Earth Sciences
Earth Sciences and Geographical Information Systems (GIS) underpin key aspects of the Environmental Initiatives Research Group's activities at the University of the West of Scotland.
Earth Science provides insights from the predominantly solid part of the Earth System and offers the methodologies used in geological investigations.
GIS is a growing area centred upon our recently acquired Spatial Pattern Analysis (SPAR) Laboratory. Here we can apply geo-spatial software tools and methods to the evaluation of any data set that is geographically distributed, model spatial patterns relevant to the environment and develop environmental decision-making tools. The SPAR laboratory is now the focus for work across all activity areas of the EIRG. There are also software tools for non-GIS work in geology and geochemistry.
Earth Sciences
Our Earth Sciences research focuses on "geo-materials" issues, encompassing mineralogical, petrological and structural aspects of solid-Earth and related systems. In addition to fundamental research on aspects of deep-lithospheric dynamics and orogenic evolution, mineralogical and petrological studies in the wider sense underpin several aspects of research in the Environmental Initiatives Research Group, including soils, sediments and wastes and water quality. It also supports research by the Historic Masonry Group into construction materials, for example linking environmental / biotic factors to materials in weathering of natural stone. The main active research areas involving the Earth Science are:
- Mineralogical aspects of soils and contaminated land research
- Durability, conservation and resource availability of natural stone construction materials
- Microbial interactions with minerals and rocks
- Novel imaging techniques using scanning electron microscopy
- Geodynamics of crust-mantle interactions at ultra-high pressures in continental collision zones
For publications in the Earth Sciences, please click here.
Mineralogical aspects of soils and contaminated land research
Soils, mine wastes and many other industrial wastes are complex aggregates of solids that are largely constituted from mineral, or mineral-like materials, i.e. crystalline or amorphous materials originating, or processed, from rocks or ore deposits. The physical properties of such materials and their local environment (both physical and biotic) combine to drive weathering processes that may lead to the release of toxic compounds into the biosphere and hydrosphere, and ultimately to human consumption. When developing risk assessments for dealing with contaminated sites it is important to build conceptual models incorporating factors that influence the mobility of pollutant chemical species. Application of methods from the mineral and geochemical sciences allows us to evaluate the stability of mineral or mineral-like phases in soil, spoil and sediment derived from them. Mobilisation of pollutants may involve simple or incongruent dissolution, but may also involve adsorption onto mineral surfaces, so that mineral particles can act as pollutant carriers in sedimentary systems. In all cases the factors influencing mobility combine in a complex interplay of geochemical, physical and biological processes.
Our Earth Science research seeks to unravel these factors through a combination of field and laboratory studies, experimental model systems and theoretical modelling. To date, this work has focused upon chromium, zinc, arsenic and antimony. A particular application of the mineralogical approach is petrography and X-ray element mapping using the SEM. This facilitates identification of the primary source mineral phases of potential pollutants, their weathering products, and particles which may be effective in surface adsorption processes. We have also made preliminary investigation on zinc-rich steel process by-products using synchrotron EXAFS analysis at Daresbury. Such observations may be combined with bulk geochemical extraction methods and Geochemist's Workbench modelling to give more detailed insights into pollutant behaviour. We have also investigated uptake of bio-available pollutant species into the biota, including the role of bio-mineralisation in sequestering As and Sb.
Some recent projects include:
- Biogeochemistry of arsenic and antimony: Risk assessment in mining areas - based upon a small-scale, but long-term mining and smelting site in an upland catchment at Glendinning in the Scottish Southern Uplands, and the Po basin, northern Italy. PhD project funded by University of Paisley, in collaboration with University of Turin. Click here for more details...
- Characterisation of steel process by-products for remediation and recycling - focusing on zinc-enriched smelter waste in settling ponds in active UK steel production sites. Funded by Corus UK. Click here for more details...
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Microbial interactions with minerals and rocks
Single celled organisms such as bacteria, fungi and algae are well known for producing mineral material (bio-mineralisation) and degrading or corroding it (biodegradation). As such they have important influences in natural weathering processes and surface damage to natural stone construction materials. Biodegradation results directly from action by the living cell, but also indirectly due to the decomposition products of dead microbes and due to the local micro-environments that they create, such as the slimy biofilms that colonies of micro-organisms often generate. Biofilms may influence the physical properties of mineral surfaces as well as the local chemical environment.
We have undertaken two very different studies of microbial interactions with minerals and rock:
- Algal degradation of natural stone masonry: The effects of micro-algae on natural rock and masonry surfaces are less well known, and thought to be less aggressive than fungi, lichens and cyano-bacteria. However, algal biofilms are commonly oberved on porous natural stone buildings as the familiar green staining. Carefully controlled experiments in which algal biofilms were grown on common rock-forming mineral specimens demonstrated that dissolution was, indeed, mediated by micro-algae. Experiments in which algae were cultured on sandstone showed that the biofilm helps to maintain a humid, and hence potentially corrosive micro-environment. Furthermore, when dessication does take place the algal filaments are strong enough to cause disaggregation of the rock fabric as they shrink and pull against surface grains to which they are attached. The results have implications for conservation and maintainence practice on natural stone masonry, and for weathering rates of rock surfaces in humid climates. The research was done during 2003-6 as part of a PhD project funded by the University of Paisley (now UWS) from 2003-2006. See publications by Welton et al. here.
- Microbial influences on properties of oilfield sandstone core samples: Wettability of mineral surfaces in porous rocks has a strong influence on the distribution and flow of multiphase fluids such as water, oil and gas. Quartz is the major mineral constituent of sandstones, and often often forms pore-lining surfaces, especially where diagenetic quartz cement has formed. We examined the wettability characteristics of quartz surfaces by direct observation in an environmental scanning electron microscope (ESEM), where it possible to image wet samples and to grow water droplets by adjusting the water vapour pressure in the sample chamber. Pristine quartz surfaces are usually hydrophilic (water-wetted), but when coated with a fungal or bacterial biofilm it becomes hydrophobic (water-repellent). Oilfield core may become colonised with microbes within days of drilling, and tests for petrophysical properties may not take place until after that. Hence wettability and flow-properties of core may be changed prior to testing. The work was undertaken during 2003-6 as part of a PhD project in collaboration with the ESEM facility at the Institute of Petroleum Engineering at Heriot-Watt University.
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Durability, conservation and resource availability of natural stone construction materials
See Historic Masonry Group under Advanced Concrete & Masonry Centre web pages...
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Novel imaging techniques using scanning electron microscopy
The environmental scanning electron microscope (ESEM) has many advantages for analysis of difficult geological materials. Its capability to image surfaces of insulating materials without a conductive coating is the key to its usefulness. This is achieved by introducing a carefully controlled amount of vapour (usually water) into the sample chamber, which dicharges the accumulated charge on the sample surface, and cascades this charge to a special detector. By varying the vapour pressure it is possible to allow a controlled amount of charge to accumulate, which influences the amount of charge subsequently released to the detector (see Griffin, 1997 Microscopy & Micro-analysis 3 (supp. 2), 1197-1198, and Watt et al., 2000 American Mineralogist 85, 1784-1794). The image brightness can be correlated to microstructural and chemical features of the material, possibly due to the way in which lattice defects influence the rates of charge trapping and release. The mechanism is not well understood, but has close links to the mechanism causing cathodoluminescence (CL).
This little-known method - Charge Contrast Imaging (CCI) - has advantages over CL in that it can image samples high in quenching elements such as Fe. Thus we have been applying CCI to metamorphic almandine-rich garnets and other high-pressure phases, in collaboration with J. Buckman at the ESEM suite at the Institute of Petroleum Engineering at Heriot Watt University, Edinburgh, along with some ion-probe analysis of trace elements at the NERC ion probe facility at Edinburgh University. It has proved to offer an effective method for imaging microstructures that are invisible to other SEM methods, and for rapid reconnaisance mapping of trace element variation that could save costs for machine time in the use of quantitative microbeam techniques. There is potential for use in analysis of synthetic, industrial garnetoids. For further details see Cuthbert & Buckman (2005) American Mineralogist 90, 701-707. Current research is evaluating similarities with CL images in low-Fe, ultra-high pressure silicates from Dora Maira, Italian Alps in collaboration with workers at Bochum University, Germany.
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Geodynamics of crust-mantle interactions at ultra-high pressures in continental collision zones
The Earth's continents are traversed by linear zones of deformed rocks associated with the formation mountain chains. The Alps and the Himalaya are spectacular examples of these "orogens", but there are many others that are older and less obvious, such as the Caledonide orogen of northern Britain, eastern USA, Greenland and Scandinavia. Orogens are created where continents collide due to the motions of tectonic plates. Among the metamorphic rocks of orogens we find zones of rare, enigmatic rocks called eclogites that have formed at great depths, below that of the normal crust-mantle boundary or "moho", indicating that the crust in which they are found has been subducted some distance into the mantle. This is indicated by the presence of minerals that form at very high pressures, such as coesite or even diamond.
The discovery of rocks formed at "ultra-high" pressures during the last 25 years has challenged ideas about convergent plate boundary processes. Continental crust had been considered too buoyant to subduct in the same way that denser, oceanic crust is known to do, but it is now apparent that continental crust may be taken down to >150km. Eventually its buoyancy does take control and large masses of the subducted crust returns to the normal crustal levels, but some may be permanently sequestered in the mantle. During its sojourn in the mantle the crust undergoes profound transformations including densification, dehydration, decarbonation and even melting. Crust and mantle interact mechanically and exchange chemically. This may have profound consequences for mantle geochemistry, magmatism and ore genesis.
The interaction of subducted continental crust with the mantle is apparent from masses of mantle rocks (garnet peridotites) found within them. These have been caught up and carried to the surface by the subducted crust as it returned to the surface. Such "orogenic peridotites" are not only evidence supporting ideas about continental subduction, but they provide the only mappable samples of subcontinental mantle and give the "underside" story of the creation and modification of continents, complimenting studies of crustal rocks that once lay above them.
Current research includes:
- Metasomatic interactions between felsic and mafic/ultramafic rocks at ultrahigh pressures as analogues for mantle metasomatism due to continental subduction, Norwegian Caledonides.
- Decompression melting during exhumation - the case of the Western Gneiss Region, Norway.
- Eclogite facies metamorphism in the Scottish Highlands - implications for Rodinian supercontinent assembly and break-up (funding for field studies from Carnegie Trust for the Universities of Scotland).
- Structures and fabrics formed during "ultra-deep" continental subduction and emplacement of orogenic peridotites.
See details of last summer's UWS-hosted International Eclogite Field Symposium in Lochalsh, Northwest Highlands of Scotland.
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Geographical Information Systems (GIS)
Under construction......
Picture Highlights
Extremely coarse-grained, ultrahigh pressure garnet websterite near Selje, Norway - product of metasomatism during transient subduction of continental crust?
Polarising micrograph of relict diopside (bright colours) + plagioclase (white/grey) symplectite after the high-pressure clinopyroxene omphacite in a garnet amphibolite from the Central Highland Migmatite Complex, Grampian Highlands, Scotland. Dark grey to black grains are titanite and rutile. This is evidence for (Neoproterozoic) eclogite facies metamorphism in the sub-Dalradian basement to the Grampian block.
Electron microprobe X-ray map for calcium concentration in garnet (yellow to red), quartz (black) and pyroxene (speckled) in a Norwegian eclogite. Note healed crack pattern - this is mimicked by charge contrast image patterns (see below) resulting from different trace element abundances in new (yellow) versus old (red) garnet, which follow the Ca pattern. Analysis carried out at Bayerisches Geo-Institut, Germany.
Standard backscattered electron image of polished thin section cut through a garnet grain in an eclogite from Norfdjord, Norway. Garnet is pale grey. The image is featureless apart from cracks in the crystals and inclusions of other minerals.
Charge contrast image of the same garnet as above produced by gaseous secondary electron imaging on the environmental scanning electron microscope (ESEM) at Heriot-Watt University. The network of dark lines (e.g. at red arrow) appear to be sealed fractures. Ion probe data indicate that darker areas correspond to garnet volumes with lower concentrations of REE, Ti, Y and P and thus have lower vacancy defect densities.
Zinc-enriched smelter-waste settling pond, Redcar, England.
Sampling an old arsenic and antimony mining and smelter site, Glendinning, Scotland.
SEM image of algal filaments and biofilm cultured on a feldspar surface - small double window in smooth biofilm near centre shows corroded mineral surface.
Environmental SEM image of water droplets on kaolinite (spherical droplets, left) and quartz (low dome droplets, right) in sandstone, showing contrasting wetting characteristics of different mineral sufaces (image created in collaboration with Heriot-Watt University Dept. of Petroleum Engineering ESEM facility).