Fractured Crystalline Rocks (FCR) are being considered in several countries as hosts for radioactive waste repositories. In FCR, radionuclides may be transported relatively rapidly by bulk groundwater flow through open fractures, but much more slowly by diffusion through porewater in the rock matrices. Rock matrix diffusion (RMD) is the diffusion of radionuclides in the aqueous phase, between open fractures and rock matrices. Sorption or co-precipitation on the fracture surfaces and walls of the matrix pores causes further radionuclide retardation. RMD may be important in a repository's safety case and has been investigated by many published short-term (to a few years) laboratory and in-situ experiments. To improve understanding over longer timescales, we investigated evidence for RMD of several natural radioelements, and radioelement analogues, in five exemplar fractured crystalline rock (FCR) samples aged between c. 70 Ma and c. 455 Ma. The sample suite consisted of two samples of Borrowdale Volcanic Group (BVG) meta-tuff from northwest England, a sample of Carnmenellis Granite from southwest England and two samples of Toki Granite from central Japan. Uptake or loss of the studied elements is limited to an altered damage zone in each sample, coupled to mineral alteration processes. These zones are most extensive (a few tens of millimetres) in the Toki Granite samples. We also found unstable primary igneous minerals to persist in the immediate wallrocks of fractures in studied granite samples, suggesting that pores were not permanently water saturated in these samples. Although only a small sample suite was studied, the results show that while RMD may be important in some kinds of FCR, in others it may be negligible. Site-specific information is therefore needed to determine how much reliance can be placed on RMD when developing a safety case.
Abstract Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments. However, details of the syn-depositional chemical processes by which the isolated spherical shape developed and the associated carbon sources are little known. Here we present evidence that spherical carbonate concretions (diameters φ : 14 ~ 37 mm) around tusk-shells ( Fissidentalium spp.) were formed within weeks or months following death of the organism by the seepage of fatty acid from decaying soft body tissues. Characteristic concentrations of carbonate around the mouth of a tusk-shell reveal very rapid formation during the decay of organic matter from the tusk-shell. Available observations and geochemical evidence have enabled us to construct a ‘Diffusion-growth rate cross-plot’ that can be used to estimate the growth rate of all kinds of isolated spherical carbonate concretions identified in marine formations. Results shown here suggest that isolated spherical concretions that are not associated with fossils might also be formed from carbon sourced in the decaying soft body tissues of non-skeletal organisms with otherwise low preservation potential.
Generic approaches for determining the spatial and temporal variability of a fault's hydrogeological properties are being developed by studying the reversed Tsukiyoshi Fault at Tono, central Japan. This fault is associated with zones of deformation/damage that are sometimes wider than the fault's displacement. The hydraulic characteristics probably vary laterally over metres to tens of metres and the hanging wall and foot wall have different hydraulic properties. It is also possible that some of these properties may have changed over time, due to physical processes and/or to water/rock interactions, even at relatively low-temperatures and pressures (to a few tens of degrees centigrade and hundreds of bars). It is suggested that mineralogical and structural data can be used to estimate the most transmissive conditions within a fault in the past. These estimates can then be used to select conservative (‘worst-case’) fault parameters for assessing the future safety of underground waste repositories. Such information can also be used to design a repository to avoid faults with permeable crush zones. The study demonstrates the value of integrating detailed mineralogical and petrological studies into a borehole drilling programme for characterizing the hydraulic properties of faults.
Journal Article Priessnitz Get access Richard Metcalfe Richard Metcalfe 1Priessnitz House Hydropathic Establishment, Paddington Green, W. Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume s7-XI, Issue 271, 7 March 1891, Page 198, https://doi.org/10.1093/nq/s7-XI.271.198b Published: 07 March 1891
Abstract Following the early Eocene collision of India and Asia, continental subduction occurred on the northward-dipping Main Central Thrust (MCT). In western Garhwal, N. India, upper amphibolite-facies gneisses on the High Himalayan Slab are thrust southwards over unmetamorphosed to greenschist facies quartzites, carbonates and metabasics of the Lesser Himalaya. In the Bhagirathi valley, the MCT forms a c. 10 km thick shear zone composed of mylonitic augen gneiss, amphibolite and metasediments. Metamorphic grade increases both northwards and with structural height. The MCT zone is bounded to the north by the Vaikrita (roof) Thrust and to the south by the Munsiari (floor) Thrust. The Vaikrita Thrust is a diffuse high-temperature shear zone, whereas the Munsiari Thrust is a relatively discrete fault formed under brittle-ductile conditions. North of the MCT zone, at the top of the High Himalayan Slab a northward-dipping extensional shear zone, the Jhala normal fault, was responsible for the downthrow of the Tethyan sediments to the north with respect to the uplifting High Himalayan Slab gneisses to the south. Thermobarometic transects reveal a sudden increase in both pressure and temperature across the Vaikrita Thrust from south to north but with subsequent decreases accompanying structural height in the High Himalayan Slab. Temperatures increase going up-structural section from about 500° C to 770° C across the MCT zone, but then decrease again to the north varying between about 550 and 640° C. Similarly, pressures increase sharply up-structural section across the MCT zone from 6 to 12 kbar, then decrease towards the top of the slab to between 7 and 8.9 kbar. The inverted P-T gradient across the MCT zone changes to approximately isothermal and isobaric conditions in the top 9 km (horizontal distance) of the High Himalayan slab. Cooling rates for the upper MCT zone determined from 40 Ar/ 39 Ar (hornblende) and K-Ar (muscovite and biotite) cooling ages suggest a return to erosion-controlled denudation following extension at the top of the High Himalayan Slab. Additional K-Ar (muscovite) cooling ages from a transect through the MCT zone and High Himalayan Slab are progressively younger towards the south, reflecting the southward propagation of the deformation sequence with time. Hornblende 40 Ar/ 39 Ar cooling ages from the MCT zone suggest that structurally lower rocks have not been heated above c . 500° C since the Precambrian, whilst a 19.8 ± 2.6 Ma hornblende age from the MCT zone dates the latest high-temperature shearing at higher structural levels in the MCT zone and places a minimum age constraint on Himalayan metamorphism in the Garhwal sector of the Himalaya.
This paper reviews the application of a freely accessible on-line database of generic Features, Events and Processes (FEPs), designed to support the analysis of geological CO2 storage systems during performance assessments. The Generic CO2 FEP Database was established by Quintessa in 2004 through international collaboration under the auspices of the Weyburn project. Subsequently, development of the database has continued and its use has become widespread, with over 1000 people having registered to access the database. Most commonly, the database has been used as an audit tool to help build confidence that a systems analysis covers all relevant FEPs and to document transparently those FEPs that are not being considered. In other applications the generic FEP database has been screened to identify relevant FEPs that are then used directly to build conceptual models. As a generic resource, the Generic CO2 FEP Database covers the range of FEPs that might be relevant to assessments, from those associated with the storage formation and cap rock to potential impacts on humans and the environment. The range of applications to date demonstrates its use in support of different scales of assessment for different components of the system. Examples include total-systems models, assessments focusing solely on potential loss of containment from the storage formation and natural analogue studies of potential impacts. Over the past five years the use of the Generic CO2 FEP database has helped to build confidence in assessments relating to long-term geological storage. Additionally, the database represents a knowledge base relating to the potential performance and safety of storage systems. The experience gained from application of the database to date helps to inform the way in which it can be applied in future. The database continues to be developed, based on experience gained in its application. Recently references and links have been updated and a targeted review has revised descriptions and FEPs relating to the marine environment. Further targeted reviews and updates are planned. For the database to continue to structure the latest knowledge and understanding relating to geological storage, on-going feedback from its user base is sought.
This paper presents a structured qualitative approach to analysing the varied kinds of information from a CO2 storage site, so as to produce scenarios that are amenable to numerical analysis. The approach is illustrated by application to an industrial scale CCS project at Krechba, In Salah, in Algeria. A structured approach is needed to support assessments of the likely performance of CCS systems over operational, monitoring and longer term time-frames. Very varied information concerning such systems' engineered and environmental components must be obtained and evaluated to attain sufficient confidence that performance will be acceptable. Computer simulations and risk assessment models are needed to help understand the behaviour of CO2 and place plausible bounds on the temporal evolution of all aspects of the system. The outcomes will be uncertain, even if underpinning data sets are of good quality The approach included identification of the important the Features, Events and Processes (FEPs) that together describe the Krechba system and its likely evolution. An 'expected evolution' scenario was then identified by systematically evaluating existing knowledge. Scenarios describing potential situations that could involve alternative evolution mechanisms were also identified; these included consideration of mechanisms that could in principal lead to containment failure. These scenarios need to be analysed to show that they are either unlikely to occur and/or will be of limited impact and so do not represent threats to adequate performance. After audit against Quintessa's freely available generic online CO2 FEP database to ensure and demonstrate comprehensiveness, the site-specific scenarios identified and the associated list of remaining uncertainties, were used to prioritise future (e.g. systems modelling) work. The outcomes of this and other data analysis and modelling programmes will be used to update the FEP and scenario descriptions.
Abstract In granitic rocks, fracture networks typically provide pathways for groundwater flow and solute transport that need to be understood to assess the long‐term performance of deep underground storage or disposal facilities such as radioactive waste repositories. However, relatively little is known about the long‐term processes of fracturing and/or the longevity of flow paths ( FP ) in granitic rocks distributed within orogenic belts. To clarify these issues, J apanese plutons of different ages and in situ fractures in granite at the M izunami U nderground R esearch L aboratory ( MIU ) located in central J apan were studied. Detailed structural characterization and geochemical analysis of in situ fracture fillings sampled from a depth of 300 m were carried out to clarify the relationship between fracturing and mineral infilling processes. Different plutons show identical episodes of fracturing and fracture filling, consisting of: brittle tensile fracturing, due to decreasing temperature through the ductile–brittle transition after plutonic intrusion (Stage I); relatively rapid uplifting (ca. a few mm/year) accompanied by hydrothermal water circulation, which produced uncrushed layered mineral fillings (Stage II ); and a period of low‐temperature meteoric water circulation following exposure after uplift (Stage III ). The parageneses of carbonate mineral fracture fillings and their carbon isotopic compositions ( 14 C, δ 13 C) show that there were distinct episodes of carbonate mineral precipitation during the rapid uplifting of a pluton. The carbonate minerals that formed during each episode incorporated carbon from a distinct source. The evolution of fillings identified here enables development of a specific model of fracturing and persistence of fluid‐conducting systems in the plutons of the orogenic field.
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