A Study of Macro-Rhythmic Layering and Cumulate Processes in the Jimberlana Intrusion, Western Australia. Part I: The Upper Layered Series

The upper layered series of the Jimberlana Intrusion rests unconformablyon the lower layered series and has resulted from a major newpulse of magma which entered the magma chamber during the finalstages of crystallization of the lower series. All parameterswhich vary systematically with fractionation are sharply reversedat the contact between the two layered series. The lower portion of the ultramafic zone of the upper layeredseries is composed of a repeated macro-rhythmic succession ofolivine cumulates, bronzite-olivine cumulates, and bronzitecumulates. A detailed investigation was made of this sequenceso that the contacts between the units could be compared withthe contact between the upper and lower layered series. Cu,Ni, Cr, P, and U were measured on a whole rock basis; the Mg/Mg?Feratios of the pyroxenes and olivines, the Cr content of pyroxenesand the Ni content of olivines were determined by the electronmicroprobe. Each of the macro-rhythmic units is associated witha reversal in mineral variation and in the Ni-Cr trends andhas a zone of high sulphide values at its base. These featuresare also found at the contact between the upper and lower layeredseries and, if the upper series is due to a new influx of magma,it follows that the macro-units are also due to multiple injection.This conclusion is strongly supported by the size of the reversalswhich are too large to be explained by the alternative hypothesesto multiple injection suggested by Jackson (1961) and Wager(1959). The anomalous sulphide-rich zones at the contacts between theupper and lower layered series and between the macro-rhythmicunits are thought to have formed from a narrow supercooled zonewhich developed for a brief period at the bottom of the magmachamber following each new magma pulse. The olivines from thesesulphide-rich zones are depleted in Ni, suggesting that Ni hasbeen scavenged by the sulphides. This is only possible if theolivine grains crystallized with the sulphides in the restrictedsupercooled zone at the bottom of the magma chamber.     

Palaeo-ice streams and the subglacial landscape mosaic of the North American mid-continental prairies

The analysis of the glacial landscape of southern Saskatchewan (Canada) through multiple data sets (e.g. digital elevation model, till compositional data) has revealed previously unrecognized subglacial sediment–landform assemblages. A southwest-trending corridor of mega-scale till lineations (Maskwa corridor) bounded on each side by hummocky terrain extends from the Canadian Shield to southwestern Saskatchewan. This landform assemblage is clearly cross-cut by a broad south to southeast trending corridor (Buffalo corridor) consisting of subparallel curvilinear till ridges. The carbonate content of the surface till is spatially consistent within these assemblages, suggesting a strong sediment–landform relationship. The two corridors are interpreted as the product of palaeo-ice streams. The Maskwa palaeo-ice stream flowed up the regional slope and across preglacial valleys, indicating it was thick and stable. Narrow dispersal trains extending across as well as down-glacier from the Athabasca Basin suggest that the Maskwa palaeo-ice stream extended far into the ice sheet across contrasting shield and platform terrains. In comparison, the Buffalo palaeo-ice stream was thinner and largely controlled by subglacial geology and topography. Its catchments were located at the Canadian Shield boundary and the system was oriented along-slope. It experienced lateral shifts and it was fed by a network of tributaries. The glacial dynamics shift from the Maskwa to the Buffalo system occurred at about 13.5 ¹⁴C kyr BP. The Buffalo system later evolved into thin outlet lobes until final deglaciation of the area. The proposed model has implications for ice-sheet reconstruction and the assessment of till properties in the prairies and in similar terrains.     

Climate change policy responses for Canada's Inuit population: The importance of and opportunities for adaptation

We identify and examine how policy intervention can help Canada's Inuit population adapt to climate change. The policy responses are based on an understanding of the determinants of vulnerability identified in research conducted with 15 Inuit communities. A consistent approach was used in each case study where vulnerability is conceptualized as a function of exposure-sensitivity to climatic risks and adaptive capacity to deal with those risks. This conceptualization focuses on the biophysical and human determinants of vulnerability and how they are influenced by processes and conditions operating at multiple spatial-temporal scales. Case studies involved close collaboration with community members and policy makers to identify conditions to which each community is currently vulnerable, characterize the factors that shape vulnerability and how they have changed over time, identify opportunities for adaptation policy, and examine how adaptation can be mainstreamed. Fieldwork, conducted between 2006 and 2009, included 443 semi-structured interviews, 20 focus groups/community workshops, and 65 interviews with policy makers at local, regional, and national levels. Synthesizing findings consistent across the case studies we document significant vulnerabilities, a function of socio-economic stresses and change, continuing and pervasive inequality, and magnitude of climate change. Nevertheless, adaptations are available, feasible, and Inuit have considerable adaptive capacity. Realizing this adaptive capacity and overcoming adaptation barriers requires policy intervention to: (i) support the teaching and transmission of environmental knowledge and land skills, (ii) enhance and review emergency management capability, (iii) ensure the flexibility of resource management regimes, (iv) provide economic support to facilitate adaptation for groups with limited household income, (v) increase research effort to identify short and long term risk factors and adaptive response options, (vi) protect key infrastructure, and (vii) promote awareness of climate change impacts and adaptation among policy makers.     

Mineral equilibria constraints on open‐system melting in metamafic compositions

The recent development of activity–composition relations for mineral and melt phases in high‐grade metamafic rocks allows mineral equilibria tools to be used to further aid our understanding of partial melting and the mineralogical consequences of melt segregation in these rocks. We show that bulk compositional data from natural amphibolites cover a wide compositional range, with particular variability in the content and ratios of Ca, Na and K indicating that low‐grade metasomatic alteration can substantially alter the igneous protolith chemistry and potentially affect the volume and composition of melt generated. Mineral equilibria calculations for five samples that span the compositional variability in our data set indicate that melting occurs primarily via the fluid‐absent breakdown of amphibole+quartz to produce a pressure‐sensitive peritectic assemblage of augite, orthopyroxene and/or garnet. The introduction of orthopyroxene at the onset of the amphibolite‐to‐granulite‐facies transition at lower pressure results in an increased rate of melt production until quartz is typically exhausted, and this is similarly seen for the introduction of garnet at higher pressure. Calculated melt compositions are dependent on the protolith composition, but initial solidus melting and biotite breakdown produce 1–3 mol.% of K‐rich granitic melts. As hornblende melting proceeds, 15–20 vol.% of either more granodioritic‐to‐tonalitic or granodioritic‐to‐trondhjemitic melt is produced. Once quartz is exhausted, intermediate to mafic melt compositions are produced at ultrahigh‐temperature conditions. Quartz‐rich lithologies with high Ca coupled to low Na and K are the most fertile under orogenic conditions, yielding up to 25 mol.% of sub‐alkalic granitic melt by 850°C. Such rocks did not experience significant subsolidus alteration. Altered compositions with low Ca and elevated Na and K are not as fertile, yielding less than 15 mol.% of alkalic granitic melt by 850°C. These melt volumes are enough to be segregated, and can make a contribution to granite magmatism and intracrustal differentiation that should not be overlooked.     

Spatial and Temporal Validation of In-Situ and Satellite Weather Data for the South West Agricultural Region of Australia

Seasonal variations in weather have significant impacts on crop yields. The accuracy of weather data is an import-ant consideration for crop yield models. This ...     

Pluriactivity in (and beyond?) a Regulationist Crisis

The study of rural pluriactivity in New Zealand has been based on the assumption that it is a temporary phenomenon: a survival strategy in times of crisis. This paper seeks to position both pluriactivity and ‘rural crisis’ in a more sound theoretical framework by referring to recent work in regulation theory. Case studies from the Mid-Canterbury and Catlins areas are used to suggest the role that pluriactivity may fulfil in any future mode of growth in rural New Zealand. In doing so, questions are raised regarding rural ideology and agency in the process of economic change.     

A Strontium Isotopic Investigation of the Bjerkreim--Sokndal Layered Instrusion, Southwest Norway

The 230 km² Proterozoic Bjerkreim—Sokndal layered instrusionhas a monzonoritic bulk composition and comprises a 6 km thick,broadly leuconoritic Layered Series (LS) overlain by unlayeredmangerite and quartz mangerite. In the Bjerkreim lobe the LScomprises six megacyclic units (MCU 0, IA, IB, II, 11 and IV)in a syncline. This lobe is surrounded by migmatitic gneisses;the roof to the instrusion is missing. The mg-number opx, An% and whole-rock initial ⁸⁷Sr/⁸⁶Sr isotope ratios (Sr₀) displaybroadly parallel trends through MCUs II and III, and into MCUIV, with decreasing mg-number (75–58) and An % (50–40)accompanying increasing Sr₀ (0.7050–0.7085). This correlationbreaks down in the upper part of MCU IV and mangerite; the quartzmangerite has Sr₀ values of 0.7085. Abrupt reversals occur acrossthe MCU boundaries. The LS crystallized on the floor of a periodically replenishedmagma chamber that was continually assimilating country rockgneisses. Strong compositional zoning of the magma developedas a result of repeated replenishments with relatively dense,primitive ferrobasaltic magma (Sr₀ = 0.7049) along the floorand the development of extensive buoyant roof melts. Assimilationtook place on a massive scale (up to 50%) in the upper partsof the chamber. KEY WORDS: assimilation; fractional crystallization; hybrid magma; layered intrusion; Sr-isolopes ^*Corresponding author.     

Observing Convective Aggregation

Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a ground-based observational network.     

High-resolution analysis of submarine lobes deposits: Seismic-scale outcrops of the Lauzanier area (SE Alps, France)

The Lauzanier area represents the northernmost extension of the Annot Sandstone series and contains deposits between 650 and 900 m-thick. This basin was active from upper Bartonian or lower Priabonian to early Rupelian. It is composed of two superposed units separated by a major unconformity. The sediment supply is due to channelled flows coming from the south. Flow processes include mass flow to turbidity currents. The size of the particles and the absence of fine-grained sediment suggest a transport over a short distance. The Lower Unit is made of coarse-grained tabular beds interpreted as non-channelled lobe deposits. The Upper Unit is made of massive conglomerates interpreted as the channelled part of lobes. These lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale. The abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area. This uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts.This field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse-grained turbidite system. The outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non-channelled lobe system. These results of high-resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep-sea turbidite system that are either restricted to cores, or with a lesser resolution (seismic).