High-temperature deformation in the Neoproterozoic transpressional Ribeira belt, southeast Brazil     

Marcos Egydio-Silva  Alain Vauchez  Jrme Bascou  Joo Hippertt 《Tectonophysics》2002,352(1-2)

The Neoproterozoic Ribeira belt is subdivided in two domains with contrasting tectonic characteristics. The northern domain is dominated by shallowly dipping foliations and orogen-normal thrust tectonics. The southern domain is characterized by a 1000-km-long network of anastomosing transcurrent shear zones parallel to the belt. This contrast is interpreted as reflecting continent–continent convergence that is almost orthogonal to the margins in the northern domain and significantly oblique in the southern domain. The central, transitional, domain of the Ribeira belt displays the northern termination of the transcurrent shear zone network: the Além Paraíba–Pádua shear zone system (APPSS). The 250-km-long Além Paraíba–Pádua system involves granulites facies mylonites deformed through transpression.A detailed study of the microstructure and lattice preferred orientation (LPO) of the rock-forming minerals in these granulite mylonites allow a better understanding of deformation mechanisms active at high temperature in the crust. Plagioclase crystals are plastically deformed; they display curved twins and cleavages, mechanical twins, and evidence of dynamic recrystallization. LPO of plagioclase is consistent with activation of the (010) [100] and (010) [001] slip systems. LPO of orthopyroxene and amphibole indicates that these minerals have been deformed through dislocation creep with the activation of the (100) [001] slip system. Quartz in granulite mylonite displays evidence of extensive growth through grain boundary migration. The LPO of quartz is therefore the result of a static transformation of an initial, syn-kinematic LPO, and cannot be straightforwardly interpreted in terms of deformation mechanisms active during mylonitization.  相似文献   

The lamprophyres of Afyon stratovolcano,western Anatolia,Turkey: description and genesis     

Erkan Aydar  Hasan Bayhan  Alain Gourgaud 《Comptes Rendus Geoscience》2003,335(3):279-288

The Afyon stratovolcano exhibits lamprophyric rocks, emplaced as hydrovolcanic products, aphanitic lava flows and dyke intrusions, during the final stages of volcanic activity. Most of the Afyon volcanics belong to the silica-saturated alkaline suite, as potassic trachyandesites and trachytes, while the products of the latest activity are lamproitic lamprophyres (jumillite, orendite, verite, fitztroyite) and alkaline lamprophyres (campto-sannaite, sannaite, hyalo-monchiquite, analcime–monchiquite). Afyon lamprophyres exhibit LILE and Zr enrichments, related to mantle metasomatism.  相似文献   

Evidence for an important extensional event during the Latest Proterozoic and Earliest Paleozoic in Morocco     

Alain Piqué 《Comptes Rendus Geoscience》2003,335(12):865-868

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Datation UPb sur zircons des dolérites tholéiitiques pyrénéennes (ophites) à la limite Trias–Jurassique et relations avec les tufs volcaniques dits « infra-liasiques » nord-pyrénéens     

Philippe Rossi  Alain Cocherie  C.Mark Fanning  Yves Ternet 《Comptes Rendus Geoscience》2003,335(15):1071-1080

The tholeiitic doleritic magmatism (ophites) in the Aspe valley of the Pyrenees has been dated on the Triassic–Jurassic boundary (199±2 Ma) by the UPb method on zircon (SHRIMP). Emplacement of the ophites was probably synchronous with that of the earliest ‘Infraliassic’ Ségalas tuffs. The ophites are thus related to the Central Atlantic Magmatic Province (CAMP) whose emplacement linked with the fracturing of Pangea, preceded the opening of the Atlantic Ocean. To cite this article: P. Rossi et al., C. R. Geoscience 335 (2003).  相似文献   

An Urban Surface Exchange Parameterisation for Mesoscale Models   总被引：9，自引：11，他引：9  

Alberto Martilli  Alain Clappier  Mathias W. Rotach 《Boundary-Layer Meteorology》2002,104(2):261-304

A scheme to represent the impact of urban buildings on airflow in mesoscale atmospheric models is presented. In the scheme, the buildings are not explicitly resolved, but their effects on the grid-averaged variables are parameterised. An urban quarter is characterised by a horizontal building size, a street canyon width and a building density as a function of height. The module computes the impact of the horizontal (roof and canyon floor) and vertical (walls) surfaces on the wind speed, temperature and turbulent kinetic energy. The computation of the shortwave and longwave radiation, needed to compute the temperature of the urban surfaces, takes into account the shadowing and radiation trapping effects induced by the urban canyons. The computation of the turbulent length scales in the TKE equation is also modified to take into account the presence of the buildings.The parameterisation is introduced into a mesoscale model and tested in a bidimensional case of a city over flat terrain. The new parameterisation is shown to be able to reproduce the most important features observed in urban areas better than the traditional approach which is based only on the modification of the roughness length, thereby retaining the Monin–Obukhov similarity theory. The new surface exchange parameterisation is furthermore shown to have a strong impact on the dispersion characteristics of air pollutants in urban areas.  相似文献   

Datation Ar/Ar des leucogranites sous couverture du complexe plutonique de Charroux–Civray (Vienne)Ar/Ar dating of leucogranites in the sediment-covered Charroux–Civray complex (Vienne)     

Paul Alexandre  Christian Le Carlier de Veslud  Michel Cuney  Gilles Ruffet  Denis Virlogeux  Alain Cheilletz 《Comptes Rendus Geoscience》2002,334(16)

⁴⁰Ar/³⁹Ar dating on muscovites, performed on leucogranitic intrusions of Charroux–Civray plutonic complex, points out the existence of two peraluminous magmatic activities, whose equivalents are known in the Limousin: (1) garnet-bearing leucogranitic veins at ca. 340 Ma; (2) a specialised leucogranite associated with W ± Sn deposits at ca 310 Ma. However, available ⁴⁰Ar/³⁹Ar data do not allow us to provide further data concerning the age and the geometry at depth of a large leucogranitic body identified by geophysics. To cite this article: P. Alexandre et al., C. R. Geoscience 334 (2002) 1141–1148.  相似文献   

Traceurs sédimentaires des variations du niveau marin et de la mousson sud-est asiatique depuis 450 ka en mer de Chine du Sud     

Sbastien Boulay  Christophe Colin  Alain Trentesaux 《Comptes Rendus Geoscience》2008,340(6):367-378

In order to reconstruct the past variations of the Southeast Asian monsoon intensity and estimate the sedimentary system reactivity to climatic changes in Southeast Asia over the last 450 kyr, mineralogical and sedimentological analyses have been performed on the terrigenous fraction of the South China Sea sediment. End-member modelling coupled with grain size data discriminates three end-members that determine the nature and intensity of the main sediment transport vectors. Low sea-level stands are characterized by sediment reworking that allows transportation of a coarse end-member (20–40 μm) to the deep-basin. By contrast, the other end-members (4–6 μm; 9–13 μm) are controlled by the shoreline position (sea level) and/or by changes of the rivers capacity transport (monsoon). Finally, aeolian input to the northern margin of the South China Sea can be considered negligible compared to the massive fluvial input and the reworking of the sediments.  相似文献   

Badlands as a hot spot of petrogenic contribution to riverine particulate organic carbon to the Gulf of Lion (NW Mediterranean Sea)          下载免费PDF全文

Yoann Copard  Frédérique Eyrolle  Olivier Radakovitch  Alain Poirel  Patrick Raimbault  Stéphanie Gairoard  Christian Di‐Giovanni 《地球表面变化过程与地形》2018,43(12):2495-2509

Determining the riverine carbon fluxes to oceans is critical for an improved understanding of C budgets and biogeochemical cycles (C, O) over a broad range of spatial and time scales. Among the particulate organic carbon (POC) involved in these fluxes, those yielded by sedimentary rocks (petrogenic POC: pPOC) remain somewhat uncertain as to their source on continental surfaces. Based on time series from long‐term observatories, we refine the POC and sediments flux of the Rhône River, one of the major tributaries to the Mediterranean Sea. Radiocarbon measurements on a set of riverine samples and forward modelling were used to (i) determine a modelled pPOC content and pPOC/POC ratio for each sample set, (ii) assess pPOC flux delivered to the NW Mediterranean Sea, and (iii) estimate the badlands contribution from the Durance catchment to both the pPOC and to sediment discharges. The weighted pPOC flux contributes up to 26% of the POC flux (145 Gg yr^‐1) discharged into the Mediterranean Sea, whereas the weighted pPOC content reaches 0.31 wt%. Despite their low contributive surface area (0.2%), badlands provide, respectively, 12, 3.5 and 14% of the pPOC, POC and sediment fluxes to the Rhône River. Consequently, such rocks can be considered as a major source of pPOC and sediments for the NW Mediterranean Sea and potentially for oceans. We suggest that river‐dominated ocean margins, such as the Rhône River, with badlands in their catchment could export a significant amount of pPOC to the oceans. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Quantitative assessment on basin-scale hydrological services of wetlands     

Wu  Yanfeng  Zhang  Guangxin  Rousseau  Alain N. 《中国科学:地球科学(英文版)》2020,63(2):279-291

Despite recognizing the importance of hydrological function of wetlands, basin-scale wetlands services have rarely been investigated. The PHYSITEL/HYDROTEL modelling platform was used to quantitatively assess the impact of wetlands on quickflow and baseflow with paired simulation scenarios in Duobukuli River Basin, namely with wetlands and without wetlands.Simulation results showed that wetlands exert significant impact on basin hydrological processes by decreasing streamflow and altering streamflow regime(magnitude, frequency, duration and time of flow events). The intensity(significant or not) of wetlands influences on quickflow had daily, monthly and annual variation. Wetlands significantly attenuated quickflow during flood season while slightly support daily, monthly and annual baseflow. The average quickflow attenuation and baseflow support of wetlands were 5.89% and 0.83%, respectively. Although the intensity and effect(mitigation or augment) of wetlands on streamflow temporally varied at daily, monthly, seasonal and annual scales, wetland overall mitigated quickflow and augment baseflow in Duobukuli River Basin. Our results could provide insights for future decision-making for rehabilitation and conservation of wetlands as well as integrated basin water resources management.  相似文献   

Post-rift volcanism and high heat-flow at the ocean-continent transition of the eastern Gulf of Aden     

Francis Lucazeau  Sylvie Leroy  Julia Autin  Alain Bonneville  Bruno Goutorbe  Louise Watremez  Elia d'Acremont  Doga Düsünur  Frédérique Rolandone  Philippe Huchon  Nicolas Bellahsen  Patrick Tuchais 《地学学报》2009,21(4):285-292

A high heat-flow (∼900 mW m⁻²) has been observed over a volcanic structure at the Ocean-Continent Transition in the Eastern Gulf of Aden (Oman margin). The anomaly is superposed to a progressive increase of heat-flow across the margin and can be interpreted either by (1) heat refraction, (2) fluid discharge or (3) cooling magma. The two first explanations cannot be ruled out definitely by modelling analysis, but require unlikely thermal conductivity or permeability values. The third one implies that the latest activity of the volcano was about 100 000 years old and therefore continued c. 18 Ma after the break-up of Africa and Arabia. This potential mechanism is consistent with other lines of evidence of post-rifting activity in the Gulf of Aden and could invalidate the conventional assumption that rifted-margins become passive after the break-up of continents.  相似文献