Search results for "Cru"
showing 10 items of 1385 documents
The Impact of a Very Weak and Thin Upper Asthenosphere on Subduction Motions
2019
Recent geophysical observations report the presence of a very weak and thin upper asthenosphere underneath subducting oceanic plates at convergent margins. Along these margins, trench migrations are significantly slower than plate convergence rates. We use numerical models to assess the role of a weak upper asthenospheric layer on plate and trench motions. We show that the presence of this layer alone can enhance an advancing trend for the motion of the plate and hamper trench retreat. This mechanism provides a novel and alternative explanation for the slow rates of trench migration and fast-moving plates observed globally at natural subduction zones.
The geological roots of South America: 4.1 Ga and 3.7 Ga zircon crystals discovered in N.E. Brazil and N.W. Argentina
2015
International audience; We present new LA-ICP-MS in situ geochronological results for seven Eoarchean zircons dated at 3.7 Ga coming from Cretaceous ash layers of NW Argentina and one Hadean single crystal sampled within the São Francisco Craton in NE Brazil. This zircon comprises a zoned magmatic core dated at 4.1 Ga surrounded by a 1.9 Ga overgrowth related to Paleoproterozoic reworking. This Hadean age is consistent with previously published Nd model ages on orthogneisses from the same domain. These two results represent among the oldest geological witnesses discovered to date in South America, which demonstrates the occurrence of a primitive crust. The contrasting age patterns recorded …
Numerical modelling of magma dynamics coupled to tectonic deformation of lithosphere and crust
2013
Many unresolved questions in geodynamics revolve around the physical behaviour of the two-phase system of a silicate melt percolating through and interacting with a tectonically deforming host rock. Well-accepted equations exist to describe the physics of such systems and several previous studies have successfully implemented various forms of these equations in numerical models. To date, most such models of magma dynamics have focused on mantle flow problems and therefore employed viscous creep rheologies suitable to describe the deformation properties of mantle rock under high temperatures and pressures. However, the use of such rheologies is not appropriate to model melt extraction above …
Upper Ovetian trilobites from Spain and their implications for the palaeobiogeography and correlation of the Cambrian Stage 3 in Gondwana
2016
Abstract The upper part of the La Herreria Formation in Los Barrios de Luna (Leon Province, N Spain) has been revised from a palaeontological and biostratigraphical point of view. Two stratigraphic sections have been studied including their trilobite and ichnofossils contents. The ichnofossil assemblages have a high diversity of species characterising the Cruziana ichnofacies, suggesting a shallow sublittoral environment for the upper part of the La Herreria Formation. The trilobites species recognised are Lunagraulos antiquus , Dolerolenus formosus , Dolerolenus longioculatus , Lunolenus lunae , Metadoxides richterorum , Metadoxides armatus and Sardaspis ? sp. from the upper Ovetian (lower…
Impacts of soil conditions and light availability on natural regeneration of Norway spruce Picea abies (L.) H. Karst. in low-elevation mountain fores…
2018
Abstract • Key message Natural regeneration ofP. abies(L.) H. Karst. may reach high densities in lower mountain elevations. The highest densities were found in sites with moderate light availability, with low pH, and not near the riverbank. However, age-height classes differed in the predicted magnitude of response, but were consistent in response directions. Mosses and understory species typical of coniferous forests were positively correlated with regeneration density. • Context Norway spruce Picea abies (L.) H. Karst. in Central Europe is at risk under climate change scenarios, particularly in mountain regions. Little is known about the impact of environmental factors on the natural rege…
Experimental δ13C evidence for a contribution of methane to pelagic food webs in lakes
2006
We tested the hypothesis that low stable carbon isotope (δ13C) values commonly observed for zooplankton in humic lakes are due to their feeding on isotopically light methane-oxidizing microbes, and thus that methane-derived carbon is important in the food webs of these lakes. In replicate laboratory cultures, Daphnia longispina, a common crustacean zooplankter in humic lakes, were fed microbial suspensions with or without enrichment by biogenic methane. The δ13C values of Daphnia indicated consumption of 13C-depleted methanotrophic bacteria, while growth rates, survival, and reproduction of Daphnia in cultures enriched with methane were equal to or greater than those in nonenriched cultures…
Arable-weed flora and its pollen representation: A case study from the eastern part of France
2007
International audience; Local pollen deposition in human-influenced vegetation types is studied with the aim of establishing the relationship between arable-weed vegetation and its pollen representation as an aid in interpreting human presence and impact on vegetation from pollen assemblages. The study area is located in the Franche-Comté region, eastern part of France. The presence of plants within 100 m2 plots and their pollen representation in moss samples within the same plots was recorded from different crops and annual fallows. Patterns in the vegetation and pollen assemblages were investigated separately using principal coordinate analysis (PCoA). Procrustean co-inertia analysis (PCI…
Characterization of recruitment through tandem running in an Indian queenless ant Diacamma indicum
2017
Tandem running is a primitive recruitment method employed by many ant genera. This study characterizes this behaviour during the recruitment of colony mates to a new nest in an Indian antDiacamma indicum. Tandem leaders who have knowledge of the new nest lead a single follower at a time, to the destination by maintaining physical contact. In order to characterize tandem running, we captured and analysed 621 invitations, 217 paths and 226 termination events. Remarkably, not a single colony member was lost. While invitations were stereotypic in behaviour, termination was not. Analysis of speed revealed that the average transport speed was 4.2 cm s−1. Coupled adult-brood transport was slower t…
Variation in the immune state of Gammarus pulex (Crustacea, Amphipoda) according to temperature: are extreme temperatures a stress?
2017
9 pages; International audience; Temperature is known to impact host-parasite interactions in various ways. Such effects are often regarded as the consequence of the increased metabolism of parasites with increasing temperature. However, the effect of temperature on hosts' immune system could also be a determinant. Here we assessed the influence of temperature on the immunocompetence of the crustacean amphipod Gammarus pulex. Amphipods play a key ecological role in freshwater ecosystems that can be altered by several parasites. We investigated the consequences of three weeks of acclimatization at four temperatures (from 9 °C to 17 °C) on different immunological parameters. Temperature influ…
Changes in freshwater sediment microbial populations during fermentation of crude glycerol
2020
This work was supported by the Latvian Council of Science , project NN-CARMA, project No. lzp-2018/1-0194.