Mario Barbieri

The campi flegrei (Italy) geothermal system: A fluid inclusion study of the mofete and San Vito fields

Abstract A fluid inclusion study of core from the Mofete 1, Mofete 2, Mofete 5, San Vito 1, and San Vito 3 geothermal wells (Campi Flegrei, Campania, Italy) indicates that the hydrothermal minerals were precipitated from aqueous fluids ( ±CO 2 ) that were moderately saline (3–4 wt.% NaCl equiv.) to hypersaline (> 26 wt.% NaCl equiv.) and at least in part, boiling. Three types of primary fluid inclusions were found in authigenic K-feldspar, quartz, calcite, and epidote: (A) two-phase [ liquid (L) + vapor (V) ], liquid-rich inclusions with a range of salinity; (B) two-phase ( L + V ), vaporrich inclusions with low salinity; and (C) three-phase [ L + V + crystals (NaCL) ], liquid-rich inclusions with hypersalinity. Results of microthermometric and crushing studies are reported for twenty drill core samples taken from the lower portions of the five vertical wells. Data presented for selected core samples reveal a general decrease in porosity and increase in bulk density with increasing depth and temperature. Hydrothermal minerals commonly fill fractures and pore-spaces and define a zonation pattern, similar in all five wells studied, in response to increasing depth (pressure) and temperature. A greenschist facies assemblage, defined by albite + actinolite , gives way to an amphibolite facies, defined by plagioclase (andesine) + hornblende , in the San Vito 1 well at about 380°C. The fluid inclusion salinity values mimic the saline and hypersaline fluids found by drilling. Fluid inclusion V/L homogenization temperatures increase with depth and generally correspond to the extrapolated down-hole temperatures. However, fluid inclusion data for Mofete 5 and mineral assemblage data for San Vito 3, indicate fossil, higher-temperature regimes. A limited 87 Sr/ 86 Sr study of leachate (carbonate) and the leached cores shows that for most samples (except San Vito 3) the carbonate deposition has been from slightly 87 Sr-enriched fluids and that Sr isotopic exchange has been incomplete. However, San Vito 3 cores show an approach to fluid/rock Sr equilibrium with a fluid similar to modern ocean water in 87 Sr/ 86 Sr ratio. The Campi Flegrei volcanic system has evolved undersaturated products, mostly trachyte, and defines a large ( ≈ 12 km ) caldera. The hydrothermal system developed in this location can be used as an analog for fossil systems in similar trachytic environments. The potential for ore mineralization is expressed by the recognition, from fluid inclusion and drilling data, of ore-forming environments such as boiling and brine stratification.

The new chronology of the Ceprano calvarium (Italy)

IntroductionThe fossil human calvarium known as Ceprano (Latium, Italy) iscommonly dated to 800e900 ka, on the basis of geological andstratigraphical inferences (Ascenzi et al., 1996, 2000). This chro-nology appeared somehow consistent with the “archaic”morphology of the calvarium and its peculiar combination offeatures, which gave rise to a controversial taxonomic identity(Ascenzietal.,1996,2000;Clarke,2000;Manzietal.,2001;Mallegniet al., 2003; Bruner and Manzi, 2005, 2007). A re-evaluation of thislate Early Pleistocene chronology has been advanced by Muttoniet al. (2009) on the basis of paleomagnetic data. This hypothesis istested here, based on the combined evaluation of the multidisci-plinary evidence collected during recent systematic excavations.The specimen was discovered on 13 March 1994 within a claylevel partly destroyed by bulldozers working for a new road ina locality known as Campogrande (Fig. 1), about 3 km SW ofCeprano and 100 km SE of Rome, in Central Italy (for review andreferences see Manzi, 2004). The sediment containing the cranialfragments yielded more than 50 fragments. However, the craniumremainedincompletebecauseneitherportionsof thefacenorteethwere retrieved.The geological history of the Campogrande area was initiallyreferred to two main stratigraphic complexes (Ascenzi et al., 1996,2000; Ascenzi and Segre, 1997a,b): 1) upper fluvio-colluvialdeposits, with variable occurrence of volcanoclastic products (lateEarly to Middle Pleistocene); 2) lower lacustrine deposits, withoutvolcanoclastic products (roughly predating 1.0 Ma). The layercontaining the human calvarium was considered to belong to thelower portion of the upper stratigraphic complex. Its chronologywas inferred as more ancient than the Acheulean site of FontanaRanuccio, near Anagni (458 5.7 ka; Segre and Ascenzi, 1984),possiblyolderthan700ka,adatecorrespondingtothebeginningofthe volcanic activity in the region (Fornaseri, 1985).Given the presence in the Ceprano basin of various LowerPaleolithic assemblages, the archaic features of the calvarium andits hypothetical chronological position were considered in associ-ation with Mode 1, or Oldowan, techno-complexes (Biddittu,1984;Ascenzietal.,1996,2000).Mode1Paleolithicintheareacomefromvarious localities, including Arce, Castro de’ Volsci, Fontana Liri(Biddittu, 1972, 1974), as well as from the Campogrande area itself(see SOM-1), whose assemblages are characterized by flint orlimestone pebble-tools (mostly choppers, chopping-tools andpercussion tools), by debitage with hammerstone flakes, and byrelatively frequent cores, with a low degree of exploitation, mostoften unifacial, and high frequencyof cortical striking platforms. Asfor Mode 2 or Acheulean assemblages, new recent data (excava-tions 2001e2006; see below) have made it possible to bettercharacterize the material from Campogrande. These materials arenot numerically rich, but they yield evidence of each production

Chemical evolution, petrogenesis, and regional chemical correlations of the flood basalt sequence in the central Deccan Traps, India

The lava sequence of the central-western Deccan Traps (from Jalgaon towards Mumbai) is formed by basalts and basaltic andesites having a significant variation in TiO2 (from 1.2 to 3.3 wt%), Zr (from 84 to 253 ppm), Nb (from 5 to 16ppm) and Ba (from 63 to 407 ppm), at MgO ranging from 10 to 4.2 wt%. Most of these basalts follow a liquid line of descent dominated by low pressure fractionation of clinopyroxene, plagioclase and olivine, starting from the most mafic compositions, in a temperature range from 1220° to 1125°C. These rocks resemble those belonging to the lower-most formations of the Deccan Traps in the Western Ghats (Jawhar, Igatpuri and Thakurvadi) as well as those of the Poladpur formation. Samples analyzed for87Sr/86Sr give a range of initial ratios from 0.70558 to 0.70621. A group of flows of the Dhule area has low TiO2 (1.2–1.5 wt%) and Zr (84–105 ppm) at moderate MgO (5.2–6.2 wt%), matching the composition of low-Ti basalts of Gujarat, low-Ti dykes of the Tapti swarm and Toranmal basalts, just north of the study area. This allows chemical correlations between the lavas of central Deccan, the Tapti dykes and the north-western outcrops. The mildly enriched high field strength element contents of the samples with TiO2 > 1.5 wt% make them products of mantle sources broadly similar to those which generated the Ambenali basalts, but their high La/Nb and Ba/Nb, negative Nb anomalies in the mantle normalized diagrams, and relatively high87Sr/86Sr, make evident a crustal input with crustally derived materials at less differentiated stages than those represented in this sample set, or even within the sub-Indian lithospheric mantle.

Origin and distribution of strontium in the travertines of Latium (central Italy)

Abstract The Sr contents of 54 samples of Quaternary travertines from 23 deposits of Latium were measured. Sr isotope ratios of only selected samples were also determined. On the basis of the Sr contents, ranging 20–3700 ppm, it is possible to distinguish two different geographic areas: the northwestern part of Latium (“A” zone) characterized by high Sr contents ( x = 1219 ppm ) and the southeastern part (“B” zone), where the travertines have low Sr contents ( x = 151 ppm ). Such low contents are quite compatible with a provenance of the element from the dissolution of marine limestones. The Sr isotope ratios ( 0.7078 ⩽ 87 Sr 86 Sr ⩽ 0.7089 ) of the travertines from the A zone are significantly lower than the values characteristic of the Sr-rich volcanics from the same area. This suggests that leaching of the volcanic rocks was not generally a major factor in providing Sr to the travertine-bearing waters. Due to the high Sr content, the Upper Triassic evaporties seem to be the most likely source of the element for the travertines from the A zone. Only the Palidoro deposit has an isotopic ratio (0.7125) close to the value of the local volcanics, clearly suggesting a provenance of the element from the leaching of such rocks.

Petrology and geochemistry of the Passa Quatro alkaline complex, southeastern Brazil

Abstract The Passa Quatro alkaline complex is formed by strongly undersaturated, felsic intrusive and subvolcanic rocks (nepheline-syenites and phonolites). The abundance and fractionation of alkali feldspar, together with lesser amounts of femic phases, generates a suite which tends, as a whole, to become peralkaline and nepheline-enriched. Variation diagrams indicate, however, strong scatter of the data, reflecting non-homogeneous distribution of major and accessory phases and, probably, slightly different liquid lines of descent. Judging from the absence of restitic phases of crustal origin and other petrologic features, these rocks are probably products of extreme fractionation from basanitic magmas. On the basis of potassic affinity and initial 87 Sr/ 86 Sr isotopic ratios (0.70505), these rocks closely resemble other alkaline complexes of the Rio de Janeiro littoral belt, confirming provincialism in the Meso-Cenozoic alkaline province of eastern continental Brazil.

Oxygen and strontium isotope ratios in some ejecta from the Alban Hills volcanic area, Roman comagmatic region

Oxygen and strontium isotope analyses have been obtained for minerals of some ejected blocks found in the Albano “peperino”, one of the largest pyroclastic formations of the Alban Hills volcanic district, Roman comagmatic region. Also analyzed for 87Sr/86Sr were one leucititic lava and one pyroclastic rock from this same area.None of the ejecta analyzed shows 18O/16O and 87Sr/86Sr as low as one would expect for rocks of deep-seated origin. In fact, the Sr isotope ratios range from 0.7101 to 0.7109 and pyroxenes have δ18O-values 0.7 to 1.4 per mil higher than pyroxenes from carbonatites, basalts, gabbros and ultramafic rocks throughout the world (excluding one peculiarly 18O-rich sample, which very likely has undergone metamorphic interactions with the country rocks).Thus, the ejected blocks from the Alban Hills derived from magmas contaminated with crustal material rich in 18O and 87Sr. In addition, the fact that the ejecta are practically indistinguishable in their 87Sr/86Sr from the lava and pyroclastic rock indicates that these rocks all derive from the same silicate melts; this implies that the so-called homoeogenic blocks from this volcanic district do not represent early differentiates of a primitive, uncontaminated magma.

The role of fractional crystallisation, crustal melting and magma mixing in the petrogenesis of rhyolites and mafic inclusion-bearing dacites from the Monte Arci volcanic complex (Sardinia, Italy)

Abstract Rhyolitic lavas and mafic inclusion-bearing dacites (MIBD) form the dominant products of the Monte Arci volcanic complex, one of the most active sites of volcanic activity in Sardinia during the Pliocene. The massif is composed of four distinct eruptive episodes (Phase 1: rhyolites; Phase 2: dacites and andesites; Phase 3: quartz-normative trachytes; Phase 4: mafic lavas ranging from subalkaline to mildly alkaline). Monte Arci magmatism has been characterized by open-system behaviour, with both mantle and crustal contributions and magma mixing. Although the mafic products are restricted to the latest stage of activity, mafic inclusions are quite common in many rhyolites and dacites. The mineral assemblages of the inclusions are dominated by plagioclase + orthopyroxene ± augite, with minor olivine, FeTi oxides and variable amounts of residual trapped liquid giving rise to a fine-grained groundmass. They represent blobs of magma entrained in a partly molten state and provide evidence of a basaltic contribution to the petrogenesis of their enclosing lavas, both as parental magmas or as a source of heat for partial melting of crustal rocks. Rhyolites are metaluminous to slightly peraluminous rocks with a wide range of SiO2 contents (67–75%). They fall into two groups: (1) Mafic inclusion-bearing rhyolites (MIBR). These have initial 87 Sr 86 Sr ratios between 0.70526 and 0.70897 and commonly show relatively high values of Ti, Mg, Fe, Ca, Sr and compatible trace elements (Ni, Cr, V); cordierite-bearing, highly restitic, crustal xenoliths are rare. (2) Inclusion-free rhyolites (IFR). They include both porphyritic lavas (IFR1) and obsidians (IFR2, IFR3), which share low values of Ti, Fe, Mg, Ca, Sr and are strongly depleted in compatible trace elements. IFR1–2 have a marked LREE/HREE fractionation and a narrow range of 87 Sr 86 Sr ratios (0.70885–0.70972), whereas IFR3 have larger Sr isotopic ratios (0.71529–0.71553), low Th, Zr, Hf, LREE contents and low LREE/HREE. Nd isotopic composition is quite uniform for all rhyolite types, with relatively low 143 Nd 144 Nd ratios (0.51216–0.51228, ϵNd ranging between −9.3 and −6.9). MIBR appear to be the product of fractionation of subalkaline (tholeiitic) magmas + assimilation of a crustal component moderately enriched in 87Sr and/or with low Sr content. IFR1–2 may be derived from partial melting of moderately 87Sr-rich crustal lithologies with retention of garnet and plagioclase (+K-feldspar) in the restite, although AFC processes (followed by effective separation from the basalts) cannot be excluded. Obsidians IFR3 need a crustal source with higher 87 Sr 86 Sr ; their peculiar geochemical features most probably reflect the complex behaviour during partial melting of accessory minerals carrying REE, Th, Zr, Hf. Among the eruptive products of Phase 2, mafic inclusion-bearing dacites (MIBD) provide evidence of basalt-rhyolite mixing: (a) coexistence of glasses with SiO2 content ranging from 64 to 72 wt.%; (b) a phenocryst assemblage including phases of basaltic and rhyolitic provenance; and (c) abundant crystal-rich inclusions related to a basaltic intrusion. The extrusion of these lavas has been preceeded by an explosive eruption of rhyolitic tuffs ( 87 Sr 86 Sr initial ratio =0.71097 ). The most satisfactory petrogenetic model for MIBD includes: (1) differentiation of subalkaline (tholeiitic) magma to a silica-poor and Ti-Fe-P rich liquid; (2) partial melting of wall-rocks yielding a rhyolitic magma segregated at the top of the basaltic reservoir; and (3) explosive eruption of the uppermost portion of the magma chamber followed by mixing of rhyolite with the underlying part of the system to form a hybrid dacite.

The Messinian ‘Vena del Gesso’ evaporites revisited: characterization of isotopic composition and organic matter

Abstract The ‘Vena del Gesso’ (Gessoso-Solfifera Fm, Messinian) is a 227 m-thick ridge along the western Romagna Apennines (Italy) consisting of up to 16 selenite cycles separated by shales and minor carbonate. The total organic carbon values of these deposits range between 0.087–0.016% (gypsum) and 3% (shales). Organic matter is dominated by black debris associated with continental debris. Algae and dynocysts are rare (<1%). The amount of amorphous organic matter is low but it may reach up to c. 40%. The 87Sr/86Sr of gypsum and carbonate vary from 0.708890 to 0.709024, yielding non-oceanic values with several exceptions that plot within error of coeval oceanic values only in the upper part of the section (from the 6° bed). The sulphur isotope composition of gypsum range between δ34S =+21.8 and +23.7‰ and may represent precipitation of δ34S-enriched gypsum due to the fractionation effect or recycling of coeval gypsum with contributions of brine-sediment redox variations. The isotope values of carbonates show a large variability (−6.4<δ18O<+6.05‰; −14.68<δ13C<+2.5‰), suggesting a complex origin by mixing of marine and non-marine waters with a significant contribution of reduced organic matter. These data point to an evaporite basin dominated by continental waters which received significant phases of marine recharge in the upper part together with a marked facies change. Because seawater recharges and a similar facies change are present in other Messinian sections, it follows that we have new possible geochemical and facies markers to correlate the Lower Evaporites across the Mediterranean.

Rubidium and potassium relationship in some volcanoes of central Italy

Abstract The rubidium and potassium content of extrusive and pyroclastic rocks of Alban Hills, Vico and Cimino Volcanoes as well as of their minerals such as leucite, sanidine, biotite and zeolites have been investigated. The extrusive rocks of Alban Hills (Colli Albani) have a K/Rb ratio of 174; the rocks of Vico Volcano have a ratio of 141 and those of Cimino Volcano a ratio of 188. The pyroclastic rocks of Alban Hills show a K/Rb ratio of 104, and those of Vico Volcano a ratio of 78. Both are significantly lower as compared with respective rocks. The relative enrichment of Rb observed in pyroclastics is explained by terms of the behaviour of the elements during the magmatic crystallization, and during weathering and other secondary alteration processes affecting the pyroclastic rocks. The leucite phenocrysts of extrusive rocks show a rather variable Rb content (from 1,160 to 3,000 p.p.m.), but a K/Rb ratio in any case lower than the K/Rb ratio of the groundmass. Sanidine phenocrysts likewise show a rather variable Rb content (from 285 to 620 p.p.m.), but a K/Rb ratio in any case higher than the corresponding ratio of the groundmass. It follows that the early separation of leucite or of sanidine can control the K/Rb ratio of the residual melt. The behaviour of rubidium during the weathering and other secondary alteration processes affecting the extrusive and pyroclastic rocks is here discussed. Analcimization gives rise to an indirect enrichment of rubidium: alteration of feldspars and feldspathoids leading to illitic or to amorphous clay minerals produces a depletion of rubidium. The influence of the structural type of the host mineral and of the secondary alteration processes on the K/Rb ratio is emphasized.

Strontium geochemistry in the epithermal barite deposits from the Apuan Alps (northern Tuscany, Italy)

Abstract The strontium contents of 18 barite samples from three epithermal deposits in the Apuan Alps range from 3000 to 8000 ppm, with an average value of 5508 ± 1409 ppm. The Sr contents do not distinguish the three deposits, suggesting a provenance of this element from the same source. Sr-isotope ratios (0.7102, 0.7101, 0.7101) measured in three barites from the three deposits support this suggestion; moreover, indicating a large participation of radiogenic 87 Sr derived from a continental reservoir, the “Verrucano Formation”, in the Palaeozoic basement.