Timing of orogenic gold mineralisation in northeastern Tasmania: implications for the tectonic and metallogenetic evolution of Palaeozoic SE Australia

New ⁴⁰Ar/³⁹Ar data from sedimentary rock-hosted orogenic gold deposits in northeastern Tasmania constrain most ore formation to between 395 Ma and 385 Ma. These 385–395 Ma ages for the formation of orogenic gold agree well with an inferred Early to Middle Devonian timing for peak deformation and folding across much of northeastern Tasmania. Data from micas within alteration halos in some deposits give dates of ~420–430 Ma; these dates confirm the occurrence of an earlier Silurian phase of deformation and suggest that at least some of the mineralisation was possibly generated during this event. Gold mineralisation hosted by Middle Devonian post-tectonic granites may be genetically related to magmatism following orogeny, but these deposits formed virtually synchronously with peak deformation-related systems. Early to Middle Devonian deformation in northeastern Tasmania also reactivated older structures in western Tasmania, and the formation of quartz vein-hosted gold mineralisation there. Based on geological, structural, tectonic and metallogenetic similarities, northeastern Tasmania is interpreted as a lateral equivalent of the turbidite-dominated fold-thrust belt of the western Lachlan Orogen. However, unlike Victoria, where the sedimentary rock sequence developed on oceanic crust, northeastern Tasmania was probably underlain by thinned Proterozoic crust, either as part of a promontory along the Gondwana margin or as a microcontinental fragment. This may have protected the Palaeozoic succession from large-scale, pre-Devonian orogeny, with collision not beginning until the Middle Devonian. These variations in the structural and tectonic evolution, and the timing of deformation and ore formation can explain the difference in contained gold, and the distribution and number of major orogenic gold deposits within the Palaeozoic of northeastern Tasmania.Electronic supplementary material Supplementary material is available for this article at     

The interaction between hydrology and geomorphology in a landscape simulator experiment

An experimental landscape simulator has been developed which uses a rainfall simulator to create overland flow and erosion. The simulator uses rainfall sprinklers that eliminate rainsplash and an artificial soil which has little cohesion. Experimental landscapes developed in the simulator evolved according to Howard's headward growth model. Elements of Glock's model could be identified during evolution (i.e. initiation and maximum extension), but other stages of this model were not observed (i.e. extension and integration). The Horton concept of cross‐grading and micropiracy and stream piracy was not observed despite the dominance of overland flow, nor the groundwater headward growth mechanism proposed by Dunne, the latter due to experimental design, which eliminated any perched groundwater table. The experimental apparatus produced model landscapes that are scaled‐down analogues of real world processes. Copyright © 2001 John Wiley & Sons, Ltd.     

Contribution de l'hydrogéomorphologie à l'évaluation du risque d'inondation : le cas du Midi méditerranéen français

The hydrogeomorphological method for delimiting flood risk zones in France was developed some twenty years ago. It is based on a simple principle: the outer limits of a stream's flood plain constitute the outer envelope of past floods. These limits are determined with the use of aerial photographs and field surveys of micro-topography as well as analyses of deposit granulometry and colour. Indications of present or past land use (fields, location and distribution of archaeological sites, houses and farm buildings, roads) are also useful. This field-based method long remained ignored, but being reliable, easy to use and inexpensive, it has now been incorporated into the package of methods recommended by French risk-prevention plans (PPRI). The many recent catastrophes that have occurred over the past fifteen years in the Mediterranean regions of southern France demonstrated both the inadequacy of the hydrological–hydraulic method and the reliability of the hydrogeomorphological method, which can, however, be improved by setting observations for the present period against information on the more ancient Holocene evolution of flood plains. To cite this article: J.-L. Ballais et al., C. R. Geoscience 337 (2005).     

The production of digital elevation models for experimental model landscapes

Automated digital photogrammetry was used to produce digital elevation models of experimental model landscapes under controlled laboratory conditions as part of a series of rainfall erosion experiments looking at the evolution of landforms in response to erosion. The method allowed the elevations of the experimental landscapes to be studied in great detail on a regular grid digital terrain map with relatively very little effort. Digital photogrammetry produced elevation data at a resolution of 6 mm with a standard deviation of 2·0 mm over an experimental catchment relief of approximately 200 mm; this resolution is considerably better than that achievable by conventional manual photogrammetry. The density of grid points was sufficiently high that small‐scale details such as knickpoints developing in channels were represented. The method can facilitate the study of both experimental and natural landscapes in great detail. Copyright © 2001 John Wiley & Sons, Ltd.     

Implications of decadal to century scale glacio‐hydrological change for water resources of the Hood River basin,OR, USA

In glacier‐fed rivers, melting of glacier ice sustains streamflow during the driest times of the year, especially during drought years. Anthropogenic and ecologic systems that rely on this glacial buffering of low flows are vulnerable to glacier recession as temperatures rise. We demonstrate the evolution of glacier melt contribution in watershed hydrology over the course of a 184‐year period from 1916 to 2099 through the application of a coupled hydrological and glacier dynamics model to the Hood River basin in Northwest Oregon, USA. We performed continuous simulations of glaciological processes (mass accumulation and ablation, lateral flow of ice and heat conduction through supra‐glacial debris), which are directly linked with seasonal snow dynamics as well as other key hydrologic processes (e.g. evapotranspiration and subsurface flow). Our simulations show that historically, the contribution of glacier melt to basin water supply was up to 79% at upland water management locations. We also show that supraglacial debris cover on the Hood River glaciers modulates the rate of glacier recession and progression of dry season flow at upland stream locations with debris‐covered glaciers. Our model results indicate that dry season (July to September) discharge sourced from glacier melt started to decline early in the 21st century following glacier recession that started early in the 20th century. Changes in climate over the course of the current century will lead to 14–63% (18–78%) reductions in dry season discharge across the basin for IPCC emission pathway RCP4.5 (RCP8.5). The largest losses will be at upland drainage locations of water diversions that were dominated historically by glacier melt and seasonal snowmelt. The contribution of glacier melt varies greatly not only in space but also in time. It displays a strong decadal scale fluctuations that are super‐imposed on the effects of a long‐term climatic warming trend. This decadal variability results in reversals in trends in glacier melt, which underscore the importance of long‐time series of glacio‐hydrologic analyses for evaluating the hydrological response to glacier recession. Copyright © 2016 John Wiley & Sons, Ltd.     

Laboratory simulation of the salt weathering of schist: 1. Weathering of schist blocks in a seasonally wet tropical environment

Data describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long‐term landform evolution. This paper presents such data for the salt weathering of a quartz‐chlorite schist obtained from the Ranger Uranium Mine in northern Australia. Rock fragment samples are subjected to three different climate regimes: (1) a dry season climate; (2) a wet season climate (both based on observations at the Ranger site); and (3) an oven‐drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures. Two MgSO₄ salt solutions are applied, one being typical of wet season runoff and the other a more concentrated solution. Salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments. Results of the experiments reveal four stages of weathering. The kinetics of each stage are described and related to the formation of sediment of different sizes. Wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates. However, salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations, the dry and wet season experiments weather at approximately equal rates. Finally, small variations in rock properties were shown to have a large impact on weathering rates, leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale. Copyright © 2006 John Wiley & Sons, Ltd.