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A number of factors are driving the provision of power system analysis tools in new directions. These include: growing uncertainties in the planning and operation of power systems; growing pressures in market-oriented industries for transparency and accountability in decision making; increasing need for exchange of data between different market players; and the entry of contemporary software technologies and numerical methods into the power industry. These pose opportunities and challenges to software providers. The position of a power system operator as an arbiter in market-oriented electricity supply industries means its decisions must be shown to be free from commercial bias. The separation of different power system services among many providers has led to an increasing need for exchange of data. This can lead to uncertainty regarding the accuracy of data, the management of which may require new tools. The cost and technology drivers, statistical and probabilistic methods, maintenance of legacy software and the nature of new facilities are discussed in the article.

One of the most exciting advances in Earth science in the last several decades has been our increased understanding of the structure and composition of the mantle. Seismic tomography and isotope geochemistry have been major players in those advances. The isotopic studies used basalts from ocean basins to minimize the problems of possible crustal contamination. Data from mid-ocean ridge basalts (MORBs) and oceanic island basalts (OIBs) revealed a relatively detailed picture of the isotope geochemistry of the sub-oceanic mantle [e.g. Hofmann, 1997] that led to the recognition of four principal magma components that define end-member compositions. These are DMM, HIMU, EMI, and EM2 (see Table 1 for further details). All of these components except DMM have been attributed to subduction of different materials, such as oceanic and continental crust and lithosphere, down into the mantle. Several studies have indicated that the mantle is isotopically heterogeneous with heterogeneities that were probably established at least several billions of years ago.

Pyroxene phenocrysts from nephelinites associated with the Tertiary carbonatite-nephelinite Napak volcano are not in isotopic equilibrium with their host rocks and reveal a complicated evolutionary history that involved fractional crystallization of a melt undergoing continuous isotopic change. Intrasample pyroxene populations have different isotopic compositions and are interpreted as earlier formed pyroxenes that failed to isotopically equilibrate with the host liquids and that were later scavenged by ascending melts. The Napak data show that the pyroxenes can be effective in monitoring isotopic shifts that occur during magma evolution.

The 206Pb/204Pb ratios of fine-grained fractions from glacial tills indicate the presence of known Proterozoic volcanogenic massive sulfide deposits at Chisel Lake, near Snow Lake, Manitoba, Canada. Data from

About half of the 330 occurrences listed in the global inventory of carbonatites have been dated, mostly by the K-Ar method, and they fall into groups that appear to be temporally and spatially linked to major orogenic events. Overall, however, the temporal pattern is one of exponential increase in frequency with time. This secular trend has been interpreted as an increase in carbonatite activity in the course of terrestrial evolution. In an alternative interpretation, the observed trend may be viewed as an artifact of preservation, because the probability of preservation decreases exponentially with increasing age of the crustal segments. The secular trend for carbonatites since at least 1.8 Ga, the time that continental crust attained its near-modern extent, is compatible with a steady-state process of carbonatite generation and destruction that has a half-life of ∼445 m.y. The most acceptable model for the temporal distribution of carbonatites involves a combination of orogenic activity and erosional dispersal.

Nd and Sr isotope compositions of nephelinites, carbonatites, and phonolites from Shombole, a Pliocene volcano in East Africa, show that the phonolites cannot be derived by simple fractional crystallization of nephelinite magma. For a given initial {sup 87}Sr/{sup 86}Sr ratio, {sup 143}Nd/{sup 144}Nd is lower in most phonolites than in the nephelinites and carbonatites. Interaction between nephelinitic magma and lower-crustal granulites can account for these differences. The similar ranges in isotopic composition of the carbonatites and nephelinites are consistent with repeated melting events involving heterogeneous mantle. The carbonatites could have formed by immiscibility with nephelinite magma or by direct partial melting of the same mantle source(s) as the nephelinites.

Assessment of available geochronological information, as well as new whole-rock Rb-Sr data from several granitoid rocks of Saskatchewan, shows a close relationship between magmatic-metamorphic events in the Hudsonian orogen and uranium mineralization. Most uranium deposits lie to the west of the Needle Falls Shear Zone and occur as either: (i) vein-type deposits or (ii) unconformity-type deposits close to the contact between the Athabasca sediments and their basement. At least two metamorphisms have affected the pre-Athabasca rocks: the Kenoran at about 2500 Ma ago, and the more pervasive ‘main’ Hudsonian event at 1740 Ma. A much younger thermal event (perhaps associated with uplift and cooling) at 1540 Ma is also indicated. The post-Kenoran K-Ar dates suggest prolonged thermal activity from about 1900 Ma through to about 1500 Ma ago. Granitoid events at 1870 Ma and 1740 Ma ago are outlined by both U-Pb zircon and Rb-Sr whole-rock isochron data. Whole-rock Rb-Sr data from the unmetamorphosed Athabasca sediments suggest an approximate depositional age of 1450±50 Ma, a figure that is consistent with the age of the underlying Hudsonian basement and the truncation of the sediments by the Cree Lake diabase dyke swarm at about 1200–1300 Ma ago. Although several episodes of uranium deposition have been documented, the main ones seem to have occurred at 1860 Ma (syngenetic uraninite in pegmatites), 1740 Ma (the Beaverlodge vein-type deposits) and between 1300 and 800 Ma (the epigenetic uranium of the unconformity-type deposits). Whereas the two earlier episodes can be correlated with periods of either magmatic or metamorphic activity, the late Proterozoic episodes cannot. The close agreement between the age of the Cree Lake dyke swarm and the late Proterozoic mineralization suggests that at about 1300 Ma ago possible hydrothermal activity from relatively deep-seated fractures may have been responsible for the solution and transportation of the uranium of the unconformity-type deposits. The period 1300 Ma to about 900 Ma, in other parts of the Canadian Shield, was a time of crustal rifting, basic magmatism, carbonatite activity, and intense deformation. Prior to the deposition of the Athabasca sediments uranium was concentrated by Hudsonian magmatic and metamorphic processes whereas subsequently, transportation and intermittent deposition of the unconformity-type deposits were related to fairly long-lived, low-temperature hydrothermal activity.

Whole-rock Rb–Sr isochron ages from nine granitic plutons that intrude the Central Mobile Belt and the Avalon Zone of Newfoundland are consistent with the view that most of the magmatic activity for this segment of the Appalachian Orogen is related to the Acadian Orogeny. Most of the granites are between 400 Ma and 340 Ma old, although two from the Avalon Zone are significantly different. One, the foliated Swift Current granite, is late Cambrian – early Ordovician (500 ± 30 Ma), whereas the other, the peralkaline St. Lawrence granite, is Carboniferous (315 ± 5 Ma).Several foliated granites from the Gander Zone of the Central Mobile Belt, formerly considered to be older than Mid-Ordovician, are Silurian or Devonian in age. Five megacrystic biotite granites have ages ranging between 420 ± 20 Ma and 340 ± 10 Ma, and a leucocratic granite, the Middle Ridge Pluton, gives an age of 370 ± 15 Ma. None of the granites from the Gander Zone is older than 420 ± 20 Ma, and geochronological evidence for a Precambrian basement in the Central Mobile Belt has still to be found.The initial 87Sr/86Sr ratios show no correlation with age, although the initial ratio of 0.722 for the St. Lawrence granite is much higher than the ratios of between 0.704 and 0.709 for the other granites; this high ratio is consistent with derivation of the granite by partial melting of the continental crust.The isotopic data impose certain constraints on models proposed for the evolution of Newfoundland, the most important being: (i) extensive Devonian magmatism; (ii) intense post-400 Ma cataclasis; (iii) generation of petrographically similar granites at different times; and (iv) Carboniferous magmatism.

ARCHAEAN greenstone belts have commonly been correlated on the basis of similarities in their stratigraphic successions1. Conclusive radiometric tests of these correlations have rarely been made, because of the difficulty of dating the rocks of the greenstone belts themselves, and because of uncertainties in their relationships to the more easily dated granitoid rocks with which they are normally associated. We report here radiometric evidence from eastern Africa, which clearly contradicts previous lithostratigraphic correlations between the Tanzanian and Kaapvaal Cratons by establishing a minimum age difference between the uppermost parts of their respective greenstone belt successions.

Rb–Sr and U–Pb data from the Borden complex of northern Ontario, a carbonatite associated with the Kapuskasing Structural Zone, indicate a mid-Proterozoic age. A 207Pb/206Pb age of 1872 ± 13 Ma is interpreted as the emplacement age of this body, grouping it with other ca. 1900 Ma complexes that are the oldest known carbonatites associated with the Kapuskasing structure. A 206Pb–238U age of 1894 ± 29 Ma agrees with the Pb–Pb age but has a high mean square of weighted deviates (MSWD) of 42. A Rb–Sr apatite–carbonate–mica whole-rock isochron date of 1807 ± 13 Ma probably indicates later resetting of the Rb–Sr system.An εSr(T) value of −6.2 ± 0.5 (87Sr/86Sr = 0.70184 ± 0.00003) and an εNd(T) value of +2.8 ± 0.4 for Borden indicate derivation of the Sr and Nd from a source with a time-integrated depletion in the large-ion lithophile (LIL) elements. These closely resemble the ε values for Sr and Nd from the Cargill and Spanish River complexes, two other 1900 Ma plutons. The estimated initial 207Pb/204Pb and 206Pb/204Pb ratios from Borden calcites plot significantly below growth curves for average continental crust in isotope correlation diagrams, a pattern similar to those found in mid-ocean ridge basalts (MORB) and most ocean-island volcanic rocks, again suggesting a source depleted in LIL elements. The combined Nd and Sr, and probably Pb, data strongly favour a mantle origin for the Borden complex with little or no crustal contamination and support the model of Bell et al. that many carbonatites intruded into the Canadian Shield were derived from an ancient, LIL-depleted subcontinental upper mantle.

Initial 87 Sr 86 Sr and 143 Nd 144 Nd ratios of some carbonatites and related alkalic rocks intruded into the Canadian Shield between 2700 Ma and 110 Ma ago define development lines on a plot of initial ratio versus age. The isotopic data show that these complexes have been derived from a mantle source with a Rb Sr ratio of 0.020 ± 0.002 and a Sm Nd ratio of 0.358 ± 0.008, which are lower and higher respectively than the values for the silicate portion of the Earth. An estimate of the mean age of formation of this LIL-depleted reservoir, based on the intersection of the development lines with those of bulk Earth, is about 2900 Ma, a figure similar to the age of most Superior Province rocks. A model is proposed that involves differentiation, ca. 2900 Ma ago, of mantle similar in chemical composition to bulk Earth, into granitoid rocks (the Superior Province), and a depleted, residual upper mantle. The source for the Nd and Sr contained in the carbonatites is thought to lie within this depleted sub-continental lithosphere. Measured Sm Nd ratios of about 0.15 for the carbonatites are much lower than the calculated Sm Nd ratio of their source, and support enrichment of the light REE either slightly before or at the same time as carbonatite magma generation.

The spontaneous deposition of short-lived radon decay products onto solid surfaces (“collectors”) provides the basis for a simple and efficient way of prospecting for uranium. The alpha activity of two of the decay products, 218 Po and 214 Po, can be measured by conventional counting techniques following the exposure of a collector to a radon source. Laboratory studies have shown: (a) radon decay products can be collected on a wide variety of materials; (b) the number of radon decay products increases with the collector surface area; (c) a negative charge applied to the collectors enhances the number of decay products collected; (d) the shape of the collectors is relatively unimportant; and (e) reproducibility is about ± 5% of the measured value. Field tests on known uranium anomalies involved suspending collectors for an overnight exposure, in either covered holes or inverted containers buried in soil. Subsequent removal of the collectors was immediately followed by counting the alpha activity. Anomalies were readily detected at three different test sites. Replicate measurements at selected sites both on an hour-to-hour and on a day-to-day basis showed remarkably good agreement. Some anomalies were also outlined using activity measurements from collectors suspended above soil aliquots in sealed containers. Because the half-lives of two of the thoron ( 220 Rn) decay products are much longer than those of the radon ( 222 Rn) decay products, a thoron correction can be applied to the original activity measured from the collectors, thus discriminating against thoron in thorium-rich terrains. The counting of radon decay products deposited onto collectors is an effective method for delineating radon anomalies in uranium exploration. The field techniques are simple to apply, and results are available after very short exposure times (about 18 hours) and after short counting intervals (5 minutes).

Midcontinent Rift flood basalts represent a sample of the relatively shallow, sub-continental upper mantle beneath the Canadian Shield at 1.1 Ga. A thick sequence of olivine tholeiite lavas, including minor intermediate to rhyolitic lavas, from the Portage Lake Volcanics (PLV) in northern Michigan have initial Nd and Sr isotopic compositions which cluster near Bulk Earth values. The effects of assimilation of old LREE-enriched continental crust into mantle-derived fractionating liquids are isotopically discernible in evolved lavas as well as in olivine tholeiites from the lowest portion of the volcanic pile. However, the effects of crustal contamination decrease with stratigraphie height and are absent in more primitive lavas in the upper half of the section. Therefore, the youngest olivine tholeiites preserve the isotopic characteristics of their sub-continental mantle source area which, at 1095 Ma, had ϵNd(T) and ϵSr(T) values of about +0.8 and +2, respectively. Incompatible trace element compositions from the PLV olivine tholeiite suite support the interpretation of a mantle source slightly enriched in LIL elements relative to chondritic compositions as opposed to a suite of hybrid magmas resulting from mixtures between depleted mantle and enriched crustal end-members. The source for PLV tholeiites is substantially less depleted than previously reported mantle values from the Superior Province. An origin for the PLV source is compatible with either of several mantle evolution models. The PLV source may have been associated with upwelling of a LIL element-enriched, asthenospheric plume which emplaced non-depleted material from deeper sources into the shallow subcontinental mantle beneath the Midcontinent Rift during continental break-up. Alternatively, the PLV source may have originated by enrichment of refractory sub-continental lithospheric mantle which was previously depleted in incompatible trace elements during Archean-aged melt extraction and continental crust formation. Concurrent generation of carbonatite magmas in other areas beneath the Superior Province indicates the widespread presence of sub-continental mantle with substantially higher ϵNd(T) and lower ϵSr(T) than the PLV source. Combined tholeiite and carbonatite data indicates the presence of large, chemically distinct regions in the upper mantle beneath the Superior Province at 1.1 Ga.

Conflicting evidence exists regarding the ability of PGE 1 to normalize blood pressure in renal hypertensive rats. We performed experiments to determine the effect of PGE 1 (15 μg/kg i.p. daily for 3 weeks) in renal hypertensive Wistars and found no significant change in systolic pressure. A higher dose (150 μg/kg i.p.) lowered pressure after 14 days of treatment, but not back to control levels. Further investigations are required to establish the mechanism whereby PGE 1 evokes this fall. To test the hypothesis that endogenous prostaglandins have a hypotensive function in renal hypertension, experiments were performed using sodium meclofenamate to inhibit prostaglandin biosynthesis. In chronic hypertensive rats the drug had no significant effect, while in the acute phase of renal hypertension there was a dose-dependent inhibition of the pressure rise. The possibility is suggesteed that prostaglandins may initiate or sustain the acute phase of renal hypertension in rats.

The Davis Lake complex (DLC), composed of biotite monzogranite, leucomonzogranite, and cassiterite–topaz greisen, hosts the East Kemptville tin mine in southwestern Nova Scotia. The DLC monzogranite contains glomeroporphyritic biotite with ilmenite and many rare-earth-element (REE) bearing accessory minerals, zircon-bearing quartz phenocrysts, and xenoliths of biotite granite. Primary muscovite is rare. Major- and trace-element geochemical trends indicate well-defined, but limited, magmatic differentiation trends. REE patterns of the least-evolved granites are flat and show a Ce/Yb ratio of 10.The DLC was previously considered cogenetic with the Devonian South Mountain batholith (SMB) on the basis of its location, lithologies, and similarities in major- and trace-element geochemistry. However, new Rb–Sr whole-rock isotopic data indicate an Rb–Sr date of 330 ± 7 Ma (mean square of weighted deviates (MSWD) = 2.8) for the DLC, implying that it is at least 35 Ma younger than the SMB. The initial 87Sr/86Sr ratio of 0.727 ± 0.004 is significantly higher than those for other Meguma Terrane granites and is the highest yet reported from Appalachian granitoid rocks. Rb–Sr data from biotite indicate open-system behaviour between 260 and 240 Ma and provide more evidence for previously documented tectonothermal events after 300 Ma in the Meguma Terrane.The peraluminous nature of the DLC, its high Rb/Sr and high 87Sr/86Sr ratios, high P, F, and Sn contents, low Ca and B contents, and high differentiation indices indicate that the complex was derived from a highly evolved felsic source. Geochemical distinctions indicate that the DLC is neither derived from nor cogenetic with the SMB. A more probable source for the DLC magma is a dehydrated felsic granulite from which a previous H2O-, B-, Cl-, and Zn-rich granitic magma (perhaps the SMB) had been extracted. Such a source is analogous to that postulated for A-type granites and topaz rhyolites.The DLC shows more similarities to the "stitching" Carboniferous Appalachian volatile- and metal-rich granites than to Devonian Meguma granites. Unlike most of these Appalachian plutons, which occur marginal to terrane boundaries and were probably crystallized from locally generated, anatectic magmas, the DLC was emplaced in the centre of the most-outboard Meguma Terrane, adjacent to the Tobiatic shear zone.

Lead isotopic compositions are presented for 8 calcite, 1 pyrite and 1 melilite separates from the Oka, Quebec, carbonatite complex. Pyrite, melilite and two calcite samples with small in situ decay corrections yield similar initial isotope ratios, averaging 206 Pb 204 Pb = 19.65 , 207 Pb 204 Pb = 15.56 , 208 Pb 204 Pb = 39.00 . This composition shows a close affinity for Pb isotope ratios from ocean island basalts (OIB) and indicates an origin of the Pb in large-ion lithophile (LIL)-element depleted mantle sources. The Pb probably results from a mixture from a LIL-element depleted source and possibly, metasomatic fluids. Four calcites fail to yield accurate initial ratio information due to large in situ decay corrections. In addition three samples exhibit high initial 207 Pb 204 Pb ratios indicative of probable crustal contamination. The silicate fraction of one okaite and a sample of country rock gneiss near Oka contain Pb with isotopic compositions that illustrate the kinds of contamination that could be involved. Sr isotope data are reported for 2 whole-rock sovites, plus 1 nepheline, 4 calcite and 2 apatite separates. All samples yield nearly identical isotopic compositions, with a mean 87 Sr 86 Sr ratio of 0.70331 ± 0.00002 at the 2 sigma level. This result verifies an earlier value reported by Bell et al. (1982) and supports their suggestion of a LIL-element depleted mantle source for the Sr. The Sr data do not show the apparent crustal contamination detected by some of the Pb data, presumably because of the high Sr contents of the carbonate samples. The Oka data are compared with results of a similar study by Lancelot and Allegre (1974) on carbonatite complexes from eastern Uganda. We conclude that the African data, as presently known, are compatible with the model developed for the mantle-derived Oka suite.

THE Archaean–Proterozoic boundary, it has been suggested, marks a fundamental change in the behaviour of the Earth, ending an early phase of cratonisation and the beginning of a period characterised by stable shelf sedimentation and linear orogens1,2,3. Almost all Archaean terrains, other than those dominated by granulites and migmatites, seem to be characterised by a variety of granitoid rocks intimately associated with ultramafic through mafic to calc-alkalic sequences, and their sedimentary associations. These greenstone belt assemblages are remarkably similar from one craton to another; they are usually folded into keel-shaped troughs, subjected to greenchist facies metamorphism and usually show similar structural styles which suggest that they were acted on by predominantly vertical forces. Their alleged antiquity (2,000 Myr or more) and widespread distribution have been attributed to either a change in the geothermal gradient as the Earth became colder3 or the existence of a relatively thin, Archaean, continental crust4,5.

Neutron activation determination of La, Ce, Sm, Eu, Tb, Yb, Lu, Ta, Hf, Sc, Co and Th in potassic lavas from the Birunga and Toro-Ankole regions show that the rocks are characterized by high rare earth element (REE) contents (161–754 ppm) and form two groups based upon differing La/Yb ratios. One group is made up of katungite, ugandite and mafurite with La/Yb =146–312, and the other of rocks of the leucitite and phonolitic tephrite series, La/Yb =30–56. The trace element content of the ugandite group is similar to that of kimberlites. The data do not indicate any trends of differentiation or simple relationships between the two groups of rocks, although katungite is unlikely to be parental to rocks of lower La/Yb ratios. It is unlikely that in terms of La/Yb ratios that partial melting of mica-garnet-lherzolite mantle can form katungite because of the very small amounts of partial melting required (0.2%), although the La/Yb ratios of 150–200 (ugandites, mafurites) and 30–60 (leucitites, phonolitic tephrites) can be accounted for by 0.3–1.5% and 1–9% melting respectively, if the REE are then concentrated without further La and Yb fractionation. Partial melting of mantle which has been metasomatized by alkaline earths and REE bearing fluids or mixing of carbonatite and nephelenite are also compatable with the observed geochemistry of the lavas. It is considered that gas transfer processes which selectively enrich the light REE may have obscured REE evidence pertaining to early partial melting and/or differentiation processes and therefore that REE geochemistry is of little use in determining the petrogenetic processes involved in the formation of potassic lavas.

A detailed isotopic study of minerals and whole rocks from the Cretaceous Oka complex, Quebec, Canada, shows a very small variation in initial Nd and Sr isotopic compositions. Assuming an age of 109 Ma for the complex, apatite, calcite, garnet, melilite, monticellite, olivine and pyroxene and whole rocks yield a range for initial 87Sr/86Sr of 0.70323–0.70333; and for initial 143Nd/144Nd of 0.51271–0.51284 (eSR(T)= −14.8 to −16.2; eNd(T)=+4.1 to +6.6). The negative eSR and positive eNd indicate derivation of the Nd and Sr from a source with a time-integrated depletion in the large-ion lithophile (LIL) elements. This agrees with data from other Canadian carbonatites and confirms that a large part of the Canadian Shield is underlain by a source region depleted in the LIL elements. The new data from Oka suggest that the depleted source may have remained coupled to the continental crust until recent time.

210 Po and 210 Pb measurements of soils delineated uranium anomalies at three out of four test sites in Ontario, Canada. Measurements were made of 210 Po in solutions produced by both complete digestion and partial leaching of soil samples. Direct plating of 210 Po onto metal plates was followed by measuring the alpha activity. Subsequent plating of 210 Po in-grown from 210 Pb in solution several months later confirmed the anomalies. The 210 Po and 210 Pb anomalies at three of the test sites coincided with 226 Ra and 222 Rn anomalies. Samples from the fourth uranium occurrence associated with a known 222 Rn anomaly failed to show either a 226 Ra anomaly on the one hand, or 210 Po or 210 Pb anomalies on the other. This suggests that the 210 Po and 210 Pb anomalies were probably produced by the decay of 226 Ra contained within secondary dispersion haloes. Although anomalies due to the 210 Po and 210 Pb products of 222 Rn have now been documented, prospecting methods based on their use as direct tracers of the migration paths of 222 Rn require much further development.

Pervasive hydrothermal alteration zones in quartz-feldspar porphyry domes underly all massive sulfide lenses in the D-68 Zone Cu-Zn deposit, Noranda. Alteration pipes are mineralogically zoned and contain chloritic cores consisting of stringer sulfides, enveloped by sericitic haloes. Silicified rocks are found locally. Alteration took place at nearly constant volume. Na depletion, and K enrichment relative to the least altered rocks, are found in all alteration zones. Fe and Mg have been added to the chloritic zone and subtracted in the sericitic and silicic zones. Ca and Si are enriched mainly in the silicic zone. Al, Ti and Zr were the least mobile of the elements studied. Whole-rock δ18O values vary from +5.6 to +6.2 per mil in chloritized rocks, +5.8 to + 7.3 per mil in sericitized rocks and + 7.2 to + 8.3 per mil in silicified rocks. δD values for two chloritized samples are − 63 and − 70 per mil whereas in two sericitized samples they are close to −62 per mil. Quartz from the chlorite alteration zone is isotopically heavier (δ18O = 8.6 per mil) than that from the sericite alteration zone (δ18O = 6.4 per mil), suggesting equilibration with different hydrothermal fluid or different temperature of alteration. Assuming an alteration temperature of 300° + 50°C the fluid in equilibrium with quartz and chlorite had δ18O and δD values of about 1.5 ± 2.0 per mil and −23 ± 5 per mil, respectively. The fluid in equilibrium with quartz and sericite had δ18O and δD values of about −0.5 ± 2 per mil and −30 ± 5 per mil, respectively. On the basis of isotopic data, seawater was probably the major constituent of the hydrothermal fluids.

New whole-rock Rb-Sr isochron dates from the Tanzanian Shield of East Africa fall in the range $2500 \pm 100$ Myr and outline a major period of granitoid magmatism that has not, until now, been documented from this part of the African continent. Although at least two events can be delineated, one at 2740 Myr, the other at 2540 Myr, the younger is more widespread and reflects extensive granitoid magmatism throughout large areas of Tanzania, southeastern Uganda and western Kenya. Lacking ages greater than 2800 Myr, the Tanzanian Shield is unique among the Archaean cratons of Africa. Initial 87Sr/86Sr ratios lie typically between 0.7010 and 0.7020, similar to late Archaean igneous rocks in other cratons, and provide little evidence to support the origin of the 2500 Myr Tanzanian crustal segment by simple reworking of ancient continental crust The chemical composition of the granitoid rocks ranges from granite (sensu stricto) to granodiorite, but none of the analyses falls within the tonalite field. Compariso...

Initial Sr87/Sr86 ratios and rubidium and strontium contents have been measured in 83 specimens from 8 suites of alkalic and ultrabasic rocks. The range of initial Sr87/Sr86 ratio observed and the number of specimens (in parentheses) analysed for each suite are: West Kimberley, Australia (8), 0.7125–0.7215; Jumilla, Spain (6), 0.7136–0.7158; Bearpaw Mountains, Montana (9), 0.7062–0.7086; Highwood Mountains, Montana (10), 0.7072–0.7087; Hopi Buttes, Arizona (8), 0.7038–0.7094; Leucite Hills, Wyoming (17), 0.7055–0.7070; Montana diatremes (13), 0.7034–0.7073; Navajo Province, Arizona and New Mexico (12), 0.7052–0.7099. The initial Sr87/Sr86 ratios of the West Kimberley and Jumilla rocks are the highest yet found in strontium-rich basic rocks. Some of the individual specimens from West Kimberley have initial ratios as high as some estimates of the present Sr87/Sr86 ratio of average crustal material. This is interpreted to mean that the West Kimberley and Jumilla rocks contain substantial amounts of radiogenic strontium, and possibly other elements, from a crustal source.

In a recent paper, Mattinson (1977) reports some U-Pb zircon data from the Burlington Peninsula, Newfoundland, and proposes a synthesis of the isotopic data from this area. His synthesis, albeit tentative, is as follows (the geological units are shown in Fig. 1): (1) ophiolite formation -500-510 Ma ago (basal part of the Snooks Arm Group), followed by deposition of sediments in Arenig time; (2) emplacement of the Cape St. John Group and the Cape Brule porphyry -475 Ma; (3) intrusion of the Burlington granodiorite, Dunamagon granite, and Seal Island Bight syenite -440 Ma ago; and (4) resetting of some mineral ages in the Burlington granodiorite by an event -340 Ma ago. Since the Burlington granodiorite, Seal Island Bight s yenite, and Dunamagon granite are all either preor syn-kinematic intrusions, Mattinson also suggests that both deformation and metamorphism in the Burlington Peninsula had begun by -440 Ma, but not prior to 475 Ma. Mattinson's (1977) data represent a welcome , contribution to the understanding of the evolution I of the region, but we do wish to dispute some of his I findings. To begin with, we take strong exception to what we consider to be a misrepresentation by Mattinson of our Rb-Sr data, which we documented in a preliminary report to the Newfoundland Department of Mines and Energy (Bell and Blenkinsop 1975). Not only does the omission of our inferences give a distorted and unrealistic picture of our findings, but it denies us any credit for earlier drawing conclusions similar to Mattinson's regarding the Cape St. John volcanics. To set the record straight, we quote from our report (the quotation refers only to the Cape St. John volcanics)

A RECONSTRUCTION of the continental blocks for the central and North Atlantic has led to the widespread acceptance of the continuity of the Palaeozoic orogenic belts on both sides of the Atlantic. A reconstruction of the land masses during the Carboniferous and Permian shows the Variscan Belt of Europe, the Mauritanides of Morocco, and the Southern Appalachians as being continuous1. Although the Hercynian Front has now been recognised in New Brunswick2 the situation in Newfoundland is unclear. We suggest, on the basis of the geochemical data outlined in Table 1, that the continuation of these belts can be interpolated between New Brunswick and south-west England to include at least the Central Mobile Belt and the Avalon Zone of Newfoundland. We find the earlier correlation by Holmes3 particularly attractive in view of our new isotopic data, a correlation which extends the Hercynian Front westwars from south-west England and Wales into Canada, where it passes along the Cabot Fault into the New Brunswick seaboard and the Bay of Fundy (Fig. 1). Cherkis et al.4 link the Charlie Gibbs Fracture Zone to the Hercynian Front on both the European and North American continents, and have recently offered new evidence for the emergence of the front in Newfoundland5. The intersection of the Charlie Gibbs Fracture Zone and the continental shelf of Newfoundland lies about 100km east of the Cabot Fault, so that their delineation of the front lies further to the south than the one outlined here.

THE susceptibility of fine-grained, volcanic rocks to open-system behaviour during regional metamorphic activity has long been suspected in Rb/Sr geochronology1–5. The evidence that we present here shows that not only can open-system behaviour occur, but that it is partly a function of bulk chemical composition. We have studied the Burlington Peninsula area of northern Newfoundland (Fig. 1) which is underlain by the Cape St John Group, a volcanic pile of sub-aerial, calc-alkalic volcanic and sedimentary material, about 3,500 m thick. Coarse calcareous units and minor conglomeratic beds form its basal part; overlying units consist of basic volcanic flows and sills, commonly vesicular, associated with andesitic and silicic pyroclastic rocks and flows. The Cape St John Group is similar to calc-alkalic rocks associated with modern island arcs, although there is a predominance of high-silica rocks in the former; a marked compositional gap between 62 and 67% SiO2 for the Cape St John succession corresponds to a lack of high-silica andesite and low-silica dacite and illustrates its bimodal nature. Sub- to low-greenschist facies metamorphism has affected the entire volcanic pile, and the metamorphic grade gradually increases from the southern part of the peninsula to the north, where it reaches amphibolite facies. An east-west trending syncline forms the major structure in the area and at least four phases of folding have been documented6. The Cape St John Group rests unconformably on the Snooks Arm Group (Arenig)7,8 and should, therefore, be younger than about 500 Myr.

A recent Rb–Sr study of selected suites of samples, mainly from Precambrian alkaline rocks of northern Ontario, may have some bearing on mantle differentiation and evolution of the continental crust. We show here that initial 87Sr/86Sr ratios from most of the complexes, plotted as a function of age, define a straight line, and imply a source region for the Sr with a Rb–Sr ratio of 0.018 ± 0.002 that has behaved as a closed system for at least 2,600 Myr. Furthermore, the intersection of this line with the development line for ‘bulk Earth’ at about 2,800 Myr can be interpreted as evidence for a mean time of differentiation of bulk Earth material into an enriched crust and a residual, depleted mantle.

Liberalisation of electricity markets, changing patterns in the generation and use of electricity and new technologies are some of the factors that result in increased uncertainty about the future operating conditions of our power system. In this context, planning for future investments in power system requires careful selection and assessment of future operating conditions. This paper revisits the notion of power system adequacy and highlights the need for consideration of some factors that have hitherto tended not to be part of a transmission expansion planning process, in particular in respect of the credible range of possible values of system operating conditions and transitions between successive operating states. Firstly, we present some definitions of power system operational regions. Secondly, we present a stochastic optimisation model that measures the adequacy of a transmission network for given future operating conditions. Uncertainties in demand and generation are modelled using a large number of scenarios. The optimisation model identifies the critical future operating conditions needing the special attention of a power system planner. The proposed model is simulated on a 39-bus network, whereby it is shown that this model can identify critical operating conditions that need the attention of a system planner.

The GB power network suffers from regular faults with a significant percentage of them caused by adverse or extreme weather. There are current worries surrounding climate change and with some of the effects already being seen, such as a rise in coastal temperatures and more extreme weather, greater research into how society will be affected is required. The research discussed in this paper focuses on extreme weather and its effects on the GB transmission network. With the possibility of increased frequency and intensity of adverse or extreme weather, there is a concern that this will significantly affect the reliability of the network. The research described here has investigated the current effects of weather on the transmission system using data supplied by the three transmission companies that own and operate the GB network: Scottish Power Ltd., National Grid plc. and SSE plc. And will present the current effects of weather on the transmission network, how changes in the weather present challenges in ensuring security of supply and the beginnings of a relationship between weather types and weather related faults

The TIMES energy system model has been used for informing energy and climate change policies in several countries and regions around the world. The type and scope of the studies varies, but many works consider (at least briefly) energy efficiency in their findings. However, very few include explicit energy efficiency scenarios and/or direct analysis of energy efficiency improvements. The studies that consider explicitly energy efficiency scenarios (in some cases in combination with other type of scenarios such as emission reduction targets) show significant differences on the modelling approach taken, potentially affecting the results and the impact policy decisions. Moreover, a direct comparison between energy efficiency modelling approaches in TIMES has not been developed yet. The work developed in this paper aims to provide insight on this issue, analysing the implications of different energy efficiency modelling approaches in TIMES, and discussing best practices on informing energy efficiency policy. Three types of residential energy efficiency scenarios are analysed using the UK TIMES model, all of them with the objective of reducing 10% of energy consumption on residential heating. Results show that these energy efficiency scenarios, which are in theory equivalent, produced different results, suggesting that the modelling approach taken can significantly impact the outcomes of the model. Also, not all energy efficiency scenarios performed as expected. In one of the scenarios, other user constraints (which are common to all the analysed scenarios) limited the amount of conservation technologies available, so the expected energy savings were lower than in other cases. Therefore, the outcomes obtained show the importance of not solely relying on a particular scenario or model for policy analysis, as this might lead to partial views or suboptimal solutions.

The Cretaceous Amba Dongar Complex contains one of the largest fluorite deposits (11.6 million tons at 30 wt % CaF 2 ) associated with any carbonatite. Fluorite mineralization postdates carbonatite emplacement and takes the form of replacement hydrothermal veins concentrated at the carbonatite-country rock contact. Sr isotope ratios from the Amba Dongar fluorites reveal large isotopic variations that can only be attributed to reaction between a carbonatite-derived, F-rich fluid and continental crust (or crustal-derived fluid). The extremely variable initial 87 Sr/ 86 Sr ratios (0.70910-0.71729) are intermediate between those of the carbonatites (0.70549-0.70628) and the host Bagh sandstones (0.75359-0.78274); they correlate negatively with Sr abundances- dances. Sr isotope ratios from intrasample fluorites show large isotopic variations (0.70910-0.71425) that cover almost the entire range of values found for all of the fluorites measured from Amba Dongar. The Pb isotope ratios from the fluorites are also variable and differ from those of the country rocks. Compared to the carbonatites, most contain similar 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios but more radiogenic 206 Pb/ 204 Pb values. Galena and pyrite coeval with fluorite mineralization have Pb isotope ratios which overlap those from most of the fluorites, but which are isotopically distinct from one another. In contrast, initial 143 Nd/ 144 Nd isotope ratios from most of the fluorites are relatively uniform (0.51240-051247), quite different to those from the surrounding Bagh sandstones (0.51122-0.51149), but similar to those from the carbonatites (0.51248-0.51253). The new isotopic results are partly consistent with a model for fluorite deposition involving interaction between ground waters within the surrounding country rocks and an F-rich, carbonatite-derived fluid (Deans and Powell, 1968). The variation in the Sr isotope composition for the fluorites suggests that certain physio-chemical parameters of the mineralizing fluids were changing with time of deposition.

This paper demonstrates the potential benefits of utilisation of distributed generation (DG) in reducing network losses and of automatic post-fault actions in maximising DG output. A number of quantified examples are presented, based on simulations, for two actual distribution networks in the UK using reconfiguration of normally open points and inter-tripping of generation. The results show that a noteworthy reduction in losses might be achieved, and demonstrate the extent to which the actual results depend on the configuration of the network, the level of demand and the amount of DG in operation. It is argued that the benefits in terms of reduction of losses and maximisation of DG output are significant enough and the automation technology mature enough to justify investment in appropriate metering, communication and control, but that current commercial arrangements often prevent appropriate automation measures from being implemented.

When representing the stochastic characteristics of wind generators within power system simulations, the spatial and temporal correlations of the wind resource must be correctly modelled to ensure that reserve and network capacity requirements are not underestimated. A methodology for capturing these correlations within a vector auto-regressive (VAR) model is presented, and applied to a large-scale reanalysis dataset of historical wind speed data for the British Isles. This is combined with a wind speed-to-power conversion model trained against historically metered data from wind farms on the Great Britain (GB) electricity system in order to derive a lightweight model for simulating injections of wind power across a transmission network. The model is demonstrated to adequately represent ramp rates, both at a site and network level, as well as the individual correlations between sites, while being suitable for network adequacy studies which may require the simulation of many years of operation.

Some of the most diverse igneous rocks found on Earth occur along the length of Italy and in many of the islands in the southeastern Tyrrhenian Sea, all the result of Cenozoic magmatism. Magmas extremely rich in alkalis, particularly potassium, and many undersaturated with respect to silica, were erupted, as well as others of calc-alkalic affinity (see legend in Figure 1). Their origin has been the subject of heated debate, and there is still no general consensus about how they formed. Most attribute them to subduction-related processes (see Beccaluva et al. [2004] for a review); others consider them to be the result of within-plate magmatism [e.g., Vollmer, 1976; Lauecchia and Stoppa, 1996]. Still others consider magmatism the result of a deep, mantle upwelling within a slab window coupled with mixing between isotopically different reservoirs [Gasperini et al., 2002].