Factors controlling the lengths of channel-fed lava flows     

Harry Pinkerton  Lionel Wilson 《Bulletin of Volcanology》1994,56(2):108-120

Factors which control lava flow length are still not fully understood. The assumption that flow length as mainly influenced by viscosity was contested by Walker (1973) who proposed that the length of a lava flow was dependent on the mean effusion rate, and by Malin (1980) who concluded that flow length was dependent on erupted volume. Our reanalysis of Malin's data shows that, if short duration and tube-fed flows are eliminated, Malin's Hawaiian flow data are consistent with Walker's assertion. However, the length of a flow can vary, for a given effusion rate, by a factor of 7, and by up to 10 for a given volume. Factors other than effusion rate and volume are therefore clearly important in controlling the lengths of lava flows. We establish the relative importance of the other factors by performing a multivariate analysis of data for recent Hawaiian lava flows. In addition to generating empirical equations relating flow length to other variables, we have developed a non-isothermal Bingham flow model. This computes the channel and levee width of a flow and hence permits the advance rates of flows and their maximum cooling-limited lengths for different gradients and effusion rates to be calculated. Changing rheological properties are taken into account using the ratio of yield strength to viscosity; available field measurements show that this varies systematically from the vent to the front of a lava flow. The model gives reasonable agreement with data from the 1983–1986 Pu'u Oo eruptions and the 1984 eruption of Mauna Loa. The method has also been applied to andesitic and rhyolitic lava flows. It predicts that, while the more silicic lava flows advance at generally slower rates than basaltic flows, their maximum flow lengths, for a given effusion rate, will be greater than for basaltic lava flows.  相似文献   

Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)     

Lionel Siame  Olivier Bellier  Rgis Braucher  Michel Sbrier  Marc Cushing  Didier Bourls  Bruno Hamelin  Emmanuel Baroux  Beatrice de Voogd  Grant Raisbeck  Franoise Yiou 《Earth and Planetary Science Letters》2004,220(3-4):345-364

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured ¹⁰Be concentrations has been modelled using a χ² inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.  相似文献   

Testing the genetic relationship between fluid alteration and brecciation in CM chondrites     

Maximilien J. Verdier‐Paoletti  Yves Marrocchi  Lionel G. Vacher  Jrme Gattacceca  Andrey Gurenko  Corinne Sonzogni  Matthieu Gounelle 《Meteoritics & planetary science》2019,54(8):1692-1709

Boriskino is a poorly studied CM chondrite with numerous millimeter‐ to centimeter‐scale clasts exhibiting sharp boundaries. Clast textures and mineralogies attest to diverse geological histories with various degrees of aqueous alteration. We conducted a petrographic, chemical, and isotopic study on each clast type of the breccia to investigate if there exists a genetic link between brecciation and aqueous alteration, and to determine the controlling parameter of the extent of alteration. Boriskino is dominated by CM2 clasts for which no specific petrographic type could be assigned based on the chemical compositions and modal abundances of constituents. One clast stands out and is identified as a CM1 lithology, owing to its lack of anhydrous silicates and its overall abundance of dolomite‐like carbonates and acicular iron sulfides. We observe that alteration phases near clast boundaries exhibit foliation features, suggesting that brecciation postdated aqueous alteration. We measured the O‐isotopic composition of Ca‐carbonates and dolomite‐like carbonates to determine their precipitation temperatures following the methodology of Verdier‐Paoletti et al. (2017). Both types of carbonates yield similar ranges of precipitation temperatures independent of clast lithology, ranging from ?13.9 ± 22.4 (2σ) to 166.5 ± 47.3 °C, precluding that temperature alone accounts for the differences between the CM1 and CM2 lithologies. Instead, we suggest that initial water/rock ratios of 0.75 and 0.61 for the CM1 and CM2 clasts, respectively, might control the extent of aqueous alteration. Based on these estimates, we suggest that Boriskino clasts originated from a single parent body with heterogeneous distribution of water either due to local differences in the material permeability or in the initial content of ice available. These conditions would have produced microenvironments with differing geochemical conditions thus leading to a range of degrees of aqueous alteration.  相似文献   

Deciphering the conditions of tochilinite and cronstedtite formation in CM chondrites from low temperature hydrothermal experiments     

Lionel G. Vacher  Laurent Truche  Franois Faure  Laurent Tissandier  Rgine Mosser‐Ruck  Yves Marrocchi 《Meteoritics & planetary science》2019,54(8):1870-1889

Tochilinite/cronstedtite intergrowths are commonly observed as alteration products in CM chondrite matrices, but the conditions under which they formed are still largely underconstrained due to their scarcity in terrestrial environments. Here, we report low temperature (80 °C) anoxic hydrothermal experiments using starting assemblages similar to the constituents of the matrices of the most pristine CM chondrite and S‐rich and S‐free fluids. Cronstedtite crystals formed only in S‐free experiments under circumneutral conditions with the highest Fe/Si ratios. Fe‐rich tochilinite with chemical and structural characteristics similar to chondritic tochilinite was observed in S‐bearing experiments. We observed a positive correlation between the Mg content in the hydroxide layer of synthetic tochilinite and temperature, suggesting that the composition of tochilinite is a proxy for the alteration temperature in CM chondrites. Using this relation, we estimate the mean precipitation temperatures of tochilinite to be 120–160 °C for CM chondrites. Given the different temperature ranges of tochilinite and cronstedtite in our experiments, we propose that Fe‐rich tochilinite crystals resulted from the alteration of metal beads under S‐bearing alkaline conditions at T = 120–160 °C followed by cronstedtite crystals formed by the reaction of matrix amorphous silicates, metal beads, and water at a low temperature (50–120 °C).  相似文献   

Benthic remineralization at the land–ocean interface: A case study of the Rhône River (NW Mediterranean Sea)     

Bruno Lansard  Christophe Rabouille  Lionel Denis  Christian Grenz   《Estuarine, Coastal and Shelf Science》2009,81(4):544-554

Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC (δ¹³C_OC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O₂ uptake (5.2 to 29.3 mmol m⁻² d⁻¹) and NH₄⁺ release (−0.1 to −3.5 mmol m⁻² d⁻¹) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ¹³C_OC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (52%) or remineralized (8%), mostly on the prodelta area. The remaining fraction (40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms.  相似文献   

Cellular energy allocation in the Arctic sea ice amphipod Gammarus wilkitzkii exposed to the water soluble fractions of oil     

Olsen GH  Carroll J  Sva E  Camus L 《Marine environmental research》2008,66(1):213-214

Increasing offshore oil and gas activities in the European Arctic has raised concerns of the potential anthropogenic impact of oil-related compounds on the polar marine ecosystem. We measured cellular energy allocation (CEA) in the sea ice amphipod Gammarus wilkitzkii after exposure for one month to the water soluble fraction (WSF) of oil. The CEA biomarker measures the energy budget of organisms by biochemically assessing changes in carbohydrates, protein and lipid content as well as the electron transport system activity. A significantly higher protein content was observed in the medium dose compared to controls, while the total energy budget was not affected in G. wilkitzkii. This indicates that parts of the energy budget of G. wilkitzkii, which is a key species in the Arctic ecosystem, is affected by a WSF of oil.  相似文献   

Meteoritic and other constraints on the internal structure and impact history of small asteroids     

Edward R.D. Scott  Lionel Wilson 《Icarus》2005,174(1):46-53

Studies of the internal structure of asteroids, which are crucial for understanding their impact history and for hazard mitigation, appear to be in conflict for the S-type asteroids, Eros, Gaspra, and Ida. Spacecraft images and geophysical data show that they are fractured, coherent bodies, whereas models of catastrophic asteroidal impacts, family and satellite formation, and studies of asteroid spin rates, and other diverse properties of asteroids and planetary craters suggest that such asteroids are gravitationally bound aggregates of rubble. These conflicting views may be reconciled if 10-50 km S-type asteroids formed as rubble piles, but were later consolidated into coherent bodies. Many meteorites are breccias that testify to a long history of impact fragmentation and consolidation by alteration, metamorphism, igneous and impact processes. Ordinary chondrites, which are the best analogs for S asteroids, are commonly breccias. Some may have formed in cratering events, but many appear to have formed during disruption and reaccretion of their parent asteroids. Some breccias were lithified during metamorphism, and a few were lithified by injected impact melt, but most are regolith and fragmental breccias that were lithified by mild or moderate shock, like their lunar analogs. Shock experiments show that porous chondritic powders can be consolidated during mild shock by small amounts of silicate melt that glues grains together, and by friction and pressure welding of silicate and metallic Fe,Ni grains. We suggest that the same processes that converted impact debris into meteorite breccias also consolidated asteroidal rubble. Internal voids would be partly filled with regolith by impact-induced seismic shaking. Consolidation of this material beneath large craters would lithify asteroidal rubble to form a more coherent body. Fractures on Ida that were created by antipodal impacts and are concentrated in and near large craters, and small positive gravity anomalies associated with the Psyche and Himeros craters on Eros, are consistent with this concept. Spin data suggest that smaller asteroids 0.6-6 km in size are unconsolidated rubble piles. C-type asteroids, which are more porous than S-types, and their analogs, the volatile-rich carbonaceous chondrites, were probably not lithified by shock.  相似文献   

Fold interference patterns in the Late Palaeozoic Anti-Atlas belt of Morocco     

Caritg Séverine  Burkhard Martin  Ducommun Romain  Helg Urs  Kopp Lionel  Sue Christian 《地学学报》2004,16(1):27-37

We document two phases of folding within the central part of the Late Palaeozoic Anti‐Atlas chain of Morocco. A first generation of SW–NE folds involve a horizontal shortening of 10–20%, accommodated by polyharmonic buckle folding of contrasting wavelengths in Ordovician Jbel Bani quartzites and Devonian Jbel Rich carbonates. A second generation of folds with similar style and wavelengths in an E–W direction lead to complex interference patterns. Dome and basins are developed within the Jbel Rich and within Lower Cambrian dolomites. Both folding phases are related to thick‐skinned uplift of Precambrian basement in a Laramide style. In contrast to the typical Rocky Mountain foreland style, however, cover deformation in the Anti‐Atlas is mostly decoupled from the undying basement along thick incompetent horizons such as the Lower Cambrian Lie‐de‐Vin and Silurian shales.  相似文献   

Structure profonde de la Chaîne des Puys     

M. Aubert  G. Camus 《Bulletin of Volcanology》1974,38(1):445-457

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Susceptibility to oxidative stress of mussels (Mytilus galloprovincialis) in the Venice Lagoon (Italy)     

Pampanin DM  Camus L  Gomiero A  Marangon I  Volpato E  Nasci C 《Marine pollution bulletin》2005,50(12):512-1557

The aim of this study was to evaluate the susceptibility to pollutant mediated oxidative stress of the Mediterranean mussel Mytilus galloprovincialis in the Venice lagoon (Italy).

In June 2003, mussels from a farm were transplanted to eight sites in the lagoon for five weeks. Oxidative stress responses were measured by: (i) total oxyradical scavenging capacity (TOSC) assay, for an overall evaluation of the oxidative stress response capability; (ii) catalase (CAT), as a key enzyme involved in the antioxidant defence system; (iii) malondialdehyde (MDA), as an indicator of lipid peroxidation, to evaluate an oxidative damage; (iv) metallothioneins (MTs), as they play a role in the antioxidant defence.

The TOSC analysis revealed a reduced capability to eliminate: (i) peroxyl radical in mussels transplanted at Palude della Rosa, Valle Millecampi and Chioggia; (ii) hydroxyl radical at Campalto and Valle Millecampi; (iii) peroxynitrite at Valle Millecampi.

Inhibition in CAT activity, observed in all the monitored sites, confirms the presence of an oxidative pressure in transplanted mussels.

In addition, Pearson correlation analysis was performed in order to observe possible links between the various parameters. The PCA was a powerful tool to discriminate impacted sites, suggesting that the mussels transplanted throughout the Venice lagoon were subjected to different levels of oxidative pressure. Furthermore, it provided an easy and useful tool to summarize the obtained results.  相似文献