organised) 1/f forcing, motion threshold, and saltation inertia. The evolution of various types of bare-sand dunes and dune field patterns have been simulated successfully with self-organising cellular automata that incorporate only simplified physically-based interactions (rules). Because of their undefined physical scale, however, it not clear whether they in fact simulate ripples (bedforms) or dunes (landforms), raising fundamental cross-cutting questions regarding the difference between aeolian dunes, impact ripples, and subaqueous (current) ripples and dunes. An extended cellular automaton (CA) model, currently under development, incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas, blow-outs, and parabolic coastal dunes. Preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes. Progress is limited, however, by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale. State variables currently used in the bare-sand models are far from capturing the rich 3D topography and patterns and are not sufficiently discriminative to distinguish different attractors. The vegetation component in the extended model, and indeed ecogeomorphic systems in general, pose even graver challenges to establishing appropriate state variables. A re-examination of older concepts, such as landscape entropy, perhaps complemented by recent developments in information theory, may be a potentially fruitful avenue for research, although the outlines of such an implementation are still rather vague.     

On the nature of turbulent kinetic energy in a steep and narrow Alpine valley

This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions. The Riviera Valley in southern Switzerland was chosen for a detailed case study, in which the evaluation of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350-m horizontal grid spacing) large-eddy simulations using the numerical model ARPS. The simulations verify what has already been observed on the basis of measurements: TKE profiles scale surprisingly well if the convective velocity scale w _* is obtained from the sun-exposed eastern slope rather than from the surface directly beneath the profiles considered. ARPS is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production mechanism. Therefore, the surface heat flux (and thus w _*) on the eastern slope does not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction of thermally-driven cross-valley and along-valley flows. Excellent correlation between w _* and the up-valley wind speed solidifies this hypothesis.     

An efficient discontinuous Galerkin method for advective transport in porous media

We consider a discontinuous Galerkin scheme for computing transport in heterogeneous media. An efficient solution of the resulting linear system of equations is possible by taking advantage of a priori knowledge of the direction of flow. By arranging the elements in a suitable sequence, one does not need to assemble the full system and may compute the solution in an element-by-element fashion. We demonstrate this procedure on boundary-value problems for tracer transport and time-of-flight.     

Hierarchical evaluation of IPCC AR4 coupled climate models with systematic consideration of model uncertainties

The capability of reproducing observed surface air temperature (SAT) changes for the twentieth century is assessed using 22 multi-models which contribute to the Intergovernmental Panel on Climate Change Fourth Assessment Report. A Bayesian method is utilized for model evaluation by which model uncertainties are considered systematically. We provide a hierarchical analysis for global to sub-continental regions with two settings. First, regions of different size are evaluated separately at global, hemispheric, continental, and sub-continental scales. Second, the global SAT trend patterns are evaluated with gradual refinement of horizontal scales (higher dimensional analysis). Results show that models with natural plus anthropogenic forcing (MME_ALL) generally exhibit better skill than models with anthropogenic only forcing (MME_ANTH) at all spatial scales for different trend periods (entire twentieth century and its first and second halves). This confirms previous studies that suggest the important role of natural forcing. For the second half of the century, we found that MME_ANTH performs well compared to MME_ALL except for a few models with overestimated warming. This indicates not only major contributions of anthropogenic forcing over that period but also the applicability of both MMEs to observationally-constrained future predictions of climate changes. In addition, the skill-weighted averages with the Bayes factors [Bayesian model averaging (BMA)] show a general superiority over other error-based weighted averaging methods, suggesting a potential advantage of BMA for climate change predictions.     

Distribution and speciation of arsenic around roots in a contaminated riparian floodplain soil: Micro-XRF element mapping and EXAFS spectroscopy

Riparian soils are periodically flooded, leading to temporarily reducing conditions. Diffusion of O₂ through plants into the rhizosphere maintains oxic conditions around roots, thereby promoting trace element fractionation along a redox gradient from the reduced soil matrix towards the oxic rhizosphere. The aim of this study was to determine the distribution and speciation of arsenic around plant roots in a contaminated (170-280 mg/kg As) riparian floodplain soil (gleyic Fluvisol). The analysis of soil thin sections by synchrotron micro-X-ray fluorescence (μ-XRF) spectrometry showed that As and Fe were enriched around roots and that As was closely correlated with Fe. Arsenic contents of three manually separated rhizosphere soil samples from the subsoil were 5-9 times higher than respective bulk As contents. This corresponds to the accumulation of about half of the total As in the subsoil in Fe-enrichments around roots. The speciation of As in the soil was assessed by oxalate extractions at pH 3.0 as well as by X-ray absorption near edge structure (XANES) and extended X-ray fine structure (EXAFS) spectroscopy. More than 77% of the total As was oxalate extractable in all samples. XANES and EXAFS spectra demonstrated that As was predominantly As(V). For the accurate analysis of the EXAFS data with respect to the bonding of As(V) to the Fe- or Al-octahedra of (hydr)oxides and clays, all 3-leg and 4-leg multiple scattering paths within the As^(V)O₄-tetrahedron were considered in a fully constrained fitting scheme. We found that As(V) was predominantly associated with Fe-(hydr)oxides, and that sorption to Al- and Mn-hydroxides was negligible. The accumulation of As in the rhizosphere may affect As uptake by plants. Regarding the mobility of As, our results suggest that by oxygenation of the rhizosphere, plants attenuate the leaching of As from riparian floodplain soils during periods of high groundwater levels or flooding.     

The northern Upper Rhine Graben: basin geometry and early syn-rift tectono-sedimentary evolution

A large-scale transfer zone subdivides the northern parts of the Upper Rhine Graben into a northern and a southern sub-basin. These sub-basins display the geometry of asymmetric half-grabens with opposing tilt directions. The transfer zone connects the western master fault of the northern half-graben with the eastern master fault of the southern half-graben. In the northern Upper Rhine Graben early syn-rift sedimentation (Late Priabonian to Late Rupelian) was controlled by the tectonically induced subsidence of these half-grabens (autogenetic), as well as by regional third-order sea level variations (allogenetic). Within the graben, lateral changes in subsidence rates (in dip and strike direction of fault blocks) controlled the development of accommodation space and thus, sediment thickness and facies. Furthermore, a low-displacement segment along the western border fault acted as a sediment entry point. Tectonics controlled the distribution of early syn-rift deposits and the palaeogeography of the northern Upper Rhine Graben.     

Magmatic-to-hydrothermal crystallization in the W–Sn mineralized Mole Granite (NSW, Australia): Part II: Evolving zircon and thorite trace element chemistry

The Sn–W mineralized Mole Granite in Eastern Australia hosts zircon populations that crystallized at several stages during a protracted magmatic to hydrothermal evolution. Thirty-four elements have been quantified by laser-ablation inductively-coupled-plasma mass-spectrometric microanalysis with the aim of relating the chemistry of zircon to its growth environment. Trace element contents are highly variable for all textural occurrences. Zircon inclusions in earliest quartz phenocryst suggest that zircon was a liquidus phase that crystallized probably deep in the crust. Trace element contents are conspicuously high, showing only a slight positive Ce anomaly but a pronounced negative Eu-anomaly. Successive crystallization stages of magmatic zircon are characterized by progressive depletion in trace element contents, notably the rare earth elements, with an increasingly important positive Ce-anomaly. This evolution reflects saturation of REE accepting minerals such as monazite, thorite, xenotime and possibly apatite and is affected little by the exsolution of a magmatic–hydrothermal fluid. Zircon that is interpreted to have precipitated from aqueous fluids in Sn–W-bearing quartz veins shows REE patterns indistinguishable from those of late magmatic zircon. When combined with experimental evidence on the fluid–melt partitioning of REE, it indicates that the REE distribution coefficients for zircon/melt and zircon/fluid are largely comparable.

The second example of hydrothermal zircon crystallized some 2 My after the host granite. These crystals reveal an intragranular zonation of increasing trace element concentrations from core to rim. Therefore, REE abundances and patterns alone are not conclusive indicators of the geological environment in which zircon crystallized. Nevertheless, variations in trace element contents of zircon that relate to the chemistry of the melt or fluid from which zircon crystallized, as measured in cogenetic melt and fluid inclusions, are promising for future petrogenetic modeling.

Lead and Cs are strongly incompatible in hydrothermal zircon, with estimated zircon–fluid distribution coefficients D ≤ 0.001, while Sn and Li are moderately incompatible, D_Sn  0.6 and D_Li  0.1, and Ce is compatible, D_Ce  14. Moreover, hydrothermal zircon has a more pronounced negative Eu-anomaly and higher Ta/Nb and U/Th ratios than the magmatic zircons of the Mole Granite.