Offshore granulites from the Bay of Biscay margins: fission tracks constrain a Proterozoic to Tertiary thermal history

Zircon and apatite fission track ages were determined on granulites dredged along the Bay of Biscay margins. A sample from Ortegal Spur (Iberia margin) yielded 725 ± 67 Ma (zircon). A sample from Le Danois Bank (Iberia margin) yielded 284 ± 58 Ma (zircon), indicating post‐Variscan cooling. Apatite from this sample gave 52 ± 2 Ma, interpreted as final cooling after ‘Pyrenean’ thrust imbrication. Two other samples from Le Danois Bank have Early Cretaceous apatite ages (138 ± 7 and 120 ± 8 Ma), interpreted to result from exhumation during rifting. Finally, a granulite from Goban Spur (Armorican margin) gave 212 ± 10 Ma (apatite), coinciding with a precursory rifting phase. Together with published radiometric results, these data indicate a Precambrian high‐grade terrane at the site of the current margins. The distribution of the granulites on the seafloor reflects tectonic and erosional processes related to (a) Mesozoic rifting and (b) Early Tertiary incipient subduction of the Bay of Biscay beneath Iberia.     

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Abstract— Jull et al. propose an alternative interpretation of our depth vs. ¹⁴C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable.     

Assessing spatial associations between perceptions of landscape value and climate change risk for use in climate change planning

This study examines spatially referenced perceived landscape values and climate change risks collected through public participation geographic information systems for potential use in climate change planning. Using survey data from the Southern Fleurieu Peninsula, South Australia, we present a method for identifying perceived landscape values and climate change risks to describe and quantify their spatial associations. Two spatial data models??vector and raster??and two analytical methods??Jaccard coefficients and spatial cross-correlations were used to describe the spatial associations. Results indicate that perceptions of climate change risk are driven, in part, by the values people assign or hold for places on the landscape. Biodiversity and intrinsic landscape values have strong spatial association with biodiversity loss risk while recreation values have strong spatial association with riparian flooding, sea-level rise and wave action risks. Other landscape values show weak to no spatial association with perceived climate change risks. The methodology described in this research provides a mechanism for government agencies to develop place-based adaptation strategies based on these associations.     

Thermal and isotopic profiling of the Pipeline hydrothermal system: Application to exploration for Carlin-type gold deposits

New exploration techniques are vital to the search for new orebodies in mature terranes, as well as for extensions of existing orebodies. This research focused on application of low-temperature dating techniques (primarily apatite fission-tracks) and stable isotope measurements (carbon and oxygen in carbonate rocks) in and around the Pipeline deposit, a Carlin-type gold system. The primary purpose of the project was to assess whether these techniques could provide exploration vectors that might be used in conjunction with other geologic, geochemical, and geophysical techniques to determine the locus of fossil hydrothermal fluid flow, and the attendant possibility of finding economic mineral deposits.At Pipeline, measurements of apatite fission-tracks and (U − Th) / He geochronometry yield a clear indication of the elevated temperatures associated with the fossil hydrothermal system. The pattern is one of a central target (Pipeline deposit) with decreasing thermal effects as far as several kilometers laterally from the known ore zone. Because of the irregular nature of fluid flow through fractures, a significant number of samples are required to discern this pattern, but the pattern is quite clear from the 32 samples in and around the Pipeline pit.Stable isotope measurements of carbonate rocks yield patterns centered on the Pipeline pit area. Oxygen isotopes in particular are shifted toward lower values as the result of interaction between the hydrothermal fluids and carbonate rocks. Carbon isotopes show a pattern, but it is somewhat more difficult to interpret than the oxygen isotope pattern. As with the geochronometric patterns, isotopic indications of fluid flow are present several kilometers from the ore zone at Pipeline. Also as with the geochronometric data, a relatively large sample set is required to see the pattern. At Pipeline, the patterns are evident in approximately 45 surface samples and very clearly in the cross-sections containing approximately 100 samples.From these data, it is clear that thermal and stable isotopic measurements on rocks at a significant distance from the known Pipeline hydrothermal system record the passage of hot fluids through the rock. Both techniques provide a footprint of the Pipeline system that is several diameters larger than the ore zone (as presently known). Therefore, thermochronologic and stable isotopic measurements can be utilized in conjunction with other techniques as part of an overall exploration strategy for Carlin-type deposits. Although these techniques do not provide a direct indication of the metal content of the fossil hydrothermal fluids, they do provide an indication of the robustness of fluid flow and the potential size of a hydrothermal system.     

Impacts of Present and Future Climate Change and Climate Variability on Agriculture in the Temperate Regions: North America

The potential impact of climate variability and climate change on agricultural production in the United States and Canada varies generally by latitude. Largest reductions are projected in southern crop areas due to increased temperatures and reduced water availability. A longer growing season and projected increases in CO₂ may enhance crop yields in northern growing areas. Major factors in these scenarios analyzes are increased drought tendencies and more extreme weather events, both of which are detrimental to agriculture. Increasing competition for water between agriculture and non-agricultural users also focuses attention on water management issues. Agriculture also has impact on the greenhouse gas balance. Forests and soils are natural sinks for CO₂. Removal of forests and changes in land use, associated with the conversion from rural to urban domains, alters these natural sinks. Agricultural livestock and rice cultivation are leading contributors to methane emission into the atmosphere. The application of fertilizers is also a significant contributor to nitrous oxide emission into the atmosphere. Thus, efficient management strategies in agriculture can play an important role in managing the sources and sinks of greenhouse gases. Forest and land management can be effective tools in mitigating the greenhouse effect.     

Dawn; the Vesta–HED connection; and the geologic context for eucrites,diogenites, and howardites

The Dawn mission has provided new evidence strengthening the identification of asteroid Vesta as the parent body of the howardite, eucrite, and diogenite (HED) meteorites. The evidence includes Vesta's petrologic complexity, detailed spectroscopic characteristics, unique space weathering, diagnostic geochemical abundances and neutron absorption characteristics, chronology of surface units and impact history, occurrence of exogenous carbonaceous chondritic materials in the regolith, and dimensions of the core, all of which are consistent with HED observations and constraints. Global mapping of the distributions of HED lithologies by Dawn cameras and spectrometers provides the missing geologic context for these meteorites, thereby allowing tests of petrogenetic models and increasing their scientific value.