Paleomagnetism of Jurassic to Miocene sediments from the Apenninic carbonate platform (southern Apennines, Italy): evidence for a 60° counterclockwise Miocene rotation

The tectonic evolution of the Apennine belt/southern Tyrrhenian Sea system is addressed through a paleomagnetic study of Lias to Langhian sediments from the Apenninic carbonate platform (southern Apennines, Italy). Reliable paleomagnetic data gathered from 21 sites document a regional-scale post-Langhian 80° counterclockwise (CCW) rotation. Since previous studies of the Plio-Pleistocene clays spread over the orogen had shown a ∼20°CCW rotation, we conclude that the southern Apennines rotated by 60° during Middle-Late Miocene. Our data provide evidence that the southeastward drift of Calabrian block (and synchronous spreading of the southern Tyrrhenian Sea) induced ‘saloon door’ like deformation of the southern Apennines and Sicily, which underwent similar magnitude (although opposite in sign) orogenic rotations. A paleomagnetically derived paleogeographic reconstruction shows that at 15 Ma (Late Langhian) the Alpine-Apennine belt collided with a NNE-oriented carbonate platform corridor surrounded by oceanic basins. We speculate that both the end of the Corsica-Sardinia rotation and the eastward jump of the locus of back-arc extension (from the Liguro-Provençal to the Tyrrhenian Sea) may have been consequences of this event.     

Mercury in Eledone cirrhosa from the Northern Tyrrhenian Sea: Contents and relations with life cycle

The Hg concentration in horned octopus was studied in relation to its biological cycle. The metal was measured in the muscle tissue of specimens of different size, sex and maturity. This species proved to be a strong accumulator of mercury, whose concentration was found to be correlated with length independently of the sex. The relationship with size was found also for the organic form. Consideration was given to the danger of frequent consumption of this cephalopod and to its use as a biomonitor of environmental mercury impact.     

Preliminary geochemical and thermodynamic assessment of the geothermal resources, Sulphur Springs area, St Lucia, W.I.

A high-temperature geothermal resource has been located on the island of St Lucia (W.I.), which was tapped by means of a well drilled in 1988 to a total depth of 1410 m, in the Sulphur Springs area. The well encountered mainly dacitic agglomerates and lava flows and a permeable zone below ≈1340 m, with a maximum temperature of ≈290°C.Well productivity decreased from an initial value close to 62 t/h to about 33 t/h under well-head pressures of 1.5 MPa (15 bar a) after 255 h of production. Initial reservoir static pressure was 7.5 MPa (75 bar a). A decline in reservoir pressure of about 15% was observed at the end of the production test. During the first two days of exploitation the well initially produced a two-phase fluid with high steam fraction, which then developed into superheated steam with a high content of non-condensable gas exceeding 100 1/kg at standard conditions and a computed P(CO₂) of 1 MPa (10 bar).The average steam fraction at reservoir conditions, computed from gas composition after 120 h of production is 0.3.High HCl concentrations of about 300 ppm are present in the condensate steam indicating the presence of a high concentrated boiling brine to the point of halite saturation. All data support the hypthesis of a hydrothermal hot-water system prior to drilling, that underwent a very rapid drawdown with production.     

Crystal-chemistry and cation ordering in the system diopside-jadeite: A detailed study by crystal structure refinement

The Nybö eclogite pod in Norway is characterized by a great variety of clinopyroxene compositions with Jd contents ranging from less than 5% up to nearly 80%, whilst Ac+Hd contents remain almost constant (mostly within 10±5%).Unconstrained X-ray structure refinement has been carried out on 16 pyroxene crystals (8 with C2/c and 8 with P2/n space group) from the Nybö eclogite, and also on one omphacite crystal (from Lago Mucrone in the Sesia-Lanzo Zone, Western Alps) which displays the highest degree of cation ordering yet described. The final discrepancy factors range from 0.014 to 0.029. The population of the sites has been determined on the basis of bond length considerations and of the results of the site occupancy refinement. Six of these crystals were subsequently analysed by electron microprobe.The tetrahedral sites are occupied by Si with negligible amounts of Al. Al, Mg, Fe³⁺ and Fe²⁺ occur at the octahedral sites; in the ordered P2/n crystals Al and Fe³⁺ are concentrated at the M11 site, whilst Mg and Fe²⁺ are concentrated and the M1 site. The eight-coordinated sites contain Ca and Na with negligible amounts of Fe and/or Mg. Ordering of Ca and Na takes place in the P2/n samples in such a way that in the most ordered crystal the M2 site contains almost exactly 0.75 Na+0.25 Ca and the M21 site 0.25 Na+0.75 Ca.Some geometrical features of the tetrahedra as well as of the octahedra (e.g. tetrahedral quadratic elongation and TILT angle) are not a simple linear function of composition, even when no change in space group occurs. The crystals evidently do not behave like a binary system of the two components, Di and Jd, but behave rather as if the composition Di_0.50 Jd_0.50 was a distinct end member.The boundaries between disordered and ordered phases in the Nybö pyroxenes fall at about 0.35 and 0.65 Jd/(Di+ Jd), in close agreement with the previous TEM investigations.The degree of order varies with composition following a bell-shaped curve: different coaxial bell-shaped curves can be drawn for crystals which have similar compositions but come from different metamorphic environments. The order vs composition diagrams may be useful for the interpretation of the P-T-t histories of the host rocks.     

Violan revisited: Mn-bearing omphacite and diopside

Summary Violet clinopyroxenes (violan) from the manganese deposit of Praborna, near St. Marcel (Aosta Valley, Italy) occur in two different varieties: euhedral crystals grown in vugs and massive lamellar to fibrous aggregates. The euhedral crystals are predominantlyP2/n omphacite with a(Di+Hd+Jo)/(Jd+Ac+Mnjd) ratio close to unity. The lamellar aggregates consist mainly of disorderedC2/c impure diopside with alternating patches of pure diopsidic and moderately omphacitic compositions.The deep violet colour, occasionally shading to blue, is presumably due to the presence of both Mn³⁺ and Mn²⁺ ions. Detailed crystal structure determinations andEPR spectra investigations, however, did not clearly solve the question of the oxidation state of manganese because of the low amounts of manganese being present in violan. Crystal structure determinations and microprobe analyses nevertheless clearly showed that violan is not a mineral species. The name should therefore be reserved for the ex-colore violet varieties of both diopside and omphacite.

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Violan, ein Mn-führender Omphacit und Diopsid

Zusammenfassung Violett gefärbte Klinopyroxene (violan) von der Manganlagerstätte Praborna bei St. Marcel (Aosta-Tal, Italien) bilden entweder idiomorphe Kristalle in Hohlräumen, oder massive lamellare bis feinfaserige Aggregate. Die idiomorphen Kristalle sind zum überwiegenden TeilP2/n Omphazite mit einem (Di+Hd+Jo):(Jd+Ac+Mnjd) Verhältnis von etwa 1 1. Die lamellaren Aggregate bestehen hauptsächlich aus ungeordnetemC2/c Diopsid, wobei die chemische Zusammesetzung partienweise zwischen diopsidisch und leicht omphazitisch wechselt.Die tief violette Farbe wird wahrscheinlich durch das Vorhandensein von Mn³⁺ und Mn²⁺-Ionen verursacht. Eine eindeutige Klärung dieser Frage war jedoch trotz detaillierter Kristallstruktur-Bestimmung und Auswertung vonEPR Spektren nicht möglich, da der Mangangehalt der Violane überraschend gering ist.Die detaillierten Kristallstruktur-Analysen ergaben jedoch eindeutig, daß Violan keine selbständige Mineralspecies ist. Dieser Name sollte daher nur für die violetten Farbvarietäten von Omphaziten und Diopsiden verwendet werden.

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Poisson's ratio at high pore pressure

Laboratory investigations suggest that a precise relationship exists between Poisson's ratio, pore pressure and fluid type. Values of Poisson's ratio for dry samples are significantly smaller than those for fluid-saturated samples. The values are anomalously high for high pore pressure, with the possibility of differentiating between gas-saturated, brine-saturated and oil-saturated porous rocks.
The present study considers two overpressure models, based on oil/gas conversion and disequilibrium compaction, to obtain Poisson's ratio versus differential pressure (confining pressure minus pore pressure). The model results are in good agreement with experiments. Poisson's ratio is approximately constant at high differential pressures and increases (decreases) for saturated (dry) rocks at low differential pressures. Fluid type can be determined at all differential pressures from Poisson's ratio. The analysis is extended to the anisotropic case by computing the three Poisson's ratios of a transversely isotropic rock versus differential pressure. While one of them is practically independent of effective pressure, the others increase with increasing pore pressure. Experiments performed on cores under different pressure conditions, and calibration of the models with these data, provide a tool for inverting pore pressure from seismic data.     

LAI and chlorophyll estimation for a heterogeneous grassland using hyperspectral measurements

The study shows that leaf area index (LAI), leaf chlorophyll content (LCC) and canopy chlorophyll content (CCC) can be mapped in a heterogeneous Mediterranean grassland from canopy spectral reflectance measurements. Canopy spectral measurements were made in the field using a GER 3700 spectroradiometer, along with concomitant in situ measurements of LAI and LCC. We tested the utility of univariate techniques involving narrow band vegetation indices and the red edge inflection point, as well as multivariate calibration techniques, including stepwise multiple linear regression and partial least squares regression. Among the various investigated models, CCC was estimated with the highest accuracy (, ). All methods failed to estimate LCC (), while LAI was estimated with intermediate accuracy ( values ranged from 0.49 to 0.69). Compared with narrow band indices and red edge inflection point, stepwise multiple linear regression generally improved the estimation of LAI. The estimations were further improved when partial least squares regression was used. When a subset of wavelengths was analyzed, it was found that partial least squares regression had reduced the error in the retrieved parameters. The results of the study highlight the significance of multivariate techniques, such as partial least squares regression, rather than univariate methods such as vegetation indices in estimating heterogeneous grass canopy characteristics.     

The Mesozoic continental rifting in the Mediterranean area: insights from the Verrucano tectofacies of southern Tuscany (Northern Apennines,Italy)

In the Alpine-Mediterranean region, the continental redbeds and shallow-marine siliciclastics related to the early depositional phases of the Late Permian-Mesozoic continental rifting are referred to as the most common representative of the “Verrucano tectofacies”. The Verrucano-type successions exposed in southern Tuscany are diachronous, spanning from Triassic to earliest Jurassic in age, and accumulated within the Tuscan domain, a paleogeographic region of continental crust that due to the opening of the Piedmont–Ligurian ocean formed part of the Adria passive-margin. They belong to the metamorphic Verrucano Group and the non-metamorphic Pseudoverrucano fm. Viewed overall, these Verrucano-type successions appear to manifest five episodes or pulses of an ongoing continental rifting. With the exception of the first episode that developed entirely within a terrestrial setting, each one is represented by basal Verrucano-type continental siliciclastics overlain by compositionally mixed marine deposits, which resulted from four diachronous, post-Middle Triassic transgressions. This suite of tectonic pulses produced the progressive westward widening (backstepping) of the Tuscan domain in the rifting south-Tuscany area.