Petrogenetic links between lepidolite-subtype aplite-pegmatite,aplite veins and associated granites at Segura (central Portugal)     

Isabel Margarida Horta Ribeiro Antunes  Ana Margarida Ribeiro Neiva  João Manuel Farinha Ramos  Paulo Bravo Silva  Maria Manuela Vinha Guerreiro Silva  Fernando Corfu 《Chemie der Erde / Geochemistry》2013

In the Segura area, Variscan S-type granites, aplite veins and lepidolite-subtype granitic aplite-pegmatite veins intruded the Cambrian schist-metagraywacke complex. The granites are syn D3. Aplite veins also intruded the granites. Two-mica granite and muscovite granite have similar ages of 311.0 ± 0.5 Ma and 312.9 ± 2.0 Ma but are not genetically related, as indicated by their geochemical characteristics and (⁸⁷Sr/⁸⁶Sr)₃₁₁ values. They correspond to distinct pulses of magma derived by partial melting of heterogeneous metapelitic rocks. Major and trace elements suggest fractionation trends for: (a) muscovite granite and aplite veins; (b) two-mica granite and lepidolite-subtype aplite-pegmatite veins, but with a gap in most of these trends. Least square analysis for major elements, and modeling of trace elements, indicate that the aplite veins were derived from the muscovite granite magma by fractional crystallization of quartz, plagioclase, K-feldspar and ilmenite. This is supported by the similar (⁸⁷Sr/⁸⁶Sr)₃₁₁ and δ¹⁸O values and the behavior of P₂O₅ in K-feldspar and albite. The decrease in (⁸⁷Sr/⁸⁶Sr)₃₁₁ and strong increase (1.6‰) in δ¹⁸O from two-mica granite to lepidolite-subtype aplite-pegmatite veins, and the behaviors of Ca, Mn and F of hydroxylapatite indicate that these veins are not related to the two-mica granite.  相似文献   

Three-dimensional tomographic inversion of the seismic velocity structure of the crust and upper mantle of northwestern Nicaragua     

Domínguez  Jaime  Suárez  Gerardo  Gorbatov  Alexei  Segura  Fabio 《Journal of Seismology》2021,25(6):1427-1439

Journal of Seismology - A three-dimensional tomographic image of the seismic velocity structure in the crust and upper mantle of northwestern Nicaragua was performed using the back-projection...  相似文献   

The evolution of the hydrothermal IOCG system in the Mantoverde district,northern Chile: new evidence from microthermometry and stable isotope geochemistry     

Ana?A.?RiegerEmail author  Robert?Marschik  Manuel?Díaz 《Mineralium Deposita》2012,47(4):359-369

New microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested cooling–mixing model for the iron oxide–copper–gold mineralization in the Mantoverde district. Fluid inclusions show characteristics of a CO₂-bearing aqueous NaCl ± CaCl₂ salt system. The evolution of the Mantoverde hydrothermal system is characterized by (1) an early hypersaline, high to moderate temperature fluid; (2) a moderate saline, moderate temperature fluid; and (3) a low saline, moderate to low temperature fluid. Early magnetite formation took place at median temperatures of 435.0°C, whereas hematite formed at median temperatures of 334.4°C. The main sulfide mineralization texturally post-dates the iron oxides and occurred before late-stage calcite, which developed at a median temperature of 244.8°C. Boiling occurs only locally and is of no relevance for the ore formation. The microthermometric and stable isotope data are supportive for a fluid cooling and mixing model, and suggestive for a predominantly magmatic–hydrothermal fluid component during the iron oxide and main sulfide mineralization. Thereafter, the incursion of a nonmagmatic fluid of ultimately meteoric or seawater gains more importance.  相似文献   

Effect of galvanic distortions on the series and parallel magnetotelluric impedances and comparison with other responses     

Enrique Gómez-Treviño  Francisco Javier Esparza Hernández  José Manuel Romo Jones 《Geofísica Internacional》2013,52(2):135-152

The series and parallel impedances of the magnetotelluric tensor are appraised in relation to their relative immunity to galvanic electric distortions. The distorted responses are modeled using the Groom-Bailey decomposition of the tensor in terms of twist, shear, statics and strike direction. These four parameters and the undistorted responses are normally considered as unknowns, and are obtained from field data through the solution of an inverse problem. In the present work we use the decomposition as a forward model to simulate distorted sounding curves. Starting with undistorted 2-d te and tm responses, the tensor is distorted by assuming arbitrary values of twist, shear, static and strike direction. By default, both series and parallel responses are immune to the strike direction because they are invariants under rotation. In addition, series responses are immune to twist and shear and parallel responses only to twist. The dependence of the latter on shear is in the form of a real factor that shifts downwards the amplitude curves. On the other hand, the effect of statics on both series and parallel responses is more complicated than that on the impedance tensor because it cannot be accounted for by a simple shift of the curves. On the whole, there is a positive balance on the part of the series and parallel impedances over the te and tm responses because some of the distortions are filtered out by the invariants. It is shown that invariance is not sufficient to be immune to any of the distortions. The example chosen is Eggers’ eigenvalues, which are immune only to the by-the-fault strike direction. Invariance is not necessary either, as evidenced by the phase tensor, whose elements depend on strike but are immune to all distortions. The derivations are illustrated using soundings from the synthetic coprod2s1 and field-recorded coprod2 and bc87 data sets.  相似文献   

Cumulative impacts on seabed habitats: An indicator for assessments of good environmental status     

Samuli Korpinen  Manuel MeidingerMaria Laamanen 《Marine pollution bulletin》2013

The European seas are under anthropogenic pressures impacting the state of water quality, benthic habitats and species. The EU Marine Strategy Framework Directive (MSFD) requires the Member States to assess the impacts of pressures and make a programme of measures leading to good environmental status (GES) by 2020. This study presents a method for assessing the quantity and distribution of anthropogenic impacts on benthic habitats in the Baltic Sea by using spatial data of human pressures and benthic habitats. The southern sub-basins were more extensively impacted than the northern sub-basins. Over the entire sea area, deep sea habitats were more impacted than shallower infralittoral and circalittoral habitats. Sand and coarse sediments were the seabed types relatively most impacted in the Baltic Sea scale. A comparison against tentative thresholds for GES showed that in the sub-basin scale only one third of the habitat types was in GES.  相似文献   

Range imaging: a new method for high‐resolution topographic measurements in small‐ and medium‐scale field sites     

Manuel Nitsche  Jens M. Turowski  Alexandre Badoux  Dieter Rickenmann  Tobias K. Kohoutek  Michael Pauli  James W. Kirchner 《地球表面变化过程与地形》2013,38(8):810-825

Topographic measurements are essential for the study of earth surface processes. Three‐dimensional data have been conventionally obtained through terrestrial laser scanning or photogrammetric methods. However, particularly in steep and rough terrain, high‐resolution field measurements remain challenging and often require new creative approaches. In this paper, range imaging is evaluated as an alternative method for obtaining surface data in such complex environments. Range imaging is an emerging time‐of‐flight technology, using phase shift measurements on a multi‐pixel sensor to generate a distance image of a surface. Its suitability for field measurements has yet not been tested. We found ambient light and surface reflectivity to be the main factors affecting error in distance measurements. Low‐reflectivity surfaces and strong illumination contrasts under direct exposure to sunlight lead to noisy distance measurements. However, regardless of lighting conditions, the accuracy of range imaging was markedly improved by averaging multiple images of the same scene. For medium ambient lighting (shade) and a light‐coloured surface the measurement uncertainty was approximately 9 mm. To further test the suitability of range imaging for field applications we measured a reach of a steep mountain stream with a horizontal resolution of approximately 1 cm (in the focal plane of the camera), allowing for the interpolation of a digital elevation model on a 2 cm grid. Comparison with an elevation model obtained from terrestrial laser scanning for the same site revealed that both models show similar degrees of topographic detail. Despite limitations in measurement range and accuracy, particularly at bright ambient lighting, range imaging offers three‐dimensional data in real time and video mode without the need of post‐processing. Therefore, range imaging is a useful complement or alternative to existing methods for high‐resolution measurements in small‐ to medium‐scale field sites. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Uranium-series isotopes transport in surface,vadose and ground waters at San Marcos uranium bearing basin,Chihuahua, Mexico     

Juan Carlos Burillo Montúfar  Manuel Reyes Cortés  Ignacio Alfonso Reyes Cortés  Ma. Socorro Espino Valdez  Octavio Raúl Hinojosa de la Garza  Diana Pamela Nevárez Ronquillo  Eduardo Herrera Peraza  Marusia Rentería Villalobos  María Elena Montero Cabrera 《Applied Geochemistry》2012

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Espacio,Ambiente y los Inicios de la Agricultura Indígena en el Noroeste Argentino: Un Enfoque Arqueológico. María Marta Sampietro Vattuone. 2010. JAS Arqueología Editorial S.L.U., Madrid. 188 pp., ISBN978‐84‐938146‐4‐9, 19€ (paperback).     

Manuel R. Palacios‐Fest 《Geoarchaeology》2012,27(2):183-184

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Interpretation and modelling of regional gravity data of the Aveiro Basin (Northwest Portugal)     

František Mantlík  Manuel J.S. Matias 《Comptes Rendus Geoscience》2010,342(11):823-836

The gravity map of the Aveiro Basin, North West Portugal was produced in 2000/2001 and some limited two dimensional (2D) interpretation was carried out. It is intended in this article to advance the interpretation and modelling of the original Aveiro basin gravity data. Thus, the data were processed and the horizontal gradient, the second vertical derivative and downward continued field computed. The corresponding maps have been processed and a new interpretation of the basin tectonic features has been proposed. This is compared with the previous geological and tectonic information obtained from former surveys and local boreholes. As the next step a more detailed modelling of the Aveiro Basin took place. Bearing the interpretation of the basin tectonic features in mind, several north–south and east–west gravity profiles were established and modelled. The proposed models were presented and discussed. As a result, a comprehensive mass distribution model for the basin was proposed. Finally, comparison was made between the new gravity model and the previously published tectonic features map. This modelling is particularly useful for groundwater protection, exploration and exploitation and also for the dimensioning of drilling operations. Bearing in mind the geomorphology of the basin the gravity method is a very economical tool for the investigation of basin structures.  相似文献   

Phytoliths infer locally dense and heterogeneous paleovegetation at FLK North and surrounding localities during upper Bed I time, Olduvai Gorge, Tanzania     

Doris Barboni  Gail M. Ashley  Manuel Dominguez-Rodrigo  Henry T. Bunn  Audax Z.P. Mabulla  Enrique Baquedano   《Quaternary Research》2010,74(3):344-354

The phytolith content of 10 samples collected immediately under Tuff IF (~ 1.785 Ma) at FLK N and other surrounding localities (~ 2 km²) provides a direct botanical evidence for woody vegetation in the eastern margin of Olduvai Gorge during uppermost Bed I time. Observation and counting of 143 phytolith types (5 to >150 μ) reveal dense but heterogeneous woody cover (~ 40–90%) of unidentified trees and/or shrubs and palms associated to the freshwater springs surrounding FLK N, and more open formation (presumably ~ 25–70% woody cover) in the southeast at localities VEK, HWK W and HWK E. The paleovegetation is best described as groundwater palm forest/woodland or bushland, which current analogue may be found near Lake Manyara in similar hydrogeological context (freshwater springs near saline/alkaline lake). Re-evaluating the published pollen data based on this analogy shows that 70% of the pollen signal at FLK N may be attributed to thicket-woodland, Acacia groundwater woodland, gallery and groundwater forests; while < 30% is attributed to swamp herbage and grasslands. Micro-botanical, isotopic, and taphonomical studies of faunal remains converge on the same conclusion that the area surrounding FLK N, which attracted both carnivores and hominins in the early Pleistocene, was densely wooded during uppermost Bed I time.  相似文献