Transient and steady-state deformation of synthetic rocksalt

Synthetic rocksalt with a porosity less than 2.5% and an average grain size of about 0.35 mm was made by warm-pressing at 100°C, 150 MPa and for 15 min. Cylinders of this material, 25 mm in diameter by 50 mm long, were deformed at strain rates of 0.1 ksec⁻¹ at confining pressures of 20, 50, 100 and 200 MPa and at temperatures of 100, 200 and 300°C. The resulting stress-time data show transient-stress behavior before steady-state stress occurs. Very little variation in the stress/time data occurs for the above confining pressures at a constant temperature. Many of the tests reach steady state at 10% strain, where all the experiments were terminated. The differential stress at 10% varies from about 22 MPa at 100°C to about 6 MPa at 300°C. These “strengths” are slightly less than those measured by Heard (1972) (also on synthetic, polycrystalline rocksalt) and are similar to those measured by Wawersik and Hannum (1980) and by Hansen and Mellegard (1980) in modified creep tests on coarse-grained, natural rocksalt under similar pressure and temperature conditions. Activation energies computed from these steady-state stresses vary between 7.5 and 25 kcal/mole and are consistent with those obtained by Heard (1972) and by Parrish and Gangi (1977, 1981). The stress/time data were fit using one- and two-mechanism, transient-stress functions which assume independent mechanisms or processes. The rms errors decrease from about 1 MPa for the one-mechanism fits to about 0.2 MPa for the two-mechanism fits, indicating at least two mechanisms are operative in these tests. Similar one- and two-mechanism fits were made to creep tests performed by W. Wawersik et al. on New Mexico bedded rocksalt. Similar improvements in the fits were obtained for those tests that lasted long enough so that the effect of a second mechanism could be noted. It was found that the “steady-state” strain rate found in creep tests could be interpreted as the beginning of another mechanism. This raises the question of whether the “steady-state” phenomena exist at all or whether it is just an approximation to a mechanism with a time constant that is long compared to the length of the test.     

Review of Microstructural Evidence of Magmatic and Solid-State Flow

Evidence of magmatic flow includes: (a) parallel to sub-parallel alignment of elongate euhedral crystals (e.g., of feldspar or hornblende) that are not internally deformed, (b) imbrication (‘tiling’) of elongate euhedral crystals that are not internally deformed, (c) insufficient solid-state strain in regions between aligned or imbricated crystals to accommodate phenocryst rotation, (d) elongation of microgranitoid enclaves without plastic deformation of the minerals, (e) magmatic flow foliations and elongate microgranitoid enclaves deflected around xenoliths, and (f) schlieren layering (if due to flow sorting) in the absence of plastic deformation of the minerals involved. These features are consistent with rotation of crystals in a much weaker medium, namely a melt phase, at a stage when the magma has become viscous enough to preserve the alignment.Evidence of solid-state flow includes: (a) internal deformation and recrystallization of grains, (b) recrystallized “tails,” (c) elongation of recrystallized aggregates (e.g. of quartz and mica), (d) grainsize reduction, (e) fine-grained folia anastomosing around less deformed relics, (f) microcline twinning, (g) myrmekite, (h) flame perthite, (i) boudinage of strong minerals, typically with recrystallized aggregates of weaker minerals (e.g. quartz and mica) between the boudins, (j) foliation passing through, rather than around enclaves, and (k) heterogeneous strain with local mylonitic zones.Several criteria suggest “submagmatic flow,” including recrystallized feldspar, inferred transitions from magmatic imbrication to solid-state S/C arrangements, evidence of c-slip in quartz, and especially evidence of migration of residual melt into lower-pressure sites.Recent experimental studies indicate that a change from grain-supported flow to suspension flow typically occurs in deforming magmas at melt contents of between 20% to 40%, and that large amounts of strain may accumulate in magmas without being recorded by the final fabric. At lower melt percentages, perhaps as low as a few percent, depending on the minerals and their shapes, strain may be accommodated by: (a) melt-assisted grain-boundary sliding, (b) contact-melting assisted grain-boundary migration, (c) strain partitioning into melt-rich zones, (d) intracrystalline plastic deformation (c-slip in quartz indicating plastic deformation at temperatures near the granite solidus), and (f) transfer of melt to sites of low mean stress. The only indication of strain in the absence of crystal plasticity may be an alignment of crystals. Moreover, magmatic flow microstructures may be destroyed by fracturing, crystal plasticity and recrystallization before the magma reaches its solidus.Many rocks show evidence of solid-state flow superimposed on magmatic flow. Evidence of magmatic flow is commonly preserved in deformed felsic metamorphic rocks: for example the alignment of rectangular K-feldspar megacrysts and of microgranitoid enclaves. However, absence of alignment does not preclude a magmatic origin for K-feldspar megacrysts in felsic gneisses, as magmatic flow may cease before the magma becomes viscous enough to preserve an alignment.     

Ductile faulting, dynamic recrystallization and grain-size-sensitive flow of olivine

Twiss (1976) has suggested that the “ductile faulting” events observed by Post (1973) during high temperature creep of dunite are due to a transition from creep by dislocation movement to a diffusion accommodated, grain-boundary sliding mechanism following a reduction in grain size by dynamic recrystallization. Similarly, Goetze (1978) has explained both ductile faulting and water weakening of dunite by transition to a “nonlinear Coble” creep mechanism. However, the fundamental assumption made by Twiss (1976) that the stress exponent, n, reduces to unity during ductile faulting events is questionable. If the stress exponent remains high, (n≥3), then a diffusion-accomodated grain-boundary sliding mechanism is excluded. “Nonlinear Coble” creep would remain a viable alternative; however, this model fails to adequately explain the water weakening phenomenon, and the available data do not constrain us to this model. Assuming that the water-weakening phenomenon can be explained by other models (e.g., Blacic, 1972), it will be shown (by analogy with the behavior of metals) that a third model, also consistent with the available data, also qualitatively explains the observations associated with ductile faulting without appeal to a transition in creep mechanisms. The model is similar to one for metals undergoing deformation by dislocation movement and recovery by dynamic recrystallization, which commonly exhibit behavior virtually identical to that observed in dunite during ductile faulting events without transition to grain-size-sensitive creep mechanisms.     

Flow behaviour and physical chemistry of bouncing putties and related polymers in view of tectonic laboratory applications

The initiation of analogue studies of rock flow is stimulated by improving our knowledge of suitable model materials. Bouncing Putties and “Plasticines” are the most frequently used model materials in analogue studies of flow instabilities in deforming rocks. Polydimethyl-siloxane (PDMS) and polyborondimethylsiloxane (PBDMS), both substrates of Bouncing Putty, are introduced as convenient geological model materials. The chemistry of PDMS, PBDMS, Bouncing Putties and “Plasticines” is reviewed. A comprehensive set of instructions and graphs is provided for the manipulation of these model materials.In particular, a high viscosity PDMS produced as an intermediate compound under the code name SGM36 by Dow Corning (Great Britain) opens exciting possibilities for analogue studies of rock flow, because it is perfectly transparent. This allows continuous observation of three-dimensional strain markers during an experiment.The polymeric flow mechanisms are compared with the flow behaviour and crystal plasticity theory of rocks. The flow of natural rocks is taken to be of Reiner-Rivlin type with powers n varying between 1 and 10.Flow curves have been constructed for Bouncing Putties, Plastilinas (cf. Plasticines) and SGM36 (cf. PDMS). These original curves are supplemented with extensive data on similar materials compiled from the literature. The combined data reveal a consistent flow curve pattern for each group of model materials considered.Strain-rate softening of commercially available Bouncing Putties and “Plasticines” at low strain rates can be attributed to the solid filler concentration. The power n, which describes the departure from Newtonian flow, appears to be dependent on the angular filler volume concentration c and is governed by the preliminary equation n = 1−11c + 48c². This finding provides a technique for manipulating liquid polymers to simulate natural rock flow with various powers of n.The (T, P) dependence of the viscosity and thermal properties of PDMS are outlined to stimulate modelling which includes natural (T, P) gradients.     

Stress and viscosity in the asthenosphere

Stresses and effective viscosities in the asthenosphere to a depth of 400 km are calculated on the basis of Weertmans “temperature method” i.e., on relating viscosity to the ratio of the temperature to the melting point (=homologous temperature). Some oceanic and continental geotherms and two melting point—depth curves, the dry pyrolite solidus and the forsterite₉₀ melting curve are used for the conversion of the homologous temperature to the effective viscosity. Two creep laws are considered, the linear, grain-size-dependent Nabarro—Herring (NH) creep law, and a power creep law, in which the creep rate is proportional to the third power of the stress. A plate tectonic model yields creep rates of 2 · 10⁻¹⁴ s⁻¹ for the oceanic and 3 · 10⁻¹⁵ s⁻¹ for the continental asthenosphere. These values are held constant for the calculations and may be valid for regions inside plates.The dry pyrolite mantle model results in high homologous temperatures in the asthenosphere below oceans (0.9), very low stresses (a few bars and lower) and shows a low viscosity “layer” of about 200-km thickness. Below continental shields the homologous temperature has a maximum value of 0.73, stresses are around 5–20 bar and the low-viscosity region is thicker and less pronounced than in the oceanic case. The Fo₉₀ mantle model generally gives lower homologous temperatures (maximum value below oceans beside active ridges 0.75). The stresses in the asthenosphere beneath oceans vary from a few bars to about 50 bar and below continents to about 100 bar. The low-viscosity region seems to reach great depths without forming a “channel”. The Figs. 1 and 2 show the approximate viscosity—depth distribution for the two mantle models under study.Assuming a completely dry mantle and a mean grain size of 5 mm, power law creep will be the dominating creep process in the asthenosphere. However, grains may grow in a high-temperature—low-stress regime (i.e., below younger oceans), an effect which will further diminish the influence of NH creep. In the upper 100–150 km of the earth some fluid phases may affect considerably creep processes.     

Evidence for cyclic reactions between andalusite, “sericite” and sillimanite, mount franks area, willyama complex N.S.W

In the Mt. Franks area of the Willyama Complex, microfabric evidence suggests that the alteration of andalusite to sillimanite has taken place by a process similar to that suggested by Carmichael (1969). Andalusite is pre- to syn-S₂ in age. Alteration to “sericite” has resulted in the formation of “sericite” laths, some of which are crenulated about S₂, and some which are syn- and post-S₂. “Fibrolite” occurs in these andalusite—“sericite” aggregates within the sillimanite zone and is wholly embedded in “sericite”. “Fibrolite” is pre- to syn-S₂ in age. This evidence is interpreted as suggesting that the formation of sillimanite from andalusite took place via a “sericite” phase.Further microfabric observations are interpreted to imply constant volume for the reaction aluminosilicate → “sericite”. This suggests a situation in which Al³⁺ is relatively mobile but Al⁴⁺ is relatively immobile. This suggestion differs from Carmichael's (1969) idea of Al³⁺ immobility.     

Ductile deformation of garnet in mylonitic gneisses from the Münchberg Massif (Germany)

Mylonitic gneisses from the Münchberg Massif contain single grains (type I) and polycrystalline aggregates (type II) of garnet displaying a distinct elongation parallel to a macroscopic lineation which is interpreted as the result of ductile deformation. Lattice-preferred orientations of quartz (textures) symmetrical to the macroscopic foliation and lineation and the lack of rotational microfabrics indicate that the bulk deformation was pure shear at least during the latest strain increments. Garnet textures measured by EBSD together with microprobe analyses demonstrate that these two structural types of garnet can be related to two different processes of ductile deformation: (1) For the single grains stretching can be attributed to diffusion creep along grain boundary zones (Coble creep). The related mass transfer is indicated by the fact that primary growth zones are cut off at the long faces of the grains while the related strain shadow domains do not show comparable chemical zoning. Pressure solution and precipitation suitable to produce similar structures can be largely ruled out because retrogressive reactions pointing to the presence of free hydrous fluids are missing. (2) For the polycrystalline garnet aggregates consisting of cores grading into fine-grained mantles, dislocation creep and associated rotation recrystallization can be assumed. Continuous lattice rotation from the core to the outer polycrystalline rim allow a determination of the related dominant slip systems which are {100}<010> and equivalent systems according to the cubic lattice symmetry. The same holds for garnets which appear to be completely recrystallized. For this type of fine-grained aggregates an alternative nucleation model is discussed. Due to penetrative dislocation glide in connection with short range diffusion and the resulting lattice rotation, primary growth zones are strongly disturbed.Since for the considered rock unit of the Münchberg Massif peak metamorphic temperatures between 630 and 670 °C can be assumed, this study clearly demonstrates that the inferred processes of ductile garnet deformation can occur not only in HT regimes as often suggested in the literature even if embedded within a matrix of “low-strength” minerals like quartz, feldspars and micas.     

A tentative explanation of the origin of “transform faults” (with a critical remark on the term)

The offsets on the ocean floor, usually called “transform-faults” are not shear faults common in solid Hookian rocks, but reflect the viscous Newtonian properties of laminar flow at the time when the upwelling magma along the spreading center was still in a liquid state. During spreading this liquid is carried away with the walls of the spreading center. This movement creates a pattern of stream lines in the liquid which run parallel to the direction of spreading. “Transform faults” are initiated along zones where a larger rate of shear disturbs the process of solidification. Consequently the strength of the basalt after solidification will be impaired along these zones. These weak zones will fracture under the thermo-elastic stresses during the final stage of cooling.The history of the term “transform fault” is discussed and the name “spreading offset” is proposed.     

Long-term creep experiment on some rocks observed over three years

Since August 1974 the authors have been carrying out an experiment on creep by bending three small granite beams and three gabbro beams. While making measurements, an optical flat is set to produce interference fringes of Na-D light upon the upper polished surface of the beam, which was previously bent convex upward. By analyzing the fringes the profile of the surface is determined with in an accuracy of one-tenth of a wavelength. The routine determination of profiles gives a change in the amount of bending with time.A similar experiment on two large beams of granite was carried out for 21 years by Kumagai and Itô. It took 10 years in order to find out the secondary creep of granite. However, in this three-year experiment it has been found that the secondary creep of the granite specimens gives a viscosity of about 1 · 10²⁰ poise, which is comparable to that obtained over 20 years in the previous experiment (Kumagai and Itô). As for the gabbro specimens, the present authors cannot yet definitely recognize the secondary creep, because gabbro creeps much more slowly than granite.Both this and the previous experiments have revealed that the creep of rocks does not show a steady and monotonous progress, but a repeated “turn back” with various periods, some of which are longer than one year. In order to explain the creep accompanied by the “turn back” phenomenon, the authors venture to hypothesize that the elastic constants of a test-piece slightly vary with time during the advance of creep.     

Rheologic properties of the lithosphere and applications to passive continental margins

Thermal and petrologic models of the crust and upper mantle are used for calculating effective viscosities on the basis of constant creep rates. Viscosity—depth models together with pressure—depth models are calculated for continental and oceanic blocks facing each other at continental margins. It is found from these “static models” that the overburden pressure in the lower crust and uppermost mantle causes a stress which is directed from the ocean to the continent. The generally low viscosity of 10²⁰–10²³ poise in this region should permit a creep process which could finally lead to a “silent” subduction. In the upper crust static stresses act in the opposite direction, i.e. from the continent to the ocean, favouring tension which could produce normal faulting in the continent. Differences between observations and the results obtained from the static models are attributed to dynamical forces.     

Unusual transition in quartzite dislocation creep regimes and crystal slip systems in the aureole of the Eureka Valley–Joshua Flat–Beer Creek pluton, California: a case for anhydrous conditions created by decarbonation reactions

Microstructures and quartz c-axis fabrics were analyzed in five quartzite samples collected across the eastern aureole of the Eureka Valley–Joshua Flat–Beer Creek composite pluton. Temperatures of deformation are estimated to be 740±50 °C based on a modified c-axis opening angle thermometer of Kruhl (J. Metamorph. Geol. 16 (1998) 142). In quartzite layers located closest (140 m) to the pluton-wall rock contact, flattened detrital grains are plastically deformed and partially recrystallized. The dominant recrystallization process is subgrain rotation (dislocation creep regime 2 of Hirth and Tullis (J. Struct. Geol. 14 (1992) 145)), although grain boundary migration (dislocation creep regime 3) is also evident. Complete recrystallization occurs in quartzite layers located at a distance of 240 m from the contact, and coincides with recrystallization taking place dominantly through grain boundary migration (regime 3). Within the quartzites, strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains.The c-axis fabrics indicate that a slip operated within the quartzites closest to the pluton-wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism [c] slip. The spatial inversion in microstructures and slip systems (apparent “high temperature” deformation and recrystallization further from the pluton-contact and apparent “low temperature” deformation and recrystallization closer to the pluton-contact) coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units. Marble and calc-silicate assemblages dominate close to the pluton-wall rock contact, whereas mixed quartzite and pelite assemblages are dominant further from the contact.We suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton. Decarbonation reactions in marble layers interbedded with the inner aureole quartzites and calc-silicate assemblages in the inner aureole quartzites may have produced high X_CO2 (water absent) fluids during deformation. The presence of high X_CO2 fluid is inferred from the prograde assemblage of quartz+calcite (and not wollastonite)+diopside±K-feldspar in the inner aureole quartzites. We suggest that it was these “dry” conditions that suppressed prism [c] slip and regime 3 recrystallization in the inner aureole and resulted in a slip and regime 2 recrystallization, which would normally be associated with lower deformation temperatures. In contrast, the prograde assemblage in the pelite-dominated outer part of the aureole is biotite+K-feldspar. These “wet” pelitic assemblages indicate fluids dominated by water in the outer part of the aureole and promoted prism [c] slip and regime 3 recrystallization. Because other variables could also have caused the spatial inversion of c-axis fabrics and recrystallization mechanisms, we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz. Our conclusions are based on a small number of samples, and therefore, the unusual development of crystal fabrics and microstructures in the aureole to the EJB pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks.     

Magma in forearcs: implication for ophiolite generation

Forearc areas (“non-volcanic” arcs) of contemporary island arcs at convergent plate boundaries contain magmatic rocks. Geological evidence, seismic profiles, heat flow data, density considerations and petrological and geochemical arguments suggest that a forearc tholeiitic association (FAT) (containing high-Mg calc-alkaline andesites) is present in “non-volcanic” arcs at some stage of island-arc development. The fractionated, as well as primitive magma, is unable to penetrate low-density sediments and underplates thick piles of unconsolidated accreting rocks. The underplating causes upwelling. The occurrence of magma in forearcs provides an alternative interpretation for the tectonic setting of some ophiolitic masses. Rather than “ocean-ridge formation” and later “obduction” it offers an autochthonous (island-arc bound and geologically-substantiated) interpretation for the ophiolite suite.     

The optical features and hydrocarbon-generating model of “barkinite” from Late Permian coals in South China

Leping coal is known for its high content of “barkinite”, which is a unique liptinite maceral apparently found only in the Late Permian coals of South China. “Barkinite” has previously identified as suberinite, but on the basis of further investigations, most coal petrologists conclude that “barkinite” is not suberinite, but a distinct maceral. The term “barkinite” was introduced by (State Bureau of Technical Supervision of the People's Republic of China, 1991, GB 12937-91 (in Chinese)), but it has not been recognized by ICCP and has not been accepted internationally.In this paper, elemental analyses (EA), pyrolysis-gas chromatography, Rock-Eval pyrolysis and optical techniques were used to study the optical features and the hydrocarbon-generating model of “barkinite”. The results show that “barkinite” with imbricate structure usually occurs in single or multiple layers or in a circular form, and no definite border exists between the cell walls and fillings, but there exist clear aperture among the cells.“Barkinite” is characterized by fluorescing in relatively high rank coals. At low maturity of 0.60–0.80%R_o, “barkinite” shows strong bright orange–yellow fluorescence, and the fluorescent colors of different cells are inhomogeneous in one sample. As vitrinite reflectance increases up to 0.90%R_o, “barkinite” also displays strong yellow or yellow–brown fluorescence; and most of “barkinite” lose fluorescence at the maturity of 1.20–1.30%R_o. However, most of suberinite types lose fluorescence at a vitrinite reflectance of 0.50% Ro, or at the stage of high volatile C bituminous coal. In particular, the cell walls of “barkinite” usually show red color, whereas the cell fillings show yellow color under transmitted light. This character is contrary to suberinite.“Barkinite” is also characterized by late generation of large amounts of liquid oil, which is different from the early generation of large amounts of liquid hydrocarbon. In addition, “barkinite” with high hydrocarbon generation potential, high elemental hydrogen, and low carbon content. The pyrolysis products of “barkinite” are dominated by aliphatic compounds, followed by low molecular-weight aromatic compounds (benzene, toluene, xylene and naphthalene), and a few isoprenoids. The pyrolysis hydrocarbons of “barkinite” are mostly composed of light oil (C₆–C₁₄) and wet gas (C₂–C₅), and that heavy oil (C₁₅⁺) and methane (C₁) are the minor hydrocarbon.In addition, suberinite is defined only as suberinized cell walls—it does not include the cell fillings, and the cell lumens were empty or filled by corpocollinites, which do not show any fluorescence. Whereas, “barkinite” not only includes the cell walls, but also includes the cell fillings, and the cell fillings show bright yellow fluorescence.Since the optical features and the hydrocarbon-generating model of “barkinite” are quite different from suberinite. We suggest that “barkinite” is a new type of maceral.     

“Traditional” women, “modern” water: Linking gender and commodification in Rajasthan, India

In this paper, I analyze the connections made between women and water in a Rajasthani drinking water supply project as a significant part of drinking water’s commodification. For development policy makers, water progressing from something free to something valued by price is inevitable when moving economies toward modernity and development. My findings indicate that water is not commodified simply by charging money for it, but through a series of discourses and acts that link it to other “modern” objects and give it value. One of these objects is “women”. I argue that through women’s participation activities that link gender and modernity to new responsibilities and increased mobility for village women involving the clean water supply, a “traditional” Rajasthani woman becomes “modern”. Water, in parallel, becomes “new”, “improved” and worth paying for. Women and water resources are further connected through project staff’s efforts to promote latrines by targeting women as their primary users. The research shows that villagers applied their own meanings to latrines, some of which precluded women using them. This paper fills a gap in feminist political ecology, which often overlooks how gender is created through natural resource interventions, by concerning itself with how new meanings of “water” and “women” are mutually constructed through struggles over water use and its commodification. It contributes to critical development geography literatures by demonstrating that women’s participation approaches to natural resource development act as both constraints and opportunities for village constituents. It examines an under-explored area of gender and water research by tracing village-level struggles over meanings of latrines.     

Structure and late cenozoic evolution of the upper lithosphere in Southwest Tuscany (Italy)

Geological and geophysical data on southwest Tuscany are reviewed in order to define the structure and evolution of the upper lithosphere from the Miocene to the Quaternary. Petrologic studies reveal the existence, below all of Tuscany, of Hercynian and older polyphased metamorphic rocks and of Hercynian granite, whose top is an important seismic reflecting horizon. The basement is characterized by NE-SW trending structures, in contrast with the main NW-SE “Alpine” structures of the uppermost levels. The heat flow map shows two broad areas with values higher than 80 mW/m², reaching maximum values of 10.5 and 15 H.F.U. in the geothermal areas, which are also characterized by negative Bouguer anomalies. A Landsat study revealed a NE-SW band of subcircular structures passing through Larderello and coinciding with a regional fault system and a steep rise in the Moho. Petrologic, geochemical and radiometric data on the Tuscan igneous rocks show that partial melting took place in the Tuscan crust at different levels and to varying degrees from the Miocene to Quaternary, producing a continuous “Alpine” granitic layer. The known Tuscan intrusive bodies and two batholiths below the Larderello and Mt. Amiata geothermal fields represent culminations of the “Alpine” granite. The rise of the Tuscan magmas was closely correlated to a post-Tortonian tensional tectonics and followed its N-E migration. Tensional tectonics started after the last compressional phase (10–11 Ma B.P.) as a consequence of the anticlockwise rotation of Italy, the opening of the Tyrrhenian Sea and the swelling of the mantle below southwest Tuscany.     

Measurement of partition coefficients of phenol and cresols in gas-charged crude oil/water systems

An instrument has been constructed for monitoring the partition coefficients of phenol and cresols between crude oil and water under sub-surface conditions. The device has the capacity for introducing methane gas into crude oil, thereby allowing measurements under live oil (solution gas-containing) conditions. The partition coefficients of phenol and cresols have been measured in crude oil: water substrates under “live” oil and “dead” oil (without solution gas) conditions over a temperature range 25–150 °C. Over the range investigated it is seen that the introduction of gas (crude oil saturated at 100 bar with methane) into the system resulted in an approximate doubling of partition coefficients compared to the equivalent dead oil: brine systems. The partition coefficient data obtained using the device may be employed in a number of petroleum exploration and production activities such as the determination of residual oil saturation of a water-flooded petroleum reservoir. Partition coefficient measurements may help in predicting toxic organic solute loadings in oilfield discharge waters.     

Magnetic overprints in granitoids and metamorphic rocks from Limousin (France): evidence for Late Variscan rotations, crustal folding and tilting

Generally, the lack of bedding criteria in basement units hampers the interpretation of paleomagnetic results in terms of geotectonics. Nevertheless, this work demonstrates that successive remagnetizations recorded in Early Carboniferous metamorphic and plutonic units, without clear bedding criteria, can be used to constrain a polyphased tectonic evolution consisting of a regional clockwise rotation, followed by a folding phase, a tilting phase and a second regional clockwise rotation.Metamorphic, ultrabasic, tonalitic and granitic rocks from different parts of Limousin (western French Massif central; 45.5°N/1.25°E), which underwent metamorphism during Devonian–Early Carboniferous or were intruded in the Early–Middle Carboniferous, were sampled in order (a) to identify the magnetic overprinting phases and the related tectono-magmatic events and (b) to constrain the regional and plate tectonic evolution of Limousin. Paleomagnetic results from 32 new and 26 sites investigated previously show that at least 90% of the magnetization isolated in rocks older than 330 Ma are overprints. In agreement with results from adjacent areas of the Variscan belt, the major overprinting phases occurred: (a) in the last stages of the major exhumation phase [332–328 Ma; mean Virtual Geomagnetic Pole (VGP) “Cp”: 37°N/70.5°E], (b) during the post-collisional syn-orogenic extension (325–315 Ma; VGP “B”: 11°N/114°E), (c) in the Latest Carboniferous and Early Permian (VGP “A1”: 27°N/149°E) and (d) in the Late Permian (VGP “A”: 48°N/146°E). The Middle–Late Carboniferous overprints “Cp” and “B” are contemporaneous with emplacement of leucogranitic, crustal derived plutons, and probably result from the hydro-thermal activity related to the magmatism. The drift from “Cp” directions to “B” directions implies that after 330 Ma, Limousin underwent a clockwise rotation by 65°, together with the Central Europe Variscides. The “Bt” components, the VGPs of which deviate from the mean apparent polar wander path (APWP) of the belt, are interpreted as “B” overprints tilted during Late Variscan tectonics, that is, in the time range 325–315 Ma. The first and most important generation of “Bt” overprints was tilted during NW–SE folding associated with NE–SW shortening, updoming and emplacement of leucogranitic plutons. The second generation reveals southeastward tilting due to NE-striking normal faulting. The drift from “B” to “A1” directions implies that Limousin has participated to the second clockwise rotation by 40° of the whole belt in Westphalian times.     

Using data from natural environments to improve models of uranium speciation in groundwaters

It is essential that computer-based models used in the safety assessment of radioactive waste repositories accurately represent the processes occurring in real field systems. Confidence in long-term predictions of radionuclide migration will then depend upon the completeness of data available, particularly those obtained from the disposal site, and correct implementation of the model. The study of natural geochemical systems provides information on the adequacy of the underlying “generic” database and enhances our understanding of the transport mechanisms which form the basis of performance assessment. This paper concentrates on speciation-solubility modelling and describes four natural occurrences of uranium, each of which displays a different facet of uranium migration behaviour. The attributes of each site and the means by which uranium is immobilised are described. Retardation is highly species specific and this is illustrated through the use of site data in equilibrium speciation and coupled chemical transport calculations. Oxidation of U(IV) to U(VI) species promotes leaching of uranium ore at all the locations studied, emphasising the need to ensure that reducing conditions persist in a repository dominated by its actinide inventory.     

Evaluation of approaches to calculate debris-flow parameters for hazard assessment

Many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment. The present article reviews the empirical, analytical, simple flow routing and numerical techniques. All these techniques were applied to back-calculate a debris flow, which occurred in 1982 at La Guingueta catchment, in the Eastern Pyrenees. A sensitivity analysis of input parameters was carried out, while special attention was paid to the influence of rheological parameters. We used the Voellmy fluid rheology for our analytical and numerical modelling, since this flow resistance law coincided best with field observations. The simulation results indicated that the “basal” friction coefficients rather affect the runout distance, while the “turbulence” terms mainly influence flow velocity. A comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones. The values of our rheological parameters calibrated at La Guingueta agree with data back-calculated for other debris flows. Empirical relationships represent another method to estimate total runout distance. The results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions, which were the basis for their development. With regards to the simple flow routing algorithm, this methods could satisfactorily simulate the total area affected by the 1982 debris flow, but it was not able to directly calculate total runout distance and velocity. Finally, a suggestion on how different runout prediction methods can be applied to generate debris-flow hazard maps is presented. Taking into account the definition of hazard and intensity, the best choice would be to divide the resulting hazard maps into two types: “final hazard maps” and “preliminary hazard maps”. Only the use of numerical models provided final hazard maps, because they could incorporate different event magnitudes and they supplied output-values for intensity calculation. In contrast, empirical relationships and flow routing algorithms, or a combination of both, could be applied to create preliminary hazard maps. The present study only focussed on runout prediction methods. Other necessary tasks to complete the hazard assessment can be looked up in the “Guidelines for landslide susceptibility, hazard and risk zoning” included in this Special Issue.