Behaviour of geochronometers and timing of metamorphic reactions during deformation at lower crustal conditions: phase equilibrium modelling and U–Pb dating of zircon,monazite, rutile and titanite from the Kalak Nappe Complex,northern Norway

This study investigates the behaviour of the geochronometers zircon, monazite, rutile and titanite in polyphase lower crustal rocks of the Kalak Nappe Complex, northern Norway. A pressure–temperature–time–deformation path is constructed by combining microstructural observations with P–T conditions derived from phase equilibrium modelling and U–Pb dating. The following tectonometamorphic evolution is deduced: A subvertical S1 fabric formed at ~730–775 °C and ~6.3–9.8 kbar, above the wet solidus in the sillimanite and kyanite stability fields. The event is dated at 702 ± 5 Ma by high‐U zircon in a leucosome. Monazite grains that grew in the S1 fabric show surprisingly little variation in chemical composition compared to a large spread in (concordant) U–Pb dates from c. 800 to 600 Ma. This age spread could either represent protracted growth of monazite during high‐grade metamorphism, or represent partially reset ages due to high‐T diffusion. Both cases imply that elevated temperatures of >600 °C persisted for over c. 200 Ma, indicating relatively static conditions at lower crustal levels for most of the Neoproterozoic. The S1 fabric was overprinted by a subhorizontal S2 fabric, which formed at ~600–660 °C and ~10–12 kbar. Rutile that originally grew during the S1‐forming event lost its Zr‐in‐rutile and U–Pb signatures during the S2‐forming event. It records Zr‐in‐rutile temperatures of 550–660 °C and Caledonian ages of 440–420 Ma. Titanite grew at the expense of rutile at slightly lower temperatures of ~550 °C during ongoing S2 deformation; U–Pb ages of c. 440–430 Ma date its crystallization, giving a minimum estimate for the age of Caledonian metamorphism and the duration of Caledonian shearing. This study shows that (i) monazite can have a large spread in U–Pb dates despite a homogeneous composition; (ii) rutile may lose its Zr‐in‐rutile and U–Pb signature during an amphibolite facies overprint; and (iii) titanite may record crystallization ages during retrograde shearing. Therefore, in order to correctly interpret U–Pb ages from different geochronometers in a polyphase deformation and reaction history, they are ideally combined with microstructural observations and phase equilibrium modelling to derive a complete P–T–t–d path.     

Sedimentation and continental slope processes in the vicinity of an ocean waste‐disposal site,southeastern Tasmania

Digital echo sounding, SeaBeam swath bathymetry data and sediment cores were collected on the continental slope (1500–3700 m water depth) off southeastern Tasmania in order to study sedimentary processes in the vicinity of an ocean disposal site. The new bathymetry data show that the shallower limits of the disposal site are positioned on the seaward edge of a gently dipping (3°) mid‐slope shoulder, between 1200 and 2100 m water depth. The slope below the disposal site is relatively steep (6.5°) and is cut by submarine canyons which lead into the adjacent East Tasman Saddle. The SeaBeam bathymetry data show a small submarine canyon traversing the slope in 2400 m water depth directly downslope from the disposal site, with local slopes of up to 22°. The canyon feeds into a perched basin at 2450 m, which could be acting as a local sediment trap. Short (<90 cm) gravity cores indicate that indurated erosional surfaces characterise the slope environment. The cores contain Upper Cretaceous (upper Campanian) sandstones and siltstones, which in places crop out on the sea floor where they are locally draped by a thin (0–30 cm), modern layer of hemipelagic calcareous ooze. Five cores collected from the vicinity of the disposal site had lead and zinc concentrations in the surface 1 cm of 10.3 ± 5.0 and 39.5 ± 19.6 mg/kg, respectively, significantly greater than the background values (2.9 ± 1.4 for lead and 21.2 ± 5.4 for zinc) which characterise the underlying unit that is composed of the same hemipelagic calcareous ooze. Lead and zinc are constituents of the dumped material, jarosite, which, after mixing with slope sediments, can be used as sediment tracers. One core contains a fining‐upwards bed which is also elevated in lead and zinc. This is interpreted as evidence for dispersal of the jarosite from the disposal site downslope to depths >3000 m via turbidity flows sometime during the past 24 years. Current meter data collected from 30 m above the sea floor over one year at the disposal site show that bottom currents attain speeds of up to 0.46 m/s. The current events are attributed to eddies shed by the East Australia Current. The measured bottom currents are capable of transporting fine‐grained hemipelagic muds and could provide a trigger mechanism for turbidity flows.     

Origins,closed system formation and preservation of calcites in glaciated crystalline bedrock: evidence from the Palmottu natural analogue site,Finland

A study of the geochemistry of fracture filling calcite from the Palmottu research site, a U–Th deposit located about 100 km NW of Helsinki, Finland, was part of a comprehensive natural analogue research project considering the migration of U in the crystalline bedrock environment. Fracture filling minerals act as records of the paleohydrological and chemical conditions and therefore provide insight into magmatic processes, ore deposits and long-term stability of the crystalline bedrock environment in relation to deep disposal of radioactive waste. An earlier investigation of calcite and associated U minerals identified a recent origin for these fracture infillings. Uranium series disequilibrium data indicated that relatively recent, glacial water had penetrated to a depth of 62 m. A fluid inclusion study, combined with the isotope geochemistry of several generations of fracture calcite, was undertaken to further study this aspect and to better understand the thermal and fluid history in the crystalline rock environment in general. The study revealed that at least 3 fluids were recorded by fracture calcites: 1) A crystalline calcite precipitated at 139–238 °C from a low salinity, Na–Cl fluid of magmatic or metamorphic origin, 2) A massive calcite (with high salinity fluid inclusions) precipitated at 136–141 °C from a high salinity, Ca–Na–Cl fluid of magmatic or metamorphic origin and 3) A massive calcite (with low salinity fluid inclusions) precipitated at 43–286 °C from a low salinity, Na–Cl fluid of magmatic or metamorphic origin that underwent equilibrium fractionation during cooling in a rock dominated system. The preservation of high temperature infillings and the cooling trend, indicating isotopic re-equilibration of water due to a very low water/rock ratio, demonstrate that the downward percolation of geologically recent waters is limited, despite the reworking of highly soluble U compounds in the upper tens of metres of the bedrock that was shown by U series disequilibrium studies. The veins in which these calcites occur have not experienced a later phase of fluid activity that dissolved or altered the calcites. Therefore, it is likely that they have not been reactivated as transmissive fractures since that initial hydrothermal episode, even during the Quaternary history in which the formation was subjected to ice sheet loading and unloading.     

Morphology, Chemistry and U-Pb Geochronology of Zircon Grains In Quartz Monzodiorite from the Sunzhuang Area, Fanshi County, Shanxi Province

The morphology, REE geochemistry and U-Pb geochronology of zircons from quartz monzodiorite in the Sunzhuang area, Fanshi County, Shanxi Province are presented in this study. The zircon crystals can be classified into four main types as: AB, L, S and P, and 24 subtypes such as AB4, AB5, L5, and S3. The maximum crystallization temperature of zircon was estimated as 850°C, with the minimum of 550°C. The peak temperatures of the zircon crystallization range from 650°C to 700°C. The abundances of Th and U in the zircon grains show large variation with the Th/U values 0.4. The Th and U values also show a positive correlation in most zircons. The REE abundance of zircon in the quartz monzodiorite ranges from 280.4 ppm to 2143 ppm with an average of 856.4 ppm. The chondrite normalized zircon REE patterns show two types, one is characterized by HREE enrichment and LREE depletion with positive Ce-anomaly and negative Eu-anomaly whereas the other is HREE enriched and LREE depleted with negative Eu-anomaly but without positive Ce-anomaly, and relatively flat patterns. The LA-ICP-MS U-Pb geochronology on the zircons yields a mean age of 133±0.87 Ma. Our data on zircon morphology, composition and U-Pb geochronology reveal that the parent magma of the quartz monzodiorite which was emplaced during late Yanshanian had a mixed crust-mantle source, with crustal components dominating. The magma is inferred to have been water rich and alkaline with initial high oxygen fugacity. Post-magmatic hydrothermal activity occurred under relatively reducing conditions which was conductive for gold precipitation in the Yixingzhai gold deposit.     

Vesicles,water, and sulfur in Reykjanes Ridge basalts

Dredge hauls of fresh submarine basalt collected from the axis of the Reykjanes Ridge (Mid-Atlantic Ridge) south of Iceland were taken aboard R/ V TRIDENT in 1967 and 1971. The samples show systematic changes as the water depth of collection (and eruption) decreases: radially elongate vesicles and concentric zones of vesicles appear at about 700 m depth and are conspicuous to shallow water; the smoothed volume percent of vesicles increases from 5% at 1000 m, 10% at 700 m, to 16% at 500 m, and the scatter in degree of vesicularity increases in shallower water; specific gravity decreases from 2.7±0.1 at 1000 m to 2.3±0.3 at 100 m. Bulk sulfur content for the outer 2 cm averages 843 ppm up to a depth of 200 m, then drops off rapidly in shallower water owing to degassing. Sulfur content below 200 m is independent of depth (or geographic position), and the melt is apparently saturated with sulfur, but the excess cannot escape the lava unless another vehicle carries it out. Only shallower than 200 m, where intense vesiculation of other gases occurs can excess sulfur be lost from the lava erupting on the sea floor. H₂O^+110° averages about 0.35 percent and H₂O^+150° about 0.25 percent, and both apparently decrease in water shallower than 200 m as a result of degassing. H₂O⁺ (below 200 m) decreases with distance from Iceland or increasing depth, presumably as a result of either adsorption of water on the surface of shallower, more vesicular rocks; or more likely due to the presence of the Iceland hot mantle plume supplying undifferentiated primordial material, relative to lavas of the Reykjanes Ridge supplied from the low velocity layer already depleted in volatiles and large lithophile elements. The H₂O^+110°/S ratio of lava erupting below 200 m water depth ranges from 3 to 5 which is comparable to reliable gas analyses from oceanic basaltic volcanoes. Publication authorized by the Director, U.S. Geological Survey.     

Design and costs for a system to reduce chloride levels in the Red River by shallow-well collection and deep-well disposal

 The Red River drains 242000 km² with 90% of this area being downstream of discharges from naturally occurring brine seeps and springs. The upstream area has been designated as a major chloride emission area in Texas and Oklahoma. Ten major brine source emission areas along the tributaries to the Red River were identified by U.S. Public Health Service and U.S. Army Corps of Engineers. Eight of these areas were deemed suitable for the control of brine emissions by structural methods including a ring dike to enclose brine springs; low flow dams to capture and divert stream flows with high chloride content to evaporation lakes; and shallow aquifer brine collection wells with a deep-well disposal system. Two adjacent emission areas, designated as Areas XIII and XIV, contribute 500 metric tons of salt per day to the Red River. These areas, along Jonah Creek and Salt Creek, tributaries to the Prairie Dog Town Fork of the Red River were selected for investigation to control brine emission by utilization of shallow collection wells and disposal by deep injection wells. Drilling programs and pumping tests were performed to determine the number and location of shallow collection wells. Eighteen wells with 12 operating full time, will be located in the primary emission areas. The collected brine will be conveyed through corrosion-resistant pipelines to a treatment facility for filtration at a rate of 300 l/s. Additional pipelines will convey the filtered brine to deep injection wells for disposal. Nine deep wells will be installed with seven operating full time. Design criteria for the project are 100-year life expectancy and automated operation with minimum supervision and maintenance. The required minimum operating, maintenance and supervision coupled with 100-year life expectancy of the project added significantly to the estimated US $58 million capital cost of the project. However, the reduction in annual cost for labor, repairs and replacement of the component of the system should result in a lower life cycle cost. The estimated annual operating and maintenance cost is US $4.7 million. Received: 5 May 1998 · Accepted: 30 June 1998     

Effectiveness of rice husk ash in stabilizing Kenyan red coffee soil for road subgrades construction

The high cost of traditional stabilizing agents such as lime and cement has led to the research on industrial and agricultural wastes as suitable alternatives. Rice growing areas of Kenya accumulate large quantities of rice husk which pose serious disposal problems. When burnt as a means of disposal, the rice husk ash formed is difficult to coagulate and thus contribute to air and water pollution, require a large space for disposal, and cause respiratory health problems when inhaled. Red coffee soil poses serious engineering problems such as swelling due to wetting, shrinkage due to drying, low bearing capacity, and differential settlement leading to cracks and needs improvement for strength and stability in service. Red coffee soil and rice husks samples were obtained from Gatundu and Mwea, respectively. The rice husk was burnt at temperatures between 500 and 700 °C to ensure maximal formation of siliceous component. Chemical analysis on the rice husk ash gave the sum of SiO₂, Fe₂O₃, and Al₂O₃ as 85.5 % indicating that it has pozzolanic activity. Rice husk ash was applied at 4, 6, 8, and 10 % by weight of dry soil. Plasticity index, liquid limit, and linear shrinkage decreased from 26.1, 67.1, and 13.0 % for lean sample to 18.5, 63.6, and 9.2 %, for 10 % rice husk ash stabilized samples, whereas plastic limit increased from 41.0 to 45.15 %. The soaked California bearing ratio value for rice husk ash stabilized samples increased from 5 to 22 % corresponding to soil subgrade class S4. However, lime-stabilized samples gave higher values.     

Entrainment of circumpolar water in the Indian Ocean region of the Antarctic

The net influx of the circumpolar water on the western (approximately along 10°E) and eastern (approximately 115°E) boundaries of the Indian Ocean, adopting the method of Montgomery and Stroup is computed on bivariate distribution of potential thermosteric anomaly and salinity to identify the characteristics of the flux. The zonal flux at both the boundaries indicates an alternate strong easterly and westerly flow between 36°S and 45°S, south of which the flow is mainly easterly but weak up to 56°S. At the western boundary the easterly flow is 146 Sv and westerly is 98.07 Sv, while at the eastern boundary (115°E) the corresponding fluxes are 123.46 Sv and 27.20 Sv respectively, indicating a net outflux of 48.33 Sv. This water should have been accounted by the melting of ice and influx of the Equatorial Pacific Ocean Water.     

Heat-induced changes in speciation and extraction of uranium associated with sheet silicate minerals

Three samples of gouge from a U-mineralised fault, and two model samples, montmorillonite and muscovite, spiked with U, were heat-treated at a range of temperatures up to 1100 °C. Mineralogical changes were followed by thermal analysis, powder XRD and electron microscopy, and U extractability was measured by extraction with NH₄⁺. Changes in U speciation in the montmorillonite sample were followed using EXAFS spectroscopy. On heating, the minerals progressively dehydrate, dehydroxylate and eventually decompose to form new phases in a glassy matrix. In the case of montmorillonite (90% of U extractable from unheated material), U extractability increased slightly on heating to temperatures around 400 °C. Almost 50% of U was extracted from unheated muscovite, and this increased slightly by 450 °C. Above 500–600 °C, U extractability from both montmorillonite and muscovite declined to very low levels, reflecting dehydration of the uranyl ion and trapping in the new phases and glassy matrix. Uranium extractability from the natural samples was much lower in all cases (0.25–5% of the total before heating). In 2 samples, a significant increase in U extraction was associated with dehydroxylation at around 600 °C, followed by a decrease to very low levels at higher temperatures. Uranium extraction from the third natural sample, which contained X-ray amorphous U minerals, decreased steadily on heating. The results show that changes in U extraction can be related to structural and morphological changes in sheet silicate minerals. Heat treatment has potential to fix U but only if temperatures above 800 °C are reached. If only lower temperatures, in the range 400–600 °C, are used, then U extraction may increase.     

Harmonic analysis of summer mean wind at 200 mbar level during contrasting monsoon years over India

Summer (June–August) mean zonal and meridional wind components at 200 mbar level are subjected to harmonic analysis for the years 1970, 1971, 1972 and 1979. It is found that the small scale disturbances are intense during normal monsoon years. The westerlies in the belt 10°S to 30°S are stronger during drought years. During normal monsoon years (1970, 1971) the northward transport of westerly momentum by wave number 1 at 19.6°N is large as compared to drought years (1972, 1979). The transport of westerly momentum by standing eddies is northward for all the years between 5°S and 28.7°N but large during the normal monsoon years.     

Effect of different growth parameters on endoglucanase enzyme activity by bacteria isolated from coir retting effluents of estuarine environment

The cellulolytic enzyme-endoglucanase activity against coir fibre, a major biowaste by bacteria such as Cellulomonas, Bacillus and Micrococcus spp. isolated from coir retting effluents of estuarine environment was studied. The enzyme assay was carried out by using various concentrations (0.5 ? 2%) of substrate of coir powder as a carbohydrate in different pH (5–9) and temperature (20–50 °C). The enzyme activity was minimum in 0.5% substrate concentration at lower pH 5 (0.0087, 0.0143 and 0.0071 U/mL) and at 20 °C temperature (0.0151, 0.0154 and 0.0122 U/mL) by the bacterial strains such as Cellulomonas, Bacillus and Micrococcus spp respectively. Then this level was increased and reached maximum at the neutral pH (0.0172, 0.0165 and 0.0121 U/mL) and at 40 °C (0.0336, 0.0196 and 0.0152 U/mL) by the selected bacterial species. Further increase of pH and temperature, the enzyme activity reduced considerably to 0.0083, 0.0143 and 0.0037 U/mL at pH 9 and 0.0154, 0.0197 and 0.0121 U/mL at 50 °C by the tested bacterial strains. The same trend was also obtained in oth er substrate concentrations such as 1.0, 1.5 and 2.0 %. With in the four substrate concentrations, the endoglucanase enzyme activity was more in 1.5% concentration at the tested pH and temperatures. From the over all result, it was observed that, among the three bacterial strains, the enzyme activity was more in Cellulomonas sp, followed by Bacillus and Micrococcus spp. in varying pH and temperature.     

Past methane release events and environmental conditions at the upper continental slope of the South China Sea: constraints by seep carbonates

Authigenic carbonates and seep biota are archives of seepage history and record paleo-environmental conditions at seep sites. We obtained the timing of past methane release events at the northeastern slope of the South China Sea based on U/Th dating of seep carbonates and seep bivalve fragments from three sites located at 22°02′–22°09′N, 118°43′–118°52′E (water depths from 473 to 785 m). Also, we were able to reconstruct the paleo-bottom water temperatures by calculating the equilibrium temperature using the ages, the corresponding past δ¹⁸O of seawater (δ¹⁸O_sw) and the δ¹⁸O of the selected samples formed in contact with bottom seawater with negligible deep fluid influence. A criterion consists of mineralogy, redox-sensitive trace elements and U/Th-isotope systematics is proposed to identify whether the samples were formed from pore water or have been influenced by deep fluid. Our results show that all methane release events occurred between 11.5 ± 0.2 and 144.5 ± 12.7 ka, when sea level was about 62–104 m lower than today. Enhanced methane release during low sea-level stands seems to be modulated by reduced hydrostatic pressure, increased incision of canyons and increased sediment loads. The calculated past bottom water temperature at one site (Site 3; water depth: 767–771 m) during low sea-level stands 11.5 and 65 ka ago ranges from 3.3 to 4.0 °C, i.e., 1.3 to 2.2 °C colder than at present. The reliability of δ¹⁸O of seep carbonates and bivalve shells as a proxy for bottom water temperatures is critically assessed in light of ¹⁸O-enriched fluids that might be emitted from gas hydrate and/or clay dehydration. Our approach provides for the first time an independent estimate of past bottom water temperatures of the upper continental slope of the South China Sea.     

Kinetics of Hydrothermal Reactions of Minerals in Near-critical and Supercritical Water

This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400℃ and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, AI and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300℃, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300℃. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatu     

Hydrogen and oxygen isotope ratios in nodular and bedded cherts

Hydrogen and oxygen isotopic compositions of cherts (δD for hydroxyl hydrogen in the chert, δ¹⁸O for the total oxygen) have been determined for a suite of samples from the central and western United States. When plotted on a δD-δ¹⁸O diagram, Phanerozoic cherts define domains parallel to the meteoric water line which are different for different periods of geologic time. The elongation parallel to the meteoric water line suggests that meteoric waters were involved in the formation of many cherts.The existence of different chert δ-values for different geologic times indicates that once the granular microcrystalline quartz of cherts crystallizes its isotopic composition is preserved with time. An explanation for the change with time of the isotopic composition of cherts involving large changes with time in the isotopic composition of ocean water is unlikely since δ¹⁸O of the ocean would have had to decrease by about 3‰between Carboniferous and Triassic time and then increase about 5%.` from Triassic to Cretaceous time. Such isotopic changes cannot be accounted for by extensive glaciation, sedimentation of hydrous minerals, or input of water from the mantle into the oceans.The variation with time of the chert δ-values can be satisfactorily explained in terms of past climatic temperature fluctuations if the chert-water isotope fractionation with temperature is approximated by 1000 lnα = 3.09 × 10⁶T^?2 – 3.29. Crystallization temperatures so inferred suggest that the average climatic temperatures for the central and western U.S. decreased from about 34 to 20°C through the Paleozoic, increased to 35–40°C in the Triassic, and then decreased through the Mesozoic to Tertiary values of about 17°C. A few data for the Precambrian suggest the possibility that Earth surface temperatures may have reached about 52°C at 1.3 b.y. and about 70°C at 3 b.y.     

Geochemical nature and age of the plagiogranite-gabbronorite association of the oceanic core complex of the Mid-Atlantic ridge at 5°10′S

Our newly obtained data on the geochemistry and age of plagiogranite-gabbronorite association in the oceanic core complex of the Mid-Atlantic Ridge (MAR) at 5°10′S suggest close genetic relations between these rocks in this segment of the ridge. The U/Pb zircon age of an oceanic plagiogranite (OPG) sample is 1.059 ± 0.055 Ma and is in good agreement with the zircon age of plutonic rocks in the oceanic core complex of northern MAR. A distinctive geochemical feature of the rocks is their unusually depleted ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios, which suggest that the plutonic rocks of the gabbronorite-plagiogranite association in MAR at 5°10′S could be derived from the most strongly depleted mantle reservoir of all known to occur beneath the axial MAR zone. The COMAGMAT-5.2 numerical thermodynamic simulation of the possible crystallization links between the plagiogranite and gabbronorite from the MAR segment at 5°10′S led us to conclude that the leading role in the origin of the plagiogranite was played by a two-stage process: the partial melting of the gabbronorite and the subsequent fractionation of the newly generated melt. The regional differences between the isotopic-geochemical parameters of MAR plagiogranites can, perhaps, reflect local specifics of so-called hydrothermal anatexis, such as the geochemical features of the rocks involved in this process and the parameters of the hydrothermal process, for example, variations in the W/R ratio.     

Diversity of recent planktonic foraminifera in the southern Indian Ocean and Late Pleistocene paleotemperatures

Planktonic foraminiferal assemblages have been examined in 25 trigger core top samples and 51 piston core top samples collected between latitudes 28° S and 55° S and longitudes 79° E and 120° E from the southern Indian Ocean during cruises of the U.S.N.S. Eltanin. Samples taken from water depths exceeding 4000 m and/or showing evidence of calcium carbonate dissolution were eliminated from further analysis. The final piston core data set consists of 34 samples; the trigger core data set containing 21 samples. A close relationship exists between changes in the planktonic foraminiferal assemblages in the surface sediments and surface water temperatures. Species diversity values were computed for each of the core top assemblages using the Shannon-Wiener Index and the Brillouin Index, each of which takes into consideration the number of species and the proportionment of individuals among the species. The Shannon and Brillouin diversity values for all samples are positively correlated (correlation coefficient (r) = +.999). Regression analysis of latitude versus Shannon diversity values in the trigger core samples clearly shows a decrease in diversity with increasing latitude (r = ?.979). Furthermore, a strong correlation (r = +.977) exists between decreasing species diversity (Shannon) and decreasing average summer-winter temperature of the overlying surface waters. A paleotemperature equation derived from the relationship of diversity in trigger core samples and surface water temperature was used to generate paleotemperature curves for five trigger cores and a 6 m piston core of Late Pleistocene age, located beneath the present position of the Subtropical Convergence. A 7–8° C temperature range is suggested between the interglacial and glacial episodes in this Late Pleistocene sequence, and probably reflects latitudinal shifts of the Subtropical Convergence and Australasian Front during the Late Pleistocene.     

Retention behaviour of natural clayey materials at different temperatures

The water retention capacity of geomaterials, and especially clayey soils, is sensitive to temperature changes as the physical mechanisms of retention, such as capillarity or adsorption, are affected by it. It is therefore a major issue to be able to define temperature-dependent behaviour of materials, especially for geo-energy and geo-environmental applications involving non-isothermal conditions. This paper presents results of experiments conducted on two representative materials: a hard clay (Opalinus clay) and a plastic clay (Boom clay), both of which have been considered as buffer materials for underground radioactive waste disposal, in Switzerland and Belgium, respectively. Two new devices were developed for this purpose to permit the analysis of water retention behaviour at different temperatures. The behaviour of these two materials at ambient (20 °C) and high temperature (80 °C) was observed and described through the evolution of the degree of saturation, the water content and the void ratio with respect to suction. It appears that the retention capability of the clays reduces significantly with an increase in temperature; on the other hand, the change in temperature had less of an effect on the total volume variation.     

Water characteristics and transport of the Antarctic circumpolar current in the Indian Ocean

Geostrophic velocities are computed across meridians 37 °E and 105 °E using hydrographic data. The estimated mass transport is represented on a temperature-salinity diagram. The characteristics of the water within the Antarctic circumpolar current at 37 °E and 105 °E are discussed. The computed transport agrees with the previous estimates. Transports due to the current between 45 °S and the Antarctic continent at these two meridians are comparable. The westerly flow south of 42 °S at 105 °E is associated with a cyclonic eddy which appears to be a permanent feature, whereas the one at 50 °S is related to the topography of the region.     

Exfoliation and diffusion following helium ion implantation in fluorapatite: implications for radiochronology and radioactive waste disposal

The properties of fluorapatite, both a useful radiochronometer and a potential storage matrix specific for minor actinides produced by the reprocessing of spent nuclear fuel, have been investigated with emphasis to its response to alpha decay. Exfoliation, which occurs after implantation of high doses of 1.6-MeV He-ions (>1.4×10¹⁷ ions cm⁻², corresponding to 5% atomic proportion), could set an upper limit to the concentration of imbedded actinides (about 2 atoms % corresponding to 20 wt. %) or storage age unless significant diffusion of radiogenic He intervenes. This process has been studied by combining He implantation, thermal treatments in the temperature range 124–250°C and measurement of the resulting He profile by an ion beam technique (ERDA) using 8.5-MeV C ions. The diffusion coefficient follows an Arrhenius' law with an activation energy of 120 (±2) KJ/mole and a frequency factor of 14.5 (±7)×10⁻³ cm² sec⁻¹ in agreement with literature data. The inferred closure temperature which validates the U,Th–He radiochronological method also fits previous values: 97 (±10)°C for grain size 165 μm. With respect to radwaste disposal. He volume diffusion is too small to exclude the occurrence of exfoliation unless diffusion at grain boundary is much higher and a fine-grain matrix is deliberately chosen.     

Murataite as a universal matrix for immobilization of actinides

A new variety of matrices based on synthetic phases whose structure is close to that of murataite (a natural mineral) is proposed for immobilization of nuclear wastes. Murataite is Na, Ca, REE, Zn, and Nb titanate with a structure derived from the fluorite lattice. This very rare mineral was found in alkali pegmatites from Colorado in the United States and the Baikal region in Russia. The synthetic murataite-like phases contain manganese instead of zinc, as well as actinides and zirconium instead of sodium, calcium, and niobium. Varieties with threefold, as in the mineral, and five-, seven-, and eightfold repetition of the lattice relative to the fluorite cell have been established. Correspondingly, the structural varieties M3, M5, M7, and M8 are recognized among the synthetic murataites. A decrease in the contents of actinides, rare earth elements, and zirconium occurs in the series M7-M5-M8-M3, along with enrichment in Ti, Al, Fe, and Ga. Murataite-based ceramics are characterized by high chemical and radiation stability. The rate of U, Th, and Pu leaching with water at 90°C in static and dynamic tests is 10^?6–10^?5 g/m² per day. These values are lower than the leaching rate of other actinide confinement matrices, for example, zirconolite-or pyrochlore-based. Murataite is close to other titanates in its radiation resistance. At 25°C, amorphization of its lattice is provided by a radiation dose of 2 × 10¹⁸ α decays/g, or 0.2 displacements/atom. Murataite-based matrices are synthesized within a few hours by cold compacting combined with sintering at 1300°C or by melting at 1500–1600°C and subsequent crystallization. The melting technology, including induction smelters with a cold crucible, makes it possible to produce samples with zonal murataite grains. The inner zone of such grains is composed of structural variety M5 or M7; the intermediate zone, of M8; and the outer zone, of M3. The contents of actinides, zirconium, and rare earth elements reach a maximum in the inner zone and drop to a minimum in the outer zone, while the amounts of nonradioactive elements—Ti, Al, Fe, and Ga—vary conversely. The U, Th, and Pu contents in the inner and outer zones differ by three to five times. Such a distribution precludes removal of actinides by interaction of the matrix with solution after its underground disposal. Individual actinides (Np, Pu, Am); the actinide-zirconium-rare earth fraction of high-level radioactive wastes (HLW); Am-Ga residues of weapons plutonium reprocessing with its conversion into U-Pu mixed oxide (MOX) fuel; and other sorts of HLW enriched in actinides, REE, and products of corrosion (Mn, Fe, Al, Zr) can be incorporated into a murataite-based matrix. As much as 350 kg of HLW components can be included in 1 t of such a ceramic. An actinide matrix that is composed of titanates with a pyrochlore structure is its nearest analogue. The advantage of murataite in comparison with pyrochlore consists in its universal character; i.e., a murataite-based matrix can be used for utilization of a wider range of actinide-bearing highly radioactive wastes.