Trace element geochemistry and Sr-Nd characteristics of Mesoproterozoic mafic intrusive rocks from Rondonia, Brazil, SW Amazonian Craton： Petrogenetic and tectonic inferences     

Girardi  V.A. V. Teixeira  W. Bettencourt  J.S. Andrade  S. Navarro  M.S. Sato  K. 《《幕》》2008,31(4):392-400

The Amazonian Craton comprises an Archean domain surrounded by four successively younger Proterozoic tectonic provinces. Within the Rio-Negro-Juruena province the Serra da Providencia Intrusive Suite （1.60 and 1.53 Ga） consists of A-type rapakivi gran- ites, charnockites and mangerites genetically associated with diabase dikes, gabbros and amphibolites. The original mafic melts were derived from a depleted mantle source （εN（T） ＋2.5 to ＋2.8;εSr（T） -12.1）. Underplated mafic magma induced melting of a short-lived felsic crust, thus originating coeval felsic-mafic magmatism in a conti- nental intraplate setting. The Colorado Complex, assigned to the Rondonian-San Ignacio province, comprises 1.35-1.36 Ga intrusive bimodal magmatism represented by monzonite gneisses associated with amphibolite, gabbro and metadiabase dikes intercalated with metasediments with detrital zircon that yield U- Pb ages of 1.35 to 1.42 Ga. Mafic samples dis- play juvenile signatures （εNd（T） 0.0 to ＋5.2; εSr（T） --5.0 to --30.7） and are less contaminated than the Serra da Previdencia and Nova Brasilandia ones. The generation of the basaltic magma is related to the subduction of an oceanic slab below the peridotite wedge （intraoceanic arc setting）. Fluids and/or small melts from the slab impregnated the mantle. The Nova Brasilandia Sequence （Sunsas-Aguapef province） comprises a metasedimentary sequence intruded by 1.10-1.02 Ga metadia- bases, gabbros, meta-gabbros, and amphibolites associated with granitic plutons （bimodal mag- matism）. The original tholeiitic magmas, derived from a depleted source （εNd（T） = ＋3.1 to ＋5.0）, in a proto-oceanic setting, underwent subsequent contamination by the host rocks, as indicated by the isotopic and trace element data.  相似文献   

Distortion of tidal currents and the lateral transfer of salt in a shallow coastal plain estuary (O estuário do Mira, Portugal)     

Jackson O. Blanton  Francisco A. Andrade 《Estuaries and Coasts》2001,24(3):467-480

We describe the tidal circulation of a coastal plain estuary across a flood tide delta located at its entrance. The area connects the downstream portion of the main estuary extending 30–40 km inland to the more complex delta reach that consists of a shallow main channel and a series of smaller side channels. The delta acts as a frictionally dominated zone that modifies the tidal wave from a simple sinusoid to one with ebb currents that accelerate to maximum early in the tidal cycle and last more than one-half of the tidal cycle. Along smaller side channels, the tidal currents favor stronger flood or ebb currents, depending upon the local surrounding morphology. The phase difference between ebb currents in the small channels relative to those in the main channel cause some of the salt to be retained thus reducing the tendency of freshwater discharge to flush salt out of the system. This mechanism of retention differs from the selective withdrawal mechanism described for this estuary in Blanton et al. (2000).  相似文献   

Channel avulsion and river metamorphosis: The case of the Thomson River,Victoria, Australia     

Sandra O. Brizga  Brian L. Finlayson 《地球表面变化过程与地形》1990,15(5):391-404

Channel avulsion occurred on the Thomson River in Victoria, Australia, in 1952 along a 12 km length of the valley. A comparison of the old and new channels reveals considerable differences in channel characteristics. The old channel was perched above the floodplain on an alluvial ridge such that when bankfull capacity was exceeded, floodwaters concentrated on the lowest part of the floodplain some distance away. This is where the new channel formed. It is an incised channel with larger capacity and longer meander wavelength than the old channel and is also shorter and steeper. The new channel is subject to larger floodflows and a more variable flood regime than the old course because of the differences in the channel/floodplain relationship and channel capacity. The resulting concentration of stream power along the new course is responsible for the contrast in channel characteristics and for the more rapid meander migration. This example shows that river metamorphosis can occur without major environmental changes. Measures of channel geometry such as gradient, sinuosity, and meander wavelength therefore cannot be used in palaeohydrological work to infer climatic or other environmental changes without independent supporting evidence. Differences in channel geometry can arise simply from changes in the relationship between the channel and its loodplain.  相似文献   

Simulated Effects of Quarry Dewatering Near a Municipal Well Field   总被引：4，自引：0，他引：4  

Sandra M. Eberts  E. Scott Bair 《Ground water》1990,28(1):37-47

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Balanced Sediment Fluxes in Southern California’s Mediterranean-Climate Zone Salt Marshes   总被引：1，自引：0，他引：1  

Jordan A. Rosencranz  Neil K. Ganju  Richard F. Ambrose  Sandra M. Brosnahan  Patrick J. Dickhudt  Glenn R. Guntenspergen  Glen M. MacDonald  John Y. Takekawa  Karen M. Thorne 《Estuaries and Coasts》2016,39(4):1035-1049

Salt marsh elevation and geomorphic stability depends on mineral sedimentation. Many Mediterranean-climate salt marshes along southern California, USA coast import sediment during El Niño storm events, but sediment fluxes and mechanisms during dry weather are potentially important for marsh stability. We calculated tidal creek sediment fluxes within a highly modified, sediment-starved, 1.5-km² salt marsh (Seal Beach) and a less modified 1-km² marsh (Mugu) with fluvial sediment supply. We measured salt marsh plain suspended sediment concentration and vertical accretion using single stage samplers and marker horizons. At Seal Beach, a 2014 storm yielded 39 and 28 g/s mean sediment fluxes and imported 12,000 and 8800 kg in a western and eastern channel. Western channel storm imports offset 8700 kg exported during 2 months of dry weather, while eastern channel storm imports augmented 9200 kg imported during dry weather. During the storm at Mugu, suspended sediment concentrations on the marsh plain increased by a factor of four; accretion was 1–2 mm near creek levees. An exceptionally high tide sequence yielded 4.4 g/s mean sediment flux, importing 1700 kg: 20 % of Mugu’s dry weather fluxes. Overall, low sediment fluxes were observed, suggesting that these salt marshes are geomorphically stable during dry weather conditions. Results suggest storms and high lunar tides may play large roles, importing sediment and maintaining dry weather sediment flux balances for southern California salt marshes. However, under future climate change and sea level rise scenarios, results suggest that balanced sediment fluxes lead to marsh elevational instability based on estimated mineral sediment deficits.  相似文献   

Evaluating water management processes in Germany: conceptual approach and practical applications     

Sabrina Kirschke  Jeanette Völker  Sandra Richter 《Environmental Earth Sciences》2016,75(14):1098

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Geochemical mobility of arsenic in the surficial waters from Argentina     

Alicia Daniela Robles  Paula Polizzi  María Belén Romero  Leila Natalia Chiodi Boudet  Sandra Medici  Agustín Costas  Marcela Gerpe 《Environmental Earth Sciences》2016,75(23):1479

The presence of arsenic (As) in surface water constitutes an important environmental risk, where mobility and adsorption processes are responsible for its behavior in the sediment–water interface. Therefore, the assessment of adsorption, mobility and water availability of arsenic in freshwater sediments, with agricultural, livestock and urban soil uses was performed. Arsenic concentrations in sediments ranged from 5.4 to 15.9 mg kg^?1 (total) and 2.8 to 6.5 mg kg^?1 (labile), and those of iron and manganese were 11,563–23,500 and 140.6–662.1 mg kg^?1, respectively. The As levels in water were significantly lower than those of sediments. Results would suggest that As co-precipitation and adsorption on Fe oxides are probably the major route of immobilization, determining its low lability. Manganese did not present an outstanding contribution to the retention, and cation-exchange capacity, pH and organic matter of sediments did not show an influence on the mobility of As.  相似文献   

Adaptation services and pathways for the management of temperate montane forests under transformational climate change     

Matthew J. Colloff  Michael D. Doherty  Sandra Lavorel  Michael Dunlop  Russell M. Wise  Suzanne M. Prober 《Climatic change》2016,138(1-2):267-282

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Modeling the Stakeholder Profile in Territorial Management: The Segarra-Garrigues Irrigation System,Spain     

Sandra Ricart  Anna Ribas  David Pavón 《The Professional geographer》2016,68(3):496-510

Interest in obtaining a more accurate snapshot of irrigation management from a geographical perspective is increasingly relevant. This proposal is based on existing qualitative approaches in combination with an alternative method (the territorial irrigation management model) to identify and present key stakeholders attitudes and perceptions in the Segarra-Garrigues irrigation system in Spain. Advantages are (1) the focus on interrelations and context, (2) the applicability and extrapolation of the irrigation system, and (3) the irrigator-driven rather than researcher-driven perspective. Results revealed that there are conceptual and practical heterogeneities between the preferences of stakeholders' groups regarding water resources management, environmental protection, and agricultural challenges.  相似文献   

Spatial Thinking Assists Geographic Thinking: Evidence from a Study Exploring the Effects of Geospatial Technology     

Sandra Metoyer  Robert Bednarz 《The Journal of geography》2017,116(1):20-33

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