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The present study deals with the geochemical changes observed along Nile Delta inner shelf sediments over a period of 20 years (1995–2015). Major, minor, and trace constituents as well as rare earth elements (REE) were investigated in the surface sediments collected from seven transects along the inner shelf on five years intervals. Geochemical composition of sediments in Nile Delta inner shelf exhibits continuous changes over time due to the depositional and sediment transport processes. The sediments are generally enriched with Fe and Ti oxides, as well as Ta, Nb, Y in comparison to the Upper Continental Crust (UCC). These alterations signify the impact of processes such as erosion and sediment transport, as well as the impact of anthropogenic interferences such as damming the Nile River Flow. The reduction of the sediment input from the Nile River has somehow altered the geochemical signature of the inner shelf sediments. The REE patterns indicate weathering in areas subjected to erosion, while trace elements and major oxides spatial and temporal distributions concentrate eastwards under the influence of the easterly sediment transport pattern. Nile Delta inner shelf presented a typical case for understanding the link between geochemistry and sedimentary processes in nearshore and deltaic systems.

The Triassic alkaline basaltic rocks (TABR) of North Kamarbon are located in Central Alborz, which is regarded as the northern part of the Alpine-Himalayan orogenic belt. Fractional crystallization does not appear as a major process in the genesis of TABR while different degree of partial melting may be regarded as the main process, based on petrography and geochemistry studies. The geochemical characteristics of TABR are in conflict with a substantial involvement of continental crust or crustal contamination. High (La/Yb)N and (Dy/Yb)N ratios, along with other geochemical features, in the TABR magma, suggest an asthenospheric origin, with low degree of partial melting of a garnet-bearing mantle sources. Enrichment patterns of LILE (Ba, Sr and Th), HFSE (Nb, Ta and Zr) and P, and depletion at HREE (Yb, Lu) are similar to what observed for OIB or intraplate alkaline magmatic rocks. The Sr and Nd isotopic ratios range from 0.70448 to 0.70522 and from 0.51269 to 0.51280, respectively, suggesting time-integrated slightly depleted magma sources. The data indicate that the evolution of TABR could be related to the rifting basin, in Late Triassic, which caused their development by upwelling and decompressional melting of an asthenospheric mantle, without a major involvement of subcontinental lithospheric mantle or crustal contamination. Keywords: Mantle source, Rifting basin, Central Alborz, Iran

Thallium is among the most toxic elements to humans. Environmental regulations of the European Community adopted by Italy pose a maximum concentration level for Tl in groundwater of 2 μg/L. However, at present drinkable water must not abide any concentration threshold for thallium and this element is not routinely monitored. In the past-mining area nearby the Valdicastello Carducci village (northern Tuscany, Italy), characterized by Tl-bearing ores, water from a spring that has been tapped for human consumption contains thallium in the range 4.3–27.8 μg/L. The challenge of this study is to highlight the mechanisms leading to Tl contamination in groundwater, by crossing hydrochemical and O-H isotopic data with hydrogeological information. We propose that the Tl-contamination in the spring results from a binary mixing that occurs within a karst system involving an uncontaminated Ca-HCO3 water (mainly interacting with limestone) and a component originated by the interaction of acid drainages (generated by the weathering of Tl-bearing mineral phases in the area) with dolomitic host rocks. In this process, most of the potentially toxic elements released during the weathering are scavenged by the carbonate neutralization of the acid plume due to adsorption onto the iron and manganese oxyhydroxides that formed during pH changes. Nevertheless, the aquifer has little or no attenuation capacity for thallium. Moreover, O-H isotopic data and hydrogeological constraints are compatible with a spring feeding mechanism related to a piston displacement effect.

The present paper deals with a field experiments on evaporite rock samples and groundwater investigations in the Quinis test site, a hamlet of the Enemonzo municipality in NE Italy, were sinkholes occurred in the past and are still occurring causing severe damage to the existing infrastructures. The area is characterised by a Carnian evaporitic bedrock made of gypsum and anhydrite mantled by alluvial and colluvial deposits. In order to evaluate the loss of weight and volume of the subcropping evaporites as responsible for sinkholes, a field-experiment was carried out. Inside seven piezometers, at different depths, evaporitic rock samples were exposed to the naturally occurring variable climatic conditions such as degree of humidity, different air flow and hydrodynamic. The rock samples were installed at the beginning of April 2017 in the dry sections of piezometric tubes, in the vadose zone and in the phreatic zone. Data related to water level fluctuations were recorded by using data-logger devices and highlight significant changes in the water table. After 13 months of data recording (May 2018), rock samples were removed, reweighted and the volume loss measured. In addition, water from piezometer-experiment, representative of the groundwater circulation, were collected at different depths. The obtained results indicate that rock sample reduction is dependent on the hydrological regime and water chemistry and not on the number of days during which the samples remained submersed. In particular, the water geochemistry highlights the possible role in gypsum/anhydrite dissolution due to NaCl water admixing in a complex scenario. In additional, the geochemical data highlight the occurrence of some potentially toxic elements (As, Fe, Mn) at concentrations of concern in some water. This approach represents a novel contribution in the study of karst hazard in evaporites adding a tile to the knowledge of the fast evolutionary processes which cause sinkhole formation.

The oxygen and hydrogen isotopic composition of stream water, springs, groundwater tapped from irrigation wells and acid mine drainages were determined during two different surveys in 2015 in an area highly impacted by past-mining activity of Apuan Alps (Italy), as a guidance on good practices for water management. The isotopic local meteoric water line (LMWL) was built by monthly collecting rainwater between 2014 and 2018, given by delta D = 7.02 +/- 0.35 x delta O-18 + 8.54 +/- 2.89. The obtained results indicate that acid mine drainages (AMD) are supplied by freshwater from karst systems which flow throughout the post-mining workings. Such waters contaminate by interactions with sulfides (pyrite) that remained unmined in the ore-bodies. During rainstorms, infiltration rainwater displaces water ponding within mine, sharply increasing the outflow rate of highly-contaminated AMD. Acidic drippings in tunnels show an isotopic shift in both delta O-18 and delta D values attributable to pyrite oxidation and Fe hydrolysis. The data reveal that karst-springs represents the primary supply for the stream. The isotopic data also reveal that waters flowing in the bedrock carbonate aquifer represent the main feeding component for the overlying alluvial aquifer tapped by wells. The prevailing transfer of clean freshwaters from the carbonate aquifer towards the alluvial aquifer system mitigates the possible influence of contaminated water from stream seepage. However, these observations require a monitoring program on water quality to be established.

The analysis of trace metals and metalloids, and the Sr-isotopic systematics were applied to 16 must samples from vines growing in the Sesia Val Grande Supervolcano UNESCO Global Geopark in the northern Piedmont Region (Italy), a land worldwide famous for the production of quality Nebbiolo-based red wines. Twenty-four elements were measured in each sample with inductively coupled plasma-mass spectrometry (ICP-MS). The results indicate a wide variability in trace element concentration in musts from the different vineyards. In particular, Rb and Sr reach their maximum at 5110 and 694 µg L−1, respectively, reflecting the geological nature of the magmatic bedrocks. Fe, Cu, Pb and Ba concentrations reach 3118, 1200, 130 and 720 µg L−1, respectively, suggesting a source from iron oxide, Pb–Zn and Ba ores associated to the volcanic activity. The 87Sr/86Sr ratio is in the range 0.711608–0.718160, showing a highly radiogenic signature which is uncommon in must/wine. This is consistent with the high 87Sr/86Sr isotopic ratio of the old rhyolitic bedrocks. Furthermore, the 87Sr/86Sr ratio in musts linearly correlates with the corresponding 87Rb/86Sr ratio, reflecting the Rb and 87Sr release from primary minerals during pedogenesis and matching the initial 87Sr/86Sr ratio of the parent bedrocks magmatic reservoir, thus assuming importance for authenticity assessment.

While monitoring the physico-chemical characteristics, trace elements and O-H-Sr-B isotopic data were obtained in superficial waters from a number of irrigations canals and ditches in the Ravenna coastal plain, in order to highlight the cycling of potentially toxic elements and the different sources of the solutes. Surveys were conducted during March and July 2008, and considered as representative of the waters in winter and summer, respectively. In summer, the water mass balance in the network is mostly controlled by the ingression of freshwaters from the Canale Emiliano Romagnolo (CER). The O-H isotopic data indicated that, in winter, waters are primarily recharged from Apennine catchments and undergo evaporation to different extents. The boron isotopic signature indicates the important role played by the marine component. A major seawater contribution was evidenced in canals close to the coastline; however, the process controlling the origin of dissolved boron is not solely related to direct mixing with sea water but comprises an additional source probably related to water-soil exchanges and boron of marine origin leaching, owing to the prolonged exposure of alluvial sediments to sea water. An additional boron contribution from the agricultural practice was is also evidenced. Calculation based on the conservative behaviour of chloride ions indicated that in canals and ditches not directly connected with the sea up to the 80% of the Sr budget did not originate from seawater, indicating a source from Al-silicate minerals and upporting the hypothesis of significant soil-water interactions and chemical exchanges. The positive correlation between pH and dissolved oxygen in winter waters is likely to reflect CO2 consumption during algal photosynthesis, favouring the in-situ generation of colloidal particles due to the oxidative precipitation of ferric iron oxy-hydroxides and probably small carbonate particles able to adsorb trace metals on their surface and contribute to the ecosystem dynamics facilitating the transport of metals and affecting their bio-availability and cycling. During summer, the input of freshwater from CER lowered the concentration of most ions and became superimposed to the evaporation-precipitation-exchange cycle, possibly dispersing the colloidal particles which could act as pollutant carriers and enhancing flocculation and precipitation, scavenging trace metals into the sediments.

The Raibl mine (Cave del Predil village, northern Italy) belongs to the Pb–Zn minerogenetic district in the southeastern Alps, hosted in Middle Triassic carbonates. The drainage water quality reflects the high acid-buffering capacity of the carbonate rocks, which controls the mobility of most metals. In particular, Fe is non-detectable in solution, having formed hydrous-oxides precipitates. Molybdenum, Ni, Zn, Cd, Pb, and Tl are present, and the Pb, Tl, and Zn concentrations sometimes exceed the Italian regulatory thresholds. Thallium concentrations substantially exceed the 2 µg/L limit at some sampling stations, ranging between 12 and 30 µg/L in the mine drainage, and reaching 5 µg/L downstream of the mine site, despite strong dilution. The data indicate that Tl behaves almost conservatively and is not significantly scavenged by the Fe precipitates. The elevated Tl represents a potential risk for the stream ecosystem. Although Tl is not regulated in drinking water in Italy or the European Community, its distribution in natural waters may help to determine if health actions should be taken.

The alkali-basalt and basaltic trachy-andesites volcanic rocks of south Marzanabad were erupted during Cretaceous in central Alborz, which is regarded as the northern part of the Alpine-Himalayan orogenic belt. Based on petrography and geochemistry, en route fractional crystallization of ascending magma was an important process in the evolution of the volcanic rocks. Geochemical characteristics imply that the south Marzanabad alkaline basaltic magma was originated from the asthenospheric mantle source, whereas the high ratios of (La/Yb) N and (Dy/Yb) N are related to the low degree of partial melting from the garnet bearing mantle source. Enrichment pattern of Nb and depletion of Rb, K and Y, are similar to the OIB pattern and intraplate alkaline magmatic rocks. The K/Nb and Zr/Nb ratios of volcanic rocks range from 62 to 588 and from 4.27 to 9 respectively, that are some higher in more evolved samples which may reflect minor crustal contamination. The isotopic ratios of Sr and Nd respectively vary from 0.70370 to 0.704387 and from 0.51266 to 0.51281 that suggest the depleted mantle as a magma source. The development of south Marzanabad volcanic rocks could be related to the presence of extensional phase, upwelling and decompressional melting of asthenospheric mantle in the rift basin which made the alkaline magmatism in Cretaceous, in northern central Alborz of Iran.

A seismic swarm characterized by a Ml = 5.9 mainshock occurred in the Po Valley, northern Italy, in 2012. The area has been studied for active compressional tectonics since the beginning of the twentieth century. A variety of geophysical and geochemical parameters have been utilized with the purpose of identifying possible precursory signals. This paper considers groundwater level data and geochemical data both in groundwaters and in gases. All considered parameters have led to the conclusion that possible long and medium precursory trends have been identified in geofluids. No short-term precursors have been clearly identified. Hydrogeological and geochemical monitoring could be more effectively utilized in a different geological context, and seismic hazard reduction procedures could benefit from geofluid monitoring.

The major, trace (including rare earth) element abundances, and Sr-Nd-Pb isotopic compositions, have been analysed for andesitic basalt and andesitic sills and lavas of the Jurassic Ferrar Magmatic Province, Prince Albert Mountains, Antarctica. The typical “crustal signature” of the Ferrar magmatism, characterized by relatively high SiO2, LREE and LILE contents in these samples, is associated with high 87Sr/86Sr and low 143Nd/144Nd. Systematic correlations of major and trace elements indicate that fractional crystallization was important. However, increases in incompatible elements are positively correlated with initial 87Sr/86Sr, suggestive of crustal assimilation processes. The observed correlations between initial 87Sr/86Sr and LREE enrichments have been modelled by an AFC process, starting from the least evolved sample and assuming the compositions of the orthogranulites of Victoria Land as contaminants. The REE patterns of the least evolved Ferrar rocks approach those of E-type MORB, differing only by higher LREE/IREE. The enrichment in LREE, accompanying high initial 87Sr/86Sr, 207Pb/204Pb and low 143Nd/144Nd compared with E-type MORB, can be explained by interaction of “primary Ferrar basalt” with crystalline basement. We propose a petrological model whereby Ferrar magmas were generated through high degrees of melting of an E-type MORB mantle source, and subsequently these “primary” melts underwent AFC processes inheriting a crustal signature. The Sr-Nd-Pb isotopic compositions required by the AFC model for the primary Ferrar basalt are similar to those of the Dupal signature of the oceanic basalts of the Southern Hemisphere (Hart 1984). Transantarctic Mountains would have been located inside the Dupal anomaly in pre-Gondwana dispersion times.

The major element chemistry and SrNd isotope composition of three basaltic glasses and two whole rock samples dredged from the Nereus Deep, in the central Red Sea, were used to constrain the nature of the magmatism in the Nereus axial valley. The glass and whole rock compositions show the tholeiitic character of magmas and their affinity with MORB. The chemical composition of the most magnesian glass (mg# = 69.9) would suggest an origin from a melting event in the mantle at a pressure in the range 8–10 kbar. Magma differentiation modelling using the major element chemistry of the more evolved glasses indicates mineral-melt equilibration at moderate pressure, followed by most of the fractionation under low pressure conditions. The observed Ti content and Sr isotope composition suggest the occurence of additional processes besides fractionation, and could reflect different degrees of partial melting of a slightly heterogeneous mantle source. The SrNd isotope composition reveals the time-integrated depleted nature of the mantle, and overlaps the fields of MORB and basalts from the southern Red Sea axial ridge. The Sr isotope data on glasses resemble more closely the compositional range reported for the Indian Ocean ridges, and suggest a dominant asthenospheric source, with minor enriched components.

Geochemical investigations were carried out to define the origin of the low- to moderate-temperature thermal waters feeding the Monfalcone springs in northern Italy. Chemical data indicate that waters approach the composition of seawater. Mixing processes with cold low-salinity waters are highlighted. The δ18O and δD values are in the range −5.0 to −6.4 ‰, and −33 to −40 ‰, respectively, suggesting the dilution of the saline reservoir by karst-type freshwaters. A surplus of Ca2+ and Sr2+ ions with respect to a conservative mixing is ascribed to diagenetic reactions of the thermal waters with Cretaceous carbonates at depth. The measured Sr isotopic composition (87Sr/86Sr ratio) ranges between 0.70803 and 0.70814; after correction for the surplus Sr, a 87Sr/86Sr ratio indicating Miocene paleo-seawater is obtained. The dissolved gases indicate long-lasting gas–water interactions with a deep-originated gas phase of crustal origin, dominated by CO2 and marked by a water TDIC isotopic composition in the range −5.9 to−8.8 and helium signature with 0.08 < R/Ra < 0.27, which is a typical range for the crust. A possible scenario for the Monfalcone thermal reservoir consists of Miocene marine paleowaters which infiltrated through the karstic voids formed within the prevalently Cretaceous carbonates during the upper Eocene emersion of the platform, and which were entrapped by the progressive burial by terrigenous sediments.

Transitional basalts of the Treinta y Tres region intrude late Proterozoic granites in northeast Uruguay. The age of the swarm is assumed to be close to 750 Ma. Major and trace geochemical diagrams indicate gabbro type fractionation, which is supported by MPR plots. In comparison to the Florida and Nico Perez suites, the Treinta y Tres swarm is enriched in Ti, P, Zr and Sr and depleted in LILE and REE. These features and the Sro and Ndo isotope values are discussed in terms of source heterogeneity and crustal contamination. The geochemical characteristics do not support crustal contamination. The Treinta y Tres suite is better explained by a source affected by two melting episodes. The dikes were originated from the latter melting, which occurred in a an isotopically heterogeneous source. Diagrams related to several incompatible elements ratios indicate that the mantle source of Uruguaian dikes and of continental basalts of Brazil have similar geochemical features since Early Proterozoic up to Mesozoic.

A periodic sampling of the groundwaters and dissolved and free gases in selected deep wells located in the area affected by the May-June 2012 southern Po Valley seismic sequence has provided insight into seismogenic-induced changes of the local aquifer systems. The results obtained show progressive changes in the fluid geochemistry, allowing it to be established that deep-seated fluids were mobilized during the seismic sequence and reached surface layers along faults and fractures, which generated significant geochemical anomalies. The May-June 2012 seismic swarm (mainshock on May 29, 2012, M 5.8; 7 shocks M >5, about 200 events 3 > M > 5) induced several modifications in the circulating fluids. This study reports the preliminary results obtained for the geochemical features of the waters and gases collected over the epicentral area from boreholes drilled at different depths, thus intercepting water and gases with different origins and circulation. The aim of the investigations was to improve our knowledge of the fluids circulating over the seismic area (e.g. origin, provenance, interactions, mixing of different components, temporal changes). This was achieved by collecting samples from both shallow and deep-drilled boreholes, and then, after the selection of the relevant sites, we looked for temporal changes with mid-to-long-term monitoring activity following a constant sampling rate. This allowed us to gain better insight into the relationships between the fluid circulation and the faulting activity. The sampling sites are listed in Table 1, along with the analytical results of the gas phase. […]

High arsenic (As) concentrations, >900 μg/L, were measured in Ca–Mg–SO4 waters from springs and drainages in the village of Pesariis in the Carnic Alps (NE Italy). Oxidation of the outcropping arsenian marcasite ore deposits of the area is proposed as the mechanism for As release into oxygenated waters during runoff. Nevertheless, the limited extension of the ore deposit and the relatively low As content of the mineralization suggest that sulfide weathering might not be the only process responsible for the highest As concentration in groundwaters. An additional mechanism involves As adsorption onto ferric iron particulate during oxidation, the drawdown in reducing environment at depth during water infiltration, and the release of ferrous iron and sorbed arsenic to the water columns by reductive dissolution of hydrous ferric oxides (HFO). This yields the observed Fe–As correlation. Newly formed HFO precipitates when groundwaters discharge to aerated conditions, leading to the removal of As, which strongly partitions into the iron-rich sediments, adsorbed onto the surface of amorphous Fe2O3·xH2O. The calculated and measured As concentration in sediments exceeds 10% by weight. Furthermore, geochemical and isotopic data indicate that the As-rich reservoir partly mixes with shallower aquifers, commonly tapped for drinking supply, representing a natural hazard for inhabitants.

Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for δD, δ18O and 87Sr/86Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show δ18O −3.36 to +3.69 and δD −15.85 to +24.23, deep Aluto-Langano geothermal wells show δ18O −4.65 to −1.24 and δD −12.39 to −9.31, groundwater wells show δ18O −3.99 to +5.14 and δD −19.69 to +32.27, whereas the lakes show δ18O and δD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: δD = 7 δ18O + 11.2, R2 = 0.94, n = 42) and the Local Evaporation Line (LEL: δD = 5.63δ18O + 8, n = 14, R2 = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (δD = −5.15 and δ18O = −2.34). These values are depleted if compared with the modern-day average precipitation, presumably indicating paleo-groundwater components recharged during previous humid climatic phases. The measured stable isotope values indicate that the geothermal wells, some of the hot springs and groundwater wells mainly consist of meteoric water. The Sr isotopic signatures in all waters are within the range of the Sr isotopic composition of the rift basalts and rhyolites. The variability of Sr isotopic data also pinpoints complex water–rock interaction and mixing processes in groundwater and surface water. The 87Sr/86Sr ratio ranges from 0.70445 to 0.70756 in the hot springs, from 0.70426 to 0.70537 in two deep geothermal wells, and from 0.70673 to 0.70721 in the rift lakes Ziway, Langano, Shala and Awasa. The radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments. There is a change in MER water composition between the recharge-infiltration zone (surrounding highlands) and the discharge areas, from depleted δD, δ18O and less radiogenic Sr isotope compositions to enriched δD, δ18O and more radiogenic Sr isotope compositions. Isotope analyses are therefore useful in providing further understanding of the hydrologeological processes occurring within a productive aquifer and the surface water system.

The Mesozoic magmatic activity in the easternmost part of NE Brazil (Ceara-Mirim) is mainly represented by two-pyroxene tholeiitic dykes; only few dykes have alkaline character. K/Ar ages and palaeomagnetism data indicate that Ceara-Mirim dykes are of Middle Jurassic (175-160 Ma) and Early Cretaceous (140-130 Ma) age. Both Middle Jurassic and Lower Cretaceous dykes have high incompatible-element concentrations and TiO2 with the lower contents generally confined to the Middle Jurassic dykes; rare tholeiitic dykes low in TiO2 and incompatible elements are present. Sr/1bNd isotopic and other chemical data do not support appreciable crustal contamination and in a 87Sr86Sr vs. 143Nd144Nd diagram almost all the dykes plot in a narrow area of the enriched quadrant of the “mantle array”. Tholeiitic and alkaline Ceara-Mirim dykes are related to different parent magmas probably originating by different degrees of melting of garnet-peridotite mantle sources characterized by distinct Sr/1bNd isotope compositions and small-scale chemical heterogeneities. Ceara-Mirim tholeiitic dykes show close mineralogical, chemical and isotopic similarities with the Lower Cretaceous high-TiO2 tholeiites from Maranhao (Sardinha intrusives) and Parana (Northern Province) basins. In general, chemical and Sr/1bNd isotope data for high- and low-TiO2 Brazilian Mesozoic tholeiites appear to be related to time-integrated enriched and depleted mantle components, respectively. Subcontinental mantle heterogeneity is believed to be due to variable “enriched” components related to “metasomatic” processes. The Ceara-Mirim Jurassic dykes correlate well in terms of composition and tectonic setting with the analogue tholeiitic dyke swarms from the Benue trough, and can be related to the opening of the Central Atlantic Ocean. The Lower Cretaceous Ceara-Mirim magmatic activity corresponds to the coeval one of the Benue trough and can be related to the early rifting events responsible for the opening of the Equatorial Domain of the South Atlantic whose oceanic crust formed between 120 and 100 Ma.

The first geochemical data showing the existence of an active degassing activity over a large seismically active sector of the Southern Alps (Friuli Region, NE Italy) are presented. The dissolved gases, helium and carbon isotopic systematics of 46 water samples taken from 13 sites running along E–W and NE–SW faults besides the natural degassing of a 5000 km 2 wide area are investigated. The chemical composition of the dissolved gases revealed that a CO 2 -rich gas phase feeds the local groundwaters. 3 He/ 4 He ratios ( R ) normalized to the atmospheric 3 He/ 4 He ratio (Ra = 1.39 × 10 − 6 ) and corrected for the atmospheric contamination ( R /Ra c ), range from 0.29 to 1 as a result of a two component (radiogenic and atmospheric) mixing. The δ 13 C values of total dissolved inorganic carbon (TDIC) ranging from − 15.28 to − 0.75‰ vs. PDB, show the occurrence of multiple gas–water interactions. The mixing between the atmospheric air and a crustal source and the gas–water interactions occurring at various extents appears to be the main control on the observed He–C systematics. The natural CO 2 degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that generated destructive seismic sequences (e.g. the Gemona sequence of 1976; main shocks M6.4 of 6th May and M6.1 of 11th and 15th September). The results obtained show that a significant amount of crustal-originated gases are released over the continental area of Eastern Southern Alps. The evidence that carbon dioxide is associated with radiogenic-type helium denotes the lack of the mantle as primary energy and degassing source, highlighting the possibility that CO 2 is produced by thermo-mechanical processes occurring at seismogenic depth. The information provided here may be used to start up a long-term geochemical monitoring of this seismically active area and could be able to detect the modifications occurring to the circulating fluids to gain a better insight on the relationships between the fluids' geochemistry and the activity of the local seismogenic faults.

Major, trace element and isotopic data are reported for Hercynian granodiorites and tonalites from Capo Vaticano, Calabria, with the aim of clarifying the relationships between acidic and intermediate lithologies in orogenic intrusive suites. These granodiorites (SiO 2 = 70.5%–73.5%) are peraluminous, relatively depleted in Rb, U, Th, and Pb, and display a large variation in many geochemical and isotopic parameters. REE show fractionated, cross-cutting chondrite-normalized patterns with small but significant negative Eu anomalies. Initial (290 Ma) Sr and Nd, and present-day Pb isotope ratios are: ( 87 Sr 86 Sr ) 290 = 0.7105–0.7110 ; ( 143 Nd 144 Nd ) 290 = 0.51175–0.51221 ; 206 Pb 204 Pb = 18.35–18.50 ; 207 Pb 204 Pb = 15.64–15.76 ; 208 Pb 204 Pb = 38.51–39.03 . Pb isotope ratios determined for separated feldspars show similar 207 Pb 204 Pb and 208 Pb 204 Pb and higher 207 Pb 204 Pb ratios compared to the present-day values for the whole rock. The tonalites (SiO 2 = 57.6%–67.3%) are typically calc-alkaline in composition and most of them are weakly peraluminous. They display large heterogeneities in trace-element abundances, REE patterns and Nd and Pb isotope ratios, both between and within individual intrusive units. Sr, Nd and Pb isotopic compositions display a range of values close to that of the associated granodiorites ( 87 Sr 86 Sr ) 290 = 0.7099–0.7111 ; ( 143 Nd 144 Nd ) 290 = 0.51185–0.51224 ; 206 Pb 204 Pb = 18.31–18.56 ; 207 Pb 204 Pb = 15.65–15.72 ; 208 Pb 204 Pb = 38.41–39.59 . The obtained data indicate that the tonalites and granodiorites share many compositional features which point to a genetic linkage. Likewise, many petrological, geochemical and field data exclude the possibility that all the granodiorites derive from intermediate magmas by any common evolutionary process, such as crystal-liquid fractionation or assimilation-fractional crystallization (AFC), and point to a different genesis for the two rock types. An origin of the granodiorites by the mixing of two separate acidic melts, one of crustal anatectic origin and one probably derived from an intermediate magma by crystal/liquid fractionation or AFC, is suggested by the data presented. The tonalites appear to have been generated by interaction of a mafic magma with crustal end-member(s) with isotopic and geochemical signatures similar to those of the granodiorites. The large involvement of crustal material in the genesis of the Capo Vaticano granitoids is responsible for the many common compositional characteristics observed in the intermediate and acidic rocks. However, a contribution from mantle components is also indicated by petrological and geochemical data, as well as by the occurrence of mafic enclaves commonly present in the tonalites. Nevertheless, the geochemical and isotopic features of such a mantle component appear to be greatly diluted by a large quantity of crustal material involved in the genesis of the studied granitoids.

The Lower Cretaceous dykes of the Ponta Grossa Arch, the most important dyke swarms in Brazil, are associated with the flood basalts and rare acid flows of the northern Parana basin. The Ponta Grossa (PG) dykes are formed by two-pyroxene tholeiites and rare acid rocks. The basaltic dykes may be distinguished into two main groups: a dominant, high-TiO2 (> 2 wt.%; HTi) group and a subordinate, low-TiO2 (< 2 wt.%; LTi) group, characterized, for similar MgO content, by high and low incompatible-element contents, respectively. Most PG dykes do not show chemical and isotope evidence supporting important crustal contamination. PG dykes with (87Sr86Sr)0 < 0.7060 plot in the mantle array (ϵSr ≈ + 17 and ϵNd ≈ −3) and can be considered virtually uncontaminated. Intra-dyke chemical variations suggest that the normal or reverse differentiation trends may be related to pre-emplacement low-pressure differentiation processes. The important chemical differences between incompatible-element-poor and incompatible-element-rich basaltic dykes cannot be accounted for in terms of fractional crystallization, but are compatible with different melting degrees of a garnet peridotite mantle source, e.g. 9% and 20% melting for the HTi and LTi tholeiites, respectively. Field distribution of the magmatism, chemistry and Sr-Nd isotope compositions support that the PG dykes may be related to the flood volcanics of northern Parana, and not to those of the central and southern Parana. Paleomagnetic data indicate that PG dykes are younger than the Parana volcanics. All the results suggest that PG dykes were probably feeders of the stratoid volcanics erupted in northern Parana towards the continental margin and later eroded. Chemistry and isotopic data reveal that asthenospheric mantle components were not significant factors in the genesis of PG dykes. Dyke emplacement occurred during early phases of rifting and/or flexuring cutting flood volcanic suites.

Two flank eruptions took place at Mt. Etna during 1989–1993. The former (September–October 1989) produced lavas among the most primitive of this century while the latter (December 1991–March 1993) was unusually long lasting and the largest of the last three centuries. Alkali basalts of 1989 displayed initial enrichments of Rb and K accompanied by an higher value of radiogenic-Sr and isotopic disequilibrium between host-rock and clinopyroxene (0.70364 and 0.70356, respectively). Subsequently, within one week, K, Rb and 87Sr86Sr ratio decreased to constant values (87Sr86Sr = 0.70355). Nd isotopic ratio did not show significant variations. These features can be explained by a selective contamination process involving essentially Rb, K and radiogenic-Sr. The bulk from the 1991–1993 eruption hawaiites, were erupted between January and May 1992. In this period, lavas (here called JML) were characterised by uniform geochemical and isotopic compositions and Sr-isotopic equilibrium between whole rock and pyroxene (0.70355). In other periods (December 1991 and June 1992) we observed lower and variable Sr isotopic compositions coupled with disequilibria between lavas and their clinopyroxenes (0.70351 in the w.r. and 0.70345 in the cpx of the sample of 15 December 1991). Starting from June 1992, the products seem to reveal fractionation effects as suggested by the continuous rise in concentrations of incompatible elements. When the observed variability cannot be ascribed to fractionation effects, we are not able to discriminate mixing from selective contamination. However, lavas erupted during December 1991 evolved towards the isotope composition of JML that was never exceeded, moreover the regular behaviour of Rb, K and radiogenic-Sr of 1989 lavas was not observed during the 1991–1993 eruption. Thus, we prefer to interpret these variations as mainly due to mixing processes between an end-member of JML composition and another one having the same, or lower, isotopic composition of the clinopyroxene found in the sample of December 1991. Several petrogenetic processes are contemporaneously active at Mt. Etna; they encompass magma mixing, selective contamination and fractional crystallization. Their relative importance varies according to the original volume of each magma batch and to the status of the shallow feeding system. The complexity of these processes, acting in the short time span of a few months, claims caution about the geochemical representativity of a single lava sample for each eruption.

Tholeiitic basaltic and basaltic andesite dikes of Brasiliano (or PanAfrican) age (≈ 600 Ma) intrude the basement of the Nico Perez region, Uruguay. Major and trace element geochemistry of the basalts indicates that they suffered fractionation in shallow magma chambers. The variation in element ratios, which remain virtually unchanged during fractionation (K/Rb, Rb/Ba, Ba/Nb, La/Nb, Zr/Nb and Ti/Zr), indicate that the dikes are not strictly comagmatic. However, they have certain features in common: LILE and LREE enrichment with respect to HFSE and HREE; high Rb/Ba (> 0.9) and Rb/Sr (> 0.08); low K/Rb ( 2; Ba/Nb > 22 Ti/Zr < 60).87Sr/86Sr and143Nd/144Nd at 665 Ma are in the range 0.7052 – 0.7119 and 0.51158 – 0.51177, respectively.

Three dyke swarms in Uruguay range in age from Palaeoproterozoic (1.86 Ga, Florida region) to Neoproterozoic (∼0.7 Ga, Nico Perez and Treinta y Tres regions). The Florida and Nico Perez swarms are basalts, basaltic andesites and andesites with tholeiitic affinity, characterized by LILE and LREE enrichment with respect to HFSE, Nb depletion with respect to K and La, K Rb , Ba Rb , Zr Nb > 13 , (La Yb) n > 4.5 . Both swarms have positive ϵ Sr and negative ϵ Nd , but the Florida isotopic array is dominated by ϵ Nd variations (EM1 type) and that of Nico Perez by ϵ Sr variation (EM2 type). The Treinta y Tres swarm consists of slightly ne -normative transitional or alkaline basalts with geochemical characteristics resembling those of OIB (e.g., Gough Island), but suggestive of a less enriched OIB source, and have slightly positive ϵ Nd and ϵ Sr . Crustal contamination does not appear to be important in the petrogenesis of the swarms. It is proposed that the geochemical characteristics of the Florida swarm derive from melting of lithospheric mantle infiltrated by hydrous fluids released from the thermal breakdown of hydrous phases, either contained in underplated oceanic crust or formed by interaction of asthenospheric fluids with the lithospheric mantle. The EM1-type isotopic features are considered as unrelated with possible fluid addition, but as a pre-existing feature. The geochemical and isotope characteristics of the Nico Perez swarm are attributed to time-integrated enrichment processes, which affected the Nico Perez lithospheric mantle during the Palaeoproterozoic Florida episode. The geochemistry of the Treinta y Tres swarm may be explained by partial melting of a lithospheric mantle which did not suffer Palaeoproterozoic LILE and LREE enrichment but which was isotopically reset in Palaeoproterozoic times. Alternatively, a residual mantle related to the Florida event is required. Mantle melting and dyke intrusion probably occurred in an ensialic environment. The geochemical and isotopic characteristics of the Uruguay dyke swarms are similar to those of the Mesozoic basalts related to the Gondwana break-up, supporting the possibility that the latter derived from a heterogeneous lithospheric mantle source which recorded Proterozoic enrichment processes.

Mafic dykes cutting the gneisses and migmatites in the Deep Freeze Range high-grade metamorphic complex of northern Victoria Land, Antarctica, have undergone strong recrystallization and deformation during amphibolite-facies metamorphism. Metamorphic mobility mostly affected the large-ion lithophile elements (LILE). Rare Earth (RE) and the high field-strength elements (HFSE) were essentially immobile during metamorphism. Together with the major-element geochemistry, this suggests primary characteristics of evolved tholeiitic magmas and mafic cumulates. No precise ages of intrusion are available for the dykes, but geological evidence suggest emplacement during the time interval 800 to 900 Ma. The Rb-Sr isotopic system in some of the dykes were also variably affected by a later thermal event, probably coincident with the time of amphibolite metamorphism, ca. 500–550 Ma ago. This event can be correlated with the Ross Orogeny in the Transantarctic Mountains. Nd isotopes and trace element abundances indicate that the dykes were derived by different degrees of partial melting and fractionation of heterogeneous sub-continental lithospheric mantle. The Nd isotopic compositions range from depleted to enriched signatures (ϵNd computed back to 850 Ma = +4.5 to −11.61), and are coupled to different trace element normalized patterns characterized by a slight positive Nb anomaly in the former case to a strong negative Mb anomaly for the latter samples. On isotopic and chemical ground the depleted signature of the mantle source resembles that reported for E-type MORB. The nature of the enriched components cannot be uniquely stated; nevertheless, on the basis of isotopic and geochemical data, it could be represented by sediments recycled into the sub-continental mantle or by crustal contamination during underplating of mafic magmas, or a combination of the two processes.

The Anari and Tapirapua formations are very similar from the point of view of paleomagnetic, geochronological and geochemical results. They date from around 197 Ma and the flows are mainly tholeiitic basalts with a low TiO2 and incompatible element content. The magnetic carriers in rocks from these two formations were highly oxidized titanomagnetites, maghemites and, probably, titanomaghemites. Paleomagnetic analysis has shown that the magnetizations are all normal in polarity and virtual geomagnetic poles obtained for both formations are indistinguishable at the 95% confidence level. The calculated mean for these poles is 250.3°E, 65.5°S (N = 15; A95 = 3.6°; KSC = 1578). This pole is compatible with Jurassic poles which have been determined for South America or transposed from Africa.

The SE-Brazil passive continental margin is characterized by tholeiitic magmatism that is particularly widespread in the marginal Campos basin, facing the inland flood basalts of the adjacent Parana basin. Campos magmatism is represented by Early Cretaceous (EC; 134–122 Ma) flood basalts and minor Upper Cretaceous-Early Tertiary basalt flows and intrusives, which were emplaced in a basin with attenuated crustal thickness (20 km). Petrography, mineral chemistry, wholerock geochemistry and Sr−Nd isotope composition emphasize that the EC-Campos basalts have suffered extensive seawater interaction which caused enrichment in MgO, FeO total, K2O, Rb and Ba, and depletion in SiO2 and CaO, while Zr, Nb, Y and REE remained virtually constant in samples with loss-on-ignition values less than 4 wt%. In general, Campos basalts have bulkrock chemistry similar to those of the inland Parana tholeiites (140–130 Ma) with relatively low concentrations of incompatible elements and TiO2 ( 16) MORB (mid-ocean-ridge basalt) mantle in simple binary mixing models. On the whole, the Early Cretaceous Campos basalts appear as an easterly, younger extension of the northern Parana volcanism and probably erupted during early stages of the major riftingprocesses which caused continental thinning. It is notable that in the Campos marginal basin both the basalt magmatism contemporaneous with the continental break-up, as well as that which occurred after the S. America-Africa separation, appears substantially related to subcontinental lithosphere and a Dupal-like OIB (ocean-island basalt) (e.g. Tristan da Cunha) source components.

Basaltic-doleritic dykes, ranging in composition from picritic to alkali basalts, are found on the island of Zabargad, an uplifted sliver of sub-Red Sea lithosphere. The dykes were injected into mantle-derived peridotite bodies and into a metagabbro-gneiss unit of lower crustal origin. Most dykes are made of phenocrysts of zoned plagioclase (from bytownite in the core to andesine in the rim) and of Ca-rich augite in a groundmass of salite, amphibole, plagioclase, Fe-Ti oxides and scarce olivine. Clinopyroxenes are partly replaced by amphiboles ranging from ferroan-pargasite to edenite and to Mg-hornblende. In some samples marialitic scapolite developed, generally at the expenses of plagioclase, during seawater interaction. The seawater interaction process strongly influences the Cs Na ratio; however, samples with ln( Cs Na ) greater or equal to −13.75 appear relatively unaffected by seawater open system exchanges. Chondrite-normalized rare earth elements (REE) abundances show flat or slightly light REE enriched patterns, intermediate between Afar-type volcanites and MORB. Major elements compositions and REE abundances of unaltered rocks are compatible with the hypothesis that the Zabargad dykes are produced by partial melting of peridotitic materials. Transition elements show depletion in Ni and Cr relative to primitive mantle abundances, as a consequence of some fractionation. The abundance of elements preferentially stabilized in the liquid phase (hygromagmatophiles of Treuil et al., 1979) in most samples is consistent with a genesis for these magmas by partial melting in a distensive area, followed by fractional crystallization. Sr and Nd isotopic compositions of unaltered samples range between 0.70328–0.70438 and 0.51292–0.51305 respectively, while altered samples have significantly higher 87 Sr 86 Sr (up to 0.7064). Trace elements and isotopic data are consistent with a chemically heterogeneous mantle source involved in the genesis of Zabargad dykes, which represent basaltic injections related to various stages of rifting, preceding the emplacement of oceanic crust and the initiation of seafloor spreading.

Two groups of rhyolites have been recognized at San Vincenzo (Tuscany, Italy). Group A rhyolites are characterized by plagioclase, quartz, biotite, sanidine and cordierite mineral assemblages. They show constant MgO and variable CaO and Na2O contents. Initial87Sr/86Sr ratios in group A samples range between 0.71950 and 0.72535, whereas the Nd isotopic compositions are relatively constant (0.51215–0.51222). Group B rhyolites are characterized by orthopyroxene and clinopyroxene as additional minerals, and show textural, mineralogical and chemical evidence of interaction with more mafic magmas. The Sr and Nd isotopic ratios range between 0.71283–0.71542 and 0.51224–0.51227 respectively. Magmatic inclusions of variable size (1 mm to 10 cm) were found in groups B rhyolites. These inclusions consist mainly of diopsidic clinopyroxene and minor olivine and biotite. They are latitic in composition and represent blobs of hybrid intermediate magmas entrained in the rhyolitic melts. These magmatic inclusions have relatively high Sr contents (996–1529 ppm) and Sr and Nd isotope-ratios of 0.70807–0.70830 and 0.51245–0.51252 respectively.87Sr/87Sr data on minerals separated from both group A and B rhyolites and magmatic inclusions reveal strong isotopic disequilibria due to the presence of both restitic and newly crystallized phases in group A rhyolites and due to interaction of rhyolites with a mantle-de-rived magma in group B rhyolites. Isotopic data on whole rocks and minerals allow us to interpret the group A rhyolites as representative of different degrees of melting of an isotopically fairly homogeneous pelitic source; conversely, group B rhyolites underwent interactions with a mantle-derived magma. The crustal source as inferred from isotopic systematics would be characterized by87Sr/86Sr and143Nd/144Nd ratios close to 0.7194 and 0.51216 respectively. The sub-crustal magma would have Sr isotopic composition close to 0.7077 and a143Nd/144Nd ratio greater than or equal to 0.51252. These isotopic features are different from those reported for the parental magmas postulated for Vulsini and Alban Hills in the nearby Roman Magmatic Province, and are similar to those of the Vesuvius and Ischia magmas.

Continental flood volcanism of the Parana basin (Lower Cretaceous) is represented by two-pyroxene tholeiitic basalts (90 vol. %). The Northern Parana Province (NPP) is dominated by basalts high in TiO2 and incompatible elements (HTiB), while the Southern Parana Province (SPP) is dominated by basalts low in TiO2 and incompatible elements (LTiB). NPP basalts show relatively small variations of initial (120 Ma) 87 Sr 86 Sr (R0) and 143 Nd 144 Nd (Nd∗) ratios (R0=0.7051−0.7062 and Nd ∗=0.5124−0.5125 , respectively) relative to those occurring in SPP (R0=0.7046−0.7120 and Nd ∗=0.5122−0.5128 , respectively). The latter basalts show significant positive correlations between R0 vs. SiO2, K2O, Rb and Ba, and negative correlations between R0 vs. (Cr + Ni) and mg-value, believed to be due to crustal “granitic” contamination. In general, the effects of contamination are pronounced in SPP and tend to vanish towards NPP. δ18O-values range from +6.5 to +10.0‰ in the basalts from NPP and SPP and essentially reflect water-magma interactions. “Uncontaminated” LTiB and HTiB basalts from NPP are isotopically distinct from the “uncontaminated” analogues from SPP (LTiB) (R0=0.7055 vs. 0.7046; Nd ∗=0.5124 vs. 0.5128, respectively). All chemical data consistently indicate distinct sources and a large-scale mantle heterogeneity. The NPP mantle source is expected to have relatively high content of “enriched” components, possibly related to small-volume melts and metasomatic fluids. Tentatively, the last stabilization age of the Parana mantle heterogeneity is 0.5–1.0 Ga old. The existence of high- and low-TiO2 basalt suites in both Parana and Karoo provinces in Brazil and southern Africa, respectively, indicates a large-scale heterogeneity in the subcontinental mantle, and suggests that basalt generation occurred in the lithospheric mantle.

Texto completo: acesso restito. p.252-261 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-02-18T14:16:07Z No. of bitstreams: 1 Bellieni.pdf: 819558 bytes, checksum: 25496ca434496a1bc68062964cedfa5c (MD5) Approved for entry into archive by Fatima Cleômenis Botelho Maria (botelho@ufba.br) on 2013-02-19T16:32:44Z (GMT) No. of bitstreams: 1 Bellieni.pdf: 819558 bytes, checksum: 25496ca434496a1bc68062964cedfa5c (MD5) Made available in DSpace on 2013-02-19T16:32:44Z (GMT). No. of bitstreams: 1 Bellieni.pdf: 819558 bytes, checksum: 25496ca434496a1bc68062964cedfa5c (MD5) Previous issue date: 1995 Early Proterozoic (2.0–2.4 Ga), unmetamorphosed mafic dykes intrude Archean (3.1–2.7 Ga) terrains of the northern Sao Francisco craton (Uaua, NE-Brazil). The dykes are composed of evolved [atomic Mg/(Mg+Fe2)

The Campi Flegrei caldera, an active volcanic field in the Campanian INTRODUCTION province, Italy, is a nested structure generated by the Campanian At any stage of their ascent from source to surface, Ignimbrite (37 ka BP) and the Neapolitan Yellow Tuff (12 ka magmas may become contaminated by assimilation of BP) eruptions. Since at least 60 ka BP Campi Flegrei has produced wall rocks. In particular, crustal contamination is conmagmas with variable chemical and Sr isotopic compositions. Sr/ sidered a possible mechanism when mantle-derived Sr ratios increase through time from 0·7068 to 0·7086, with magmas rise through thick sections of continental crust the highest ratios detected in the least-evolved shoshonitic products. and pond at different depths before reaching the surface The origin of this progressive Sr isotopic variability has been (e.g. Leeman, 1983; Hawkesworth & van Calsteren, investigated using new Sr, Nd and Pb isotopic data for volcanic 1984). rocks and entrained xenoliths. The data obtained are combined and Crustal contamination of magmas is favoured in high discussed with previous geochemical and Sr isotope data and used heat flux zones and may occur in a variety of ways to suggest a multi-stage evolution for the magmatic system, mainly including: (1) bulk assimilation of crustal material; (2) involving deeper and shallower crustal magma storage reservoirs. assimilation of partial melts of crustal materials; (3) seThe deeper reservoir is proposed to be a magma chamber periodically lective exchange of specific elements (e.g. De Paolo, 1981; refilled by primitive mafic magmas which subsequently undergo Leeman, 1983; Huppert & Sparks, 1985; Wilson, 1989). contamination by crustal material. The assimilated crustal material Sr, Nd and Pb isotopes are commonly used to model is represented by xenoliths recovered in the shoshonitic pyroclastic crustal contamination processes (e.g. Wilson, 1989, and products. Magma batches originating from the deeper reservoir references therein). However, the nature of the conmigrated towards the surface and fed a shallower complex magmatic taminant is, in some cases, difficult to identify, in parsystem. The deeper chamber was tapped during the eruption of ticular when exposures of basement rocks or occurrences least evolved magmas by regional fault systems. In addition to of entrained xenoliths in the magmas are lacking. crystal–liquid fractionation, open-system processes occurred in the At Campi Flegrei (CF) (Fig. 1) magmas of different shallower system. chemical and Sr isotopic composition have been erupted since at least 60 ka BP (Civetta et al., 1991, 1997; Orsi