Pre-alpine and alpine evolution of the South-alpine basement of the Orobic Alps     

Annibale Mottana  Massimo Nicoletti  Claudio Petrucciani  Giuseppe Liborio  Luisa De Capitani  Rosangela Bocchio 《International Journal of Earth Sciences》1985,74(2):353-366

New K-Ar age determinations on the gneisses and schists of the south-Alpine basement of the Orobic Alps and their separated minerals have been carried out to supplement and support the previous study ofBocchio et al. (1981).The cooling ages of biotites and muscovites range from 218 to 331 my and from 170 to 330 my respectively, according to a bimodal distribution with modes at 222 and 298 my for biotite, 182 and 322 my for muscovite. The whole rock ages spread from 43 to 402 my with no significant cluster. Only a few samples give statistically significant internal isochrones, and these suggest two periods of equilibration, at 226–245 and 312–368 my.These age determinations support the conclusion drawn from regional petrologic studies (Bocchio et al., 1980;Crespi et al., 1980), that the south-Alpine basement underwent two main phases of metamorphism, now preferentially preserved in different areas: an old, Hercynian phase under a regime of intermediate pressure (staur-ky type), and a young, post-Hercynian phase under a regime of low pressure (staur-sill type) reactivated by the cover of the thick sedimentary pile on top of the basement. Furthermore, radiometric ages also point out the widespread but irregularly distributed occurence of an alpine overprint under the conditions of a very low metamorphic regime, that is documented by the growth of post-kinematic stilpnomelane in rocks of suitable bulk composition (Crespi et al., 1981, 1982), as well as by fine-grained phengite.

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Zusammenfassung Neue Kali-Argon-Datierungen von Gneisen und Schiefern und ihrer abgetrennten Minerale des südalpinen Grundgebirges wurden in Ergänzung der Studie vonBocchio et al., 1981 durchgeführt. Die Abkühlungsalter der Biotite und Muskovite reichen von 218 bis 331 ma und von 170 bis 330 ma entsprechend einer bimodalen Entwicklung mit Modalwerten bei 222 und 298 ma für Biotit und 182 und 322 ma für Muskovit. Die Gesamtgesteinsalter reichen von 43–402 ma ohne signifikante Häufung. Nur wenige Proben geben eine statistisch signifikante Isochrone, woraus sich zwei Gleichgewichtsperioden zwischen 226–245 ma und 312–368 ma ablesen lassen.Diese Altersbestimmungen unterstützen die Schlußfolgerungen, die aus regional-petrologischen Studien (Bocchio et al., 1980;Crespi et al., 1980) gezogen wurden und die Aussagen, daß das südalpine Grundgebirge zwei Hauptphasen der Metamorphose mitgemacht hat, die heute in verschiedenen Gebieten erhalten sind: eine ältere herzynische Phase unter mittleren Druckbedingungen (Staur-Ky) und eine jüngere postherzynische Phase unter niedrigem Druck (Staur-Sil), die unter der Überdeckung einer mächtigen Sedimentserie über dem Grundgebirge reaktiviert wurde. Darüber hinaus deuten die radiometrischen Alter auf einen weit verteilten, aber unregelmäßig auftretenden alpinen Einfluß hin, der unter den Bedingungen einer sehr niedrigen Metamorphose aufgeprägt wurde. Dies wird dokumentiert durch das Wachstum postkinematischer Stilpnomelane in Gesteinen mit einer entsprechenden Zusammensetzung (Crespi et al., 1981, 1982) sowie von feinkörnigen Phenigiten.

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Résumé De nouvelles déterminations d'âge par la méthode K-Ar ont été effectuées sur les gneiss et les schistes du socle sudalpin des Alpes Orobiques, ainsi que sur certains de leurs minéraux, en complément aux travaux antérieurs deBocchio et al. (1981).L'âge du refroidissement des biotites s'étend de 210 à 331 Ma et celui des muscovites de 170 à 330 Ma, selon une distribution bimodale: modes à 222 à 298 Ma pour la biotite et à 183 et 322 Ma pour la muscovite. Les âges mesurés sur roche totale vont de 43 à 402 Ma sans concentration significative autour d'une valeur. Un petit nombre d'échantillons seulement fournissent des isochrones statistiquement significatives; elles suggèrent deux périodes de mise en équilibre, à 226–245 Ma et à 312–368 Ma.Ces déterminations d'âge appuient les conclusions d'études pétrologiques régionales antérieures (Bocchio et al. 1980;Crespi et al. 1980), à savoir que le socle sud-alpin a subi deux phases principales de métamorphisme, conservées aujourd'hui dans de régions différentes: une phase ancienne, hercynienne, de pression intermédiaire (type staurotide-disthène) et une phase jeune, post-hercynienne, de basse pression (type staurotide-sillimanite) réactivée sous la couverture sédimentaire épaisse reposant sur le socle. De plus, les âges radiométriques mettent en évidence une reprise alpine, d'extension régionale mais irrégulièrement distribuée, dans les conditions d'un métamorphisme de très faible degré. Cette reprise s'exprime par la croissance de stilpnomélane post-cinématique dans les roches de composition appropriée (Crespi et al. 1981, 1982) ainsi que par le développement de phengite finement grenue.

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. (1981), K/Ar-. 218 331 170 330 , 222 298 182 322 . 43–402 - . , 226–245 312–368 . . (1980) . (1980) , - : , , (Staur-Ky) , , (StaurSil) , . , , . ( ., 1981, 1982), .

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Paper presented at the Second E.U.G. Meeting at Strasbourg, April 23–26, 1983  相似文献   

Latest Triassic marine Sr isotopic variations,possible causes and implications     

Sara Callegaro  Manuel Rigo  Massimo Chiaradia  Andrea Marzoli 《地学学报》2012,24(2):130-135

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Riparian vegetation as indicator of channel adjustments and environmental conditions: the case of the Panaro River (Northern Italy)     

Bruna Gumiero  Massimo Rinaldi  Barbara Belletti  Daniele Lenzi  Giovanna Puppi 《Aquatic Sciences - Research Across Boundaries》2015,77(4):563-582

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Impact of Heterogeneity on Oxygen Transfer in a Fluctuating Capillary Fringe          下载免费PDF全文

Christina M. Haberer  Massimo Rolle  Olaf A. Cirpka  Peter Grathwohl 《Ground water》2015,53(1):57-70

We performed quasi‐two‐dimensional flow through laboratory experiments to study the effect of a coarse‐material inclusion, located in the proximity of the water table, on flow and oxygen transfer in the capillary fringe. The experiments investigate different phases of mass transfer from the unsaturated zone to anoxic groundwater under both steady‐state and transient flow conditions, the latter obtained by fluctuating the water table. Monitoring of flow and transport in the different experimental phases was performed by visual inspection of the complex flow field using a dye tracer solution, measurement of oxygen profiles across the capillary fringe, and determination of oxygen fluxes in the effluent of the flow‐through chamber. Our results show significant effects of the coarse‐material inclusion on oxygen transfer during the different phases of the experiments. At steady state, the oxygen flux across the unsaturated/saturated interface was considerably enhanced due to flow focusing in the fully water‐saturated coarse‐material inclusion. During drainage, a zone of higher water saturation formed in the fine material overlying the coarse lens. The entrapped oxygen‐rich aqueous phase contributed to the total amount of oxygen supplied to the system when the water table was raised back to its initial level. In case of imbibition, pronounced air entrapment occurred in the coarse lens, causing oxygen to partition between the aqueous and gaseous phases. The oxygen mass supplied to the anoxic groundwater following the imbibition event was found to be remarkably higher (approximately seven times) in the heterogeneous system compared with a similar experiment performed in a homogeneous porous medium.  相似文献   

A self‐limiting bank erosion mechanism? inferring temporal variations in bank form and skin drag from high resolution topographic data          下载免费PDF全文

Julian Leyland  Stephen E. Darby  Liliana Teruggi  Massimo Rinaldi  Daniele Ostuni 《地球表面变化过程与地形》2015,40(12):1600-1615

Fluvial bank erosion rates are often quantified by assuming that the erosion rate is a function of the excess (above a critical threshold) boundary shear stress applied by the flow. Research has shown that the form roughness induced by natural topographic bank features, such as slumps, spurs and embayments, is the dominant component of the spatially‐averaged total shear stress, meaning that form roughness provides an important control on bank erosion rates. However, measuring the relative components of the total shear stress for a natural system is not straightforward. In this work we use the method of Kean and Smith to partition the form and skin drag components of river bank roughness using a time series (2005–2011) of high‐resolution topographic surveys of an eroding bank of the Cecina River in central Italy. This method approximates the form drag component of the roughness along a longitudinal bank profile as a series of user‐defined Gaussian curves. The extracted metrics are used in conjunction with an estimate of the outer region flow velocity to partition the form and skin drag components of the total boundary shear stress according to the Kean and Smith analytical solution. The relative magnitude of the form and skin shear stress at each survey date is analysed alongside DEMs of difference to reveal that intense episodes of erosion are followed by periods of quiescence. We show that this is due to the protection offered by increased form drag roughness following erosion. We conceptualise the dynamic feedbacks that exist between river discharge, bank erosion processes and bank form roughness, into a simple model of the self‐limiting nature of river bank erosion. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

An integrated approach for investigating geomorphic response to extreme events: methodological framework and application to the October 2011 flood in the Magra River catchment,Italy          下载免费PDF全文

Massimo Rinaldi  William Amponsah  Marco Benvenuti  Marco Borga  Francesco Comiti  Ana Lucía  Lorenzo Marchi  Laura Nardi  Margherita Righini  Nicola Surian 《地球表面变化过程与地形》2016,41(6):835-846

A high‐magnitude flash flood, which took place on 25 October 2011 in the Magra River catchment (1717 km²), central‐northern Italy, is used to illustrate some aspects of the geomorphic response to the flood. An overall methodological framework is described for using interlinked observations and analyses of the geomorphic impacts of an extreme event. The following methods and analyses were carried out: (i) hydrological and hydraulic analysis of the event; (ii) sediment delivery by event landslide mapping; (iii) identification and estimation of wood recruitment, deposition, and budgeting; (iv) interpretation of morphological processes by analysing fluvial deposits; (v) remote sensing and geographic information system (GIS) analysis of channel width changes. In response to the high‐magnitude hydrological event, a large number of landslides occurred, consisting of earth flows, soil slips, and translational slides, and a large quantity of wood was recruited, in most part deriving from floodplain erosion caused by bank retreat and channel widening. The most important impact of the flood event within the valley floor was an impressive widening of the overall channel bed and the reactivation of wide portions of the pre‐event floodplain. Along the investigated (unconfined or partly confined) streams (total investigated length of 93.5 km), the channel width after the flood was up to about 20 times the channel width before the event. The study has shown that a synergic use of different methods and types of evidence provides fundamental information for characterizing and understanding the geomorphic effects of intense flood events. The prediction of geomorphic response to a flood event is still challenging and many limitations exist; however a robust geomorphological analysis can contribute to the identification of the most critical reaches. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Application of the parabolic bay shape equation to sand and gravel beaches on Mediterranean coasts     

Chiara F. Schiaffino  Massimo BrignoneMarco Ferrari 《Coastal Engineering》2012,59(1):57-63

The equation most commonly used to describe the bay planform was proposed by Hsu and Evans (1989) and it was obtained through empirical analysis of sand beach planforms.In the last decade interest in gravel sediments increased owing to their greater stability on beaches, compared with sand sediments. Due to the differences between the morphodynamics of sand and gravel beaches, which is strictly influenced by their different hydraulic characteristics, it was necessary to create a predictive instrument for this beach type as well.Therefore, in this study the standard Hsu and Evans equation (1989) was modified in order to make it applicable not only to sand beaches but also to gravel beaches. The shoreline was computed according to a parabolic model in polar coordinates whose coefficients are considered linearly dependent on the wave direction and related to the beach type. The estimation of the free parameters of the model was performed according to a statistical analysis of a shorelines data set of Mediterranean sand and gravel embayed beaches.  相似文献   

Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)     

Luigina Vezzoli  Massimo Matteini  Natalia Hauser  Ricardo Omarini  Roberto Mazzuoli  Valerio Acocella 《Bulletin of Volcanology》2009,71(5):509-532

The Middle-Upper Miocene Las Burras–Almagro-El Toro (BAT) igneous complex within the Eastern Cordillera of the central Andes (∼24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma) comprises facies related to: (i) andesite extruded in a subaqueous setting and generating lobe-hyaloclastite lava; and (ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water, comprising fluidal lava lobes, hyaloclastite, and juvenile clasts with glassy rims. The Lampazar member (7.8 Ma) is represented by a syn-volcanic andesite intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. The andesite intrusion is finger-shaped and grades into intrusive pillows. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment ≥50 m from the parent intrusion. The Almagro A member (7.2 Ma) shows evidence of mingling between water-saturated, coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and lobes with sharp contacts and fluidal shapes, and without quench fragmentation and formation of a hyaloclastite envelope. The presence of peperite and magma–water contact facies in the BAT volcanic sequence indicates the possible availability of water in the system between 11–7 Ma and suggests a depositional setting in this part of the foreland basin of the central Andes characterized by an overall topographically low coastal floodplain that included extensive wetlands.  相似文献   

Petrogenesis of Quebrada de la Mina and Altar North porphyries (Cordillera of San Juan,Argentina): Crustal assimilation and metallogenic implications     

Laura Maydagán  Marta Franchini  Massimo Chiaradia  Verónica Bouhier  Noelia Di Giuseppe  Roger Rey  Luis Dimieri 《地学前缘(英文版)》2017,8(5):1135-1159

We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO₂ = NNO +1.1 to +1.6) and high fH₂O conditions in their magmas. Zones and rims enriched in anorthite (An_37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (⁸⁷Sr/⁸⁶Sr_(t) = 0.70450–0.70466, ε_Nd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (²⁰⁷Pb/²⁰⁴Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (²⁰⁷Pb/²⁰⁴Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10^?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.  相似文献   

Extraction and accuracy assessment of high-resolution DEM and derived orthoimages from ALOS-PRISM data over Sahel-Doukkala (Morocco)   总被引：1，自引：1，他引：0  

Adnane Habib  Nadia Akdim  Fatima-ezzahra El Ghandour  Kamal Labbassi  Kourosh Khoshelham  Massimo Menenti 《Earth Science Informatics》2017,10(2):197-217

In Sahel-Doukkala, which is characterized by lands of a relatively low relief, global DEMs and DEMs generated from digitizing topographic maps, have been the primary source of several multidisciplinary researches. Although these products present a great value of the conducted research, the level of the given accuracy is not sufficient enough for detailed geospatial analysis. These requirements led us to generate a high-resolution DEM as an alternative of available global DEMs or/and DEMs generated from digitizing topographic maps. In this study, we present a workflow to extract high-resolution DEM at 5 m resolution and derived orthoimages from ALOS-PRISM data over Sahel-Doukkala, through photogrammetric techniques, using a variation of GCPs obtained from topographic maps at scale 1:25,000. The accuracy of the generated products is reported according to NSSDA standards. Using ten GCPs, a PRISM-DEM with 3.88 m vertical accuracy and 11.60 m horizontal accuracy, both at 95% confidence level is obtained. This DEM will serve as base dataset for further detailed geospatial analysis and mapping applications in order to identify the relationship between surface parameters and groundwater, and also to assess and understand all factors influencing the development of karst landscapes and consequently subsurface stability in the investigated area.  相似文献