Abstract - Vol LXXVI, Septmber 2006 n. 2

- Determination of the origin of unusual glass with metallic spherule inclusions found in the area between Inzingkofen and Sigmaringen (Bavaria, Germany), South-West of the Steinheim-Ries craters

- This paper reports the characteristics of a suite of pale green glass fragments and their metallic spherule inclusions (5 to 400 ?m) found over a relatively wide area between Inzigkofen and Sigmaringen (Bavaria, Germany), about 150 km SW of the Steinheim-Ries impact craters. The distribution area of these glasses and their close macroscopic similarity (apart from the spherules) with moldavite suggested us that they may shed new light on the nature of the binary asteroid which caused the Steinheim-Ries impact craters. However, our petrographic and chemical data rule out an extra-terrestrial origin. Metallographic microstructure, lack of Ni and high P contents (up to 9 wt.%) reveal the metallic inclusions as cast iron spherules. The chemical composition of the host glass consistently differs from both moldavite and suevite compositions. Our data indicate that the investigated samples are by-products of metallurgic activity. This conclusion is consistent with the presence in the Sigmaringen area of important cast iron furnaces which have been operating since the 18th century.

- Glass mosaic tesserae from Pompeii: an archeometrical investigation

-This work reports the results of an archaeometrical investigation performed, through a multi-technique approach, on a series of Roman glass mosaic tesserae found in Pompeii excavations. Chemical and mineralogical analyses of mosaic tesserae of different colours were performed in order to single out the colouring and opacifying agents employed during the Roman Imperial Age. Moreover, due to the paucity of information on the production technology of mosaic tesserae, the chemical data are compared with that of common transparent glass found at the same site, in order to evaluate whether vessels and mosaic tesserae could have been prepared with the same recipes and starting from the same glass batch. The chemical analyses were performed by electron microprobe, whereas the mineralogical investigation on the opaque samples were carried out by coupling scanning electron microscopy and X-ray powder diffraction. The results obtained show that all the samples analysed have the typical composition of natron-based glass. The similarities with the chemical composition – at least in terms of major elements – of common transparent glass could suggest the use of the same raw materials for the preparation of the batch. All opaque blue and green tesserae contain crystalline aggregates respectively of calcium and lead antimonates, except one blue tessera, which contains traces of cuprorivaite and quartz (Egyptian blue pigment). The red sample shows the presence of cuprite aggregates dispersed in a lead-rich matrix. This paper is dedicated to the memory of the friend and colleague Filippo Olmi, who prematurely passed away few months ago.

- Evolution of the hydrothermal system at La Crocetta “feldspar” mine: fluid inclusion and stable isotope constraints on the environment of late stage veins

- A significant portion (average 200,000 t/y) of the Italian production of feldspathic raw materials for ceramic industries comes from La Crocetta deposit (southern Tuscany, Elba Island). The quarried rocks (so called “eurites”) are pervasively sericitized porphyritic aplites, showing peculiar K-rich (7 to 11 wt% K2O) and Fe-Ca-S-poor compositions. The main stage of mineralization (i.e., sericitization of the aplites) was described in previous studies. This paper is focussed on the late-stage, post-sericitization veins which crosscut eurite rocks. The development of these N-S striking veins may be associated with conjugate faults related to movements along the Elba Centrale regional fault. Mineralogy of veins includes calcite with subordinate quartz and pyrite. a peculiar rock facies, locally known as “candor”, is made up by particularly abundant calcite-bearing veins, which represent the last hydrothermal event at La Crocetta. Calcite-hosted fluid inclusions show homogenization temperatures (Th) between 197° and 227° C, with salinities between 1.1 and 2.7 wt.% NaCl-equivalent. In agreement with geological background and inferred fluid circulation model, a low pressure regime of vein emplacement can be assumed. Accordingly, these Th should correspond to trapping temperatures not exceeding 250° C. The carbon (d13CPDB) and oxygen (d18OV-SMOW) values of calcite are -5.4 to -7.4‰, and 6.3 to 10.2‰, respectively. At 250°C, the calculated values of d18O of water, and d13C of CO2 in equilibrium with vein calcites are in the ranges, respectively, of 1.0 to 2.9‰, and -6.2 to -4.1‰. These data are consistent with formation of the late-stage veins from a dominantly meteoric fluid, mixed with CO2 from a deep-seated magmatic or metamorphic source.

- Plumbomicrolite from the Ploskaya Mountain, Keivy Massif, Kola Peninsula, Russia: composition and crystal structure

- A sample of plumbomicrolite from Ploskaya Mountain, Kola Peninsula (Russia) was analyzed by electron microprobe and X-ray diffraction. A single crystal [a = 10.571(1) Å] was selected and the structure was refined in the space group Fd ¯3 m to Robs = 4.89 % and Rall = 5.79%. Pb2+ was found to be completely ordered on the A site (normal structure). However, because the Y site was found to be partially occupied, the A cation may locally result in a six-, or seven-, or eight-fold coordination. Whenever two neighbour Y sites are vacant, six X atoms around the A position form a trigonally flattened octahedron, while a trigonal scalenohedron occurs when two Y sites around A are occupied. When only one neighbour Y site is occupied, the A cation assumes an asymmetrical seven-fold pyramidal coordination. Due to the stereoactive electron lone-pair of Pb2+, this last coordination should be strongly preferred. The chemical data as well as crystal chemical considerations led to assign the following crystal chemical formula: A[Pb1.30Ca0.29Na0.08U4+0.03]S=1.70B [Ta0.82Nb0.62Si0.23Sn4+0.15Ti4+0.07Fe3+0.10Al0.01]S=2.00X[O6]Y [O0.23(OH)0.25]S=0.48.

- The grey marble of Porta Praetoria (Aosta, Italy): a minero-petrographic characterisation and provenance determination

- The provenance determination of the ancient stone materials results the main insight archeometric application in the archaeological field, even if it can result difficult to reach when the studied material consists of white or coloured marbles.
A petrographic application on grey marbles, using a scanning electron microscope equipped with a electronic microprobe system, is here reported. The marbles of Porta Praetoria (Aosta, Italy), manufactured by the Ancient Romans in the Republican Age, are studied. According to historical documents, two types of marble may have been used: the marble coming from Villeneuve or from Aymaville villages (Aosta Valley). Both marble varieties occur as lenses interbedded in Upper Piedmont Zone, an ophiolitic unit belonging to Penninic domain of the Western Alps. The sample from the Porta Praetoria is constituted by a grey marble, characterized by calcite and dolomite levels of different grain size, which reflect different grey tonality and confer to the rock a typical veined appearance (“bardiglio” variety). Minor silicate minerals, concentrated in the dolomite layers, are also present. In particular, this marble is characterized by the contemporaneous presence of three dioctahedral micas, with the potassic mica enriched in the celadonitic end-member as crystallized at high pressure metamorphic conditions. In additions, phlogopite and Mg-chlorite are also present. Comparable paragenesis is shown by the Aymaville marble, whereas the marble from Villeneuve resulted devoid of phlogopite and Mg-chlorite. Therefore, on the basis of petrographic and microchemical features, it may be suggested that the grey marble used for the edification of the Porta Praetoria in Aosta comes from the village of Aymaville, located in the right side of the central Aosta Valley.

- A lamproitic component in the high-K calc-alkaline volcanic rocks of the Capraia Island, Tuscan Magmatic Province: evidence from clinopyroxene crystal chemical data

- The Island of Capraia (Tuscan Archipelago) is the westernmost volcanic centre of the Tuscan Magmatic Province. It is made by the overlap of two volcanoes: the Capraia and the Zenobito ones. The Capraia Volcano is a large composite apparatus dominated by lava flows and lava domes with a high-K calc-alkalic affinity built up over the period between 7.5 and 6.9 Ma at its top. The Zenobito Volcano is a small monogenetic apparatus that produced a cinder cone associated to a very small plateau-like lava structure in a short time spanning at 4.6 Ma, overlapping the south-westernmost edge of the Capraia Volcano. Outcropping rocks of the older volcano are high-K calc-alkalic (HKCA) rocks ranging in composition from dominant andesite and dacite to rare rhyolite, straddling latite and trachyte fields. Volcanic rocks from the Zenobito Volcano are much more uniform in composition ranging from potassic trachybasalt to shoshonite, but some sub-alkalic samples falling within the andesite basaltic field have been also found. To explore the relationships between clinopyroxene structural and chemical parameters and the physico-chemical conditions of their crystallisation, selected clinopyroxene crystals from the older high-K calc-alkalic rocks (10 crystals) and from the younger shoshonitic rocks (2 crystals) of the Capraia and Zenobito Volcanoes, respectively, have been studied. Single-crystal X-ray diffraction measurements and microprobe analyses have been carried out. The clinopyroxene from Capraia Volcano has augitic composition whereas clinopyroxene from Zenobito Volcano is enriched in the diopsidic component. Structural parameters show significant variations, in particular in the VM1 and Vcell. These volumes are larger for clinopyroxene crystals from Capraia volcanic rocks than those of clinopyroxene crystals from shoshonitic rocks of the Zenobito Volcano. It is unlikely that the increase of VM1 and Vcell observed in the clinopyroxene crystals from HKCA rocks can be simply referred to a different chemical composition of the host magmas. More likely, it could reflect different pressure of crystallisation suggesting that the magma chamber of the Capraia Volcano HKCA volcanic rocks was sited at shallower depth than that of shoshonitic volcanic rocks of the Zenobito Volcano. On the other hand, comparison between clinopyroxene diopsidic crystals from Zenobito Volcano and those from Radicofani volcanoes highlights a close structural and chemical similarit.. By contrast, clinopyroxene crystals from HKCA rocks show significant differences with respect to those of other calc-alkaline volcanic rocks from volcanic arcs, such as the Aeolian Arc. In particular, the deficiency in Al found in the clinopyroxene crystals from Capraia Volcano recalls a similar characteristic observed in clinopyroxene from lamproites. This possibly suggests that the Capraia high-K calc-alkalic magmas might be related in some ways to lamproitic magmas and that clinopyroxene crystals record this petrologic characteristic, which is not anymore observed in the bulk rock compositions. The occurrence of lamproitic component in the genesis of HKCA magmas of the Capraia Volcano may also explain the large variation in the K2O contents of the Capraia volcanic rocks, which is not easily explained by any common evolution process. It also agrees with the hypothesis that calc-alkalic, shoshonitic and lamproitic magmas in the Tuscany Magmatic Province are cogenetic, and that the lower incompatible element contents of calc-alkalic and shoshonitic rocks reflect a dilution effect generated by a larger degrees of partial melting in a veined mantle source. Finally, Capraia Volcano and Zenobito Volcano magmas are considered to represent different episodes of partial melting of different mantle sources.

- Technology and Provenance of roman ceramics from Scoppieto, Italy: a mineralogical and petrological study

- Scoppieto (Terni, Italy) was an important centre devoted mainly to the production of terra sigillata vessels, lamps, and probably utilitarian pottery in the Augustean period-production, which increased sharply from the Tiberian period onwards. Several findings of coarse ware (Opus Doliare, amphorae) suggest that the site may have been active in the production of common ceramics before that of the “Terra Sigillata Italica”. However whether these materials were imported or produced on site was completely unknown until now. A collection of coarse ware, of both good quality and waste products, were characterised by mineralogical (Rietveld and calorimetric analyses) and petrological analytical techniques (XRF, LA-ICP-MS), to investigate production techniques and provenance. Rietveld analysis indicated differing contents of amorphous contents from 17% to 52 %, with a mineralogical association always constituted of quartz, feldspar, plagioclase and pyroxenes, and in some cases by phyllosilicates and calcite. Considerable weight loss variations, from 0.5 % to 8%, are associated with the presence of calcite and phyllosilicates. Generally, the highest weight losses were measured in the good-quality products, whereas waste products turned out to have been fired at higher temperatures than those of the breakdown of calcite and phyllosilicates. The chemical and mineralogical compositions of good-quality ceramic objects and those of waste products indicate that the unsuccessful process, which produced a large quantity of discarded materials, was due to poor control of firing temperature, not to mistakes in the mixture. Trace element abundances in good-quality and waste products are similar, indicating local production and favouring the hypothesis that Scoppieto was active since pre-Augustean times. Further constraints to this hypothesis are given by a detailed study of clinopyroxene crystals of igneous origin occurring in all the studied ceramics, compared with the chemical features of the same mineral phase present in volcanic rocks of the nearby Roman Magmatic Province. Geochemical results indicate that the rocks of the Bolsena Volcanic Complex, located near the Scoppieto production site, were probably the volcanic starting materials, used as refractory components in the ceramics examined here.

- Carbon-bearing cordierite from Allumiere (Tolfa volcanic center, Latium, Italy): occurrence, crystal- structure and FTIR microspectroscopy

- This paper reports the crystal-chemical study of cordierite from a volcanic ejectum from the Tolfa volcanic center (Latium, Italy). The studied rock was sampled within the pyroclastic deposit (“tufo caotico”) outcropping in a quarry at Colle dello Spizzicatore, Allumiere Community. The sample was studied by electron microprobe analysis (EMP), single-crystal structure refinement and Fourier-transform infrared microspectroscopy (FTIR). Combination of these techniques allowed detailed characterisation of the amount, location and coordination of cations and volatile molecules in the channels. Cordierite from Allumiere is orthorhombic, space group Cccm; refined cell-parameters are (in Å): a = 17.1580(6), b = 9.7573(3) and c = 9.3228(3). EMP analyses show an intermediate XMg [Mg/(Mg+Fe) = 0.58], and a very low alkali (Na + K = 0.042 apfu) content. Single-crystal FTIR spectra are strongly polarised; the absorptions observed in the H2O-stretching region can be assigned to H2O molecules oriented with the H…H vector // a and the molecular plane // (001). The absorptions observed in the C-O stretching region can be assigned to both CO2 and CO molecules oriented // a; the spectra also show the presence of 13C and 18O in the sample. Using the molar absorption coefficients available in the literature, H2O = 0.02 wt% and CO2 = 0.22 wt% are calculated from the measured band intensities. The observed mineral assemblage and the volatile composition of cordierite are coherent with a thermometamorphic overprint on an early metapelite, which occurred at low-P (? 2 Kbar), high-T (> 700°C) and extremely reducing conditions.

- Mingling and mixing features in basaltic andesites of the Eastern Cordillera (Central Andes, 24°S): a petrographic and microanalytical study

- The basaltic andesites of the Diego de Almagro volcanic complex (Central Andes, 24°S, 66°W) were erupted during Late Miocene at 300 km from the active arc, in the Eastern Cordillera, at the easternmost end of an important strike-slip structure, the Calama-Olocapato-El Toro. These volcanic rocks preserved traces of their pristine history in the form of xenocrysts and in the diverse populations of phenocrysts coexisting due to magma mixing. In Central Andes, crustal contamination commonly conditions the composition of magmas ascending through the thick continental crust, masking the characteristics of the mantle sources. Thus, we carried out detailed petrography and mineral chemistry studies on selected Diego de Almagro basaltic andesites, with the aim to identify the populations of crystals in equilibrium with mafic melts. The results suggested that mixing of basaltic and andesitic magmas occurred during the ascent and storage in the crust. The fraction of basaltic magma prevailed in the mixing process compared to the andesitic one. Crystal zoning and disequilibrium features indicate that magma mixing produced intimate hybridisation. The preservation of primitive crystal assemblages is probably due to the geological situation in which the Diego de Almagro complex emplaced, that favoured the formation of monogenetic volcanic centres rather than of a central volcanic edifice, thus limiting the residence of mafic magmas in the crust and their interaction with crustal partial melts.

- Characterization and genetic inferences of arsenates, sulfates and vanadates of Fe, Cu, Pb, Zn from Mount Cervandone (Western Alps, Italy)

- Mount Cervandone is among the most renowned mineral deposits in the Alpine chain and type locality of several very rare REE-arsenates. The present study allowed for the characterization and description of the assemblages of a number of arsenates, sulfates and vanadates of Fe, Cu, Pb, Zn that occur with a number of rare minerals of B, Be, As, Nb, Y, REE on the Italian slope of Mount Cervandone. The mineral deposits of Cervandone mainly occur in alpine quartz fissures and pegmatitic dikes. The pegmatitic dikes are hosted by very fine grained two-mica leucocratic gneisses. Locally the pegmatite dikes are cross cut by quartz veins. The assemblages reported in this study indicate that arsenates, sulfates and vanadates of Fe, Cu, Pb, Zn are mainly hosted in quartz veins and only occur sporadically in pegmatitic dikes. In the pegmatite dikes the Be, As, Y and REE minerals occur with higher frequency than in the quartz veins. During the Alpine event we account for a “scenario” where swarms of NYF (niobium, yttrium, fluorine) granitic pegmatites intruded the leucogranitic-aplites. It is unequivocal that the pegmatites show a strong NYF geochemical signature represented by the occurrence of an unique mineralogy. Following these premises we expected that during the Alpine event As-enriched hydrothermal fluids circulating through pegmatite dikes allowed the destabilization of accessory minerals hosted in these dikes and consequently the hydrothermal fluids assimilated light elements (Be, B, F), high field strength elements (Y, Nb, Ta) and rare earth elements (La, Ce, Nd, Th, U) and allowed the crystallization of several rare and exotic minerals.

- Petrology of some amphibole-bearing volcanics of the pre-Ellittico period (102-80 ka), Mt. Etna

- We present here petrological and geochemical data on volcanics cropping out in southern and northeastern walls of the Valle del Bove (Mt. Etna), belonging to the Rocche, Serra Giannicola Grande and Canalone della Montagnola Units. These units constitute the remnants of several volcanoes that were active in the time span 102 - 80 ka, i.e. before the growth of the Ellittico-Mongibello strato-volcano. Their products (Na-alkaline in serial affinity), range in composition from hawaiites to benmoreites. Amphibole (kaersutite) is present as phenocryst in all the studied rocks, and commonly shows breakdown coronas of rhönite +/- clinopyroxene, formed during magma ascent. Nevertheless, in mafic rocks, amphibole occurs as an early liquidus-phase enclosed in a Ca-rich plagioclase (up to An87). We propose that early cotectic crystallization of amphibole and Ca-plagioclase may reflect H2O-rich melts. Variations in major and trace elements among lavas erupted from coeval centres, suggest that fractional crystallization was the principal evolutionary process but at the same time magmas feeding the various volcanoes belonging to the Rocche Unit were more heterogeneous with respect to the younger Units studied here.

- The Gladstone-Dale compatibility of the arsenate minerals follows the general trend for species in other chemical classes with the majority of the species falling into the superior and excellent categories.

- An overview of phase chemistry and magmatic evolution in the Cretaceous flood basalt province of northern Madagascar

- The Cretaceous flood basalts of northern Madagascar range in composition from picritic basalt to basaltic andesite with a serial affinity ranging from tholeiitic to slightly alkaline. Rare, more evolved rocks are represented by peraluminous rhyodacites and peralkaline rhyolites. The intrusive complexes have a large range of lithologies, from ultramafic (dunites, wehrlites, clinopyroxenites) to felsic (leucogabbros, syenites). We report here the chemical composition of olivine, Ca-rich and Ca-poor pyroxene, feldspar, Fe-Cr-Ti oxide, amphibole, glass and accessory phases; the significance of their variations for what concerns geothermobarometry and regional chemical correlations is also discussed. The evolution from the least to the most evolved compositions, and from the whole rocks towards the interstitial glasses, which are thought to be low-pressure residual liquid compositions, has been modelled with fractionation of the observed phases, leaving Mg- to Fe-rich gabbroic solids.

- Jervisite, NaScSi2O6: a new occurrence, chemical data and crystal structure

- Jervisite, scandium sodium pyroxene, has been found in cavities of the Baveno granite at Prini quarry, Piedmont (Italy). Electron microprobe analysis and single crystal X-ray diffraction study [space group C2/c, with cell parameters a = 9.844 (2), b = 9.059 (2), c = 5.328 (2) Å, b = 106.55 (2)°] pointed to an idealized crystal chemical formula (Na0.85Ca0.15)(Sc0.85Fe0.15)Si2O6. The structure was refined to a R1 = 0.038. The average bond distances in the octahedral M1 (Sc,Fe) and eightfold coordinated M2 (Na,Ca) sites are M1-O 2.110 Å and M2-O 2.550 Å.

- Nowadays a general concern “flies” over the human community regarding the increase of carbon dioxide concentration in the atmosphere. Although there are authors that suggest anthropogenic influence of such increase after the discovery of agriculture (about 8,000 years ago; e.g., Ruddiman, 2003), it is evident that the industrial revolution the 19th century in central Europe, when wood and coal were burned extensively to refine iron, definitely influenced the natural trend of CO2 variation. Only in the last thirty years has the input rate of CO2 become really fast, and will grow faster and faster in the near future, when developing countries like India and China will reach the standard of life of the western countries, requiring an increasing demand of per capita daily energy need. The greenhouse effect of carbon dioxide is a well-known phenomenon since the beginning of the 20th century when the Swedish chemist Arrhenius discovered this property by studying the transmission of heat in fluid materials. What is not commonly known is that rapid changes in the concentration of carbon dioxide in the atmosphere are natural events and that, in the past, even in a very recent past, large variations of climatic conditions have been related to sudden carbon dioxide variations in the atmosphere (Petit et al., 1999). It is very likely that mass extinction of dinosaurs and other animal species at the end of the Cretaceous may have been caused by such rapid variations. Causes of temperature variation of the atmosphere have been envisaged in both terrestrial and solar (Milankovitch Cycles in Hays et al., 1976) systems, but the quantification of the different natural sources of carbon dioxide, as the main cause of climate changes, is still quite poor. It is however well known that the weathering of silicate minerals (and about 99% of the terrestrial crust is made up of silicates) affects the consumption of CO2 from the atmosphere. Actually, without the discharge of terrestrial carbon dioxide into the atmosphere, plant and animal life would disappear in less than 300,000 years, and the temperature of the atmosphere would drop rapidly to values below 0 °C. Where is the deep “engine” that provides the continuous re-generation of carbon dioxide and allows its concentration in the atmosphere to be maintained more or less steady (varying roughly from 0.01 to 0.1 % by volume)? This engine is not shallow and is located in the Earth’s mantle, whose dynamo drives the continental drift as well as the melting of crustal material: volcanic activity continuously supplies carbon dioxide into the atmosphere. Carbon dioxide, in spite of being a minor component, in both the crust and the atmosphere, really plays a role of paramount importance for both life and climate (through the greenhouse effect). However, our knowledge of the different sources (magmatic, metamorphic, and so forth) is still matter of debate. Experience in Italy has shown that non-magmatic carbon dioxide discharging from hydrothermal systems is an important reservoir of deep-seated carbon dioxide. Nevertheless, inside the carbon cycle the ratio between: i) bicarbonates generated by organic acids in silicate weathering of soils and discharged by rivers into the oceans and ii) the production of volcanic and non volcanic carbon dioxide, remains largely unbalanced, i.e. some deep carbon dioxide is still missing. Where is this carbon dioxide from? Is the increase of carbon dioxide concentration in the atmosphere something that human beings should really care about? The answer cannot be given, yet. The problem could probably be solved in the future, at least when the natural cycle of carbon dioxide and its feedback with solar cycles will be clearer than at present.

- The stones of the Svevian castle of Rocca Imperiale (Calabria, southern Italy): characterization and provenance

- The Svevian Castle of Rocca Imperiale (north-eastern Calabria, southern Italy) was built between 1220 A.D. and 1225 A.D. by the Emperor Federico II of Svevia. This paper addresses the geochemical and petrographical characterisation of the stones used for its construction. The research evidenced that most of the Castle stony materials (marly limestones, calcareous marls, marls, arkoses and quartz arenites), were carved from siliciclastic outcrops nearby Rocca Imperiale. Stones from outer areas are more rare (biocalcarenites). These stones probably come from the nearby Puglia region and were mainly used for decoration.

- Size and textural type distributions of chondrules in three new carbonaceous chondrites: Acfer 374, HaH 337 and Acfer 366

- Three carbonaceous chondrites, Acfer 374 (CO 3.0), HaH 337 (CK 4) and Acfer 366 (CH 3), have been studied in detail, analizing three thin sections of each meteorite, in order to determine their chondrule sizes and typologies. As concerns the chondrule sizes, the measurements in the sample Acfer 374 provided a mean value of 110 µm whereas the measurements in HaH 337 and Acfer 366 showed mean values of 700 and 110 µm, respectively. Chondrule typologies display remarkably valuable differences: GO and GO-pk chondrules are prevailing in Acfer 374 (68 vol%), PO is the most abundant chondrule type in HaH 337 (68 vol%) and C type is predominant in Acfer 366 (70 vol%). These results, in agreement with the literature data, confirm the importance of the study of chondrule sizes and typologies, as well as of their distributions and relative abundances, as powerful tools for the comprehension of chondrules origin and for the classification of carbonaceous chondrites, when properly integrated with a petrographic and minerochemical characterization.

- High temperature gas-mixing furnace: experimental set up and applications to Earth Sciences

- The present paper is constituted of two parts. First the set up of a vertical quench furnace is described with special focus on technical details such as the location of the volume in which the temperature reaches its maximum and it is steadier (the hot zone). In the second part some applications in mineralogic and petrologic researches, in which the use of the furnace, is crucial are presented; they belong to on-course projects on phase relationships of hawaiitic lava under surface conditions, homogenisation of melt inclusions hosted in olivine and preparation of starting materials for high pressure-temperature experiments.

- Petrological and geological data of porphyritic dikes from the Capo Arco area (eastern Elba Island, northern Tyrrhenian Sea)

- New geological surveying at a 1:10,000 scale (CARG Project) allowed to refine the stratigraphic, structural and magmatic setting of the Elba Island. This paper aims at characterizing two dikes of likely Late Miocene age (Casa Carpini dikes), previously defined as lamprophyres (i.e. kersantite), outcropping in eastern Elba, on the eastern and southern slopes of the Monte Arco, close to Porto Azzurro and mapped as Casa Carpini dikes. The grey to light-grey Casa Carpini dikes, intercalated within the phyllites and metasandstones of the Ligurian-Piedmontese Acquadolce Unit, are quartz-diorites in composition with a maximum of 23% of mafic minerals (biotite). They show a microcrystalline porphyritic texture consisting of plagioclase, biotite, quartz, K-feldspar, and rare muscovite with scattered xenocrysts of quartz, plagioclase and K-feldspar. Plagioclase phenocrysts display normal zoning with An% = 9-23; the variability of An in the plagioclase microcrysts is wider (5-34 %). The REE patterns are characterised by fractionated LREE and MREE and negative anomaly of Eu. The mantle-normalized trace element patterns show high content of the most incompatible elements with a positive spike of Th and Pb, and high LILE/HFSE ratios. Negative spikes of Nb, P and Ti are also observable. No negative anomalies of Sr are present, and Ce/Sr ratios are much lower than other magmatic rocks from Elba. A depletion in K, Rb and Cs is also observed in the studies rocks, possibly a result of secondary processes. Sr-Nd isotopic ratios for the two outcrops of the studied dikes show significant differences, with 87Sr/86Sr = 0.711845 and 0.711769 and 143Nd/144Nd = 0.512223 and 0.512246. The Casa Carpini dikes are petrographically different from most of the dike rocks associated to the granitoid plutons and laccoliths of the Elba Island. Instead, analogies can be found with the granodiorites to quartz-monzodiorite Orano porphyries, the last magmatic product of western Elba. The petrological and geochemical characteristics of the studied dikes, are typical of the intermediate-acidic rocks of the Elba Island. As other rocks from Elba, they show petrographic and geochemical evidence of mixing between a calcalkaline mafic-intermediate magma similar to that of Capraia and a crustal anatectic melt. The geochemical signatures of the studied dikes suggest a more important role of mafic magmas with respect to the bulk of the Elba magmatism.

- “The ancient mortars, an attestation of the Material Culture: the case of Florence”

- The aim of this paper is to describe and highlight the role of artificial stone materials used by man through history in order to further the understanding of history itself. The study of artificial materials such as mortar, plaster, ceramics, etc. made and used over the centuries, augments our knowledge of the “Material Culture.” It provides information about raw materials, technologies and processes as well as data that are important from the historical standpoint and for the restoration of works of art. Specifically, the paper reviews some examples of ancient mortars used in the Florence area. Petrographic analysis alone was able to provide of data which permitted a detailed reconstruction of production methods. Scientific analyses, together with data obtained from historical sources, have brought to life materials which otherwise would have remained “dead.” These methods make it possible to reconstruct specific details of the monuments reviewed and furthermore, they clearly reveal how much of this ancient knowledge and the methods have been completely lost to the detriment of “history” and the present.

- Time Series to Petrogenesis: Analysis of Oscillatory Zoning Patterns in Plagioclase Crystals from Lava Flows

- In this contribution we present preliminary results of analyses of plagioclase oscillatory zoning from three different lava flows cropping out on the island of Capraia (Tuscan Archipelago, Italy) with the aim of understanding the causes of the oscillatory zoning. Analysis are performed using a new method that combines microanalysis with image analysis and allows us to extract compositional time series with high spatial resolution along the zoning profiles. Compositional time series are analysed by the Detrended Fluctuation Analysis (DFA) method and results indicate that most zoning profiles in the studied lava flows can be regarded as having the property of 1/f-noise. By using a simple dynamical system, the logistic map, it is shown that this property can be attributed to self-organized criticality, i.e. a feature typical of systems lying at the boundary between stability and chaos. It is suggested that the statistical properties of plagioclase oscillatory zoning may be explained by continuous restructuring of flow fields in the magmatic system due to variations of the geometrical configuration in which the magmatic processes occurred at different times. It is suggested that analyses of compositional time series extracted from plagioclase crystals may be used as an additional petrological tool to better understand the complex processes occurring in magmatic systems.

- Mineral chemistry profile: a valuable approach to unravel magma mixing processes in the recent volcanic activity of Stromboli, Italy

- A mineral chemistry study including compositional zoning profiles on clinopyroxene and plagioclase has been performed on pyroclastic deposits of recent Stromboli (with an age of about 2-3 ka), erupted just before the setting of the typical present-day Strombolian activity (Post-Pizzo series). The mineral chemistry characterisation of samples from the bottom and top of the Post-Pizzo series has revealed a complex magmatic history recorded by mineral phase compositional variations. These data suggest that the initial phase of the eruptive period of Post-Pizzo series was characterised by repeated arrival of mafic magmas emphasized by several changes in the crystal compositions. After the magma hybridizations, the system nearly recovered its initial composition by associated continuous fractional crystallisation, thus establishing a nearly steady-state dynamics of the magma system. The arrivals of mafic magma batches became more important during the late Post-Pizzo eruptive period, leading in the final stage to a more mafic magma composition, similar to that of the basaltic products erupted by the present-day activity. This plumbing system behaviour reminds the dynamics driving the pre-eruptive processes responsible of the present-day Strombolian activity. Accordingly, the Post-Pizzo series seems to represent the period during which the magmatic conditions for the present-day activity were developed. The micro-analytical approach using zoning profiles can be considered a powerful tool in revealing magma mixing processes and in helping to clarify the dynamics of magmatic systems.

- Hydrothermal alteration in the Berlin geothermal field (El Salvador): new data and discussion on the natural state of the system

- The Berlin geothermal field (Republic of El Salvador), located about 110 km ESE of the city of San Salvador, is a water-dominated system with temperature close to 300°C in the production zone. The geothermal wells at Berlin intercepted calc-alkaline more or less hydrothermally altered lava flows and pyroclastic rocks. This study presents data on hydrothermal alteration, together with their distribution with depth, microprobe analyses of hydrothermal minerals and geochemistry of altered rocks. The stability of some minerals under natural state (i.e. before exploitation and reinjection) and present state reservoir conditions have been evaluated both using mineral saturation indices and activity vs. temperature diagrams. This information contributes to the reconstruction of the thermal and chemical characteristics of the field and their temporal evolution and they, therefore, play an important role for the correct evaluation of the geothermal resource and for the future exploration strategies. Four mineral alteration zones, occurring at increasing depths, have been distinguished on the basis of the abundance and appearance of characteristic hydrothermal minerals. The hydrothermal phases may either replace the igneous minerals, or fill cavities or fractures crosscutting the rock. The shallowest alteration zone is characterized by the presence of relatively low-temperature minerals, such as saponite, montmorillonite, heulandite etc.. At greater depth, hydrothermal phases, such as epidote, wairakite, prehnite, hydro-garnets typical of higher temperature conditions, occur. Quartz, calcite and chlorite are widespread in most of these zones. Geochemical analyses show that fluid-rock interaction caused an increase of Ca and LOI, no variation of Mg and Fe and a decrease of Na and Si in an altered core sample with respect to unaltered rock. Whereas, K was totally leached out from the altered rock. The shape of the deepest alteration zones gives a record of a past natural state condition (not the most recent) and contrast with present-day thermal feature, suggesting that significant thermal variations occurred from the time of alteration formation to present-day. Recent natural state and present state conditions of the reservoir fluid were computed by using geochemical data of the present-day discharged fluids. Temperature and the CO2 content decreased, in most of the wells, evolving from the natural state of the system to the present state conditions. These variations can be explained with variable degrees of degassing due to isoenthalpic or sub-isoenthalpic boiling. Mineral saturation indices indicate that wairakite is unstable under both present and natural state conditions. Log[Ca2+]/[H+]2) vs. temperature diagram indicates that epidote is generally not stable under both present and natural state conditions, its stability depends mostly on the CO2 partial pressure. This explains why epidote compositions are not correlated to the temperature. Chlorite appears to be stable under both present and natural state conditions and its composition varies with temperature. The AlIV content in this mineral from different wells shows, in fact, a fairly good correlation with temperature following the equation: T(°C) = 47.238 x AlIV + 175.77. This equation, therefore may be used for temperature estimates for the Berlin geothermal field.

- Provenance of shales and sedimentary history of the Monte Soro Unit, Sicily

- Source area weathering, provenance and tectonic setting from the Lower Cretaceous Monte Soro Unit shales (North-eastern Sicily) have been analysed for mineralogical and chemical compositions. Samples are characterized by high values of MMI index. Among clay minerals I/S mixed-layered and illite are prevailing on chlorite and kaolinite. The amount of illite layers among mixed-layered smectite/illite reflects late diagenetic post depositional conditions reasonably reached during the post-Cretaceous subduction associated and related collision involving the European and African plate margins. Major and trace elements abuncances indicate the dominant detrital nature of the shales with minimal or absent hydrothermal and biogenic contributions. Ti2O2/Al2O3 ratios are distinctive of shales produced by weathering of felsic to intermediate continental crustal rocks. High CIA and CIW values suggest that the source area was subjected to a prolonged and/or intense chemical weathering. The chemical composition and trace element ratios Zr/Y, Zr/Nb, Zr/Ti, Nb/Y, Th/Cr, Th/Co, La/Co, K/Rb are close to those of the metamorphic basement of the Monti Peloritani segment of the European block. However, in our case, it is difficult to distinguish between a first-cycle sediment production and a recycling of the Upper Triassic – Lower Jurassic Verrucano continental sediments, being the metamorphic basement mainly formed by metagraywakes and metapelites.