Paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna during the last 225 ka inferred from the volcanic succession of the ‘Timpe’, Acireale, Sicily

The tectonic escarpments locally known as ‘Timpe’ cut a large sector of the eastern flank of Etna, and allow an ancient volcanic succession dating back to 225 ka to be exposed. Geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures, as well as important changes in the nature, composition and magmatic affinity of the exposed volcanics. In particular, the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward-dipping to the progressive tectonic tilting of strata. These elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka BP and their relationship with tectonic structures active in the eastern flank of Etna. We propose a complex paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna, in which the Timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span.     

The Role of Nuclear Starbursts in Luminous Infrared Seyfert 2 Galaxies

We present HST (WFPC2 and FOC) images and UV GHRS spectraplus ground-based optical spectra of four Luminous Infrared Galaxies (LIRGs) that have Seyfert 2nuclei (Mrk 477, NGC 7130, NGC 5135 and IC 3639). The data provide direct evidence of the existence of a central nuclearstarburst that dominates the UV and optical light and are dusty and compact. The bolometricluminosity ( 10¹⁰ L) of these starbursts is similar to the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and thus they contributein the same amount to the overall energetics of these galaxies. An extended work based on ground-based optical spectra of the 20 brightest nuclei known indicate that at least 40%of the Seyfert 2 galaxies harbor a nuclear starburst. The eight Seyfert 2 nuclei thatharbor a starburst are strong IR emitters. This suggests that nuclear starbursts can make a significant contribution or even dominate the UV and optical light of LIRGs.     

Geothermal map of Mexico

Silica temperatures were calculated for 326 water samples from hot and warm springs located throughout Mexico as an attempt to estimate heat flow. Available heat flow data (Smith, 1974; Smith et al., 1979) for northern Mexico were related to silica temperature data to obtain the appropriate constants for the regional conditions according to Swanberg and Morgan's equation (1979, 1980). The constants obtained are similar to those obtained for the United States, therefore heat flow can be estimated on the basis of silica temperature data. By contouring calculated temperatures a map is obtained where the main geothermal provinces are shown.     

Unstable flow,magma mixing and magma-rock deformation in a deep-seated conduit: the Gil-Márquez Complex,south-west Spain

The Gil-Marquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of magma transport through the continental crust. This conduit allowed the intrusion of magmas of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic magma generated by partial melting of a depletedmantle source. Both magmas rose through a common channel in which favorable conditions for unstable flow and magma mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid magmas.     

Temporal evolution of a three component system: the island of Lipari (Aeolian Arc,southern Italy)

The volcanic products from Lipari define an evolutionary trend with a high gradient of K-enrichment, similar to the calc-alkaline to potassic volcanism of other islands in the Aeolian arc. Stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages. The first stage, from 223 to 42 ka, consists of six eruptive cycles and is characterized by basalts and basalt-andesites showing progressive increase in both SiO₂ and K₂O contents with time. The second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products. Fractional crystallization, assimilation and mixing models suggest that the geochemistry of Lipari volcanism evolved with time by a complex interplay between two mantle-derived components, one sub-alkaline and the other alkaline, in addition to crustal melts and/or crustally-derived materials. A petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro- and microscopic features. Melts from the crustal and mantle end-members are almost always present in the system but the relative proportions appear to vary with time. The sub-alkaline mantle component (source of Tyrrhenian tholeiites) is an important contributor to the early evolution of the volcanism in Lipari; input from the alkaline mantle component (source of the Roman Comagmatic Province) increases with time, and the crustal component becomes dominant in the later activity. The preferred petrogenetic model for the temporal evolution of the volcanic system in Lipari involves melting initially caused by an increase in the thermal input related to the opening of the Tyrrhenian Sea and/or to subduction processes. The quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts.     

Stability and dynamics of beams on winkler elastic foundations

The dynamical properties of a foundation beam on a Winkler soil have been recently discussed by using the power series method¹⁴ and the finite element method.^{15, 17 – 19} The first method can be applied only if the Winkler soil is linearly distributed along the whole span: on the contrary, the second method is more general, but it requires considerable computational efforts. In this paper a recently developed discretization method has been shown to be particularly well suited for dynamic analysis of foundation beams, in the presence of second order destabilizing effects. The procedure is based on the Hamilton principle, and the equation of motion is deduced from the corresponding Lagrange equations. According to the proposed method, the structure is reduced to a set of rigid bars, connected together by elastic cells. The convergence of the method is shown to be quite rapid, so that a small number of Lagrangian coordinates has to be introduced, and the resulting eigenvalue problem can be easily solved. Numerical comparisons are also performed with the available data of the literature, and the agreement is shown to be excellent. Two particularly unusual cases are illustrated, in order to emphasize the method's peculiarities. Finally, the influence of the axial forces on the fundamental vibration frequency is discussed, both for conservative and non-conservative forces.     

The abandoned Pb-Zn mine of Ingurtosu, Sardinia (Italy)

The Ingurtosu Pb-Zn mine, situated in the southwestern part of Sardinia, has been in production from the beginning of the last century up to 1968. The orebody consists of galena/sphalerite/barite/siderite veins in Ordovician arenaceous and phyllitic sediments, near the contact with a Hercynian batholith.

Abundant tailings were collected in a pond from which they were discharged during the winter months into the sea via the Rio Naracauli stream. Today this area of outstanding scenic beauty, is degraded by tailings and waste rock scattered all along the stream.

Material derived from mining activities was studied for grain size, mineralogical and geochemical composition. The Rio Naracauli was sampled over a length of ten kilometers at regular intervals.

The results can be summarized as follows: (a) tailings contain a varying, but often quite high, percentage of Pb; lower percentages were found for Zn and Cd; (b) a sharp increase in dissolved Zn, Cd and Pb was observed in the Rio Naracauli where it leached the tailings; and (c) tailings and waste rocks should be recycled or revegetated.     

Mineral assemblages of the Francisco I. Madero Zn–Cu–Pb–(Ag) deposit, Zacatecas, Mexico: Implications for ore deposit genesis

The Francisco I. Madero deposit, central Mexico, occurs in the Mesozoic Guerrero Terrane, which hosts many ore deposits, both Cretaceous (volcanogenic massive sulfides) and Tertiary (epithermal and skarn deposits). It is hosted by a 600 m-thick calcareous-pelitic unit, of Lower Cretaceous age, crosscut by porphyritic dikes that strike NW–SE. A thick felsic volcanic Tertiary sequence, consisting of andesites and rhyolitic ignimbrites, unconformably overlies the Cretaceous series. At the base, the mineralization consists of several mantos developed within calcareous beds. They are dominantly composed of sphalerite, pyrrhotite and pyrite with minor chalcopyrite, arsenopyrite and galena. At the top of the orebody, there are calcic skarns formed through prograde and retrograde stages. The resulting mineral assemblages are rich in manganoan hedenbergite (Hd_75–28Di_40–4Jh_40–20), andraditic garnets (Adr_100–62Grs_38–0), epidote (Ep_95–36Czo_60–5Pie_8–0), chamosite, calcite and quartz. The temperature of ore deposition, estimated by chlorite and arsenopyrite geothermometry, ranges from 243° to 277 °C and from 300° to 340 °C, respectively. The pressure estimated from sphalerite geobarometry averages 2.1 kbar. This value corresponds to a moderately deep skarn and agrees with the high Cu content of the deposit. Paragenesis, P–T conditions and geological characteristics are compatible with a distal, dike-related, Zn skarn deposit. Its style of mineralization is similar to that of many high-temperature carbonate replacement skarn deposits in the Southern Cordillera.     

Impact of past mining activity on the quality of groundwater in SW Sardinia (Italy)

Hydrogeochemical surveys were carried out in SW Sardinia (Italy) to investigate the impact of past mining activities on the quality of groundwater. The chemistry of waters from flooded galleries, adits and dumps has been compared with that of springs and wells in the same area at sites relatively far from any mine legacy. A feature, common to all waters, is the circumneutral pH, since the carbonate formations in the area neutralise the acidity produced by the oxidation of Fe-bearing sulphide minerals in the mine impacted water. However, groundwater interacting with mine workings is degraded in quality; it shows high dissolved SO₄, Zn, Cd and Pb contents. In some cases groundwater exceeds the limit established by the guidelines of the World Health Organization for Pb content in drinking water, so that groundwater is mixed before entering the local aqueducts. Results from this study suggest that more attention needs to be paid to the impact on the streams from contaminated water flowing out from some mine areas because during the dry season these streams are only fed by mine groundwater. We recommend focusing efforts to reduce the chemical contamination prior to discharge.