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981.
The interpretation of DSS (deep seismic soundings) profiles in Central and Eastern Alps is recalled in the paper and the models of the lower crust and Moho proposed several years ago are compared to the results of the TRANSALP seismic reflection profile. This evaluation highlights a good agreement as far as the geometry of the deep crustal structure is concerned. Therefore, the reliability of the interpretative models, previously exclusively based on DSS profiles, becomes improved. The deep structure beneath the whole Alpine range is examined reconsidering the map of the Moho boundary and the structural model already proposed for the central-eastern sector. Five main interpretative transects are put side by side, starting from the Western Alps and moving eastwards to the Swiss–Lombardian Central Alps (“European Geotraverse”), to the cross section from southern Bavaria to the Euganei Hills, to the TRANSALP profile, and finally to the easternmost profile available so far (southern Bavaria–Trieste). The comparison outlines lateral variations of the deep crustal structure as well as a sharp contrast between the Adria and the European lower crust and Moho. The transition from the Adria plate to the Dinaric domain remains, up to now, undefined. 相似文献
982.
Structure of the lithosphere beneath the Eastern Alps (southern sector of the TRANSALP transect) 总被引:1,自引:0,他引:1
Alberto Castellarin Rinaldo Nicolich Roberto Fantoni Luigi Cantelli Mattia Sella Luigi Selli 《Tectonophysics》2006,414(1-4):259
The interpretation of the seismic Vibroseis and explosive TRANSALP profiles has examined the upper crustal structures according to the near-surface geological evidences and reconstructions which were extrapolated to depth. Only the southern sector of the TRANSALP transect has been discussed in details, but its relationship with the whole explored chain has been considered as well. The seismic images indicate that pre-collision and deep collision structures of the Alps are not easily recognizable. Conversely, good records of the Neo-Alpine to present architecture were provided by the seismic sections.Two general interpretation models (“Crocodile” and “Extrusion”) have been sketched by the TRANSALP Working Group [2002]. Both illustrate the continental collision producing strong mechanical interaction of the facing European and African margins, as documented by giant lithosphere wedging processes. Arguments consistent with the “Extrusion” model and with the indentation of Adriatic (Southalpine) lithosphere underneath the Tauern Window (TW) are:
- – According to the previous DSS reconstructions, the Bouguer anomalies and the Receiver Functions seismological data, the European Moho descends regularly attaining a zone south of the Periadriatic Lineament (PL). The Moho boundary and its geometry appear to be rather convincing from images of the seismic profile;
- – the Tauern Window intense uplift and exhumation is coherent with the strong compression regime, which acted at depth, thus originating the upward and lateral displacement of the mobile and ductile Penninic masses according to the “Extrusion” model;
- – the indentation of the Penninic mobile masses within the colder and more rigid Adriatic crust cannot be easily sustained. Wedging of the Adriatic stiffened lower crust, under high stresses and into the weaker Penninic domain, can be a more suitable hypothesis. Furthermore, the intrusion of the European Penninic crustal wedge underneath the Dolomites upper crust is not supported by any significant uplifting of the Dolomites. The total average uplift of the Dolomites during the Neogene appears to be 6−7 times smaller than that recognized in the TW. Markedly the northward dip of the PL, reaching a depth of approximately 20 km, is proposed in our interpretation;
- – finally, the Adriatic upper crustal evolution points to the late post-collision change in the tectonic grow-up of the Eastern Alps orogenic chain. The tectonic accretion of the northern frontal zone of the Eastern and Central Alps was interrupted from the Late Miocene (Serravallian–Tortonian) onward, as documented by the Molasse basin evolution. On the contrary, the structural nucleation along the S-vergent tectonic belt of the eastern Southern Alps (Montello–Friuli thrust belt) severely continued during the Messinian and the Plio–Pleistocene. This structural evolution can be considered to be consistent with the deep under-thrusting and wedge indentation of the Adriatic lithosphere underneath the southern side of the Eastern Alps thrust-and-fold belt.
983.
Roberto Torra 《中国地球化学学报》2006,25(3)
This paper is focused on a geologic "regional rift basin system pattern" and its stratigraphical-geochemical relationship. This is mainly based on the littoral shallow marine sedimentary succession paleogeography and deposits. These successions characterize the large extensional intracratonic Chaco rift basin system evolved from the Upper Cretaceous ( Late Campanian-Senonian-Maastrichtian-Early Paleocene) to Quaternary time. The siliciclastic littoral shallow marine successions were deposited from Early Senonian-Maastrichtian to Late Miocene during three main successive littoral shallow marine transgressions of continental extension.These transgressions happened over the wide pediplanized terrains of South America. These lands exist west of the more positive areas, between the Brazilian Shield and the foreland massifs that were settled in the more westernwards areas. Later, these regional foreland massifs were coupled and raised to the Andean Orogen Belt during the last 5 million years.The extensive intracratonic pediplanized low topographic relief areas were the reservoirs of siliciclastic littoral shallow marine succession deposits during the three successive widespread vast continental littoral shallow marine transgressions.The first transgression began at the Latest Campanian-Senonian and/or Early Maastrichtian time. After this episode, the sedimentary depositional systems continued during the Cenozoic until the Latest Miocene. These successions constitute a major allostratigraphic unit.The limit with underlying units is the regional unconformity between the regional volcanic event (Jurassic-Cretacic and interleaved eolianite sandstones) at the base and the undifferentiated Quaternary sediments (called as the Pampeano and Post-Pampeano Formations sensu lato). Based on many facies analyses there had been checked out different levels in the eustatic sea level variations within the allostratigraphic unit.Three major stages of extensional climax were recognized and related to the stages of conspicuous eustatical sea-level variations. They happened during the Latest Senonian-Paleocene, Eocene and Miocene.The first transgression occurred during the Upper Cretaceous-Paleocene although the sedimentary deposits related to this event are scarce, which are only a few meters in thickness. However, the Upper Cretaceous-Paleocene succession is very well recognized in the actual pre-Andean zone in the north-west of Argentina and Bolivia (the Sierras Subandinas and the meridional imbricated fault systems just joint to the actual orogen, I.e. , Quebrada de Humahuaca outcrops).During the Eocene and Middle to Latest Miocene occurred the second and third extensive regional littoral shallow marine transgressions. They are present either in well log registers as in most widespread outcrops on the entire Southamerican continent.The regional analysis led to the deduction of long periods of tectonic quiescence, at least three of them. They may be inferred and synchronously related with eustatic highstand sea level variations that occurred during the Late Paleocene-Early Eocene, Latest Eocene-Early to Mid Oligocene and Middle-to-Late Oligocene-Early Miocene.The structural style is related with major extensional N-S strike faultings (regional tilted and faulting blocks). On the other hand, quite a number of strike-slip faults (mainly of regional characteristic) are present crossing the area. They have a clear influence on the accommodation and transfer zones of the rift basin system. The strike is north-west to south-east on the border of the basin, to the west, in the contact with the Pampean Ridges and the narrow-meridionally-extense Sub-Andean folded trend ( mainly Paleozoic units belonging to the so-called Sierras Subandinas geological province). Also, at the western edge of the studied area, there exist many large shear zones and upthrust faults. The strike-slip regional faults dislocated the Pampean and Sub-Andean blocks due to the interaction of crossing regional tilted and fault blocks.For this reason, an en echelon regional block model is characteristic. Incipient contaminated igneous activities were associated with this cortical weak zones. Domes, needles and necks of volcanic and sub-volcanic origin appear as the landscape of the region.A part of the igneous activity was dated on Latest Pliocene although mainly corresponding to Pleistocene and Holocene. This deduction is obvious because their morphological constitution was never eroded. The volcanic aparatous are morphologically unmodified from their extrusion to present days.All the studied successions seem to resemble a long persisting erosive, transportation and deposition episode. This phenomenon is linked to a large regional (continental) unconformity dated at Late Cretaceous. The entire analyzed sedimentary succession deposits and their siliciclastic facies associations correspond clearly to a "heterolithic facies succession" which is very common within persisting tide-dominated depositional systems (passive margins). In fact, this is what happened during Cenozoic times (Torra,1998b, 2001a). The heterolithic Miocene facies deposits constitute one of the best continental exposed examples.Paleogeographical evidence showed that the Paranense and Amazonic Sea transgressions had been a littoral shallow marine connection during long time from Middle to Late Miocene. During the Late Cretaceous and Eocene periods marine connections were also active in the region. This fact is strongly supported by the tectonic and geomorphological framework of the proto-Southamerican continent, fossil remains and similar sedimentary deposits.The geochemical results showed an outstanding similarity among the three sandy-muddy successions herein studied. Both major and trace elements always show the same geochemical patterns. Specially mentioned are the elements gallium, cesium, chromium, barium, vanadium, thorium, zirconium, rubidium and strontium because they present very constant values through all successions.The Paranense and Amazonic epicontinental seas had been connected to the Pacific Ocean during the three marine episodes. The connections were formed by narrow inter-mountain valleys, present in the preAndean foreland massifs. These events occurred prior to the main orogenesis elevation of the Andean orogen belt in the last 5 to 1 Ma ( Pliocene-Latest Pleistocene).This paper shows, for the first time, a synthetic stratigraphical-geochemical "regional model" for the carries many unexamined-unexplored natural resources which need more regional and local studies for their evaluation. This is in spite of the area that has the problem of a significative vegetation coberture and scarce good outcrops. The development of modern techniques of dataacquisition will help to overcome these difficulties. 相似文献
984.
The wide boron isotopic variations occurring in natural waters mainly are derived from the 20‰ fractionation between dissolved boric acid and borate anions, associated with the preferential removal from the system of 11B depleted borate ions by adsorption and/or minerals formation. Typical adsorbants of boron dissolved in groundwater are clay minerals of the aquifer matrix. Boron (and strontium) isotopes were used in investigating two alluvial aquifers in Tuscany, where boron concentration is often above 1 mg L− 1 and may attain 8 mg L− 1. The isotopic results indicate that, in the first case (Cecina River basin), the boron contamination is anthropogenic and derives from past discharge into streams of boron-rich industrial wastes. In the second case (Cornia Plain), the dissolved boron is released by boron-rich clayey sediments of the aquifer matrix and has, therefore, a natural origin. 相似文献
985.
Giorgio Boni Luca Ferraris Francesca Giannoni Giorgio Roth Roberto Rudari 《Advances in water resources》2007
A methodology is proposed for the inference, at the regional and local scales, of flood magnitude and associated probability. Once properly set-up, this methodology is able to provide flood frequencies distributions at gauged and un-gauged river sections pertaining to the same homogeneous region, using information extracted from rainfall observations. A proper flood frequency distribution can be therefore predicted even in un-gauged watersheds, for which no discharge time series is available. 相似文献
986.
The most conspicuous waterbodies in the Pampa region of Argentina are the so-called “lagunas”. A typical Pampean laguna may be described as a relatively large (100+ha), permanent, shallow lake. Here, we report the dynamics of laguna Chascomús, sampled weekly, from April 2001 to June 2003. During the period, the lakes experienced three consecutive floods waves that affected the concentration of major ions and the optical signature of the dissolved organic matter. Despite these hydrological alterations, laguna Chascomús was permanently limited by light. Transparency was to a great extent controlled by the incident photosynthetic available radiation irradiance. We hypothesize that wind contributes to the permanent mixing of the lake, as well as to lessen the sedimentation losses of photoautotrophs. 相似文献
987.
The interaction between surface and subsurface water has a crucial influence on the biochemistry of stream environments. Even though the river discharge and the flow conditions can seldom be considered to be steady, the influence of this unsteadiness on the hyporheic exchange has often been neglected. In this work, a model for the study of hyporheic exchange during unsteady conditions has been developed. The model provides a sound analytical framework for the analysis of the effects of a varying stream discharge on the exchange between a stream and the hyporheic zone. The effects of the unsteadiness on the water exchange flux, the residence time of the solutes in the bed, and the stored mass are quantified. A synthetic example shows the substantial influence of a flood on the hyporheic exchange, and that the application of a steady model can lead to an underestimation of the exchanged mass, even after the flood has ended. 相似文献
988.
Roberto Viotti Cesare D. La Padula Domenico Nanni Agostino Vignato 《Astrophysics and Space Science》2001,276(1):81-88
We present the basic concepts of the two-mirror, three-reflection optical system (2MTRT), and discuss the important benefits of such a system for space projects: wide ( 2°) correctedand unvignetted FOV, without the use of refractive optics for thefield correction, planarity of the focal surface for an optimizedinstallation of wide area detectors, easy telescope adjustement, small volume and little mass.We also report the results of optical tests made with a 30 cm prototype,equipped with a 2k × 2k CCD camera, and give examples of scientific programmes which can be performed from space and in hostile terrestrial sites such as the Antarctic Plateau. 相似文献
989.
An assessment of marine pollution due to metals was made in the Caspian Sea based on coastal sediment collected in Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan. Despite the high carbonate content, the distribution of most metals was largely controlled by terrigenous inputs. Several metals (As, Cr, Ni) exhibited concentrations that exceed sediment quality guidelines. Such metals have a high natural background but anthropogenic activities, notably mining, may further enhance concentrations. This would explain hot spots for Cu and Zn in Azerbaijan and Iran, and Cr at the mouth of the Ural River in Kazakhstan. Contamination by Hg was observed to the south of Baku Bay, Azerbaijan. Some anomalously high concentrations of Ba in the central Caspian are probably from offshore drilling operations, but the elevated U concentrations (up to 11.1 microg g(-1)) may be natural in origin. Several metals (Ag, Cd, Pb) have relatively low levels that pose no environmental concerns. 相似文献
990.
Federico Manzini Raoul Behrend Lorenzo Comolli Virginio Oldani Cristiano B. Cosmovici Roberto Crippa Cesare Guaita Gottfried Schwarz Josep Coloma 《Astrophysics and Space Science》2012,337(2):531-542
Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained
were used to investigate the comet’s inner coma features at resolutions between 350 and 1500 km/pixel. 相似文献