ABSTRACT LXXIX, September 2010 n. 2:

Abstract - Petrological and geochemical data of volcanic rocks from several sites of the Caltanissetta Basin (central-southern Sicily) are discussed to provide information about volcanism in the northern portion of the African plate. Volcanics occur as large isolated blocks, mainly as pillows and subordinate lava flows, enclosing sedimentary levels of marly limestones. They are packed in several Paleogene and Neogene clayey lithologies, which are correlated to the sedimentation into the Miocenic Foredeep. The age of volcanism is referable to Early Oligocene (Rupelian), as revealed relative dating of the interpillow calcareous sediments. The studied samples are transitional and poorly evolved alkali basalts. Petrographic study highlights a discrete uniformity for the most samples, with porphyritic texture characterized by olivine, clinopyroxene and plagioclase phenocrysts in a microcrystalline groundmass, composed of the same phases plus opaque minerals. Major and trace element data are poorly variable and the trends show low degree of fractional crystallization with some contribution of mineral accumulation. Abundance and ratios of incompatible elements resemble OIB-type volcanics from intraplate environment. A slightly different garnet lherzolite sources that underwent a low partial melting degree can be hypothesized for the studied rocks. The Oligocene volcanism of the Caltanissetta Basin results as different magmatic pulses intruded along lithospheric fractures originated in response to flexure and uplift of the African paleomargin, in the pre-subduction stage and then incorporated in the future Sicilian accretionary prism..

Hans-Joachim Massonne - Phase relations and dehydration behaviour of calcareous sediments at very-low to low grade metamorphic conditions.

Abstract - P-T pseudosections were calculated in the system SiO₂-TiO₂-Al₂O₃-MgO-MnO-FeO-O₂-CaO-Na₂O-K₂O-H₂O-CO₂ with the PERPLE_X software package for the pressure-temperature range 1-25 kbar and 150-450°C to gain a better understanding of the phase relations of metamorphosed calcareous sediments at low temperature including their dehydration behaviour during prograde metamorphism. For this purpose the applied thermodynamic data set of Holland and Powell, augmented by data of Massonne and Willner, was enlarged by end-member data for Mnstilpnomelane. In addition, a three-component solid-solution model for stilpnomelane and a fourcomponent model for Ca-Mg-Mn-Fe carbonate with calcite structure were introduced.
For geotherms of 10-15°C/Km, which are typical for the metamorphism of rocks involved in accretionary wedge systems, a major dehydration event occurs at temperatures between 270 to 330°C in both carbonatefree and calcareous greywackes. For an investigated marly limestone this event takes place at about 100°C higher temperatures. The H₂O-CO₂ fluid formed is characterized by very low CO₂ contents. The major dehydration event is made responsible for the detachment of sediments on top of a subducting slab.

Gabriele Vola and Maurizio Marchi - Quantitative phase analysis (QPA) of the Luserna Stone.

Abstract - The Luserna Stone (Pietra di Luserna) is a leucogranitic orthogneiss, characterized by a micro-Augen texture, with a marked foliation that is mostly associated to a visible lineation: it geologically pertains to the Dora-Maira Massif, and outcrops in a quite large area (approximately 50 km²) of the Cottian Alps, on the border between the Turin and Cuneo provinces (Piemonte, Italy). In this study five samples of granulated rock (1-2 mm) are considered, from three different localities; they are representative of three facies (Massive, Splittable and Bianchetta). The mineralogical and petrographic features of this stone, used for many centuries as building material, have been characterised by complementary methods, such as: 1) Quantitative Phase Analysis (QPA) by the Rietveld method using X-ray powder diffraction data (XRPD); 2) mineral modal analysis using optical microscopy (OM) on thin-sections by point-counting a statistical number of grains; 3) scanning electron microscopy equipped with an energy-dispersive spectrometer (SEM-EDS); 4) X-Ray fluorescence spectroscopy (XRF). The proportion of minerals in each sample determined by XRPD and OM are in good agreement between them. The SEM-EDS data combined with mineral proportions determined by XRPD and OM allow to determine bulk chemical compositions of these five samples very close to those obtained by XRF. The decreasing of alkali content determines a linear increase of phyllosilicate and a decreasing of feldspar amounts. These results evidence that complementary methods can efficiently be used to evaluate undesired constituents in aggregate for concrete, such as phyllosilicates (i.e. micas and chlorites). The combination of XRF and XRPD data allows an accurate and rapid compositional and mineralogical evaluation of the different facies of the Luserna Stone.

Donatella Barca, Rosolino Cirrincione, Eloisa De Vuono, Patrizia Fiannacca, Fabio Ietto and Antonino Lo Giudice- The Triassic rift system in the northern Calabrian-Peloritani Orogen: evidence from basaltic dyke magmatism in the San Donato Unit.

Abstract - Green to gray-green metabasite dykes occur within the metasedimentary sequence of the San Donato unit, the lowest tectonic unit cropping out in the Mt. Pollino area (northern Calabria). these metabasites are intruded in the anisian-ladinian metasediments of the San Donato sequence, but not in the overlying carnic levels, suggesting a Middle triassic emplacement age.
The original porphyritic texture is locally preserved in weakly foliated samples affected by very low- to low-grade metamorphism during the alpine orogeny. the metamorphic assemblages are indicative of a polyphase evolution: an early synkinematic albite + actinolite + chlorite + epidote + quarz + Fe-Ti oxides association developed at the subgreenschistgreenschist facies transition, and a later albite+calcite+chlorite+quartz+Fe-Ti oxides mineral association, in microdomains and patches, suggests localised increase of X_CO2 in the fluid phase.
The protolith of the metabasites has been identified in alkaline to transitional basalts with geochemical features consistent with generation by partial melting of an enriched mantle source in a within plate setting. in particular, their geochemical composition is consistent with a low degree partial melting of a enriched mantle source. Based on geological constrains and on petrological considerations, these Middle triassic metabasites may document the initial break-up stage of the Pangea, evolving to continent rifting and subsequent oceanization processes.

Alberto De Bonis, Celestino Grifa, Alessio Langella, Mariano Mercurio, Maria Luisa Perrone and Vincenzo Morra- Archaeometric study of roman pottery from Caudium area (Southern Italy).

Abstract - Aim of this work is the mineropetrographical characterization of late antique painted common wares from the ancient roman settlement of Caudium (today Montesarchio, Campania region, Italy).
Twenty-two samples (4^th to 6^th century AD) collected during the archaeological survey of the area, were studied to investigate their manufacturing technology and to attest a possible local production. Ceramics shards are represented by 16 painted common ware samples; furthermore, 2 bricks, 2 kiln rejects and 2 fragments of cooking ware were investigated for comparison.
Polarized light microscopy (PLM) observations and X-ray fluorescence chemical analyses (XRF) allowed to characterize the Caudium pottery production. two main groups of fragments were distinguished: the first one composed by painted common wares, bricks and kiln rejects, the other one by cooking ware only. two textural typologies were recorded within the first group (composed by calcareous clay pastes: average CaO ~ 11.0%), one characterized by fine pastes containing tiny clasts of quartz, feldspars and few volcanic inclusions, the other by coarser pastes with predominant volcanic temper. Cooking wares (composed by non-calcareous clay: average CaO ~ 1.6%) show a large amount of temper of both volcanic and detrital origin, the latter mainly constituted by quartzarenite clasts. Multivariate statistical analysis (Hierarchical Clustering and Principal Component Analysis) confirms the already identified groups. Mineralogical analyses and scanning electron microscope observations of the sintering degree of clayey paste enabled to evaluate the firing temperatures of the most representative samples (from 800 to 1200°C).
The whole data set, along with geological features of the investigated area (wide availability of raw materials) and archaeological evidences (kiln refuses, large number of fragments of the same ceramic class), allowed to hypothesize a local production of the painted common wares and thus to define the respective reference group.

Riccardo Basso and Cristina Carbone - Relationships between crystal data and crystal chemistry of carpholite-group minerals.

Abstract - Multiple linear regression analyses have been conducted on minerals of the carpholite group, whose members have the general formula A_0-1M1₂M2₂M3₂ [(OH,F)₄|Si₂O₆]₂, to find the relations between unit cell parameters, mean polyhedral cationoxygen distances, refractive indices and composition. For the regression, the mean ionic radii of atoms occupying the octahedral coordinated sites M1, M2 and M3 have been used as compositional parameters. the investigation is based on crystal structure of 9 samples, cell metrics of 35 samples and optical data of 13 samples all belonging to the carpholite group. the resulting regression equations enhance the prediction models of crystallographic parameters reported in the literature and they can be used for minerals with chemical compositions more complex than mere Fe-Mg-carpholites. Moreover, multiple linear correlation has been detected among the lattice parameters a, b and c.