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31.
Laura Federico Giovanni Capponi Laura Crispini Marco Scambelluri Igor M. Villa 《Earth and Planetary Science Letters》2005,240(3-4):668-680
We present 39Ar–40Ar dating of phengite, muscovite and paragonite from a set of mafic and metasedimentary rocks sampled from the high-pressure (HP) metaophiolites of the Voltri Group (Western Alps) and from clasts in the basal layer conglomerates from the Tertiary molasse which overlie the high-pressure basement. The white mica-bearing rocks display peak eclogitic and blueschist-facies parageneses, locally showing complex greenschist-facies replacement textures. The internal discordance of age spectra is proportional to the chemical complexity of the micas. High-Si phengites from eclogite clasts record a 39Ar–40Ar age of ca. 49 Ma for the eclogite stage and ca. 43 Ma for the blueschist retrogression; phengites from a blueschist basement sample yield an age of ca. 40 Ma; low-Si muscovite from a metasediment dates the formation of the greenschist paragenesis at ca. 33 Ma. Our data indicate that the analyzed samples reached high-pressure conditions at different times over a time-span of c.a. 10 Ma. Subduction was continuing during exhumation and blueschist retrograde re-equilibration of higher-pressure, eclogite-facies rocks. This process kept the isotherms depressed, allowing the older HP-rocks to escape thermal re-equilibration. Our results, added to literature data, fit a tectonic model of a subduction–exhumation cycle, with different tectonic slices subducted at different times from Early Eocene until the Eocene–Oligocene boundary. 相似文献
32.
Production of a molybdophore during metal-targeted dissolution of silicates by soil bacteria 总被引:1,自引:0,他引:1
Laura J. Liermann Robin L. Guynn Ariel Anbar Susan L. Brantley 《Chemical Geology》2005,220(3-4):285-302
Although many bioessential metals are scarce in natural water and rock systems, microbial secretion of high-affinity ligands for metal extraction from solid phases has only been documented for Fe. However, we have discovered that Mo is extracted from a silicate by a high-affinity ligand (a possible “molybdophore”) secreted by an N2-fixing soil bacterium. The putative molybdophore, aminochelin, is secreted as a siderophore under Fe-depleted conditions, but is also secreted under Fe-sufficient, Mo-depleted conditions. Presumably, molybdophore production facilitates uptake of Mo for use in Mo enzymes. In contrast, an Fe-requiring soil bacterium without a special Mo requirement only enhances the release of Fe from the silicate. Fractionation of Mo stable isotopes during uptake to cells may provide a “fingerprint” for the importance of chelating ligands in such systems. Many such metal-specific ligands secreted by prokaryotes for extraction of bioessential metals, their effects on Earth materials, and their possible utility in the recovery of economic metals remain to be discovered. 相似文献
33.
Craig T. Simmons 《Hydrogeology Journal》2005,13(1):116-119
34.
Cynthia S. Simmons 《GeoJournal》2005,64(4):307-317
Brazil possesses a long history of violent struggle for land, and its most recent phase is occurring predominantly in the
Amazon Basin. Consequently, this paper attempts to territorialize land conflict in the Brazilian Amazon, and in so doing,
to illuminate the place-specific intersection of historic social, political, and economic circumstance that created a violent
landscape in the so-called “South of Pará.” The paper’s premise is that such conflict can be best viewed as resulting from
a dialectic between general social processes operating across spatial scales, which create necessary conditions for conflict,
and place-specific historical circumstances that transform necessary into sufficient conditions. The paper presents a framework
integrating the theory of contentious politics and literatures addressing violence associated with the Amazonian frontier
and with resource scarcity (and abundance). The discussion and theoretical application deconstruct the environmental, cognitive,
and relational mechanisms that created violence in the South of Pará, and set the stage for the Eldorado dos Carajás massacre in April of 1996. 相似文献
35.
The origin of oceanic islands has been the subject of much speculation, starting with Darwin almost two centuries ago. Two classes of oceanic islands can be identified: ‘volcanic islands’, which form due to excess volcanism caused by melting anomalies in the suboceanic mantle, and ‘tectonic islands’, which form due to transpressive and/or transtensional tectonics of blocks of oceanic lithosphere along transform faults. Modern and sunken tectonic islands from the Atlantic Ocean and Indian Ocean and the Caribbean Sea and Red Sea expose mantle and lower‐crust lithologies and display an elongated narrow morphology; in contrast, volcanic islands expose basalts and have near‐circular morphology. Both are often capped by carbonate platforms. The life cycle of tectonic islands tends to be more complex than that of most volcanic islands; their elongated narrow morphology, together with their tectonic instability and high seismicity, affect the architecture of the carbonate platforms capping them, limiting coral reef development and favouring rhodalgal–foramol biota associations. 相似文献
36.
Kevin J. Devito Kelly J. Hokanson Paul Adrian Moore Nicholas Kettridge Axel E. Anderson Laura Chasmer Chris Hopkinson Maxwell C. Lukenbach Carl A. Mendoza Julienne Morissette Daniel L. Peters Richard Michael Petrone Uldis Silins Brian Smerdon James Michael Waddington 《水文研究》2017,31(15):2737-2751
We compared median runoff (R) and precipitation (P) relationships over 25 years from 20 mesoscale (50 to 5,000 km2) catchments on the Boreal Plains, Alberta, Canada, to understand controls on water sink and source dynamics in water‐limited, low‐relief northern environments. Long‐term catchment R and runoff efficiency (RP?1) were low and varied spatially by over an order of magnitude (3 to 119 mm/year, 1 to 27%). Intercatchment differences were not associated with small variations in climate. The partitioning of P into evapotranspiration (ET) and R instead reflected the interplay between underlying glacial deposit texture, overlying soil‐vegetation land cover, and regional slope. Correlation and principal component analyses results show that peatland‐swamp wetlands were the major source areas of water. The lowest estimates of median annual catchment ET (321 to 395 mm) and greatest R (60 to 119 mm, 13 to 27% of P) were observed in low‐relief, peatland‐swamp dominated catchments, within both fine‐textured clay‐plain and coarse‐textured glacial deposits. In contrast, open‐water wetlands and deciduous‐mixedwood forest land covers acted as water sinks, and less catchment R was observed with increases in proportional coverage of these land covers. In catchments dominated by hummocky moraines, long‐term runoff was restricted to 10 mm/year, or 2% of P. This reflects the poor surface‐drainage networks and slightly greater regional slope of the fine‐textured glacial deposit, coupled with the large soil‐water and depression storage and higher actual ET of associated shallow open‐water marsh wetland and deciduous‐forest land covers. This intercatchment study enhances current conceptual frameworks for predicting water yield in the Boreal Plains based on the sink and source functions of glacial landforms and soil‐vegetation land covers. It offers the capability within this hydro‐geoclimatic region to design reclaimed catchments with desired hydrological functionality and associated tolerances to climate or land‐use changes and inform land management decisions based on effective catchment‐scale conceptual understanding. 相似文献
37.
Severe soil erosion during a 3‐day exceptional rainfall event: combining modelling and field data for a fallow cereal field 下载免费PDF全文
Manuel López‐Vicente Laura Quijano Leticia Gaspar Leticia Palazón Ana Navas 《水文研究》2015,29(10):2358-2372
Exceptional rainfall events cause significant losses of soil, although few studies have addressed the validation of model predictions at field scale during severe erosive episodes. In this study, we evaluate the predictive ability of the enhanced Soil Erosion and Redistribution Tool (SERT‐2014) model for mapping and quantifying soil erosion during the exceptional rainfall event (~235 mm) that affected the Central Spanish Pyrenees in October 2012. The capacity of the simulation model is evaluated in a fallow cereal field (1.9 ha) at a high spatial scale (1 × 1 m). Validation was performed with field‐quantified rates of soil loss in the rills and ephemeral gullies and also with a detailed map of soil redistribution. The SERT‐2014 model was run for the six rainfall sub‐events that made up the exceptional event, simulating the different hydrological responses of soils with maximum runoff depths ranging between 40 and 1017 mm. Predicted average and maximum soil erosion was 11 and 117 Mg ha?1 event?1, respectively. Total soil loss and sediment yield to the La Reina gully amounted to 16.3 and 9.0 Mg event?1. These rates are in agreement with field estimations of soil loss of 20.0 Mg event?1. Most soil loss (86%) occurred during the first sub‐event. Although soil accumulation was overestimated in the first sub‐event because of the large amount of detached soil, the enhanced SERT‐2014 model successfully predicted the different spatial patterns and values of soil redistribution for each sub‐event. Further research should focus on stream transport capacity. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
38.
Ryan D. Stewart Aditi S. Bhaskar Anthony J. Parolari Dustin L. Herrmann Jinshi Jian Laura A. Schifman William D. Shuster 《水文研究》2019,33(26):3349-3363
Uncontrolled overland flow drives flooding, erosion, and contaminant transport, with the severity of these outcomes often amplified in urban areas. In pervious media such as urban soils, overland flow is initiated via either infiltration‐excess (where precipitation rate exceeds infiltration capacity) or saturation‐excess (when precipitation volume exceeds soil profile storage) mechanisms. These processes call for different management strategies, making it important for municipalities to discern between them. In this study, we derived a generalized one‐dimensional model that distinguishes between infiltration‐excess overland flow (IEOF) and saturation‐excess overland flow (SEOF) using Green–Ampt infiltration concepts. Next, we applied this model to estimate overland flow generation from pervious areas in 11 U.S. cities. We used rainfall forcing that represented low‐ and high‐intensity events and compared responses among measured urban versus predevelopment reference soil hydraulic properties. The derivation showed that the propensity for IEOF versus SEOF is related to the equivalence between two nondimensional ratios: (a) precipitation rate to depth‐weighted hydraulic conductivity and (b) depth of soil profile restrictive layer to soil capillary potential. Across all cities, reference soil profiles were associated with greater IEOF for the high‐intensity set of storms, and urbanized soil profiles tended towards production of SEOF during the lower intensity set of storms. Urban soils produced more cumulative overland flow as a fraction of cumulative precipitation than did reference soils, particularly under conditions associated with SEOF. These results will assist cities in identifying the type and extent of interventions needed to manage storm water produced from pervious areas. 相似文献
39.
40.
The root‐zone moisture replenishment mechanisms are key unknowns required to understand soil hydrological processes and water sources used by plants. Temporal patterns of root‐zone moisture replenishment reflect wetting events that contribute to plant growth and survival and to catchment water yield. In this study, stable oxygen and hydrogen isotopes of twigs and throughfall were continuously monitored to characterize the seasonal variations of the root‐zone moisture replenishment in a native vegetated catchment under Mediterranean climate in South Australia. The two studied hillslopes (the north‐facing slope [NFS] and the south‐facing slope [SFS]) had different environmental conditions with opposite aspects. The twig and throughfall samples were collected every ~20 days over 1 year on both hillslopes. The root‐zone moisture replenishment, defined as percentage of newly replenished root‐zone moisture as a complement to antecedent moisture for plant use, calculated by an isotope balance model, was about zero (±25% for the NFS and ± 15% for the SFS) at the end of the wet season (October), increased to almost 100% (±26% for the NFS and ± 29% for the SFS) after the dry season (April and May), then decreased close to zero (±24% for the NFS and ± 28% for the SFS) in the middle of the following wet season (August). This seasonal pattern of root‐zone moisture replenishment suggests that the very first rainfall events of the wet season were significant for soil moisture replenishment and supported the plants over wet and subsequent dry seasons, and that NFS completed replenishment over a longer time than SFS in the wet season and depleted the root zone moisture quicker in the dry season. The stable oxygen isotope composition of the intraevent samples and twigs further confirms that rain water in the late wet season contributed little to root‐zone moisture. This study highlights the significant role of the very first rain events in the early wet season for ecosystem and provides insights to understanding ecohydrological separation, catchment water yield, and vegetation response to climate changes. 相似文献