196,043 research outputs found
Mt. Etna aerosol optical thickness from MIVIS images
No full textThis work focuses on the evaluation of Aerosol Optical Thickness (AOT) in Mt. Etna volcano area starting from the analysis of MIVIS VIS images. MIVIS images and ancillary data (atmospheric profiles, photometric measurements, atmospheric infrared radiances, surface temperatures, ground reflectances, SO2 abundances) were collected during the «Sicily 97» campaign. Data elaboration was performed with extensive use of 6S radiative transfer model, determining optical thickness with an inversion algorithm that uses atmospheric vertical profile, ground reflectance data and radiance measured by the first MIVIS spectrometer (channels 1-20; range 0.44-0.82 n). Ground reflectance is the most problematic parameter for the algorithm. In order to have a low and uniform surface reflectance, only pixels located at an altitude between 2000-3000 m a.s.l. were analysed. At this altitude,AOT is very low during non-eruptive periods: at Torre del Filosofo (2920 m a.s.l.) on June 16th 1997, during one MIVIS flight, AOT at 0.55 n was 0.19. The uncertainty about ground reflectance produces significant errors on volcanic background AOT, and in some cases the error is up to 100%. The developed algorithm worked well on volcanic plume, allowing us to determine the plume related pixelsAOT. High plume AOT values minimize the problems deriving from reflectance uncertainty. Plume optical thickness shows values included in a range from 0.5 to 1.0. The plume AOT map of Mt. Etna volcano, derived from a MIVIS image of June 16th 1997, is presented
Reconciling the Geology of the Emilia Apennines and Tuscany across the Livorno-Sillaro Lineament, northern Apennines, Italy.
No full textSurface expression of lithospheric faults may vary greatly as they can develop a wide range of geomorphic/topographic features and various kinds of superficial geological/structural mismatchings. The “Livorno-Sillaro Lineament” (Nirta et alii, 2007; Pascucci et alii, 2007; Bettelli et alii, 2012) is one of the most important transverse lineaments of the Northern Apennine orogen. The lithospheric-scale role of this structure has been recognized long time ago by various authors on the base of different geophysical, geological and geomorphic data, although its origin is still not well defined. Also the exact surface characters of this structure are still not well-defined, we think because they are mainly based on old and out-of-date geological data.
We present a review of the more recent stratigraphical and structural data related to the geology across the “Sillaro Lineament”, SL, the northeasternmost segment of the “Livorno-Sillaro Lineament”. Based on a re-examination and reinterpretation of the existing information about the regional geology of the Northern Apennines we conclude that the supposed mismatching of the Ligurian/Subligurian Units on the two sides of this lineament is mainly due to a lack of knowledge and to an inadequate correlation between corresponding units. Nevertheless, we recognize that this structure (along with the Secchia transverse lineament) greatly influenced the growth and the evolution of the oceanic accretionary prism/Ligurian/Subligurian thrust-nappe from the late Eocene to the late Serravallian, and also later on. In particular, we point out that at least the easternmost segment of this structure not only played an important role on the differential growth of the Ligurian/Subligurian accretionary prism-thrust nappe, but that it was responsible for the different amount of translation of the Ligurian Units on both side of the lineament.
Our conclusions and interpretations include:
1) the Sillano/Mt Morello succession, typically cropping out SE of the SL in eastern Tuscany, represents the source rocks of the Ligurian blocks forming the Sestola-Vidiciatico tectonic unit and similar units (e.g., Coscogno-Montepastore tectonic unit: Remitti et alii, 2013) cropping out NW of the SL and along the SL itself;
2) the External Ligurian unit variously named as Samoggia/Val Sillaro/Val Marecchia Varicoloured Shales, AVS, and the overlying lower to middle Eocene turbidites (e.g., Savigno Fm) cropping out in the Emilia Apennines - i.e., NW of the SL – represents a lateral and more internal equivalent of the Sillano/Mt Morello succession. The AVS were extensively present also SE of the SL, as testified by the large klippen in the Romagna Apennines (Savio and Marecchia valleys) and many small klippens in the Umbria area (Umbertide-Gubbio area);
3) along and SE of the SL the AVS form the stratigraphic base of the Mt Morello Fm. Therefore, also this unit is present on both sides of the SL;
4) the pre-middle Eocene Subligurian Units cropping out NW of the SL (Argille e Calcari di Canetolo Fm and Calcari del Groppo del Vescovo Fm) do not correspond to the so called Subligurian Units cropping out SE of the SL (i.e., in Tuscany). The latter are the result of the sedimentation in a particular paleogeographic domain, transitional to the Tuscan domain, absent or not preserved NW of the SL. This seems to represent the only real difference in the geology of the Ligurian/Subligurian thrust nappes NW and SE of the SL.
All the available data show that until the late Serravallian the thrust front of the Ligurian nappe was located in the same position across the SL. However, starting from the early-late Tortonian a differential translation of the Ligurian nappe NW of the SL took place, progressively reaching the present day position. With the exception of the Marecchia area, in the Romagna and Umbria Apennines (SE of the SL), instead, the thrust front of the Ligurian nappe remained more or less in the same position it reached in the late Serravallian. This implies that in the Northern Apennines the transverse SL played also an important role in the different amount of translation of the Ligurian thrust-nappe.
REFERENCES
Bettelli, G., Panini, F., Fioroni, C., Nirta, G., Remitti, F., Vannucchi, P. & Carlini, M. (2012), Revisiting the Geology of the “Sillaro Line”, Northern Aprnnines, Italy. Rendiconti Online Società Geologica Italiana, 22, 14-17.
Nirta, G., Principi, G. & Vannucchi, P. (2007), The Ligurian Units of Western Tuscany (Northern Apennines): insight on the influence of pre-existing weakness zones during ocean closure. Geodinamica Acta, 20/1-2, 71-97, doi:10.3166/ga.20.71-97
Pascucci, V., Martini, I.P., Sagri, M. & Sandrelli, F. (2007), Effects of transversal structural lineaments on the Neogene-Quaternary basins of Tuscany (inner Northern Apennines, Italy). In: G. Nichols, E. Williams & C. Paola (Eds.), Sedimentary Processes, Environments and Basins: a Tribute to Peter Friend (pp.155-182). Special Pubblication no. 38 of the International Association of Sedimentologists.
Remitti, F., Balestrieri, M.L., Vannucchi, P. & Bettelli, G. (2013), Early exhumation of underthrust units near the toe of an ancient erosive subduction zone: A case study from the Northern Apennines of Italy. Geological Society of America Bullettin, 125, 1820-1832, ISSN: 0016-7606
Impiego di dati MODIS in supporto alla valutazione del rischio associato a microrganismi patogeni in ambiente acquatico
No full textWe show the first results of a study aimed to set simplified procedures and methodologies to use MODIS data and derived products for activities of sea water control and monitoring. The research is carried out in the framework of a project supported by the Ministry for Health, concerning the development of criteria to evaluate the environmental and sanitary risk due to pathogenic micro-organisms in water environment. The remote sensing team acts in support of the biologic research teams that study the environmental conditions that favour the development and growth of such micro-organisms. MODIS data are selected, downloaded, organized in an easy-to-read format and analyzed by integrating with measurements performed by the other teams, in a georeferenced data-base. The goal of this study is to make the great information content of MODIS data available for operational use, providing public organizations in charge of environmental risk management with an operative tool, easy to use and at low cost, to support conventional techniques
Thermal and geological constraints for the timing of the activity the frontal part of an ancient subduction channel, Northern Apennines of Italy
No full textEarly forefront exhumation in an erosive subduction complex: insights from the Northern Apennines of Italy
No full textStratigraphic and structural data indicate that, at the beginning of the Miocene, the frontal part of the subductioncomplex of the Northern Apennines was removed and incorporated in a subduction channel formed duringongoing continental subduction.This stage follows the cessation of the growth of the accretionary prism by offscraping, occurred in the middleEocene. The switch to subduction dominated by frontal tectonic erosion, lasting at least to the middle Miocene, was followed by the exhumation of the chain.The exhumation history associated with accretion and retreat of the Northern Apennines has been analyzed through apatite thermochronology. The internal part of the chain started to be exhumed at 10-13 Ma, while the core of the Apennines began only at 8 Ma.Here we present new structural and thermochronological data from a tectonic mélange involved in the shallow part of the plate boundary. This mélange is composed by blocks dated from Late Cretaceous to late Oligocene. All the samples analyzed were exhumed starting at 22-17 Ma (early Miocene), hence the exhumation of the mélange occurred after short time period from its incorporation in the subduction channel and before its deactivation.Our data show that during the early stages of continent-continent subduction two simultaneous and apparently competing mechanisms were particularly actives: i) frontal and basal tectonic erosion leading to the development of a subduction channel, and ii) occasional shallow underplating leading to early exhumation of portions of the channel closely inboard. As both tectonic erosion and internal thickening, the last resulting in underplating, coexist during wedge development, they account for space variations in strain localization and material transfer
Late orogenic deformation of the shallowest portion of an orogenic wedge: coeval activity of extensional and compressional tectonics in the western Northern Apennines (Italy)
No full textIn the Northern Apennines of Italy the Ligurian and Subligurian Units (LSU) were involved, since the Late Cretaceous, in the accretionary and orogenic processes related to the convergence between Europe and Adria. Since early Miocene the Ligurian Units completely overthrusted the Subligurian Units (REMITTI et alii, 2011) and both units stacked together (i.e. the LSU) translated towards NE, above the Tuscan-Umbrian foredeep deposits, until they reached the present-day topographic front in the NW portion of the Northern Apennines. In the NE-facing side of the western Northern Apennines the present-day geometry of the LSU does not reflect neither the shape of the late Cretaceous-middle Eocene oceanic accretionary wedge (MOLLI, 2008 and references therein) nor the shape acquired during the late Oligocene, when the early orogenic collisional phases produced a wedge whose geometry tapered out towards the foreland area, i.e. to the E-NE. In fact, at present, geologic evidences indicate that the LSU have a shape whose thickness ranges from less than 1 km at the main ridge zone (SW) up to more than 3,5 km along the NE slope of the chain and then tips out again few km N of the Northern Apennines topographic front, underneath the Pleistocene-to Recent sediments of the Po Plain foredeep. Therefore, the LSU thickness increases towards its NE external tip and tapers out again in the subsurface of the Po Plain. These data imply the activation of thinning processes in the inner portion of LSU and thickening processes in the central portion of LSU; these thinning and thickening processes have to be related to the post-early Miocene progressive emplacement of the LSU over the foredeep units and to the late orogenic extensional and compressional tectonics affecting the Northern Apennines (ARGNANI et alii, 2003, BOCCALETTI et alii, 2011). In particular, the thinning processes have been identified as being of tectonic nature in the innermost portion (mainly low- and high-angle normal faults: ARTONI et alii, 2006, BETTELLI et alii, 2002, VANNUCCHI et alii - 2008) and of sedimentary nature (mass-wasting deposits) (ARTONI et alii, 2010, PAPANI et alii, 1987, REMITTI et alii, 2011) in the outermost portion of the study area. The observed thickening in the central portion of the LSU body has been interpreted as a tectonic doubling caused by the late Miocene-Recent (?) thrusting which affected the whole Apennine orogenic wedge (CAMURRI et alii, 2001; CARLINI et alii, submitted) or, alternatively, as an accumulation zone of large scale and deep-seated gravitational processes (ARTONI et alii, 2006). In order to put new constraints on the timing and modes of thinning and thickening of the LSU we focussed on the western portion of the Northern Apennines, comprised between the main ridge, the Ceno and the Secchia rivers and the Apenninic topographic front. Here we adopted a multidisciplinary approach taking into account field evidences, low temperature thermal and thermochronological data (i.e. vitrinite reflectance, clay mineral analyses, apatite fission-tracks), numerical modelling of the cooling ages through the use of Pecube finite element code (BRAUN, 2003), results from recently published works on the evolution of the external slope of the chain, and a new interpretation of seismic lines and boreholes data. This multidisciplinary approach allowed us to: 1) build a 3D representation of the LSU present-day geometry; 2) constrain to the late Miocene-early Pliocene (in the innermost portion) and to the late Miocene-Pleistocene (?) (at the Apenninic front) the thinning of the LSU; 3) identify the tectonic exhumation and consequent denudation of the foredeep units as one of the main causes which triggered the thinning processes since late Miocene; 4) define first estimates of exhumation rates affecting the LSU and the underlying foredeep units. These results allow us to give new insights, temporal and spatial constraints on the interplay between shallow (< 4 km) and deep (< 20 km), compressional and extensional tectonics which appear to be acting at the same time and at different depths within the study area since late Miocene to Recent
Deformation in a subduction channel: anatomy of the shallow portion (T< 150°C) of an ancient analogue in the Northern Apennines of Italy
No full textIn the Northern Apennines of Italy, an underthrust tectonic mélange represents the ancient analogue of a shallow subduction channel. This mélange (the Sestola Vidiciatico Tectonic Unit) has been formed during the collision between the European and the Adria plates and it is presently sandwiched between the former oceanic accretionary wedge – Ligurian thrust nappe - and the underlying fold–and-thrust belt formed by Adria sedimentary units. It has a thickness of about 500 m and it is representative of a portion ranging from the shallow diagenetic environment to temperatures of around 150°C, a critical temperature recognized in most of the subduction zones as coincident with the up-dip limit of seismogenesis. The main portion of the material forming the subduction channel is the product of frontal erosion taken place at the toe of the Ligurian prism, including its sedimentary cover, reworked through sedimentary and tectonic processes (i.e. frontal prism). Basal erosion is represented by blocks of Ligurian prism tectonically incorporated in the subduction channel and found in the upper part of the mélange.The younger deformation phase, as defined by cross-cutting relationship, is characterised by a strong difference in lithification of the various components which causes a clear partitioning of the deformation. The softer, less lithified components at the time of entrance in the subduction channel record the whole deformation evolution showing clear evidence of continuous and pervasive soft-sediment deformation passing to discontinuous brittle deformation concentrated along faults at deeper levels. Instead the components already hard at the time of entrance in the subduction channel show only the last and brittle stage of deformation. The latter developed when lithification of the softer blocks became as such that the mélange started to show a homogeneous behaviour as shown by the deactivation of the blocks’ boundaries as detachment surfaces. The strain regime in the shallow part of the subduction channel is extensional suggesting a very weak nature of the plate boundary. This character seems to be controlled by the presence of fluid and, for the deeper part, by the cyclical variation of the fluid pressure (fault-valve behaviour)
New thermal constraints on a shallow fossil subduction channel from the Northern Apennines of Italy
No full textHere we present new thermal constraints (with special regard to vitrinite reflectance, Illite percentage in Illite- Smectite mixed-layers and Kübler Index) derived from both XRD analysis of clay and optical analysis of organic matter dispersed in sediments incorporated in the Apennine erosive subduction channel. This study has the goal to define the distribution of maximum paleo-temperatures in different portion of the subduction channel as well as in the units representing its footwall and hanging wall. We then discuss the results with regards to the time-spacetectonic evolution.In the Northern Apennines of Italy, two tectonic units have been recently recognized as an ancient shallow subduction channel. The subduction channel is represented by the Sestola-Vidiciatico Tectonic Unit and its lateral equivalent, the Subligurian Units. The channel started to form at the transition from subduction to collision between the European and the Adria plates and it was active at least until the middle Miocene. The subduction channel is presently sandwiched between the former oceanic accretionary wedge - the Ligurian thrust nappe - and the underlying Adria sedimentary units deformed by folds and thrusts. The channel has a thickness of about 500 m and is representative of a portion ranging from the shallow diagenetic environment to temperatures of around 150°C, a critical temperature recognized in most of the subduction zones as coincident with the up-dip limit ofseismogenesis.The main component of the subduction channel is represented by material incorporated through frontal tectonic erosion removing the toe of the Ligurian/Subligurian wedge. This toe consisted of former accreted oceanic sediment and their slope deposits, the latter often reworked through gravitational processes. Basal tectonic erosion is shown by blocks of Ligurian rocks tectonically incorporated in the subduction channel. These blocks aregenerally located in the upper part of the mélange.Preliminary data from the clay mineral analysis from the Sestola-Vidiciatico Tectonic Unit and Subligurian Units indicate I% in I/S in a range between 80 and 90% and KI between 0.63 and 0.77. The analysis of organic matter gives Ro% generally in the mature stage of hydrocarbon generation with estimated paleo temperatures between 80°C and 140°C. The data from the footwall are highly variable -from thermally immature to mature- and allow to detect the changes in thickness of the hangingwall and the channel, i.e. the overthrust Ligurian wedge and the Sestola-Vidiciatico Tectonic Unit and Subligurian Units
Early exhumation of underthrust units near the toe of an ancient erosive subduction zone: A case study from the Northern Apennines of Italy
No full textApatite fission-track (AFT) analyses were performed on 16 sandstone samples from a tectonic mélange unit exposed in three tectonic windows located near the inferred front of the early Miocene subduction system of the Northern Apennines of Italy. The tectonic windows display a block-on-block tectonic mélange present under the Ligurian Units. The mélange is formed by portions of the upper plate incorporated in the plate
boundary shear zone as a consequence of a mechanism of frontal tectonic erosion during the Aquitanian (early Miocene). AFT and structural data, together with stratigraphic constraints, allow the reconstruction of a
complete deformation cycle with a phase of underthrusting followed by underplating and early exhumation of the tectonic mélange.
The exhumation, in particular, took place at ~10–20 km from the original subduction front. Moreover, the analysis suggests that
multiple faults were active at the same time in the frontal part of the subduction zone
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