The holocenic evolution of a stretch of an eastern italian alpine valley

The morphological evolution of a stretch of an alpine valley located in the Eastern Italian Alps is described. This has been conditioned by a great alluvial fan that was formed as a consequence of interconnected events, deriving from large rockfalls which occurred in the late glacial period at the head of the Missiaga–Bordina valley, on the left side of the Agordo basin. The aggradation of the alluvial fan blocked the Cordevole valley south of the Agordo basin and produced a lake that is documented by lacustrine sediments. Age determination by ¹⁴C techniques on wood remnants found in these sediments fixes the life of the lake at between approximately 5880 and 5300 years BP . This represents, indirectly, the age of the main phase of the development of the fan. After the building up of the alluvial fan, an erosional phase began, leading to the formation of the present landscape. A series of illustrations depicts the sequence of the fan's development.     

Mercury levels in the dissolved and particulate fractions of the Tyrrhenian sea

Determination of the actual mercury concentration in Mediterranean basin seawater was achieved by means of an instrument based on fluorescence spectrometry developed for this purpose, during a field study aboard the oceanographic ship “L.F. Marsili”, between August 1980 and May 1982.Dissolved ·total’ and ·reactive’ mercury and mercury associated with particulate matter were determined on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Concentrations in the range 1.4–19.7 ng l⁻¹ for ·total dissolved mercury’, 0.5–5.9 ng l⁻¹ for ·reactive dissolved mercury’ and 0.3–8.0 ng l⁻¹ for mercury associated with the particulate matter, were measured on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Even if the mean value of the total mercury concentration (dissolved + particulate) was found to be about twice as high as those observed for the oceans, the difference does not seem to be as high as predicted by the model proposed by Buffoni and co-workers to explain the large difference of mercury levels between tunas caught, respectively, in the Mediterranean and in the Oceans.     

Basin-wide mass-wasting complexes as markers of the Oligo-Miocene foredeep-accretionary wedge evolution in the Northern Apennines, Italy

Sedimentary bodies emplaced by mass‐wasting processes and exceeding tens of metres of thickness and a hundred of square kilometres in area are widespread in the Cretaceous–Pleistocene marine successions of the Northern Apennines of Italy. At least 10 such bodies are present in the stratigraphic record of the Oligo‐Miocene foredeep during the northeastern, time‐transgressive migration of the accretionary wedge‐foredeep system. The term mass‐wasting complex (MWC) is here adopted for these bodies to emphasize their multistory emplacement mechanism and polymictic composition with variously deformed slabs of different lithology, age and provenance. As one of the more intriguing features, their occurrence was associated with changes in turbidite deposition from basin plain to slope. Wide sectors of the internal margin of the basin (lobe‐fan) and even of the basin plain become a slope at the front of the accretionary wedge for a limited period of time (temporary slope). The temporary slope supplied the intrabasinal components of the MWCs, whereas the diffused extrabasinal components came from the front of the accretionary wedge. Therefore, an enhanced instability of the entire foredeep‐wedge system occurred systematically and cyclically. As a consequence, many variously consolidated sediments were transferred into the foredeep basin invading the depocentre and forcing the turbidite deposition towards the foreland, in a more northeasterly position. The presence of such MWCs therefore conditioned basin size and geometry in an analogous way as that reported for some modern convergent margins, as in the case of Costa Rica. Normal sedimentation was restored on top of the MWC only after the levelling of topographic irregularities.     

Mach’s principle and Yukawa-like corrections to the Newtonian potential as a bound for the mean energy density of the universe

The (Newton + Yukawa)-type gravitational potential V(r)=?(γ M/r)[1+Aexp?(?r/B)](γ= the gravitational constant as measured at infinity, M= the mass of the source, A, B are constants) is considered in the framework of the Sciama linear approach to Mach’s principle. The coupling constant A of the Yukawa component is found to be related to the mass density and size of the observable (causally connected) universe.     

Geological,petrochemical and metallogenic characteristics of the Costa Rican gold belt: Contribution to new explorations

The Costa Rican Gold Belt is located in the northwestern part of Costa Rica. The geology of this region is characterized by tectonically juxtaposed volcanic-sedimentary and igneous rock units of Tertiary age.Mineralization within the Gold Belt consists of: 1) veins and fissure fillings of epithermal type which bear gold, silver and base metals; 2) disseminated mineralization of complex sulphides (Au, Ag, Pb, Zn); 3) disseminated specks of native gold; 4) eluvial Au rich lateritic soils.Hydrothermal circulation, induced by the emplacement of epizonal plutons, together with continuous and intense pervasive tectonism has been responsible for the epithermal gold-silver mineralization occurring within the Aguacate volcanic series. Contamination and assimilation of andesitic and »shoshonitic« rocks by uprising granitic magmas generated, in association with hydrothermal phenomena, composite environments for gold deposits.Calc-alkaline rocks of the Costa Rican Gold Belt appear to be enriched in incompatible elements of low ionic potential (particularly Ba). For a similar silica concentration, there is a general increase in Y, Ni, and Zr from Miocene to Pliocene rocks. K/Rb and Rb/Sr ratios increase from older to younger suites as well.On the basis of trace element distribution it is suspected that the Guacimal intrusive rocks may represent a marginal suite comparable to those of the New Guinea Mobile Belt. This would imply that the Precambrian-Paleozoic igneous and metamorphic basement, present in northern Nicaragua, might extend further south.Four different magmatic events have been recognized and correlated with regional geodynamic conditions: Eocene-Oligocene calc-alkaline and »shoshonitic« volcanism (plate convergence and subduction), Middle-Early Miocene to Late Miocene calc-alkalic magmatism (compression and uplift), Early Pliocene alkalic magmatism (E-W trending rift), Middle-Late Pliocene calc-alkaline magmatism (crustal extension followed by compression and uplift).Correlation between tectonic events, magmatism and mineralization suggests that metal enrichment may have some relation to different stress regimes associated with active subduction.

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Zusammenfassung Der goldführende Gürtel von Costa Rica befindet sich in dem nordwestlichen Teil des Landes. Die Geologie dieses Gebietes ist durch tektonisch aneinandergelagerte vulkaisch-sedimentäre und magmatische Gesteine des Tertiärs gekennzeichnet.Die Mineralisierungen in dem goldführenden Gürtel bestehen aus: 1) quarzführenden Gängen epithermaler Art, die Gold, Silber, Zink und Blei enthalten 2) Mineralisierungen mit komplexen Sulfiden (Au, Ag, Pb, Zn) 3) punktförmige Einschlüsse von gediegenem Gold 4) eluvialem, Aureichem, lateritischem Boden.Der durch das Eindringen von epizonalen Plutonen bedingte hydrothermale Umlauf, zusammen mit einer intensiven, ununterbrochenen durchgreifenden tektonischen Tätigkeit ist für die Au-Ag epithermalen Mineralisierungen in der vulkanischen Reihe von Aguacate verantwortlich. Die Kontamination und die Assimilation von andesitischen und »shoshonitischen« Gesteinen durch die aufdringenden Granitmagmen hat, in Verbindung mit hydrothermalen Erscheinungen, verschiedene Typen von Goldmineralisierungen erzeugt.Die kalkalkalischen Gesteine des goldführenden Gürtels von Costa Rica sind anscheinend an inkopatiblen Elementen mit niedrigem Ionenpotential (insbesondere Ba) angereichert. Bei vergleichbaren Kieselsäurekonzentrationen begegnet man eine allgemeine und allmähliche Zunahme an Y, Ni und Zr in den jüngsten Gesteinen, wenn man diese mit den Miozän-Gesteinen vergleicht. Au\erdem ist eine Zunahme der K/Rb und Rb/Sr Verhältnisse zu verzeichnen.Aufgrund der Verteilung der Spurenelemente vermutet man, da\ die Intrusivgesteine von Guacimal eine Gesamtheit von marginalen Plutonen darstellen, die mit denen der mobilen Kordillere (mobile belt) in Neuguinea vergleichbar sind. Dies würde bedeuten, da\ das magmatisch-metamorphe Fundament aus dem Präkambrium-Paläozoikum, das im nördlichen Teil von Nicaragua vorhanden ist, sich nach Süden ausdehen könnte.Vier unterschiedliche Magmaerzeugnisse sind ermittelt worden: kalkalkalischer und »shoshonitischer« Vulkanismus des Späteozäns-Oligozäns (Plattenkonvergenz und Subduktion); kalkalkalischer Miozän-Magmatismus (Kompression und Aufwölbung); alkalischer Magmatismus des Frühpliozäns (Entstehung des Valle Central Senkungsgrabens, mit E-W Streichen); Kalkalkali-Magmatismus des Mittel-Spätpliozäns (Krustenausdehnung und anschlie\ende Kompression und Aufwölbung).Die Beziehung zwischen den tektonischen Ereignissen, dem Magmatismus und den Mineralisierungen lä\t vermuten, da\ die Metallanreicherung der Kruste auf veränderliche Stre\bedingungen in Verbindung mit aktiver Subduktion zurückzuführen sein könnte.

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Resumen La Cintura Aurífera de Costa Rica está localizada en el sector norte-occidental del país y está caracterizada por unidades volcano-sedimentarias e igneas de edad terciaria en yuxtaposición tectónica.Las mineralizaciones dentro de la Cintura Aurífera están representadas por: 1) vetas cuarzo-auríferas y relleno de fisuras de origen epitermal asociadas con plata y metales básicos; 2) mineralizaciones diseminadas de sulfuros complejos (Au, Ag, Pb, Zn); 3) laminillas diseminadas de oro nativo; 4) suelos lateríticos eluviales ricos en oro.Se asigna como responsable de las mineralizaciones epitermales oro-plata de la Serie Volcanica de Aguacate, al tectonismo intenso y continuado, así como a la circulación hidrotermal inducida por el emplazamiento de plutones y »stocks« en condiciones epitermales. La contaminación y asimilación de rocas andesiticas y »shoshoniticas« por parte de magmas graniticos ascendentes generó, en asociación con fenomenos hidrotermales, un ambiente de campo aurífero compuesto.Las rocas calco-alcalinas de la Cintura Aurífera de Costa Rica muestran un elevado contenido de elementos incompatibles (en particular Ba). Por contenidos de SiO₂ similares, se evidencia un enrequecimiento general en Y, Ni, Zr desde las rocas del Mioceno a las rocas del Plioceno. Paralelamente se registra un aumento de las relaciones K/Rb y Rb/Sr.En particular se suspecha, por medio de la distribución de los elementos en traza, que las rocas intrusivas de Guacimal puedan representar un »grupo« de plutones marginales comparables con aquellos de la »Mobile Belt« de Nueva Guinea. Lo que indicaria la posible extensión al Sur del basamento igneo y metamórfico de edad Precambrica-Paleozoica presente en el norte de Nicaragua.Se reconocen quatro eventos magmaticos asociados con las condiciones geodinamicas regionales: vulcanismo calco-alcalino de edad Eoceno-Oligoceno (en condiciones de convergencia y subducción de placas), magmatismo calcoalcalino del Mioceno Medio y Temprano hasta Mioceno Tardio (en condiciones de compresión crostal y levantamiento), vulcanismo alcalino del Mioceno Temprano (Rift prevalente E-W), magmatismo calco-alcalino del Plioceno Medio-Tardfo (en condiciones de extensión crostal seguida por compressión y levantamiento).Las correlaciones entre condiciones geodinámicas, magmatismo y mineralizaciones, sugieren que el enriquecimiento en metales esta vinculado con los diferentes regimenes de deformación asociados con procesos de subducción activa.

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Ground deformation and gravity changes accompanying the March 1981 eruption of Mount Etna

We present reults from simultaneous precise levelling and gravity surveys on Mount Etna covering the period August 1980–August 1981. The flank eruption of March 1981 erupted 18–35 × 10⁵m³ of lava. Following it, upward movements of more than 17 cm were observed close to the new fissure and a broad, apparently independent, uplift of 5 cm was observed 4 km to the west. A zone of about 2 cm depression to the east of the fissure is insufficient to account for the volume of magma erupted. Gravity results show positive changes of up to 63 microgal, and display good positive correlation with elevation changes. Both sets of measurements appear to be due to new intrusion of magma rather than subsurface magma drainage. Ground deformation close to the new fissure is well modelled by intrusion of a dyke in the zone 100–500 m below the surface, striking along the fissure and of dip between 75–90°. The gravity changes are modelled as due to a deeper intrusion of magma, along the same line but some 1500 m below the surface. The changes were not present immediately after the eruption but occurred during the ensuing 5 months. It is proposed that this introduction of matter occurred by crack propagation along the fissure in the aftermath of the eruption. Towards the west of the fissure, and some 4 km west of the summit, ground deformation is modelled by intrusion of a dyke in the zone 300–1500 m below the surface and dipping at 80–85°. Again, gravity changes appear to be due to magma intrusion at greater depth, close to sea level. In this case gravity changes are interpreted as due to magma density changes, as a result of pressure increase in a larger scale fissure zone. This same pressure increase may be forcing the new intrusion close to the surface, and makes this part of the volcano a region of especially high risk.     

Relationships between seep-carbonates,mud volcanism and basin geometry in the Late Miocene of the northern Apennines of Italy: the Montardone mélange

The Montardone mélange (Mm) is a chaotic, block-in-matrix unit outcropping in the Montebaranzone syncline in the northern Apennines. The Mm occurs in the uppermost part of the Termina Fm, the Middle–Late Miocene interval of a succession deposited in a wedge-top slope basin (Epiligurian succession). The Mm is closely associated with bodies of authigenic carbonates, characterized by negative values of δ¹³C (from ?18.22 to ?39.05 ‰ PDB) and chemosynthetic benthic fauna (lucinid and vesicomyid bivalves). In this paper, we propose that the Mm is a mud volcano originated by the post-depositional reactivation and rising of a stratigraphically lower mud-rich mass transport body (Canossa–Val Tiepido sedimentary mélange or olistostrome) triggered by fluid overpressure. We base our conclusion on (1) the Mm pierces the entire Termina Fm and older Epiligurian units and represents the direct continuation of the underlying Canossa–Val Tiepido mélange; (2) the geometry and facies distribution of the Montebaranzone sandstone body, which are compatible with a confined basin controlled by the rising of the Mm; (3) the systematic presence of large-scale (lateral extension 300–400 m) seep-carbonates associated with the mélange, suggesting a persistent gas-enriched fluid vent from the ascending overpressured mud; (4) blocks and clasts sourced from the Mm, hosted by the authigenic carbonates, conveyed by ascending mud and gas-enriched fluids. The Mm represents one of the few fossil examples of reactivation of a basin-scale sedimentary mélange (olistostrome); a three-stage model showing mechanisms of Mm raising is proposed.