Garzanti E.,University of Milan Bicocca |
Ando S.,University of Milan Bicocca |
Censi P.,University of Palermo |
Vignola P.,CNR Institute for the Dynamics of Environmental Processes
Earth and Planetary Science Letters | Year: 2011
Sediments carried in suspension represent a fundamental part of fluvial transport. Nonetheless, largely because of technical problems, they have been hitherto widely neglected in provenance studies. In order to determine with maximum possible precision the mineralogy of suspended load collected in vertical profiles from water surface to channel bottom of Rivers Ganga and Brahmaputra, we combined Raman spectroscopy with traditional heavy-mineral and X-ray diffraction analyses, carried out separately on low-density and dense fractions of all significant size classes in each sample (multiple-window approach). Suspended load resulted to be a ternary mixture of dominant silt enriched in phyllosilicates, subordinate clay largely derived from weathered floodplains, and sand mainly produced by physical erosion and mechanical grinding during transport in Himalayan streams. Sediment concentration and grain size increase steadily with water depth. Whereas absolute concentration of clay associated with Fe-oxyhydroxides and organic matter is almost depth-invariant, regular mineralogical and consequently chemical changes from shallow to deep load result from marked increase of faster-settling, coarser, denser, or more spherical grains toward the bed. Such steady intersample compositional variability can be modeled as a mixture of clay, silt and sand modes with distinct mineralogical and chemical composition. With classical formulas describing sediment transport by turbulent diffusion, absolute and relative concentrations can be predicted at any depth for each textural mode and each detrital component. Based on assumptions on average chemistry of detrital minerals and empirical formulas to calculate their settling velocities, the suspension-sorting model successfully reproduces mineralogy and chemistry of suspended load at different depths. Principal outputs include assessment of contributions by each detrital mineral to the chemical budget, and calibration of dense minerals too rare to be precisely estimated by optical or Raman analysis but crucial in both detrital-geochronology and settling-equivalence studies. Hydrodynamic conditions during monsoonal discharge could also be evaluated. Understanding compositional variability of suspended load is a fundamental pre-requisite to correctly interpret mineralogical and geochemical data in provenance analysis of modern and ancient sedimentary deposits, to accurately assess weathering processes, sediment fluxes and erosion patterns, and to unambiguously evaluate the effects of anthropogenic modifications on the natural environment. © 2010 Elsevier B.V.
Sulpizio R.,CNR Institute for the Dynamics of Environmental Processes |
Sarocchi D.,Institute Geologia
Journal of Volcanology and Geothermal Research | Year: 2014
Pyroclastic density currents (PDCs) are mixtures of two components, namely solid particles and fluid (gas) phase. They macroscopically behave as dense, multiphase gravity currents (flowing pyroclastic mixtures of particles and gas) immersed in a less dense, almost isotropic fluid (the atmosphere). As for other natural phenomena, their study needs a multidisciplinary approach consisting of direct observations, analysis of the associated deposits, replication through laboratory experiments, and numerical simulations. This review deals with the description of the current state of the art of PDC physics, and combines analysis of data from various methodologies. All of the above-mentioned approaches have provided significant contributions to advancing the state of the art; in particular, laboratory experiments and numerical simulations deserve a special mention here for their tumultuous growth in recent years.A paragraph of the review is dedicated to the puzzling behaviour of large-scale ignimbrites, which are (fortunately) too rare to be directly observed; they cannot be easily reproduced through laboratory experiments, or investigated by means of numerical simulations.The final part is dedicated to a summary of the whole discussion, and to a comment on some perspectives for future developments of PDC studies. © 2014 .
Prograde lawsonite during the flow of continental crust in the Alpine subduction: Strain vs. metamorphism partitioning, a field-analysis approach to infer tectonometamorphic evolutions (Sesia-Lanzo Zone, Western Italian Alps)
Zucali M.,University of Milan |
Spalla M.I.,University of Milan |
Spalla M.I.,CNR Institute for the Dynamics of Environmental Processes
Journal of Structural Geology | Year: 2011
Detailed mapping of superposed fabrics and their mineral support allows for reconstruction of the tectonometamorphic evolution of the Ivozio Complex, within the inner portion of the Sesia-Lanzo Zone (Western Italian Alps). The resulting evolution is characterized by a multi-stage structural and metamorphic re-equilibration during Alpine subduction, starting from the pre-Alpine igneous association (Amp0 + Cpx0). The prograde associations begin with S1a marked by AmpI + ZoI which pre-date the growth of GrtI (S1b); successive increase in pressure stabilizes a second generation of Amp + Grt (S1c AmpII + ZoI + GrtII). The growth of prograde lawsonite and omphacite occur during S1d (OmpI + Lws + GrtII + AmpII) within lawsonite-bearing eclogites, while S1e is associated with the break-down of lawsonite, producing the association OmpI + Ky + ZoII + GrtII + AmpII (lws-bearing eclogites); S1d-e stages are associated with AmpII + ZoI + GrtII + OmpI in eclogites. The second generation of penetrative foliation (S2), describing the retrograde evolution, is divided into S2a (AmpII + GrtII + Pg + ZoII) and S2b (Chl + AmpIII + Pg + Ab). The comparison between the reconstructed evolution of the Ivozio Complex and P-T paths inferred in the Southern Sesia-Lanzo Zone suggests a non-uniqueness of the Sesia-Lanzo Zone continental crust, during the Alpine subduction. © 2010 Elsevier Ltd.
Rebay G.,University of Pavia |
Spalla M.I.,CNR Institute for the Dynamics of Environmental Processes |
Zanoni D.,University of Pavia
Journal of Metamorphic Geology | Year: 2012
Petrological investigations supported by multi-scale structural analysis of eclogitized serpentinite in the Zermatt-Saas Zone of the Western Alps allows for the determination of mineral assemblages related to successive fabrics, upon which the P-T-d-t path of these hydrated mantle rocks can be inferred. Serpentinites of the upper Valtournanche, with lenses and dykes of metagabbro and meta-rodingite, display an Alpine polyphase metamorphic evolution from eclogite to epidote-amphibolite facies conditions associated with three successive foliations having different parageneses in these rocks. Serpentinite mainly consists of serpentine with minor magnetite; however, where S1 and S2 foliations are pervasive, metamorphic olivine, together with Ti-clinohumite and clinopyroxene, are also found. The mineral assemblage associated with D1 includes serpentine1, clinopyroxene1, opaque minerals, titanite±olivine1, Ti-clinohumite1 and ilmenite; the D2 assemblage is the same (±chlorite) but minerals have different compositions. The assemblage associated with D3 comprises serpentine3, opaque minerals, ±chlorite3, ilmenite and amphibole3. Ti-clinohumite is associated with veins that are older than D2 and pre-date D3. Veins that post-date D3 are characterized by amphibole + chlorite or by serpentine. P-T conditions for S2 parageneses evaluated using two pseudosections for different bulk compositions suggest that these rocks experienced pressures >2.5±0.3GPa at temperatures slightly higher than 600°C. The late epidote-amphibolite facies re-equilibration associated with D3 and D4 developed during late syn-exhumation deformation related to folding and testifies to a small temperature decrease. These results, which were integrated in the regional framework, suggest that different portions of the Zermatt-Saas Zone registered different P-T peak conditions and underwent different exhumation paths. In addition, the inferred P-T-d-t path suggests that the Valtournanche serpentinites re-equilibrated close to the UHP conditions registered by the Cignana meta-cherts. These results imply that tectonic slices exhumed after UHP metamorphism might be wider than previously reported or that small-size UHP units, tectonically sampled during the Alpine convergence, are more abundant than those that have been detected to date. © 2012 Blackwell Publishing Ltd.
Branca S.,Italian National Institute of Geophysics and Volcanology |
Coltelli M.,Italian National Institute of Geophysics and Volcanology |
Groppelli G.,CNR Institute for the Dynamics of Environmental Processes
Italian Journal of Geosciences | Year: 2011
An updated geological evolution model is presented for the composite basaltic stratovolcano of Mount Etna. It was developed on the basis of the stratigraphic setting proposed in the new geological map that was constrained by 40Ar/ 39Ar age determinations. Unconformitybounded stratigraphy allows highlighting four main evolutionary phases of eruptive activity in the Etna region. The Basal Tholeiitic Supersynthem corresponds to a period, from about 500 to 330 ka, of scattered fissure-type eruptions occurring initially in the foredeep basin and then in a subaerial environment. From about 220 ka, an increase in the eruptive activity built a lava-shield during the Timpe Supersynthem. The central-type activity occurred at least 110 ka ago through the Valle del Bove Supersynthem. The earliest volcanic centres recognized are Tarderia, Rocche and Trifoglietto and later Monte Cerasa, Giannicola, Salifizio and Cuvigghiuni. During the Stratovolcano Supersynthem, from about 57 ka ago, the intense eruptive activity of Ellittico volcano formed a roughly 3600 m-high stratocone that expanded laterally, filling the Alcantara and Simeto paleovalleys. Finally, effusive activity of the last 15 ka built the Mongibello volcano. Its eruptive activity is mainly concentrated in three weakness zones in which the recurrent magma intrusion generates flank eruptions down to low altitude. The four main evolutionary phases may furnish constraints to future models on the origin of Etna volcano and help unravel the geodynamic puzzle of eastern Sicily. © Società Geologica Italiana, Roma 2011.
Roda M.,University Utrecht |
Spalla M.I.,CNR Institute for the Dynamics of Environmental Processes |
Marotta A.M.,CNR Institute for the Dynamics of Environmental Processes
Journal of Metamorphic Geology | Year: 2012
A numerical modelling approach is used to validate the physical and geological reliability of the ablative subduction mechanism during Alpine convergence in order to interpret the tectonic and metamorphic evolution of an inner portion of the Alpine belt: the Austroalpine Domain. The model predictions and the natural data for the Austroalpine of the Western Alps agree very well in terms of P-T peak conditions, relative chronology of peak and exhumation events, P-T-t paths, thermal gradients and the tectonic evolution of the continental rocks. These findings suggest that a pre-collisional evolution of this domain, with the burial of the continental rocks (induced by ablative subduction of the overriding Adria plate) and their exhumation (driven by an upwelling flow generated in a hydrated mantle wedge) could be a valid mechanism that reproduces the actual tectono-metamorphic configuration of this part of the Alps. There is less agreement between the model predictions and the natural data for the Austroalpine of the Central-Eastern Alps. Based on the natural data available in the literature, a critical discussion of the other proposed mechanisms is presented, and additional geological factors that should be considered within the numerical model are suggested to improve the fitting to the numerical results; these factors include variations in the continental and/or oceanic thickness, variation of the subduction rate and/or slab dip, the initial thermal state of the passive margin, the occurrence of continental collision and an oblique convergence. © 2012 Blackwell Publishing Ltd.
Gatta G.D.,University of Milan |
Gatta G.D.,CNR Institute for the Dynamics of Environmental Processes
Microporous and Mesoporous Materials | Year: 2010
This is a comparative study on the flexibility of tetrahedral open-framework structures (i.e. zeolites and zeolites-like materials) at high-pressure (HP). Analysis of the main P-induced deformation mechanisms that force the inter-tetrahedral (T-O-T) angles toward values drastically smaller than 120°, is carried out on the basis of recent data obtained by in situ HP-diffraction experiments and theoretical calculations. The role played by the nature of the framework and extra-framework cations in isotypic structures on the framework flexibility is discussed. A comparative analysis between the structural evolution of some structures that show anomalously small T-O-T angles at high-pressure and their structural configuration at high-temperature is carried out. Tetrahedral framework silicates react in response of the applied pressure in different ways, here discussed, toward structural configurations energetically costly, with T-O-T angle ≤120°, but maintaining their topological symmetry up to the onset of the amorphization processes. Reconstructive phase-transitions, with a change in topology, do not occur in this class of materials. © 2009 Elsevier Inc. All rights reserved.
Bordogna G.,CNR Institute for the Dynamics of Environmental Processes |
Ghisalberti G.,Polytechnic of Milan |
Psaila G.,University of Bergamo
Fuzzy Sets and Systems | Year: 2012
Geographic information retrieval (GIR) is nowadays a hot research issue that involves the management of uncertainty and imprecision and the modeling of user preferences and context. Indexing the geographic content of documents implies dealing with the ambiguity, synonymy and homonymy of geographic names in texts. On the other side, the evaluation of queries specifying both content based conditions and spatial conditions on documents' contents requires representing the vagueness and context dependency of spatial conditions and the personal user's preferences. The spatial condition can be specified linguistically in the query through vague terms such as "close to the North East of Milan", whose semantic depends on the user's context and perception of distance. Further, users may want to express queries in which the content condition and the spatial condition have a distinct preference and are combined with a distinct semantics. In this paper, we propose a geographic information retrieval model and a system implementing it that represents both the uncertainty in indexing the geographic documents' content and the user's context and preferences in evaluating flexible spatial queries. It extracts the geographic content from documents' text by applying heuristic knowledge coded by bipolar rules which evaluate positive hints and negative hints for the recognition of geographic names in text. Thus, it represents the geographic content of documents by fuzzy footprints, i.e., distinct locations on the earth associated with the text with a distinct degree of significance. Finally, the system allows evaluating two types of queries flexibly combining the content based condition with the spatial condition. The spatial condition is interpreted as the soft constraint "close" on the user's perceived distance between the documents' footprint and query's footprint. For each retrieved document, two relevance scores are computed with respect to the two query conditions that are flexibly combined to generate an overall ranked list of documents. The user can choose the semantic for the combination that can be either an asymmetric "and possibly" aggregation between the mandatory content condition and the optional spatial condition, or a compensative "average" aggregation, defined as a linear combination of the two conditions; further, a relative preference between the conditions can be specified to achieve personalization and effectiveness. A prototypal geographic information retrieval system, named Geo-Finder, based on this model is described, and its evaluations are discussed. © 2011 Elsevier B.V. All rights reserved.
Pini R.,CNR Institute for the Dynamics of Environmental Processes |
Ravazzi C.,CNR Institute for the Dynamics of Environmental Processes |
Reimer P.J.,Queen's University of Belfast
Quaternary Science Reviews | Year: 2010
The sediments of Lake Fimon, N-Italy, contain the first continuous archive of the Late Pleistocene environmental and climate history of the southern Alpine foreland. We present here the detailed palynological record of the interval between Termination II and the Last Glacial Maximum. The age-depth model is obtained by radiocarbon dating in the uppermost part of the record. Downward, we correlated major forest expansion and contraction events to isotopic events in the Greenland Ice core records, via a stepping-stone approach involving intermediate correlation to isotopic events dated by TIMS U/Th in Alpine and Apennine stalagmites, and to pollen records from marine cores of the Iberian margin. Modelled ages obtained by Bayesian analysis of deposition are thoroughly consistent with actual ages, with maximum offset of ±1700 years. Sharp expansion of broad-leaved temperate forest and of sudden water table rise mark the onset of the Last Interglacial after a treeless steppe phase at the end of penultimate glaciation. This event is actually a two-step process which matches the two-step rise observed in the isotopic record of the nearby Antro del Corchia stalagmite, respectively dated to 132.5 ± 2.5 and 129 ± 1.5. ka. At the interglacial decline mixed oak forests were replaced by oceanic mixed forests, the latter persisting further for 7. ka till the end of the Eemian succession. Warm-temperate woody species are still abundant at the Eemian end, corroborating a steep gradient between central Europe and the Alpine divide at the inception of the last glacial. After a stadial phase marked by moderate forest decline, a new expansion of warm broad-leaved forests, interrupted by minor events and followed by mixed oceanic forests, can be identified with the north-alpine Saint Germain I. The spread of beech during the oceanic phase is a valuable circumalpine marker. The subsequent stadial-interstadial succession, lacking the telocratic oceanic phase, is also consistent with the evidence at the north-alpine foreland. The Middle Würmian (full glacial) is marked by persistence of mixed forests dominated by conifers but with significant lime and other broad-leaved species. A major Arboreal Pollen decrease is observed at modelled age of 38.7 ± 0.5. ka (larch expansion and last occurrence of lime), which has been related to Heinrich Event 4. The evidence of afforestation persisting south of the Alps throughout most of MIS 3 contrasts with a boreal and continental landscape known for the northern alpine foreland, pointing to a sharp rainfall boundary at the Alpine divide and to southern air circulation. This is in agreement with the Alpine paleoglaciological record and is supported by the pressure and rainfall patterns designed by mesoscale paleoclimate simulations. Strenghtening the continental high pressure during the full glacial triggered cyclogenesis in the middle latitude eastern Europe and orographic rainfall in the eastern Alps and the Balkanic mountains, thus allowing forests development at current sea-level altitudes. © 2010 Elsevier Ltd.
Blahut J.,University of Milan Bicocca |
Blahut J.,CNR Institute for the Dynamics of Environmental Processes |
van Westen C.J.,International Institute for Geo Information Science and Earth Observation |
Sterlacchini S.,CNR Institute for the Dynamics of Environmental Processes
Geomorphology | Year: 2010
For the generation of susceptibility maps on medium scales (1:25,000 to 1:50,000) using statistical techniques, a reliable landslide inventory is needed, together with factor maps used as inputs. This paper compares landslide susceptibility maps obtained with the same methodology but using different landslide inventories: the official Italian landslide inventory GeoIFFI for the Lombardy Region and a recently mapped inventory (DF2001). The analysis included four main steps: (i) preparation of debris flow inventories using both random and spatial partitions and factor maps as explanatory variables; (ii) calculation of accountability and reliability indices for a preliminary susceptibility analysis and selection of an appropriate combination of the factor maps for detailed analysis; (iii) evaluation and validation of the obtained susceptibility maps; and (iv) comparison of the results and selection of the final map. The study area is located in the Valtellina Valley in the Central Italian Alps. The analysis identified highly susceptible areas of shallow landslides that may generate debris flows. It was demonstrated that more precisely delimited source areas for landslide-induced debris flows produce better susceptibility maps. However, the improvement of these maps was relatively limited when the inventories were randomly subdivided. Higher improvements were observed after the subdivision of the inventories into three geographical parts with different geomorphological characteristics. Although the modelling showed very similar results if evaluation is made using standard techniques, the spatial pattern of the susceptibility maps was highly variable and dependent on the combination of the factor maps used. © 2010 Elsevier B.V.