Scottish Universities Press

When a laser pulse of intensity ${10}^{19}\mathrm{W}{\mathrm{cm}}^{\ensuremath{-}2}$ interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional $\ensuremath{\gamma}$-ray beam that can be used to carry out photonuclear reactions. The isotopes ${}^{11}\mathrm{C}$, ${}^{38}\mathrm{K}$, ${}^{62,64}\mathrm{Cu}$, ${}^{63}\mathrm{Zn}$, ${}^{106}\mathrm{Ag}$, ${}^{140}\mathrm{Pr}$, and ${}^{180}\mathrm{Ta}$ have been produced by $(\ensuremath{\gamma},n)$ reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in ${}^{238}\mathrm{U}$ has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the ${}^{11}\mathrm{C}$ and the ${}^{62}\mathrm{Cu}$ ${\ensuremath{\beta}}^{+}$ activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of $\ensuremath{\sim}{10}^{19}\mathrm{W}{\mathrm{cm}}^{\ensuremath{-}2}$.

A program of geologic mapping and lithogeochemical and geochronological sampling has been carried out over a 745-km2 area of the Atacama Desert surrounding the porphyry Cu deposits at Escondida, Zaldivar, and Chimborazo (Cordillera de Domeyko, northern Chile). The purpose of this study was to examine the regional tectonic and magmatic setting of this preeminent porphyry Cu district for evidence of features or processes that might explain the giant scale of mineralization at Escondida and provide predictive tools for exploration in other areas. The geologic history of this area as recorded by exposed rocks begins with voluminous, intermediate to felsic Permo-Carboniferous volcanism (La Tabla Formation), and these rocks appear to constitute the crystalline basement throughout much of the porphyry belt of northern Chile. Geochemically, they are I-type in character, but the parental magmas were relatively dry, and thus did not generate effective magmatic-hydrothermal systems (few significant ore deposits are known to be associated with them). Andean cycle arc magmatism began in the Triassic, centered on the La Negra magmatic arc (now located near the Chilean coast). Farther inland, near Escondida, back-arc processes led to the eruption of intermediate to felsic lavas and tuffs and the deposition of marine sediments in rift basins. Closure of these basins in the Late Cretaceous resulted in deformation of the volcano-sedimentary sequences and was followed by emplacement of small alkali gabbro stocks and dikes. The axis of arc magmatism moved eastward in the Paleocene (Central Valley arc) and produced widespread calc-alkaline intermediate to felsic volcanism through to the Eocene. East- to northeast-directed convergence maintained a dextral transpressive regime during this period, and early movements in the West Fissure zone, a corridor of orogen-parallel faults that runs the length of the Cordillera de Domeyko (over 1,000 km), reflect this couple. At the end of the Eocene, however, stresses in the arc appear to have relaxed, and by the late Oligocene, strike-slip movement along the West Fissure zone had reversed to sinistral. This period of stress relaxation at the end of the Eocene period coincided with the voluminous emplacement of dioritic magmas at shallow crustal levels and also with porphyry development. Six samples of hornblende from these diorites yield 40Ar/39Ar dates between 38.28 ± 0.32 and 36.94 ± 0.46 Ma (2 σ ). Porphyry emplacement at Escondida, Zaldivar, and Chimborazo was coeval with this dioritic magmatism at ~38 Ma. Where plutonism was intense, the dioritic magma is interpreted to have evolved by processes of assimilation and fractional crystallization to more felsic compositions characteristic of the ore-forming porphyry intrusions. Whole-rock trace element data indicate that hornblende fractionation was an important control on chemical evolution of the diorites and attests to high-magmatic water contents (>4 wt % H2O). Volatile saturation would have occurred during further differentiation of these magmas, evidence for which is provided by the porphyry ore deposits. Porphyry emplacement was localized within a broad zone of intersection between the West Fissure zone and a regionally extensive northwest-trending structural corridor (the Archibarca lineament). It is proposed that the geometry of this junction was conducive to the formation of transtensional pull-apart structures during relaxation or reversal of dextral shear on the West Fissure zone. Such dilational structures would have focused the ascent and pooling of magma in the upper crust and maximized the potential for formation of magmatic-hydrothermal ore deposits. The formation of giant porphyry systems such as Escondida is, therefore, considered to be the result of a fortuitous coincidence of processes, including generation of suitable volumes and compositions of magma, appropriate lithospheric stress conditions, and structural focusing of emplacement; in addition, the development of thick supergene enrichment blankets has been critical to the economic value of these deposits. None of these contributory processes are in themselves unusual or rare, but because they are largely independent of one another, their constructive cooperation in ore formation is not necessarily repeatable at different places and at different times, thus explaining the relative rarity of giant porphyry deposits.

Summary Lake sediments of the last 1000 years provide a unique record of environmental changes. Methods of dating this record are reviewed and discussed. Sediments of the last 20 years, which are of particular biological significance because of their record of man‐made changes in lakes (including enrichment and pollution) have been dated successfully by the distribution within them of the fallout product 137 Cs, present in the atmosphere since 1954 and reaching a peak of supply in 1963. The structured pattern shown by the curve for 137 Cs concentration in most sediments investigated indicates that faunal mixing of the surface muds does not destroy the vertical stratification of the sediment profile. Sediments up to 120 years old have been dated by a lead isotope technique, and the results of this proved consistent with both 137 Cs dating and with palaeomagnetic dating where this was possible. Theoretical considerations of the application of radiocarbon dating to organic material of 18th and 19th century date are reviewed. Results of application of these radionuclide techniques to the sediments of a small lake, Blelham Tarn, near Windermere, are presented. Evidence from 137 Cs and 210 Pb dating of profiles from several different positions within the lake shows that the depth of the annual increment to the sediments varies by a factor of × 2 from place to place. The concentration within the sediment of chemical and biological variables shows no significant variation from one position to another; therefore calculated values for amounts of each variable included within unit area of the annual increment depend primarily on the thickness of this at the site chosen, and so cannot be directly related to the rates of supply of, for example, pollen grains or total organic matter, and so to rates of productivity. Results from nine 14 C dates on material 400–1000 years old, when correlated with analyses for pollen and sediment composition, demonstrate the profound effects of agricultural practices in the catchment (assumed to be deforestation and ploughing) in disturbing the orderly transfer to lake sediments of material eroded from the catchment.

Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of γ rays was observed directly behind the target. The γ rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction [63Cu(γ,n)62Cu] in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of Cu62. New measurements of the bremsstrahlung radiation at 1019 W cm−2 are also presented.

Analysis of stable isotope ratios in animal tissues has emerged as a powerful tool for determining the trophic level and composition of prey and foraging location. We summarize here data on the stepwise trophic enrichment in 15 N and latitudinal gradient in 13 C in the Southern Ocean, and derive a regression equation to estimate latitudes from 13 C values. We analysed isotope ratios of feathers of the small, pelagic seabird Wilson's storm-petrel Oceanites oceanicus, in different breeding stages, in comparison to isotope ratios of 4 other seabird species breeding in close vicinity on King George Island, South Shetland Islands. 15 N analysis of feathers and albumen from Wilson's storm-petrels indicated a shift in diet from mainly crustaceans during egg formation to an increased proportion of fish during chick-feeding and moulting. 15 N values of Wilson's storm-petrels during the chick-rearing season were closer to the mainly piscivorous-carnivorous skuas than to krill-feeding penguins, confirming that fish is an important part of their diet. 13 C analysis of feathers identified 4 distinct foraging areas: 13 C values in egg-white suggest that egg-forming females moved south to the sea ice edge. This coincides with the distribution of their main prey, Antarctic krill Euphausia superba, during this period. During the breeding season, Wilson's storm-petrels fed in the area around the colony, which is also used by penguins and skuas. 13 C of the feathers indicate that adults migrated to the Subtropical Front and beyond (north of 44S) during the inter-breeding period. Feathers were also analysed from 10 Wilson's storm-petrels caught by mistnet and thought to be prebreeders because they lacked foot markings; 8 of these had moulted in the same area as breeding birds, while 2 birds had moulted in an area further north (north of 30S). Adlie penguins Pygoscelis adeliae and Gentoo penguins P. papua had significantly different 13 C, suggesting that the Adlie penguins foraged further south than the Gentoo penguins. The foraging areas of brown skuas Stercorarius antarctica and south polar skuas S. maccormicki could not be separated by their isotope ratios.

1. The numbers of cormorants Phalacrocorax carbo feeding at English freshwater fisheries during winter have increased rapidly over the last 20 years, causing concern among fishery managers and anglers. 2. In order to assess the extent of freshwater feeding, stable isotope ratios of carbon and nitrogen (δ 13 C and δ 15 N) in feathers of wild cormorants from inland freshwater fisheries were compared with those in the feathers of piscivorous birds with marine diets (captive ‘marine‐fed’ cormorants, free‐ranging shags Phalacrocorax aristotelis ) and freshwater diets (juvenile goosanders Mergus merganser ). 3. Isotope signatures of feathers represent the diet at the time of growth. Feathers grown at different times of the year were taken from wild cormorants; each feather type therefore represented the diet over a different temporal scale. 4. Isotopic analyses of feathers indicated that, when shot, nearly all of the cormorants had been feeding entirely on freshwater prey. The mean δ 13 C value of primary feathers growing when birds were shot was –22·2‰, indicative of an entirely freshwater diet. 5. The move to freshwater habitats from coastal breeding grounds occurred over several months, but once established cormorants appear to have fed at freshwater sites throughout the autumn and winter. 6. The suitability of using a two‐source isotopic mixing model in order to quantify the extent of freshwater feeding in piscivorous birds is discussed. 7. Although the results indicate long‐term residency and feeding in freshwater systems, they do not indicate whether birds were feeding regularly at the sites at which they were shot, or the composition of the diet. It is recommended that further studies using telemetry and multiple isotope analyses be carried out in order to address these issues.

The Krafla volcanic system consists of a central volcano and associated fissure swarm in the NE axial rift zone of Iceland. Lavas spanning the whole of Krafla's exposed volcanic history (estimated to be 0-> 300 ka) have been analysed and range in composition from olivine tholeiite to rhyolite. Major-element compositions suggest that fractional crystallization exerts the main control over the differentiation process. However, K2O and the very incompatible trace elements, Rb, Th, and U, are all enriched beyond the extent expected by closed-system fractional crystallization. Fractionation coupled with periodic replenishment and tapping of the reservoir is unlikely to be responsible for this enrichment, despite the geophysical evidence suggesting a large number of inflations and deflations of a shallow magma reservoir (Tryggvason, 1986). Th- and O-isotope results confirm the work of previous authors that crustal assimilation is operating on a local scale beneath Krafla. A model is suggested, fitting both the Th- and O-isotopic data, which involves the partial melting and incorporation of a hydrothermally altered wall-rock contaminant during fractional crystallization (i.e., AFC processes). This process of partial melting is likely to enhance the most highly incompatible element concentrations (e.g., increasing Rb/Zr) more than expected by closed-system fractional crystallization.

The Early Devonian Rhynie hot spring system is the oldest known and is of the low sulphidation type. It extends for at least 1.5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments, plant-bearing sinters and andesitic lavas. The age of sedimentation and hydrothermal activity has been determined by palynological (Pragian) and radio-metric (396 ± 12 Ma) techniques. The outlier is a half graben with a complex stepped western margin. The Devonian rocks show intense hydrothermal alteration along the fault zone. The main alteration minerals are quartz, K-feldspar, calcite, hematite and illitic and chloritic clays. Multiple chert veining and brecciation are widely developed, and geyserite and vent material are also present. Pyrite occurs in veins and all alteration facies. Sinters and altered rocks contain high concentrations of Au, As, Sb, Hg, W and Mo. Gold occurs in arsenian pyrite and as sub-micron particles in oxidized rocks. The fluid(s) responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water. However, incursions of high temperature (300–440°C) magmatic fluids occurred with δD–65‰ and δ 18 O around +8.5‰. δ 34 S (pyrite) and initial 87 Sr/ 86 Sr ratios (vein calcite) lie mainly within the ranges +3.4‰ to +8.5‰ and 0.71138 to 0.71402 respectively. These data indicate that late Proterozoic Dalradian metasediments are a likely source for S and Sr but other sources are possible. δ 13 C values for caliche and vein calcite imply derivation of carbon from non-organic sources. The Rhynie cherts were deposited from a low salinity fluid of probable meteoric origin (δ 18 O chert + 13.1‰ to +16.5‰) which had interacted with the basement rocks and sediments (high Xe/Ar, Br/Cl and I/Cl ratios). Plant-bearing chert yielded an 40 Ar/ 39 Ar ratio (292.1± 0.6) significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere.

Abstract 40 Ar/ 39 Ar dating has facilitated a substantial reinterpretation of the volcanic evolution of Montserrat. Three volcanic centres with non-overlapping volcanic activity are identified: Silver Hills (c. 2600 to c. 1200 ka); Centre Hills (at least c. 950 to c. 550 ka); South Soufrière Hills-Soufrière Hills (at least c. 170 ka to present). The geochronological data show that old xenocrysts are common in the porphyritic andesite, implying that reliable ages are best obtained by dating the groundmass. Soufrière Hills evolved from early eruptions dominated by two-pyroxene andesite to eruptions of hypersthene-hornblende andesite at c. llOka. Between the two varieties of andesite there was an interlude of mafic volcanism at c. 130ka to form South Soufrière Hills. There is evidence of tectonic uplift of early products of the complex along with older submarine volcanic rocks. Consideration of stratigraphy and age data indicates that only a proportion of the dome-forming eruptions are recorded as domes in the geological record. Older products are removed from the subaerial edifice by sector-collapse events. The time-averaged eruption rate of the South Soufrière Hills-Soufrière Hills centre is estimated at 0.005 m 3 s -1 (c. 0.15 km 3 ka -1 ) (dense rock equivalent). The ongoing eruption is very similar in style to previous activity at Soufrière Hills, and future activity is likely to pose similar hazards. Soufrière Hills have been characterized by alternations of periods of enhanced activity and periods of dormancy, both lasting of the order of 10 4 years. During periods of elevated activity several major dome-forming eruptions are separated by quiescent interludes lasting less than c. 10 3 years. The ongoing eruption may mark the onset of a fourth period of enhanced volcanic activity at Soufrière Hills.

Layers of volcanic ash, or tephra form widespread chronostratigraphic marker horizons which are important because of their distinctive characteristics and rapid deposition over large areas. Absolute dating of prehistoric layers effectively depends upon 14 C analysis. We focus here on Icelandic tephra layers at both proximal and distal sites and consider three strategies to obtain age estimates: 1) the conventional dating of individual profiles; 2) high-precision multisample techniques or “wiggle-matching” using stratigraphic sequences of peat; and 3) a combination of routine analyses from multiple sites. The first approach is illustrated by the dating of a peat profile in Scotland containing tephra from the ad 1510 eruption of Hekla. This produced a 14 C age compatible with ad 1510, independently derived by geochemical correlation with historically dated Icelandic deposits. In addition, the ca. 2100 bp date for the Glen Garry tephra in Scotland, determined by a series of dates on a peat profile in Caithness, is supported by its stratigraphic position within 14 C dated profiles in Sutherland, and may be applied over a very large area of Scotland. More precise dates for individual tephras may be produced by “wiggle-matching”, although this approach could be biased by changes in peat-bog stratigraphy close to the position of the tephra fall. As appropriate sites for “wiggle-match” exercises may be found only for a few Icelandic tephras, we also consider the results of a spatial approach to 14 C dating tephra layers. We combined dates on peat underlying the same layer at several sites to estimate the age of the tephra: 3826 ± 12 bp for the Hekla-4 tephra and 2879 ± 34 bp for the Hekla-3 tephra. This approach is effective in terms of cost, the need for widespread applicability to Icelandic tephra stratigraphy and the production of ages of a useful resolution. We stress the need for accurate identification of tephra deposits without which the conclusions drawn from subsequent 14 C dating will be fundamentally flawed.

Zircons from a keratophyre associated with the Tayvallich Volcanics in the Dalradian rocks of the SW Scottish Highlands have been dated by U-Pb methods, yielding an age of 595 ± 4 Ma. This age indicates that most or all of the Dalradian is Precambrian in age, and that Dalradian sedimentation may have lasted for about 200 million years. The age also constrains the time interval between cessation of Dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the Grampian Orogeny. Sm-Nd isotopic data for the Tayvallich Volcanins and related metadolerite sills yield initial ºNd values of +2 to +4, which are thought to reffect the effects of melting of lithospheric mantle.

Research Article| June 01, 1997 Laser 40Ar/39Ar dating of single detrital muscovite grains from early foreland-basin sedimentary deposits in India: Implications for early Himalayan evolution Y. M. R. Najman; Y. M. R. Najman 1Department of Geology and Geophysics, Edinburgh University, West Mains Road, Edinburgh EH9 3JW, United Kingdom2Department of Earth Sciences, Cambridge University, Downing Street, Cambridge CB2 3EQ, United Kingdom Search for other works by this author on: GSW Google Scholar M. S. Pringle; M. S. Pringle 3Scottish Universities Research and Reactor Centre, Scottish Enterprise Technology Park, East Kilbride G75 0QF, United Kingdom Search for other works by this author on: GSW Google Scholar M. R. W. Johnson; M. R. W. Johnson 1Department of Geology and Geophysics, Edinburgh University, West Mains Road, Edinburgh EH9 3JW, United Kingdom Search for other works by this author on: GSW Google Scholar A. H. F. Robertson; A. H. F. Robertson 1Department of Geology and Geophysics, Edinburgh University, West Mains Road, Edinburgh EH9 3JW, United Kingdom Search for other works by this author on: GSW Google Scholar J. R. Wijbrans J. R. Wijbrans 4Faculty of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands Search for other works by this author on: GSW Google Scholar Geology (1997) 25 (6): 535–538. https://doi.org/10.1130/0091-7613(1997)025<0535:LAADOS>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Y. M. R. Najman, M. S. Pringle, M. R. W. Johnson, A. H. F. Robertson, J. R. Wijbrans; Laser 40Ar/39Ar dating of single detrital muscovite grains from early foreland-basin sedimentary deposits in India: Implications for early Himalayan evolution. Geology 1997;; 25 (6): 535–538. doi: https://doi.org/10.1130/0091-7613(1997)025<0535:LAADOS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract In India, the Dagshai and overlying Kasauli Formations represent the oldest exposed continental foredeep sediments eroded from the Himalayan orogen. 40Ar/39Ar dating of individual detrital white micas from these sedimentary units has provided maximum depositional ages of <28 Ma for the Dagshai Formation at one locality and <25 Ma at a second locality, whereas deposition of the Kasauli Formation occurred after 28 Ma at two localities and after 22 Ma at a third locality. This timing suggests that, in India, the start of substantial exhumation and erosion from the rising Himalayan orogen was delayed until 28 Ma. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A measurement of the neutron lifetime ${\ensuremath{\tau}}_{n}$ performed by the absolute counting of in-beam neutrons and their decay protons has been completed. Protons confined in a quasi-Penning trap were accelerated onto a silicon detector held at a high potential and counted with nearly unit efficiency. The neutrons were counted by a device with an efficiency inversely proportional to neutron velocity, which cancels the dwell time of the neutron beam in the trap. The result is ${\ensuremath{\tau}}_{n}=(886.3\ifmmode\pm\else\textpm\fi{}1.2[\mathrm{stat}]\ifmmode\pm\else\textpm\fi{}3.2[\mathrm{sys}])\phantom{\rule{0.3em}{0ex}}s$, which is the most precise measurement of the lifetime using an in-beam method. The systematic uncertainty is dominated by neutron counting, in particular, the mass of the deposit and the $^{6}\mathrm{Li}$$(n,t)$ cross section. The measurement technique and apparatus, data analysis, and investigation of systematic uncertainties are discussed in detail.

Ancient Egyptians are thought to have been the only people in the Old World who were practising mummification in the Bronze Age (c. 2200-700 BC). But now a remarkable series of finds from a remote Scottish island indicates that Ancient Britons were performing similar, if less elaborate, practices of bodily preservation. Evidence of mummification is usually limited to a narrow range of arid or frozen environments which are conducive to soft tissue preservation. Mike Parker Pearson and his team show that a combination of microstructural, contextual and AMS 14 C analysis of bone allows the identification of mummification in more temperate and wetter climates where soft tissues and fabrics do not normally survive. Skeletons from Cladh Hallan on South Uist, Western Isles, Scotland were buried several hundred years after death, and the skeletons provide evidence of post mortem manipulation of body parts. Perhaps these practices were widespread in mainland Britain during the Bronze Age.

A volcanic ash-layer in peat from northern Scotland has been identified and coincides exactly with an abrupt decline in Pinus sylvestris L. (Scots pine) pollen frequencies. This provides an isochrone (time-equivalent marker horizon) with which to investigate the timing of the Holocene 'pine-decline'. Furthermore, two possible causes of the southward shift of the range of Pinus in Scotland c. 4000 BP are suggested; a direct effect of acid pollution by chemicals produced by the eruption of Hekla (H-4), or a volcanically-induced climatic perturbation. These possibilities have wider implications for the influence of volcanism on postglacial environmental change.

ABSTRACT Calcite and quartz veins have formed, and are forming, in steeply dipping fissures in the actively rising Alpine Schist metamorphic belt of New Zealand. The fluids that deposited these minerals were mostly under hydrostatic pressure almost down to the brittle‐ductile transition, which has been raised to 5‐6 km depth by rapid uplift. Some fluids were trapped under lithostatic pressures. Fluids in the fissure veins were immiscible H 2 O + NaCl‐CO 2 mixtures at 200‐350d̀ C. Bulk fluid composition is 15‐20 mol% CO 2 and &lt;4.3 total mol CH 4 + N 2 + Ar/100mol H 2 O. Water hydrogen isotopic ratio δD H2O in the fissure veins spans ‐29 to ‐68‰, δ 18 O H2O ‐0.7 to 8.5‰, and bulk carbon isotopic ratio δ 13 C ranges from ‐3.7 to ‐11.7‰. The oxygen and hydrogen isotopic data suggest that the water has a predominantly meteoric source, and has undergone an oxygen isotope shift as a result of interaction with the host metamorphic rock. Similar fluids were present during cooling and uplift. Dissolved carbon is not wholly derived from residual metamorphic fluids; part may be generated by oxidation of graphite.

ABSTRACT Carbon isotope measurements carried out on 201 carbonate samples from the early Proterozoic of the Kola Peninsula, N. Karelia and Norway yield δ 13 C (PDB) spanning ‐ 20.5% to + 11%. A general δ 13 C secular trend shows that prior to 2.33 Ga values are typically ‘normal’ marine, averaging around ‐ 3%0. Between 2.33 and 2.06 Ga, in Jatulian time, there follows a rapid excursion to positive δ 13 C of around + 6%. Post‐Jatulian time is characterized by δ 13 C of sedimentary carbonates fluctuating between ‐ 5% and +3%; also it is remarkable for the first pronounced development of diagenetic carbonates, which have δ 13 C between ‐ 14 % and ‐ 6% . The c. 6% positive δ 13 C shift with a duration of about 270 Myr coincides with a maximum in the diversity and abundance of stromatolites, and with widespread development of ‘red beds’, but does not coincide with the maximum of buried C org mass. The Fennoscandian Shield represents the largest isotoically anomalous carbonate province yet reported, and the positive δ 13 C excursion together with a series of major global palaeoenviromental changes seems to be more intense than the Precambrian/Cambrian transition events. However, it is still not clear what kind of mechanism this phenomenon could be attributed to. An increase of the ‘Ronov ratio’, and/or ‘Broecker ratio’ and other possible models are discussed as the target for future investigations.

The neutron lifetime ${\mathrm{\ensuremath{\tau}}}_{\mathit{n}}$ has been measured by counting decay protons stored in a Penning trap whose magnetic axis coincided with a neutron-beam axis. The result of the measurement is ${\mathrm{\ensuremath{\tau}}}_{\mathit{n}}$=893.6\ifmmode\pm\else\textpm\fi{}5.3 s, which agrees well with the value predicted by precise measurements of the \ensuremath{\beta}-decay asymmetry parameter A and the standard model.

Synopsis A model is presented for the genesis of the Cyprus massive cupriferous sulphide deposits, their associated stockwork mineralization and the metamorphism of the Troodos ophiolite complex based on D/H, 18 O/ 16 O and 13 C/ 12 C ratio analyses, where applicable, of 94 whole rocks and minerals, chemical, mineralogical and sulphur iso tope data. The upper 3–5 km of the hot Troodos crust — pillow lavas, Sheeted Intrusive Complex, trondhjemites and upper gabbros — were metamorphosed to zeolite facies, temperatures of about 0 to 250° C, and greenschist-amphibolite facies, temperatures of about 250 to 450–550° C, during interaction with a deep circulating sea-water geothermal system. Minimum isotopic temperatures of 320–400°C are given for the epidote-bearing vein-halo assemblages in the upper gabbros, trondhjemites and Sheeted Intrusive Complex. If temperatures at the base of the Sheeted Intrusive Complex were higher than ∼ 500° C, either a magmatic or metamorphic water component must have been present in the hydrothermal fluids. The magmatic water could be of sea-water origin, being derived from the melting or assimilation of sea-water-hydrothermally altered roof rocks overlying the gabbroic magma chambers. Minimum water/rock ratios during pervasive alteration decrease from &gt; 1 by weight in zeolite facies pillow lavas to ∼ 0.1 in the underlying green-schist facies rocks, but were an order of magnitude larger in the veins and fractures. In the stockwork zones, which underlie the sea-floor sites of massive sulphide orebodies, isotopic temperatures declined from initial values greater than 300° C (with water/rock ratios &gt; 1–5, by weight) to less than 220° C during post-sulphide later-stage vein quartz formation; these temperatures were higher than temperatures in the predominantly zeolite facies country rocks. The stockwork zones are interpreted to represent the discharge zones of the seawater-hydrothermal fluids responsible for the regional-scale mass transfer and the mineralization. At least some of the sulphide sulphur in the stockworks and orebodies is of seawater origin. Formation of massive sulphide deposits requires the coincidence of several factors, including the penetration of a brine to deep levels, where temperatures were greater than 300° C in an active spreading centre, leaching of ore metals, and discharge of the hot springs into basins where both sulphide deposition and localization could occur.

Summary The binding of metal to humic substances is problematical. The approaches for studying metal binding to organic matter are briefly reviewed. Ion‐selective electrodes (Cu 2+ and Pb 2+ ) were used to measure metal complexation by a whole peat and an extracted humic acid (HA) fraction. Scatchard plots and calculation of incremental formation constants were used to obtain values for the binding constants for the metals onto both peat and HA. Both the peat and the humic acid had a larger maximum binding capacity for Pb 2+ than for Cu 2+ (e.g. at pH = 5 HA gave 0·188 mmol Cu 2+ g −1 and 0·564 mmol Pb 2+ g −1 : peat gave 0·111 mmol Cu 2+ g −1 and 0·391 mmol Pb 2+ g −1 ). Overall, the humic acid had a larger metal binding capacity, suggesting that extraction caused conformational or chemical changes. The binding constants (K 1 ) for Cu 2+ increased with increasing pH in both peat and humic acid, and were larger in the peat at any given pH (e.g. at pH = 5 HA gave log K 1 = 2·63, and peat gave log K 1 = 4·47 for Cu 2+ ). The values for Pb 2+ showed little change with pH or between peat and humic acid (e.g. at pH = 5 HA gave log K 1 = 3·03 and peat gave log K 1 = 3·00 for Pb 2+ ). In the peat, Cu 2+ may be more able to bind in a 2:1 stoichiometric arrangement, resulting in greater stability but smaller binding capacity, whereas Pb 2+ binds predominantly in a 1:1 arrangement, with more metal being bound less strongly. Whole peat is considered to be more appropriate than an extracted humic acid fraction for the study of heavy metal binding in organic soils, as this is the material with which metals introduced into an organic soil would interact under natural conditions.