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1.
Lea Di Paolo Valerio Olivetti Sveva Corrado Luca Aldega Maria Laura Balestrieri Rosanna Maniscalco 《地学学报》2014,26(5):363-371
An extensive dataset of vitrinite reflectance, FTIR parameters on organic matter, illite content in mixed layers illite‐smectite, apatite fission tracks and U‐Th/He dating has been used to reconstruct the stepwise propagation of the Eastern Sicily fold‐and‐thrust belt during Late Palaeogene and Neogene times. The results indicate that the fold‐and‐thrust belt is divisible into two levels of thermal maturity. These levels consist of a less evolved level of thermal maturity that records limited sedimentary burial and minor heating, and a more evolved level of thermal maturity that indicates tectonic burial and exhumation at different times. Deformation and exhumation of shallowly buried units are linked to wedge forward propagation by low‐angle thrusts, whereas the evolution of deeply buried units is associated with tectonic imbrications by duplex formation and steep thrusts. The two tectonic styles alternate during evolution of the fold‐and‐thrust belt under low erosion rates. 相似文献
2.
Klapp Jaime Areu-Rangel Omar S. Cruchaga Marcela Aránguiz Rafael Bonasia Rosanna Godoy Mauricio J. Silva-Casarín Rodolfo 《Natural Hazards》2020,100(1):89-109
Natural Hazards - One of the most important aspects in tsunami studies is the behaviour of the wave when it approaches the coast. Information on physical parameters that characterize waves is often... 相似文献
3.
Upper Pollara eruption products (13 ka, Salina Island, Italy) include both homogeneous and heterogeneous pumices resulting from mixing/mingling processes between an HK andesite and a high-SiO2 rhyolite. Representative samples of heterogeneous pumices are collected and analyzed in order to check the correspondence between glass composition and morphological features of the mingling/mixing structures. Image analysis techniques are applied and eight grey color ranges (classes) are extracted from high-resolution scans of pumice. Class 1 (lighter colors) and class 8 (darker colors) show end-member glass compositions, i.e. HK andesite and high-SiO2 rhyolite, respectively. These two classes show spot- to cluster-like morphological structures. Intermediate classes show an HK dacitic to rhyolitic composition and a banding- to fold-like morphology. Fractal analysis by box-counting of the boundary pattern of eight grey classified images is performed over a length scale of 0.028–1.8 cm. Fractal dimension D is between 1.01 and 1.84. Coupled fractal analysis and geochemical data reveal that D increases as the degree of magma interaction (homogenization) increases. This feature well fits the results from numerical models on the convective mixing of fluids driven by thermal convection. We conclude that the increase of D observed in the Upper Pollara samples reflects the transition from fractal mixing to homogenization. End-member magmas (HK andesite and high-SiO2 rhyolite) represent isolated mixing regions, while homogenized magmas represent active mixing regions. In the analyzed pumices, isolated and active mixing regions coexist at scales between 10−4 and 10−2 m. Morphological and compositional features of the Upper Pollara pumices result from turbulence. 相似文献
4.
Rosanna De Rosa Herv Guillou Roberto Mazzuoli Guido Ventura 《Journal of Volcanology and Geothermal Research》2003,120(3-4):161-178
A geochronological study of the Filicudi, Salina, Lipari and Vulcano Islands (Aeolian Archipelago) using the unspiked potassium–argon technique provides new age data which, combined with stratigraphic correlation, better constrain the temporal evolution of volcanism. The unspiked K–Ar age of the oldest exposed lavas on Filicudi, 219±5 ka, is significantly younger than the previous estimation of 1.02 Ma. In the general context of Aeolian volcanism, this new date suggests that the volcanism of the western sector of the Aeolian Archipelago is younger than previously thought. Geochronological data point out on the rapid transition from calc–alkaline to potassic volcanism. The distribution of the K–Ar ages within the Salina–Lipari–Vulcano group shows that the volcanism started on Lipari and propagated over time northward on Salina and southward on Vulcano. Geochronological and geophysical data suggest that the onset of volcanism in the central sector of the Aeolian Arc may be due to a mantle upwelling structure located below Lipari. A change in the style of the eruptions occurred in the Salina–Lipari–Vulcano system at about 100 ka from the present. Low-energy magmatic eruptions occurred between 188 and about 100 ka. From about 100 ka to the present, higher-energy eruptions and low-energy events due to magma–water interaction also occurred. This change in the style of activity, together with the appearance of evolved products (i.e. rhyolites) during the last 50 ka, is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188–100-ka period. The new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval. 相似文献
5.
Eugenio Nicotra Marco Viccaro Rosanna De Rosa Marco Sapienza 《Bulletin of Volcanology》2014,76(8):1-24
Critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation. Here, we present data on densities, and vesicle size and number characteristics, for representative pyroclasts from six silicic eruptions of contrasting size and style from Raoul volcano (Kermadec arc). We use these data to evaluate histories of bubble nucleation, coalescence, and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material. Density/vesicularity distributions show a scarcity of pyroclasts with ～65–75 % vesicularity; however, pyroclasts closest to this vesicularity range have the highest bubble number density (BND) values regardless of eruptive intensity or style. Clasts with vesicularities greater than this 65–75 % “pivotal” vesicularity range have decreasing BNDs with increasing vesicularities, interpreted to reflect continuing bubble growth and coalescence. Clasts with vesicularities less than the pivotal range have BNDs that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite-rich magma, or vesiculation during slow ascent of degassing magma. Bubble size distributions (BSDs) and BNDs show variations consistent with 65–75 % representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation, consistent with the closest packing of spheres. We consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit. These processes can act in concert with multiple nucleation events, generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed. Fragmentation preserves the range in vesicularity seen as well as any post-fragmentation/pre-quenching expansion which may have occurred. We demonstrate that differing density pyroclasts from a single eruption interval can have widely varying BND values corresponding to the degree of bubble maturation that has occurred. The modal density clasts (the usual targets for vesicularity studies) have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation. 相似文献
6.
Fabio Scarciglia Rosanna De Rosa Giuseppe Vecchio Carmine Apollaro Gaetano Robustelli Filippo Terrasi 《Journal of Volcanology and Geothermal Research》2008
This paper focuses on the main morphological, physical, chemical and mineralogical features of an andic-like soil, widely outcropping in the Sila upland plateau of Calabria (southern Italy), and its potential role in tephrostratigraphy. A multidisciplinary and multiscale approach allowed identification of this soil as a “masked” distal archive of volcanic products, developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis. The study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence, limited extent or poor preservation of primary eruptive products. The soil has an Andisol-like appearance, despite laboratory data that do not match the entire suite of diagnostic criteria for the Andisol taxonomic order. Geomorphological, stratigraphic and pedologic results, coupled with tephrostratigraphic and radiometric data, concur to suggest a Late Pleistocene(?) to Holocene age of the Andisol-like soil. In particular, the rhyolitic chemical composition of small-sized glass fragments (identified by SEM–EDS analyses) indicates soil genesis contributed by volcanic ash, probably sourced from Aeolian Arc explosive activity spanning the last 30 ka. Accordingly, the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties (in turn related to the neoformation of clay minerals from the weathering of volcanic glass) are consistent with a climatic shift from a seasonally-contrasted to a constantly humid pedoenvironment. This change can be ascribed to the Lateglacial(?) or Early–Middle Holocene to Late Holocene transition. Calibrated AMS 14C dates performed on charcoal fragments sampled from three representative soil profiles, provide Late Holocene ages (3136 ± 19, 343 ± 16 and 92 ± 24 yr BP), in accord with archaeological finds. On the basis of the consistent stratigraphic position, lateral continuity and wide extent, the soil can be considered a good pedostratigraphic marker in the Sila highlands and is informally defined as the “Cecita Lake geosol”. It supplies valuable time constraints for the underlying (occasionally overlying) deposits and/or soils. Moreover, it allows regional-scale morphostratigraphic correlations and detailed reconstruction of Late Pleistocene–Holocene geomorphic events in Calabria, a very suitable region for distal tephra deposition in the central Mediterranean peri-volcanic area. The effects of high-energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals. 相似文献
7.
Roberto Sulpizio Rosanna Bonasia Pierfrancesco Dellino Mauro A. Di Vito Luigi La Volpe Daniela Mele Giovanni Zanchetta Laura Sadori 《Journal of Volcanology and Geothermal Research》2008
Ash samples from tephra layers correlated with the Pomici di Avellino (Avellino Pumice) eruption of Somma-Vesuvius were collected in distal archives and their composition and particle morphology investigated in order to infer their behaviour of transportation and deposition. Differences in composition and particle morphologies were recognised for ash particles belonging to the magmatic Plinian and final phreatomagmatic phases of the eruption. The ash particles were dispersed in opposite directions during the two different phases of the eruption, and these directions are also different from that of coarse-grained fallout deposits. In particular, ash generated during magmatic phase and injected in the atmosphere to form a sustained column shows a prevailing SE dispersion, while ash particles generated during the final phreatomagmatic phase and carried by pyroclastic density currents show a general NW dispersion. These opposite dispersions indicate an ash dispersal influenced by both high and low atmosphere dynamics. In particular, the magmatic ash dispersal was first driven by stratospheric wind towards NE and then the falling particles encountered a variable wind field during their settling, which produced the observed preferential SE dispersal. The wind field encountered by the rising ash clouds that accompanied the pyroclastic density currents of the final phreatomagmatic phase was different with respect to that encountered by the magmatic ash, and produced a NW dispersal. These data demonstrate how ash transportation and deposition are greatly influenced by both high and low atmosphere dynamics. In particular, fine-grained particles transported in ash clouds of small-scale pyroclastic density currents may be dispersed over distances and cover areas comparable with those injected into the stratosphere by Plinian, sustained columns. This is a point not completely addressed by present day mitigation plans in case of renewal of activity at Somma-Vesuvius, and can yield important information also for other volcanoes potentially characterised by explosive activity. 相似文献
8.
Stratigraphic reconstruction of the Upper Pollara eruption has allowed for the inference of eruptive mechanisms and the distillation of a sedimentological model for pyroclastic density currents (PDCs) moving across variable topography. The pre-eruptive topography in the study area was characterised by a tuff ring-like morphology, with both inward and outward dipping slopes. Highly viscous, moderately porphyritic, dacitic to rhyolitic magmas fed the eruption, which was characterised by a Vulcanian eruptive style. The stratigraphic succession was divided into five eruption units (EUs), which result from different phases of the eruption separated by stases. Sustained columns occurred only during EU1, while PDC generation dominates EU2–5. Lithofacies analysis of the PDC deposits indicates the prevalence of massive coarse-grained deposits on the inner slopes of the Pollara crater, which are interpreted as the deposits of a flow-boundary zone dominated by granular flow or fluid escape regimes. Dune-bedded, massive to stratified lithofacies dominate the outer slopes of the Pollara crater, and are interpreted as the deposits of PDCs with flow-boundary zones in which traction played a major role. Thin, massive PDC deposits are exposed on the sub-horizontal Malfa terrace, and are interpreted as representative of flow-boundary zones dominated by a granular flow regime. The occurrence of stacked deposits indicates that most of the PDCs were characterised by unsteady pulsatory behaviour, with development of trains of pulses during their transport. The downcurrent lithofacies transitions observed for the Upper Pollara deposits have finally been compared with other similar lithofacies associations which have been described for short-lived PDCs at tuff rings, in order to discuss the influence of pre-eruptive topography on lithofacies association. 相似文献
9.
Fabrizio Tursi Richard Spiess Vincenzo Festa Rosa Anna Fregola 《Journal of Metamorphic Geology》2020,38(7):771-793
Linking the deformation history of mylonitized continental rocks to the progress of devolatilization reactions that trigger reaction softening is critical for the understanding of crustal scale processes. We have analysed the field geometries and microstructures of deformed rocks within the southern Hercynian belt in Calabria, as well as modelled the pressure–temperature–deformation (P–T–d) trajectory of a main ductile shear zone that tectonically coupled the deeper crustal Mammola Paragneiss Unit with the upper crustal Stilo–Pazzano Phyllite Unit. P–T modelling of the mylonitic Mammola Paragneiss Unit was performed through calculation of phase equilibrium diagrams with the software thermocalc in the MnNCKFMASHTO model system. The prograde P–T–d trajectory is based on the zoning profiles of garnet porphyroblasts and their mineral inclusions, primarily barroisite and epidote. P–T modelling shows that peak metamorphic conditions of ~0.9 GPa and 585°C were reached during a Dn-1 under-thrusting event. The following exhumation during the Dn mylonitic event, and contact metamorphism during Dn+1 and Dn+2 folding events, have also been modelled because they are essential to restore the previous tectono-metamorphic history. The exhumation trajectory was modelled down to 0.3 GPa with temperatures of 440–460°C, under fluid-deficient conditions, as well as the final late Carboniferous contact metamorphism up to Tmax of 680–720°C. The prograde path shows clear evidence for thermal buffering during garnet growth at the expense of chlorite, with a heating-dominated stage after chlorite breakdown. Subsequently, a rheological change associated with epidote breakdown (i.e. reaction softening) occurred, highlighted by a net steepening of the P/T trajectory towards the pressure peak. On the basis of the barroisite inclusions within garnet porphyroblasts as well as the ‘hairpin’ shape of the reconstructed P–T–d path (before contact metamorphism), we infer that the unusual low T/P gradient for the Hercynian crust exposed in the Mammola Paragneiss Unit records its involvement in the Palaeotethys–Gondwana subduction beneath Laurussia during Dn-1 under-thrusting. We present a new palaeotectonic interpretation along the southern Hercynian belt in Calabria during the Upper Mississippian–Lower Pennsylvanian, that is consistent with previous geochronology studies. 相似文献
10.
The influence of thermal and cyclic stressing on the strength of rocks from Mount St. Helens, Washington 总被引：1，自引：0，他引：1
Jackie Evan Kendrick Rosanna Smith Peter Sammonds Philip G. Meredith Matthew Dainty John S. Pallister 《Bulletin of Volcanology》2013,75(7):1-12
Stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength. Here, we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks. Specifically, this laboratory study examines the properties of samples from Mount St. Helens; chosen because its strength and stability have played a key role in its history, influencing the character of the infamous 1980 eruption. We find that thermal stressing exerts different effects on the strengths of different volcanic units; increasing the heterogeneity of rocks in situ. Increasing the uniaxial compressive stress generates cracking, the timing and magnitude of which was monitored via acoustic emission (AE) output during our experiments. AEs accelerated in the approach to failure, sometimes following the pattern predicted by the failure forecast method (Kilburn 2003). Crack damage during the experiments was tracked using the evolving static Young’s modulus and Poisson’s ratio, which represent the quasi-static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models. Cyclic loading of these rocks resulted in a lower failure strength, confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice. Additionally, volcanic rocks in this study undergo significant elastic hysteresis; in some instances, a material may fail at a stress lower than the peak stress which has previously been endured. Thus, a volcanic dome repeatedly inflated and deflated may progressively weaken, possibly inducing failure without necessarily exceeding earlier conditions. 相似文献