ALBERT

Description: Various ultramafic Ni-Cu-platinum group element (PGE) deposits associated with the North American Midcontinent rift have been attributed to formation in a magma conduit setting, whereby PGE concentration is controlled by various fluid dynamic processes. The Marathon Cu-PGE sulfide deposit located within the Midcontinent rift-related Coldwell Alkaline Complex has been classified as a gabbro-associated contact-type deposit; however, both magmatic and hydrothermal processes have been proposed to account for the significant concentration of PGE. In light of the growing field of evidence for magma conduit-type settings, this study comprised a comprehensive geochemical investigation of the complicated crosscutting gabbroic to ultramafic units in the immediate vicinity of the Marathon deposit; and a thorough three-dimensional investigation of the distribution of Cu and Pd within the Main mineralized zone. The main objectives of this study were to test the applicability of the magma conduit deposit model to the Marathon deposit and to identify key exploration criteria for use elsewhere in the Coldwell Alkaline Complex. Mineralization is hosted by the Two Duck Lake gabbro, a 4-km-long and 250-m-thick unit of the Marathon Series. The Marathon Series is the latest of three magmatic series that make up the 1- to 2-km-thick Eastern Gabbro Suite, which wraps around the eastern and northern margin of the Coldwell Alkaline Complex. The three magmatic series are shown here to have distinct trace element signatures that enable reliable discrimination of potentially sulfide and PGE-bearing units of the Marathon Series from the barren rocks of either the Fine-Grained or Layered Series. At the Marathon deposit, sulfides consist of disseminated chalcopyrite, pyrrhotite, and minor bornite and occur within the Main, Footwall, and Hanging-wall zones and in the PGE-enriched W Horizon. This paper focused on sulfides located within the Main zone, including the keel-shaped feeder channel that continues downdip to over 550-m depth. The spatial distribution of Cu, Pd, and Cu/Pd were examined in relation to a three-dimensional surface model for the footwall contact; in a vertical profile through the Main zone; and in a longitudinal section that cuts the feeder channel. There are three important observations: (1) trends for elevated Cu and Pd are parallel to numerous troughs and ridges in the footwall, (2) Cu, Pd, and Cu/Pd varies up section in a saw-toothed pattern from high to low values, and (3) the proportion of high Cu/Pd sulfides is greatest within the thickest accumulations of sulfides within the feeder channel. Evaluation of interelement relationships between Cu and Pd and between Pd and Ir, Rh, Pt, and Au for mineralization within the Main zone indicate positive associative, but nonlinear behavior for all elements. Briefly, the data show nonlinear correlations between Cu and Pd in which Cu/Pd decreases with increasing Pd; and coherent but nonlinear behavior for Ir, Rh, Pt, and Pd in which Pd/Ir, Pd/Rh, Pd/Pt, and Pd/Au all increase with increasing Pd. The observed variation in Cu/Pd is consistent with a magmatic model calculated by others for deposits in the Duluth Complex, in which sulfides accumulated in a closed system from a melt with mantlelike Cu/Pd and an elevated silicate to sulfide ratio. The observed variations in Pd/Ir, Pd/Rh, and Pd/Pt are consistent with R factor fractionation related to differences in the relative partition coefficients between sulfide and silicate melts, and rule out the possibility that processes such as fractionation of sulfide melt by monosulfide solid solution (mss) or redistribution of metals during hydrothermal alteration played a significant role in the mineralizing event. The Two Duck Lake gabbro and associated sulfides of the Marathon deposit are proposed to have formed by multiple injections of plagioclase crystal mush that carried droplets of sulfide liquid along a conduit system that was controlled by radial and ring fault structures in the Coldwell Alkaline Complex. The accumulation of sulfides was controlled by flow dynamic processes within the magma channels, but Cu/Pd was controlled by local proportions of silicate melt to sulfide liquid. Key characteristics of the deposit that are critical to exploration elsewhere in the Coldwell Alkaline Complex include the following: (1) the recognition that gabbroic to ultramafic intrusions of the Marathon Series are the host for Cu and PGE mineralization, (2) the distribution of Cu/Pd data within sulfide occurrences are useful as vectors toward the feeder channel, (3) topographic lineaments are indicators of potential mineralized feeder zones, and (4) oxide- and apatite-rich, irregularly shaped gabbroic to ultramafic pods are potential indicators of an underlying feeder channel.

Description: The primary stratigraphic fabric of a chaotic rock unit in the Zermatt Saas ophiolite of the Western Alps was reworked by a polyphase Alpine tectonic deformation. Multiscalar structural criteria demonstrate that this unit was deformed by two ductile subduction-related phases followed by brittle-ductile then brittle deformation. Deformation partitioning operated at various scales, leaving relatively unstrained rock domains preserving internal texture, organization, and composition. During subduction, ductile deformation involved stretching, boudinage, and simultaneous folding of the primary stratigraphic succession. This deformation is particularly well-documented in alternating layers showing contrasting deformation style, such as carbonate-rich rocks and turbiditic serpentinite metasandstones. During collision and exhumation, deformation enhanced the boudinaged horizons and blocks, giving rise to spherical to lozenge-shaped blocks embedded in a carbonate-rich matrix. Structural criteria allow the recognition of two main domains within the chaotic rock unit, one attributable to original broken formations reflecting turbiditic sedimentation, the other ascribable to an original sedimentary mélange. The envisaged geodynamic setting for the formation of the protoliths is the Jurassic Ligurian-Piedmont ocean basin floored by mostly serpentinized peridotites, intensely tectonized by extensional faults that triggered mass transport processes and turbiditic sedimentation.

Description: Permafrost and varying land surface properties greatly complicate modelling of the thermal response of Arctic soils to climate change. The forest-tundra transition near Nadym in west Siberia provides an excellent study area in which to examine the contrasting thermal properties of soils in a forested ecosystem without permafrost and peatlands with permafrost. We investigated the effects of forest shading, snow cover and variable organic soil horizons in three common ecosystems of the forest-tundra transition zone. Based on the year-round temperature profile data, the most informative annual parameters were: (1) the sum of positive average daily temperatures at depths of 10 and 20 cm; (2) the maximum penetration depth of temperatures above 10 °C; and (3) the number of days with temperatures below 0 °C at a depth of 20 cm. The insulative effect of snow cover in winter was at least twice that of the shading and cooling effect of vegetation in summer. In areas with shallow permafrost, the presence of a thick organic horizon, with an extremely low thermal diffusivity, creates a very steep temperature gradient that limits heat penetration to the top of the permafrost in summer. Copyright © 2015 John Wiley & Sons, Ltd.

Description: The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom. This is achieved through far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric spacer between graphene and metal rods. A theoretical model that takes into account the nonlocal optical response of both graphene and metal is used to describe the results. These ultraconfined plasmonic modes, addressed with far-field light excitation, enable a route to new regimes of ultrastrong light-matter interactions.

Description: Terrestrial ecosystem responses to temperature and precipitation have major implications for the global carbon cycle. Case studies demonstrate that complex terrain, which accounts for more than 50% of Earth's land surface, can affect ecological processes associated with land-atmosphere carbon fluxes. However, no studies have addressed the role of complex terrain in mediating ecophysiological responses of land-atmosphere carbon fluxes to climate variables. We synthesized data from AmeriFlux towers and found that for sites in complex terrain, responses of ecosystem CO 2 fluxes to temperature and precipitation are organized according to terrain slope and drainage area, variables associated with water and energy availability. Specifically, we found that for tower sites in complex terrain, mean topographic slope and drainage area surrounding the tower explained between 51% and 78% of site-to-site variation in the response of CO 2 fluxes to temperature and precipitation depending on the time scale. We found no such organization among sites in flat terrain, even though their flux responses exhibited similar ranges. These results challenge prevailing conceptual framework in terrestrial ecosystem modeling that assumes CO 2 fluxes derive from vertical soil-plant-climate interactions. We conclude that the terrain in which ecosystems are situated can also have important influences on CO 2 responses to temperature and precipitation. This work has implications for about 14% of the total land area of the conterminous US. This area is considered topographically complex and contributes to approximately 15% of gross ecosystem carbon production in the conterminous US.

Description: Terrestrial ecosystem respiration (Reco) represents a large carbon source from land to atmosphere and is highly spatio-temporally heterogeneous across scales. Up-scaling of field-measured respiration data using remote sensing information is urgently needed for understanding regional and global patterns of ecosystem respiration. Using MODIS data with resolutions of one km and eight days, and flux measurements from 171 sites (total of 812 site-years) across the world from 2000 to 2014, we developed a semi-empirical, yet physiologically-based, remote sensing model, which can simulate Reco observed across most biomes with a small margin of error (R 2 = 0.55, RMSE = 1.67 gCm -2 d -1 , EF = 0.46, MBE = 0.18 gCm -2 d -1 ). The reference respiration at the annual mean nighttime Land Surface Temperature (LST) can be well represented by MODIS Enhanced Vegetation Index (EVI) and LST. A comprehensive comparison of six respiration-temperature (R-T) models shows that the more physiologically-based R-T model (extended Arrhenius model - ETA) may be most suitable for estimating the respiration rate at higher latitudes. Integrating an effect of vegetation change on Reco in different biomes effectively improves estimates of Reco in almost all of the biomes.

Description: Mineral exploration is increasingly taking advantage of real time techniques that dramatically reduce the costs and time taken to obtain results compared to traditional analytical methods. Portable X-ray fluorescence (pXRF) is now a well-established technique that is used to acquire lithogeochemical data. To date, however, benchtop scanning electron microscopes, equipped with energy dispersive systems (bSEM-EDS) have received little attention as a possible mineral exploration tool. This study examines the utility of combining pXRF and bSEM-EDS to characterize the igneous stratigraphy and its relationship to Cu-Pd mineralization in a drill hole at the Four Dams occurrence, located within the Eastern Gabbro assemblage of the Coldwell Alkaline Complex, Canada. The first part of this study compares field portable and laboratory techniques. Seventy-two powdered samples analysed by pXRF are compared with traditional major elements analysed by inductively coupled atomic emission spectroscopy (ICP-AES) and trace elements by inductively coupled plasma spectrometry (ICP-MS), and the compositions of 128 olivine, clinopyroxene and plagioclase grains analysed by bSEM-EDS are compared with traditional electron microprobe data. Our results show that each portable technique yields results similar to their lab-based counterparts within the analytical capabilities and precisions of the respective instruments. The second part presents a case study for the application of pXRF and bSEM-EDS to resolve questions related to igneous stratigraphy as an aid to mineral exploration in a complicated geological setting. A major problem for Cu-Pd exploration in the Coldwell Complex of NW Ontario is that the oxide-rich units that host Cu-Pd mineralization in the Marathon Series are petrographically similar to the barren oxide-rich units in the Layered Series. However, the mineralized units are geochemically distinctive. Our results show that the mineralized Marathon Series can be distinguished from the barren Layered Series, including oxide-rich units of both, by combinations of P 2 O 5 , Ba, Zr and V/Ti values, determined by pXRF, combined with plagioclase, olivine or clinopyroxene compositions measured by bSEM-EDS. The combination of pXRF and bSEM-EDS thus shows considerable promise as an exploration technique. Supplementary material: Comparisons of pXRF analyses with ICP-AES, ICP-MS and IR analysis are available at http://doi.org/10.6084/m9.figshare.c.3291518

Description: Common ragweed is an invasive plant in Europe, and many people are allergic to its pollen. Modelling results indicate that airborne pollen concentrations are likely to increase in Europe over coming decades, at least in part owing to climate change. Nature Climate Change 5 766 doi: 10.1038/nclimate2652

Description: Crystal Growth & Design DOI: 10.1021/acs.cgd.7b01351