ABSTRACT New geophysical data (bathymetry, electrical resistivity tomography and seismic profiles) show the structural and morphological characteristic of the Peninsula Ushuaia structural high. The bathymetry and seismic data show that... more
ABSTRACT New geophysical data (bathymetry, electrical resistivity tomography and seismic profiles) show the structural and morphological characteristic of the Peninsula Ushuaia structural high. The bathymetry and seismic data show that the structural high is bordered by two troughs controlled by the E-W Beagle channel strike-slip fault system and a NW-SE extensional system. Electrical resistivity tomography profiles allow us to identify similar oriented meso-scale structures onshore at the Peninsula Ushuaia. The collected evidence supports the idea that the NW-SE extensional system should be younger than the E-W system.
Research Interests:
A complete Bouguer gravity map of the central-eastern part of the Isla Grande de Tierra del Fuego, and a general bathymetric chart of the Lago Fagnano have been realized, on the basis of a series of field geophysical surveys carried out... more
A complete Bouguer gravity map of the central-eastern part of the Isla Grande de Tierra del Fuego, and a general bathymetric chart of the Lago Fagnano have been realized, on the basis of a series of field geophysical surveys carried out on the Island since 1998. The regional gravity anomaly trend onshore shows a progressive negative gradient from N to S. Distinct, broadly E-W-trending gravity minima are superimposed on this regional negative gradient. They follow the main trace of the Magallanes-Fagnano fault system, which represents the western segment of the left-lateral South America-Scotia transform plate boundary. The gravity minima reflect the presence in the subsurface of restricted and elongated basins developed within the principal displacement zone of the fault system. A relative positive gravity maximum is located just at the SE corner of the Lago Fagnano, and represents the response of a partially exposed crystalline body, occupying an area 3 x 3 km wide. A 2D vertical c...
Research Interests:
Although hypogene cave systems have been described since the beginning of the XXth century, the importance of ascending fluids that acquired their aggressiveness from in-depth sources in speleogenesis has been fully realized only in the... more
Although hypogene cave systems have been described since the beginning of the XXth century, the importance of ascending fluids that acquired their aggressiveness from in-depth sources in speleogenesis has been fully realized only in the last decades. Aggressiveness of waters can be related to carbonic and sulfuric acids and the related corrosion-dissolution processes give rise to different types of caves and underground morphologies. The abundance of hydrothermal springs and associated travertine deposits, and the widespread interaction between volcanic or sub-volcanic phenomena and karst in many sectors of the Italian peninsula are a strong evidence of hypogene speleogenesis. Furthermore, researches on secondary minerals have allowed to discover hypogene caves formed by highly acidic vapors in subaerial environments, also showing that most of these caves have extremely rich mineral associations. Despite this, until the late 80s the only known important cave systems of clear hypogen...
ABSTRACT The Canan area (Honduras) is characterized by a gold-bearing ore deposit that is associated with quartz-veined shear zones. Gold mineralization occurs in low-to medium-grade metamorphic host-rocks (graphitic and sericitic... more
ABSTRACT The Canan area (Honduras) is characterized by a gold-bearing ore deposit that is associated with quartz-veined shear zones. Gold mineralization occurs in low-to medium-grade metamorphic host-rocks (graphitic and sericitic schists). Hydrothermal fluids, which are associated with the emplacement of Cretaceous-Tertiary granodioritic intrusions, are responsible for the formation of quartz veins and the hydrothermal alteration of wall-rocks. Three main altered zones have been detected in the wall-rocks as far as 150 cm from the quartz veins. The distal zone (up to 50-cm thick) contains quartz, chlorite and illite. The intermediate zone is the thickest (up to 80 cm) and is marked by quartz, muscovite, sulphides, kaolinite and native elements such as Au and Ag. The proximal zone, which is close to the quartz veins, is rather thin (up to 25 cm) and contains clay minerals, Al-oxides-hydroxides and sulphides. The transition from the distal to the proximal zone is accompanied by the enrichment of SiO2 and the depletion of all other major elements, except for Fe2O3(tot). Precious metals occur in the highest concentrations in the intermediate zone (Au up to 7.6 ppm and Ag up to 11 ppm). We suggest that gold was transported as a reduced sulphur complex and was precipitated from the hydrothermal solution by the reaction of the sulphur complexes with Fe2+ from the alteration of the mafic minerals of the host-rock. Fluid–wall-rock interactions seem to be the main cause of gold mineralization. Genetic relationships with a strike-slip fault system, hydrothermal alteration zones within the metamorphic wall-rocks, and an entire set of geochemical anomalies are consistent with orogenic-type gold deposits of the epizonal class.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The geothermal area of Rio Valdez is located in the central portion of the Isla Grande de Tierra del Fuego (South Argentina), ten kilometers south of the southeastern sector of the Fagnano Lake. It consists of a series of thermal springs... more
The geothermal area of Rio Valdez is located in the central portion of the Isla Grande de Tierra del Fuego (South Argentina), ten kilometers south of the southeastern sector of the Fagnano Lake. It consists of a series of thermal springs with low discharge rates (≤1 L/s) and temperatures in the range of 20–33°C distributed in an area of <1 km2. The thermal springs are characterized by alkaline, Na-HCO3 waters with low salinity (0.53÷0.58 g/L), but relatively high fluoride contents (up to 19.4 mg/L). Their composition is the result of a slow circulation at depth, possibly through deep tectonic discontinuities connected with the Magallanes-Fagnano Fault (MFF) system. According to geothermometric calculations, thermal waters reach temperatures in the range of 100–150°C and an almost complete chemical equilibrium with the alkali-feldspars in the metavolcanic country rocks. The relatively high fluorine contents can be explained by the slow ascent and cooling of deep groundwaters followed by a progressive re-equilibration with F-bearing, hydrated Mg-silicates, such as chlorite, which has been recognized as an abundant mineral in the metavolcanics of the Lemaire Formation and metapelites and metagraywackes of the Yahgán Formation. Finally, the isotopic composition of the investigated samples is consistent with the infiltration from local snow melting at altitudes in the range of 610–770 m asl. The comparison of our data with those collected in 1991 seems to suggest a possible progressive decline of the bulk thermal output in the near future. This possibility should be seriously considered before planning a potentially onerous exploitation of the resource. Presently, the only ways to exploit this geothermal resource by the population scattered in the area are the direct use of thermal waters and/or spa structures.
Research Interests:
Home. ...
Research Interests:
Research Interests:
Within the area of Ushuaia Bay (Tierra del Fuego, southernmost South America) the deformed Lower Cretaceous sedimentary rocks of Yahgán Formation host the Ushuaia Pluton. The intrusive body is oval in map view; it is compositionally... more
Within the area of Ushuaia Bay (Tierra del Fuego, southernmost South America) the deformed Lower Cretaceous sedimentary rocks of Yahgán Formation host the Ushuaia Pluton. The intrusive body is oval in map view; it is compositionally varied with rocks ranging from the ultrabasic to the mesosiliceous realm. The emplacement time is constrained within the Albian–Cenomanian span by new amphibole K/Ar data. Meso- and microstructures of Ushuaia Pluton and its host indicate a synkinematic emplacement with a dominant extensional component. A set of transcurrent and normal faults related to the sinistral strike-slip Beagle Channel Fault System affects the pluton and its host. On the basis of aeromagnetic data combined with field information, a new model is presented for the Ushuaia Pluton. Modeling results fit well with a laccolithic body with an estimated volume of around 111 km3. The model pluton cross-section displays a central zone with an average thickness of 2000 m which progressively thins toward the margins (∼ 500 m) and a southern root which reaches 5000 m deep. The combined structural and geophysical model supports a transtensive scenario for the Ushuaia Pluton emplacement at Early–Late Cretaceous boundary.
Research Interests:
Geophysical and geological field surveys carried out in the central and eastern part of the Argentinean Tierra del Fuego Island on the Magallanes–Fagnano fault system (MFS) delineate its main structural features and tectonic setting.... more
Geophysical and geological field surveys carried out in the central and eastern part of the Argentinean Tierra del Fuego Island on the Magallanes–Fagnano fault system (MFS) delineate its main structural features and tectonic setting. Gravity and magnetic data provide critical information for those areas lacking good exposures and support a present-day transtensional tectonic regime for the MFS. In the surveyed area, the MFS segments have a clear morphological expression and are associated with localized gravity minima interpreted as pull-apart basins. In the southeastern corner of Lago Fagnano, the magnetic data suggest a prominent crystalline body in the subsurface, partially exposed in Cerro Hewhoepen. The shape and position of this intrusive body suggest that its emplacement was localized in a releasing bend. Two-dimensional density modeling along a 40 km long N–S section east of Lago Fagnano suggests a deep duplex similar to that exposed in the western part of the island. The obtained model, combined with available surface data, implies the subsurface configuration of geological units and structures, in which the structure of the deep duplex is similar to that exposed in the western part of the Island. The model indicates the southward deepening of the basement from 5 to 7 km and provides further support for the piston shape of the Hewhoepen intrusive.Se ha desarrollado un estudio geofísico y geológico, en la parte central de la Isla de Tierra del Fuego en sector argentino, a través del sistema de Fallas Magallanes–Fagnano (MFS), con el objeto de delinear sus rasgos estructurales y ambiente tectónico. Los datos de gravedad y magnetismo obenidos aportan información crítica para este sector casi totalmente cubierto por sedimentos cuaternarios. Nuestros datos apoyan un modelo tectónico transtensivo para el actual límite de placas representado por el MFS. En el sector estudiado el MFS, tiene una clara expresion morfológica superficial y está asociada con la localización de mínimos gravimétricos, interpretados como cuencas de pull-apart. En la parte SE de la cabecera del Lago Fagnano, los datos de anomalía magnética sugieren la presencia de al menos un cuerpo intrusivo en subsuelo, parcialmente expuesto en el cerro Hewhoepen. Su forma y localización sugieren que se habría emplazado en correspondencia con un área de distensión. Se ha realizado un modelado numérico, utilizando los datos de anomalía de Bouguer, a lo largo de una sección de unos 40 km de largo y 10 km de profundidad, localizada en el extremo Este del Lago Fagnano. El modelo obtenido combinado con nuestros datos geológicos de superficie nos permitieron inferir: (a) la disposición de las diferentes unidades geológicas y continuidad de estructuras principales en subsuelo; (b) la estructura en duplex en profundidad que resulta similar a la expuesta en la parte oeste de la isla; (c) el modelo en profundidad también aporta datos acerca de la profundización hacia el Sur del basamento de 5 a 7 km; y (d) permite caracterizar el intrusivo del Cerro Hewhoepen como un cuerpo cilíndrico.
Research Interests:
Research Interests:
... SISMICITÀ E TETTONICA NELL&amp;amp;amp;#x27;AREA UMBRO-MARCHIGIANA (*) Nota del Socio Giusy Lavecchia, Massimiliano Barchi, Francesco Brozzetti &amp;amp;amp;amp; Marco Menichetti ... V/ I f4b¿ Linea dì eosfa B* PSGIOKGIO ^J^,... more
... SISMICITÀ E TETTONICA NELL&amp;amp;amp;#x27;AREA UMBRO-MARCHIGIANA (*) Nota del Socio Giusy Lavecchia, Massimiliano Barchi, Francesco Brozzetti &amp;amp;amp;amp; Marco Menichetti ... V/ I f4b¿ Linea dì eosfa B* PSGIOKGIO ^J^, *- ^ASCOLI PICENO MOHO отшшшшдашда .12 je .20 .24 .28 km Fig. ...
Research Interests:
The Umbro-Marchean Apennines form an arcuate NW–SE fold-and-thrust belt of NE convexity. The orogen developed from the Early Miocene, and shortened the more than 5 km-thick Meso-Cenozoic stratigraphic succession by about 30%. The internal... more
The Umbro-Marchean Apennines form an arcuate NW–SE fold-and-thrust belt of NE convexity. The orogen developed from the Early Miocene, and shortened the more than 5 km-thick Meso-Cenozoic stratigraphic succession by about 30%. The internal part of the mountain chain is, however, overprinted by SW-dipping extensional normal faults that bound the Plio-Pleistocene continental basins. Nevertheless, the distribution of river terraces all along the main river valleys, clearly indicates that Middle–Upper Pleistocene and Holocene vertical uplift dominated over local anticlinal uplift for the entire studied area. The drainage network of the Marche region, in the external part of the Umbro-Marchean Apennines, has an overall sub-parallel pattern, oriented mainly SW–NE, and transversely breaches the main calcareous anticlinal ridges before reaching the Adriatic coast. Emergence and drainage initiation may have begun as early as the Messinian. Cave systems formed during the erosion history and document former stream levels. The breaching of the high-amplitude anticlinal ridges was controlled mainly by joint systems, and locally, by NNE–SSW striking faults. In turn, both superimposition and stream-piracy phenomena could have played a significant control in the drainage network development and, in places, complex mechanisms involving antecedence cannot be ruled out for streams bypassing anticlinal ridges.