Datation U–Pb des deux faciès du granite de Soultz (Fossé rhénan,France)

Deep boreholes drilled in the basement of the Rhine Graben at Soultz-sous-Forêts have shown the presence of an ubiquitous monzogranite. Borehole GPK-2, with a total depth of 5090 m, also intersected a more leucocratic fine-grained two-mica granite, locally present below 4860 m depth and continuously found between 5047 and 5090 m. Thanks to trace elements and in particular to REE (rare-earth elements), it could be shown that the leucocratic rock is a differentiated expression of the potassic magma that was at the origin of the monzogranite pluton. This model agrees with Sr–Nd isotope data, even though a slight contribution from the pre-existing basement should be considered as well. Use of the U–Pb method on monzogranite from EPS-1 – after zircon dissolution – has yielded an emplacement age of 334.0+3.8/?3.5 Ma $\text{(2}\text{σ)}$. Point dates obtained by SHRIMP II on the rare zircons from the fine-grained granite showed that it was emplaced in a basement with very heterogeneous ages, ranging from Early Proterozoic to Silurian. The estimated crystallization age of the last granite is 327±7 Ma $\text{(2}\text{σ)}$, slightly later than, or sub-contemporaneous with, the emplacement of the common monzogranite, in agreement with structural constrains. To cite this article: A. Cocherie et al., C. R. Geoscience 336 (2004).     

Anthropogenic CO2 fluxes in the Otranto Strait (E. Mediterranean) in February 1995

This study presents the distribution and fluxes of dissolved inorganic carbon (C_T), total alkalinity (A_T) and anthropogenic carbon (C_ant) along the Otranto strait, during February 1995. Based on a limited number of properties (temperature, dissolved oxygen, total alkalinity and dissolved inorganic carbon), the composite tracer TrOCA was used to estimate the concentration of anthropogenic CO₂ in the Otranto strait.Total alkalinity exhibits high values and weak variability throughout the water column of the strait, probably associated with the dense water formation processes in the Adriatic basin that induce a rapid transport of the coastal alkalinity to the deep waters. Elevated C_ant concentrations and high anthropogenic pH variations are observed in the bottom layer of the strait, associated with the presence of Adriatic Deep Water (ADW). The study shows that large amounts of C_ant have penetrated the highly alkaline Eastern Mediterranean waters, thereby causing a significant pH reduction since the pre-industrial era.Estimates of the transports of C_T and C_ant through the strait indicate that during February 1995, the Adriatic Sea imports through the Otranto strait natural and anthropogenic carbon and acts as a net sink of carbon for the Ionian Sea. The anthropogenic carbon that is imported to the Adriatic Sea represents less than 1% of the net C_T inflow. The Levantine Intermediate Water (LIW) contributes to about one-third of the total C_T and C_ant inflow. Although the amounts of C_ant annually transported by LIW and ADW are almost equal, the contribution of C_ant to the C_T transported by each water mass is slightly higher in ADW (3.1%) than in LIW (2.6%), as a result of its higher mean C_ant concentration. The ADW, despite its weak contribution to the total outflow of C_ant, has a vital role for the sequestration and storage of the anthropogenic carbon, as this water mass is the main component of the Eastern Mediterranean Deep Waters and, thus, the anthropogenic CO₂ is transferred in the deep horizons of the Eastern Mediterranean, where it remains isolated for many years.     

Impact of the Eastern Mediterranean Transient on the distribution of anthropogenic CO2 and first estimate of acidification for the Mediterranean Sea

In the Mediterranean Sea the carbon chemistry is poorly known. However, the impact of the regional and large-scale anthropogenic pressures on this fragile environment rapidly modifies the distribution of the carbonate system key properties like C_T (total dissolved inorganic carbon), A_T (total alkalinity), C_ANT (anthropogenic CO₂), and pH. This leads inexorably to the acidification of its waters. In order to improve our knowledge, we first develop interpolation procedures to estimate C_T and A_T from oxygen, salinity, and temperature data using all available data from the EU/MEDAR/MEDATLAS II database. The acceptable levels of precision obtained for these estimates (6.11 ??mol-kg⁻¹ for C_T and 6.08 ??mol kg⁻¹ for A_T) allow us to draw the distribution of C_ANT (with an uncertainty of 6.75 ??mol kg⁻¹) using the Tracer combining Oxygen, inorganic Carbon, and total Alkalinity (TrOCA) approach. The results indicate that: 1) all Mediterranean water bodies are contaminated by anthropogenic carbon; 2) the lowest concentration of C_ANT is 37.5 ??mol kg⁻¹; and 3) the western basin is more contaminated than the Eastern basin. After reconstructing the distribution of key properties (C_T, A_T, C_ANT) for four periods of time (between 1986 and 2001) along a west-east section throughout the whole Mediterranean Sea, we analyze the impact of the Eastern Mediterranean Transient (EMT). Not only has the concentration of C_ANT increased (especially in the intermediate and the bottom layers of the eastern basin, during and after the EMT), but also the distribution of all properties has been considerably perturbed. This is discussed in detail. For the first time, the level of acidification is estimated for the Mediterranean Sea. Our results indicate that for the year 2001 all waters (even the deepest) have been acidified by values ranging from −0.14 to −0.05 pH unit since the beginning of the industrial era, which is clearly higher than elsewhere in the open ocean. Given that the pH of seawater may affect a very large number of chemical and biological processes, our results stress the necessity to develop new programs of research to understand and then predict the evolution of the carbonate system properties in the Mediterranean Sea.     

Jobs and the Single Parent: An Analysis of Accessibility to Employment in Toronto

Abstract

In this article, we undertake an analysis of accessibility to jobs from the perspective of single-parent household members. Individuals in this demographic segment are of interest due to the fact they often face the double burden of household and employment responsibilities. A case study of the city of Toronto in Canada, an urban area that has seen an increase in absolute and relative numbers of single-parent households in recent years, is presented. Analysis is based on the application of relative accessibility deprivation indicators (RADI), which are calculated using model-based estimates of distance traveled for various population segments, as well as employment data for the city and its surroundings. The results of the analysis indicate that there are substantial differences in the levels of accessibility to jobs between members of single-parent households, in particular females, and members of other types of households.     

The Manicouagan impact structure as a terrestrial analogue site for lunar and martian planetary science

The 90 km diameter, late Triassic Manicouagan impact structure of Québec, Canada, is a well-preserved, undeformed complex crater possessing an anorthositic central uplift and a 55 km diameter melt sheet. As such, it provides a valuable terrestrial analogue for impact structures developed on other planetary bodies, especially the Moon and Mars, which are currently the focus of exploration initiatives. The scientific value of Manicouagan has recently been enhanced due to the production, between 1994 and 2006, of ∼18 km of drill core from 38 holes by the mineral exploration industry. Three of these holes are in excess of 1.5 km deep, with the deepest reaching 1.8 km. Here we combine recent field work, sampling and the drill core data with previous knowledge to provide insight into processes occurring at Manicouagan and, by inference, within extraterrestrial impact structures. Four areas of comparative planetology are discussed: impact melt sheets, central uplifts, impact-generated hydrothermal regimes and footwall breccias. Human training and instrument testing opportunities are also considered. The drill core reveals that the impact melt and clast-bearing impact melts in the centre of the structure reach thicknesses of 1.4 km. The 1.1 km thick impact melt has undergone differentiation to yield a lower monzodiorite, a transitional quartz monzodiorite and an upper quartz monzonite sequence. This calls into question the previous citing of Manicouagan as an exemplar of a relatively large crater possessing an undifferentiated melt sheet, which was used as a rationale for assigning different composition lunar impact melts and clast-bearing impact melts to separate cratering events. The predominantly anorthositic central uplift at Manicouagan is comparable to certain lunar highlands material, with morphometric analogies to the King, Tycho, Pythagoras, Jackson, and Copernicus impact structures, which have similar diameters and uplift structure. Excellent exposure of the Manicouagan uplift facilitates mapping and an appraisal of its formation and collapse mechanisms, enhanced by drill core data from the centre of the structure. Recent field studies at the edge of the central island at Manicouagan, and multiple drill core sections through footwall lithologies, provide insight into allochthonous (clastic and suevitic) and autochthonous breccia formation, as well as shock effects. The hydrothermal regimes developed at Manicouagan are akin to systems proposed for Noachian (>3.5 Ga) Mars that involve alteration of impact melts via meteoritic and surface waters, with the generation of phyllosilicates, zeolites, hematite, sulfates and sulfides that can contribute to martian soil formation and sedimentation processes.     

The effects of mid-Phanerozoic environmental stress on bryozoan diversity, paleoecology, and paleogeography

Evidence of sustained environmental degradation associated with the end-Guadalupian, end-Permian, and end-Triassic extinctions has been inferred from numerous geochemical and sedimentological studies, but the long-term impacts of this extinction-associated stress on the evolutionary trajectories of marine invertebrates have not been explored. An examination of the diversity, extinction, paleoenvironmental range, and geographical distribution of marine stenolaemate bryozoans during the Permian to Jurassic interval provides striking new evidence of the taxonomic and ecological influence of these mid-Phanerozoic extinctions on one of the most abundant components of the Paleozoic Fauna. Elevated bryozoan extinction rates during the Late Permian and Late Triassic were coupled with major changes in their habitats. Bryozoans gradually disappeared from deep-water offshore settings during the Late Permian and from nearshore and offshore settings during the Late Triassic. Re-colonization of these environments in the wake of each crisis was delayed but coupled with increases in global generic diversity. The taxonomic effects of the end-Guadalupian extinction were milder than previously described, even though ecologically bryozoans were becoming restricted to nearshore settings. The end-Permian mass extinction remained the largest for bryozoans, drastically reducing global and assemblage generic diversity and triggering a permanent change in their paleoenvironmental preferences from nearshore to mid-shelf settings. The 285 Myr dominance of stenolaemate bryozoans ended during the Late Triassic when all but one order (Cyclostomata) became extinct, initiating a taxonomic switch between stenolaemate and gymnolaemate bryozoans. Moreover, spatio-temporal variations in the paleoenvironmental history of bryozoans imply that Late Permian and Late Triassic marine environmental instability resulted largely from some stressful deep-water phenomenon. High extinction rates in nearshore environments in the Late Permian provide a link between marine and terrestrial/atmosphere extinction-related perturbations.     

The growth of point source plumes at Rayleigh numbers up to 108 and Prandtl numbers up to 1000

Two-dimensional numerical simulations were conducted of the growth of thermal plumes from a point heat source at Rayleigh numbers up to 108 and Prandtl numbers up to 1000. Scaling the convection equations by the free fall velocity rather than the thermal diffusivity, increased the Prandtl number range available to numerical simulation by one order of magnitude from Prandtl number 100 to 1000. We present animations showing how the plumes grow with time for different Prandtl numbers. Plumes with Prandtl numbers around 7 (water) were found to be unstable to sinuous instabilities; whereas those at Prandtl numbers of 1000 had straight stems and fewer sinuous instabilities. Wavelet analysis was used to analyze the scales at which plumes initiated, and the scales at which sinuous instabilities occurred. The scale of both the plume structures and instabilities was found to decrease with Prandtl number.     

Radarclinometry of the sand seas of Africa’s Namibia and Saturn’s moon Titan

Radarclinometry is a powerful technique for estimating heights of landforms in synthetic aperture radar (SAR) images of planetary surfaces. In particular, it has been used to estimate heights of dunes in the sand seas of Saturn’s moon Titan (Lorenz, R.D., and 39 colleagues [2006]. Science 312, 724-727). In this work, we verify the technique by comparing dune heights derived from radarclinometry to known topography of dune fields in the Namib sand sea of western Africa. We compared results from three different image grid spacings, and found that 350 m/pixel (the same spacing at which the Cassini RADAR data was processed) is sufficient to determine dune height for dunes of similar morphometry to those of the Namib sand sea. At this grid spacing, height estimates derived from radarclinometry are largely representative of, though may underestimate by as much as 30%, or overestimate by as much as 40%, true dune height. Applying the technique to three regions on Titan, we estimate dune heights of 45-180 m, and dune spacings of 2.3-3.3 km. Obtaining accurate heights of Titan’s dunes will help to constrain the total organic inventory on Titan.     

Low temperature hydrolysis of laboratory tholins in ammonia-water solutions: Implications for prebiotic chemistry on Titan

Laboratory tholins react rapidly in 13 wt% ammonia-water at low temperature, producing complex organic molecules containing both oxygen and altered nitrogen functional groups. These reactions display first-order kinetics with half-lives between 0.3 and 14 days at 253 K. The reaction timescales are much shorter than the freezing timescales of impact melts and volcanic sites on Titan, providing ample time for the formation of oxygenated, possibly prebiotic, molecules on its surface. Comparing the rates of the hydrolysis reactions in ammonia-water to those measured in pure water [Neish, C.D, Somogyi, A., Imanaka, H., Lunine, J.I., Smith, M.A., 2008a. Astrobiology 8, 273-287], we find that incorporation of oxygen into the tholins is faster in the presence of ammonia. The rate increases could be due to the increased pH of the solution, or to the availability of new reaction pathways made possible by the presence of ammonia. Using labeled ¹⁵NH₃ water, we find that ammonia does incorporate into some products, and that the reactions with ammonia are largely independent of those with water. A related study in confirms water as the source of the oxygen incorporated into the oxygen containing products.     

High‐calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites

Abstract— Our analyses of high quality spectra of several S‐type asteroids (17 Thetis, 847 Agnia, 808 Merxia, and members of the Agnia and Merxia families) reveal that they include both low‐ and high‐calcium pyroxene with minor amounts of olivine (<20%). In addition, we find that these asteroids have ratios of high‐calcium pyroxene to total pyroxene of >～0.4. High‐calcium pyroxene is a spectrally detectable and petrologically important indicator of igneous history and may prove critical in future studies aimed at understanding the history of asteroidal bodies. The silicate mineralogy inferred for Thetis and the Merxia and Agnia family members requires that these asteroids experienced igneous differentiation, producing broadly basaltic surface lithologies. Together with 4 Vesta (and its smaller “Vestoid” family members) and the main‐belt asteroid 1489 Magnya, these new asteroids provide strong evidence for igneous differentiation of at least five asteroid parent bodies. Based on this analysis of a small subset of the near‐infrared asteroid spectra taken to date with SpeX at the NASA IRTF, we expect that the number of known differentiated asteroids will increase, consistent with the large number of parent bodies inferred from studies of iron meteorites.