Editorial

In 2009 the Journal enters its 50^th year of publication –our "golden anniversary"! This is certainly good cause for celebrationand we will be doing just that in various ways throughout theyear. Volume 1 was published in February 1960. The very first paperby P.J. Wyllie and O.F. Tuttle on "The system CaO-CO₂-H₂O andthe origin of carbonatites" [J.Petrology 1:1-46] provided anidea for a special symposium at the 2009 Goldschmidt conference"Challenges to Our Volatile     

Petrology of the Treknattan intrusion in the Fongen-Hyllingen complex, Trondheim region, Norway: a late intrusion into an evolved layered complex

The basic-ultrabasic Treknattan intrusion is an important example of a late intrusion in a solidified, evolved, layered complex and sheds light on possible mechanisms by which such associations may develop. The Treknattan intrusion, emplaced into the basic Fongen-Hyllingen intrusion shortly after the latter had solidified, consists mainly of massive or weakly layered peridotite (olivine ± Cr-spinel cumulate) and troctolite (plagioclase + olivine ± Cr-spinel cumulate). The mineral compositional range partially overlaps the most primitive end of the much larger variation-interval in the Fongen-Hyllingen intrusion. The margin of the Treknattan intrusion is sometimes outlined by massive feldspathic websterite which appears to have formed by reaction between magma and melts of gabbroic country rock. The parental magma appears to have been a relatively water-rich picritic basalt with a possible genetic relationship to the magma parental to the enveloping Fongen-Hyllingen intrusion, both displaying tholeiitic relationship between olivine and Ca-poor pyroxene, and having crystallized from relatively water-rich magmas with an early crystallization order of olivine ± Cr-spinel-plagioclase-Ca-rich pyroxene. The recognition of the Treknattan intrusion as a separate body suggests that the bulk composition of the Fongen-Hyllingen intrusion is dioritic rather than gabbroic as previously thought.     

A normalizing procedure for comparing chemical variations in pyroxenes in mafic granulites

Data from analyses of three coexisting pairs of pyroxenes with a wide range of Fe content from each of two localities are used to show the large systematic variation and predictable correlation of Fe (or Mg) of a pyroxene with its content of Al, Mn and Na in mafic granulites. Comparisons of pyroxenes can then be made more meaningful by normalizing Al, or other elements, to an appropriate Mg value. As both P and T may affect the element distribution of the two pyroxenes differently (especially Al and Na) the factor used in normalizing is found to vary from region to region.     

Multifunctional intervention and market rationality in agricultural governance: a comparative study of England and South Australia

Critiques of the neoliberal governance of agricultural systems have led to a number of political responses which attempt to address the socio-environmental consequences of the dominant regime. In this paper two case study regions (South Australia and England) have been chosen to represent variations in agricultural policy and to highlight subsequent outcomes on the sustainability of agriculture. Interviewed governance stakeholders highlighted issues in regard to the agricultural governance of each area, from social and environmental consequences of minimal policy intervention in South Australia, to issues created by greater economic support in England. As such, the distinct variations in agricultural regimes will continue to demand scholarly attention, in order for the value of diversity within the sector to be more widely understood. The study concludes that it is likely agricultural support will continue to decline in both case study regions. Importantly, however, innovative policy mechanisms that aim to reduce local risks and value local agricultural priorities, without requiring significant financial support, might be the most promising way forward in regard to agricultural system sustainability.     

Some things old, some things new: The spatial representations and politics of change of the peak oil relocalisation movement

Despite continued uncertainty about the physical realities and political, economic and social implications of peak oil, combined concerns about oil scarcity, climate change and globalisation has spawned an energetic relocalisation movement dedicated to achieving a comprehensive reduction in oil dependency through community-scale initiatives. This paper uses a discourse approach to examine the emergence, geographical spread and practices of the Transition Network, a UK-originated relocalisation movement now involving 186 local initiatives in the UK and other countries. We trace the movement’s drawing upon, and innovation from, discourses and techniques used by other grassroots environmental movements to promote a spatial representation of peak oil as an inevitable and geographically undiscriminating problem, and its use of addiction metaphors and participatory techniques to promote personal and community-scale energy descent initiatives as a viable and necessary alternative to globalisation. We also analyse the spatial representations and techniques used in the Network’s “rhizomic” spread across multiple localities around the world and embedding in communities where relocalisation initiatives are established. We conclude by examining the future challenges these spatial constructions of peak oil pose for the relocalisation movement.     

Discussion: Structural and stratigraphic problems of the Argylla Formation near Mary Kathleen,Queensland

Circumstantial evidence indicates that Gaussberg, an isolated, 370 m high volcanic cone on the Antarctic coast at 57°S, 89°E, is the product of subglacial eruption. The vesicular, highly potassic leucitite, of which Gaussberg is composed, has been dated by K‐Ar and fission‐track methods, the former being applied to leucite concentrates, the latter to glassy leucitite from the ropy‐textured, outer rind of a pillow‐like structure. The K‐Ar geochronology yields an average date of 56 000 ± 5000 years, jwhich is interpreted as defining the time of Gaussberg's formation. The fission‐track work yields a less precise date, which supports the K‐Ar age estimate. These new age determinations indicate that previously published K‐Ar age determinations of 20 Ma and 9 Ma for Gaussberg should be rejected.     

Oxygen isotope fractionation and disequilibrium displayed by some granulite facies rocks from the Fraser Range,Western Australia

The granulites of the Fraser Range are assumed to have formed in a carbon-rich fluid, and are generally devoid of hornblende, and lack obvious hydrous retrograde features. In these granulites, pyroxene, garnet, plagioclase and quartz are the minerals most likely to retain the oxygen isotope ratios fixed at an early stage of initial granulite metamorphism. Temperature estimates using these minerals commonly suggest that oxygen isotopic exchange ceased in the range 600 to 680°C. The peak metamorphic temperature was probably ～ 850°C as based on the stability fields of the coexisting minerals and some cation temperatures from coexisting pyroxenes in these rocks. Ilmenite may be slightly out of isotopic equilibrium with the other minerals. Thus, grains of quartz, feldspar, pyroxene and ilmenite have suffered considerable oxygen isotopic exchange during the retrogressive phase of the metamorphism, in spite of the fact that very little water was present in these granulites. The observed deviation from the peak metamorphic temperatures can be explained by essentially closed system solid-state diffusion (on at least a scale of centimetres) during slow cooling of the rocks from ~850 to 650°C, followed by more rapid cooling down to ～ 300°C. Such an explanation is not at variance with the radiometric data available for rocks from the area, which suggest that the latter phase could have involved uplift rates of ?0.5 mm/yr for a period of about 40 Ma. Wholerock δ¹⁸O values on non-quartzose mafic granulites, about 7.2%., fall within the range of basalts affected by seafloor weathering.     

Metamorphic evolution, mineral chemistry and thermobarometry of schists and orthogneisses hosting ultra-high pressure eclogites in the Dabieshan of central China

As is typical of ultra-high pressure (UHP) terrains, the regional extent of the UHP terrain in the Dabieshan of central China is highly speculative, since the volume of eclogites and paragneisses preserving unequivocal evidence of coesite and/or diamond stability is very small. By contrast, the common garnet (X_Mn=0.18–0.45)–phengite (Si=3.2–3.35)–zoned epidote (Ps_38–97)–biotite–titanite–two feldspars–quartz assemblages in the more extensive orthogneisses have been previously thought to have formed under low P–T conditions of ca. 400±50°C at 4 kbar. However, certain orthogneiss samples preserve garnets with X_Ca up to 0.50, rutile inclusions within titanite or epidote and relict phengite inclusions within epidote with Si contents p.f.u. of up to 3.49 — overlapping with the highest values (3.49–3.62) recorded for phengites in samples of undoubted UHP schists. These and other mineral composition features (such as A-site deficiencies in the highest Si phengites, Na in garnets linked to Y+Yb substitution and Al F Ti₋₁ O₋₁ substitution in titanites) are taken to be pointers towards the orthogneisses having experienced a similar metamorphic evolution to the associated UHP schists and eclogites. Re-evaluated garnet–phengite and garnet–biotite Fe/Mg exchange thermometry and calculated 5 rutile+3 grossular+2SiO₂+H₂O=5 titanite+2 zoisite equilibria indicate that the orthogneisses may indeed have followed a common subduction-related clockwise P–T path with the UHP paragneisses and eclogites through conditions of P_max at ca. 690°C–715°C and 36 kbar to T_max at ca. 710°C–755°C and 18 kbar, prior to extensive re-crystallisation and re-equilibration of these ductile orthogneisses at ca. 400°C–450°C and 6 kbar. The consequential conclusion, that it is no longer necessary to resort to models of tectonic juxtapositioning to explain the spatial association of these Dabieshan orthogneisses with undoubted UHP lithologies, has far-reaching implications for the interpretation of controversial gneiss–eclogite relationships in other UHP metamorphic terrains.     

Surface and complexation effects on the rate of Mn(II) oxidation in natural waters

Montmorillonite, kaolinite, goethite, and particulate and soluble natural organic materials influence the rate of Mn(II) oxidation. While surfaces accelerate the reaction, apparently by bonding Mn²⁺ in a manner which fulfills the requirements of the transition state, soluble organic materials retard the reaction by complexing the oxidizable species. It is doubtful whether particulate matter would influence the oxidation process under natural loading conditions since 50–500 mg l^?1quantities are required to produce measurable changes in the reaction rate. Complexation by humic materials, however, might be expected to reduce the rate of oxidation by an amount proportional to the dissolved organic carbon concentration. Oxidation followed by precipitation is predicted to be an important mechanism for Mn²⁺ removal in oceanic waters. The situation is less predictable in lake waters.