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664.
Volcanic evolution of the island of Tenerife (Canary Islands) in the light of new K-Ar data 总被引:2,自引:0,他引:2
Eumenio Ancochea JosMaría Fuster Elisa Ibarrola Antonio Cendrero Juan Coello Francisco Hernan Jean M. Cantagrel Colette Jamond 《Journal of Volcanology and Geothermal Research》1990,44(3-4)
New age determinations from Tenerife, together with those previously published (93 in all), provide a fairly comprehensive picture of the volcanic evolution of the island. The oldest volcanic series, with ages starting in the late Miocene, are formed mainly by basalts with some trachytes and phonolites which appear in Anaga, Teno and Roque del Conde massifs. In Anaga (NE), three volcanic cycles occurred: one older than 6.5 Ma, a second one between 6.5 and 4.5 Ma, with a possible gap between 5.4 and 4.8 Ma, and a late cycle around 3.6 Ma. In Teno (NW), after some undated units, the activity took place between 6.7 and 4.5 Ma, with two main series separated by a possible pause between 6.2 and 5.6 Ma. In the zone of Roque del Conde (S), the ages are scattered between 11.6 and 3.5 Ma. Between 3.3 and 1.9 Ma, the whole island underwent a period of volcanic quiescence and erosion.The large Cañadas volcano, made up of basalts, trachytes and phonolites, was built essentially between 1.9 and 0.2 Ma. To the NE of this central volcano, linking it with Anaga, is a chain of basaltic emission centers, with a peak of activity around 0.8 Ma. The Cañadas Caldera had several collapse phases, associated with large ignimbrite emissions. There were, at least, an older phase more than 1 Ma old, on the western part of the volcano, and a younger one, less than 0.6 Ma old, in the eastern side. The two large “valleys” of Guimar and la Orotava were formed by large landslides less than 0.8 Ma ago, and probably before 0.6 Ma ago. The present Cañadas caldera was formed by another landslide, less than 0.2 Ma ago. This caldera was later filled by the huge Teide volcano, which has been active even in historic times. During the same period a series of small volcanoes erupted at scattered locations throughout the island.The average eruptive rate in Tenerife was 0.3 km3/ka, with relatively small variations for the different eruptive periods. This island and La Gomera represent a model of growth by discontinuous pulses of volcanic activity, separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years. The neighbouring Gran Canaria, on the other hand, had an initial, rapid “shield-building phase” during which more than 90% of the island was built, and a series of smaller pulses at a much later period.A comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation. Several gaps are present on each island, overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the Canaries. 相似文献
665.
Tectonic and oceanographic control of sedimentary patterns in a small oceanic basin: Dove Basin (Scotia Sea,Antarctica) 下载免费PDF全文
Lara F. Pérez Andrés Maldonado Francisco Javier Hernández‐Molina Emanuele Lodolo Fernando Bohoyo Jesús Galindo‐Zaldívar 《Basin Research》2017,29(Z1):255-276
Dove Basin, a small oceanic domain located within the southern Scotia Sea, evidences a complex tectonic evolution linked to the development of the Scotia Arc. The basin also straddles the junction between the main Southern Ocean water masses: the Antarctic Circumpolar Current (ACC), the Southeast Pacific Deep Water (SPDW) and the Weddell Sea Deep Water (WSDW). Analysis of multichannel seismic reflection profiles, together with swath bathymetry data, reveals the main structure and sediment distribution of the basin, allowing a reconstruction of the tectonostratigraphic evolution of the basin and assessment of the main bottom water flows that influenced its depositional development. Sediment dispersed in the basin was largely influenced by gravity‐driven transport from adjacent continental margins, later modified by deep bottom currents. Sediments derived from melting icebergs and extensive ice sheets also contributed to a fraction of the basin deposits. We identify four stages in the basin evolution which – based on regional age assumptions – took place during the early Miocene, middle Miocene, late Miocene–early Pliocene and late Pliocene–Quaternary. The onsets of the ACC flow in Dove Basin during the early Miocene, the WSDW flow during the middle Miocene, and the SPDW during the late Miocene were influenced by tectonic events that facilitated the opening of new oceanic gateways in the region. The analysis of Dove Basin reveals that tectonics is a primary factor influencing its sedimentary stacking patterns, the structural development of new oceanic gateways permitting the inception of deep‐water flows that have since controlled the sedimentary processes. 相似文献
666.
Nafiseh Salehi Siavashani Joaquin Jimenez-Martinez Guillermo Vaquero Francisco J. Elorza Justin Sheffield Lucila Candela Aleix Serrat-Capdevila 《水文研究》2021,35(6):e14250
Aquifer natural recharge estimations are a prerequisite for understanding hydrologic systems and sustainable water resources management. As meteorological data series collection is difficult in arid and semiarid areas, satellite products have recently become an alternative for water resources studies. A daily groundwater recharge estimation in the NW part of the Lake Chad Basin, using a soil–plant-atmosphere model (VisualBALAN), from ground- and satellite-based meteorological input dataset for non-irrigated and irrigated land and for the 2005–2014 period is presented. Average annual values were 284 mm and 30°C for precipitation and temperature in ground-based gauge stations. For the satellite-model-based Lake Chad Basin Flood and Drought Monitor System platform (CHADFDM), average annual precipitation and temperature were 417 mm and 29°C, respectively. Uncertainties derived from satellite data measurement could account for the rainfall difference. The estimated mean annual aquifer recharge was always higher from satellite- than ground-based data, with differences up to 46% for dryland and 23% in irrigated areas. Recharge response to rainfall events was very variable and results were very sensitive to: wilting point, field capacity and curve number for runoff estimation. Obtained results provide plausible recharge values beyond the uncertainty related to data input and modelling approach. This work prevents on the important deviations in recharge estimation from weighted-ensemble satellite-based data, informing in decision making to both stakeholders and policy makers. 相似文献
667.
RésuménLes Gneiss de Torrox font partie de l’Unité de Sayalonga, appartenant au Complexe Alpujarride des Cordillères Bétiques (Espagne). Ils ont subi une déformation hétérogène par cisaillement simple, caractérisée par le développement de zones mylonitiques à pendage subhorizontal et de linéations d’étirement de direction N070°E. Nous interprétons ces linéations comme la direction de transport dans un contexte de chevauchements ductiles vers l’Kst-Nord-est. Ce sens de mouvement est très répandu dans les Alpujarrides, et permet de mieux comprendre que les nappes Alpujarrides occidentales soient plus métamorphiques que celles des Alpujarrides centrales et orientales. 相似文献
668.
Cecilia Español Belinda Gallardo M. Rosa Pino Ana Martín Francisco A. Comín 《Aquatic Sciences - Research Across Boundaries》2013,75(3):385-397
Ecosystem metabolism is an important measure of wetland restoration efficiency, and serves to indicate if the system is capable of processing energetic resources. Despite its value, ecosystem metabolism has rarely been included in monitoring programs. In this study, we aimed to achieve the following objectives: (i) compare net ecosystem production (NEP) rates of constructed vs. natural wetlands; (ii) identify the highest NEP rate habitats; and (iii) define the main environmental factors regulating NEP in different wetland types. Pelagic and benthic NEP rates and physicochemical features were measured in three natural and five constructed wetlands in the middle Ebro River floodplain (NE Spain). Statistical analyses showed pelagic NEP rates peaked in natural wetlands, which produced up to 187.5 mg C m?3 h?1 compared to lower rates in constructed wetlands (up to 46.2 mg C m?3 h?1). Pelagic NEP responded positively to temperature, total dissolved solids, and nutrients. Benthic NEP rates were 3 to 30-fold greater than pelagic in natural (up to 994.9 mg C m?3 h?1) and constructed (up to 1,551.5 mg C m?3 h?1) wetlands, and were heavily influenced by habitat type, with NEP peaking in areas dominated by submerged vegetation and fine organic sediment. Rapid recovery in aquatic communities (i.e. macroinvertebrate diversity) has been previously reported for the studied wetlands; however, our study suggests a slower recovery of functional processes (i.e. pelagic NEP) in constructed habitats. We therefore strongly advocate the inclusion of ecosystem function in the design and evaluation of restoration projects to optimise long-term wetland ecosystem sustainability. 相似文献
669.
Hana Čížková Jan Květ Francisco A. Comín Raija Laiho Jan Pokorný David Pithart 《Aquatic Sciences - Research Across Boundaries》2013,75(1):3-26
The present area of European wetlands is only a fraction of their area before the start of large-scale human colonization of Europe. Many European wetlands have been exploited and managed for various purposes. Large wetland areas have been drained and reclaimed mainly for agriculture and establishment of human settlements. These threats to European wetlands persist. The main responses of European wetlands to ongoing climate change will vary according to wetland type and geographical location. Sea level rise will probably be the decisive factor affecting coastal wetlands, especially along the Atlantic coast. In the boreal part of Europe, increased temperatures will probably lead to increased annual evapotranspiration and lower organic matter accumulation in soil. The role of vast boreal wetlands as carbon sinks may thus be suppressed. In central and western Europe, the risk of floods may support the political will for ecosystem-unfriendly flood defence measures, which may threaten the hydrology of existing wetlands. Southern Europe will probably suffer most from water shortage, which may strengthen the competition for water resources between agriculture, industry and settlements on the one hand and nature conservancy, including wetland conservation, on the other. 相似文献
670.
In 2007, the Australian federal government introduced a ‘new’ graduate visa scheme, the 485 visa sub-class. This visa facilitates the transition from student to worker for overseas graduates from Australian higher education institutions, with the potential to significantly increase their numbers in the country. At the same time, local governments have introduced various policies designed to attract and retain human capital in rural areas to address the shortfall of highly skilled individuals. This paper redresses the current lack of research into the spatial dynamics of overseas human capital in Australia and their relation to the new visa scheme in combination with shifts in rural development policies. Drawing on survey data of graduates describing the ‘before’ (2005) and ‘after’ (2008) periods of the introduction of the 485 visa scheme, this paper shows that the propensity of overseas graduates to move between Australia's regions has increased substantially. In particular, there have been an increasing proportion of overseas graduates moving to major cities despite rural development policy efforts to attract human capital to rural areas. However, these policy efforts appear to have attracted overseas graduates with particular qualifications (education and health) to work in such locales. 相似文献