Space–time evolution of monogenetic volcanism in the mafic Garrotxa Volcanic Field (NE Iberian Peninsula)

We reconstructed the evolution of the volcanic activity within the central Garrotxa monogenetic Volcanic Field, the youngest volcanic area of the Iberian Peninsula, by investigating the stratigraphy of the volcanic successions and the morphology of the monogenetic eruptive centres. Analysis of this volcanic succession has been conducted following the Unconformity Bounded Stratigraphic Units criteria. The detailed stratigraphy of the volcanic successions shows that the central Garrotxa Volcanic Field (GVF) evolved through four main periods of volcanic activity (Synthems) represented by the eruptive products of the mafic monogenetic volcanoes and associated syneruptive reworked deposits (Eruptive Units) and by the intereruptive deposits (Epiclastic Units). The distribution and the morphologies of the monogenetic volcanoes suggest that feeder dykes were emplaced under influence of the present stress filed and along pre-existing fractures of the basement. Our facies analysis of the deposits and their distribution shows that migration of volcanism toward the centre of the basin was accompanied by a trend of increasing explosivity. Episodic hydromagmatism in central Garrotxa occurred without a specific geographic locus or obvious temporal correlation. Finally, by integrating field data with the stratigraphy extracted from water wells, we determined the volume of the volcanic deposits. The small average volume of products emitted during each eruptive period, and the long quiescence separating them, allow us to classify the GVF as a low-output rate volcanic field

Coexistence of calc-alkaline and ultrapotassic alkaline magmas at Mounts Cimini: evidence for transition from the Tuscan to the Roman Magmatic provinces (Central Italy)

The volcanic complex of Mts. Cimini (~0.90-1.30Ma) represents the geographical and chronological transition between the Tuscan Magmatic Province (TMP) and the Roman Magmatic Province (RMP), in central Italy. Major and trace elements, and Sr, Nd and Pb isotopes of whole-rock, as well as mineral chemistry analyses, were carried out on samples representative of the different petrographic and chronological units of Mts. Cimini. In particular, we focused on the olivine-bearing latites of Mts. Cimini that are the most mafic magmas, belong to the last phase of this volcanic activity, and are heterogeneous in highly incompatible element ratios and Sr-isotope compositions. We suggest that such heterogeneity reflects the occurrence of a heterogeneous upper mantle beneath central Italy, in which different portions, e.g., the sources of both the TMP and RMP, are characterized by distinct geochemical and petrographic features. In this scenario, about 900ka ago, the olivine-bearing latites mark the progressive decline of the TMP magma production in favour of partial melting of the RMP mantle region, thus recording the coexistence of both ultrapotassic alkaline and calc-alkaline magmas in the same volcanic region

Small-scale mantle heterogeneity on the source of the Gran Canaria (Canary Islands) Pliocene-Quaternary magmas

[EN] New chemical and Sr–Nd–Pb isotopic data of the Plio-Quaternary mafic lavas of Gran Canaria are used to investigate their mantle source composition. The most prominent aspects of the new dataset are the slight isotopic differences between the Plio-Quaternary (Post-Roque Nublo Group) and the older Pliocene (Roque Nublo Group) mafic parental magmas, which reflect small-scale mantle heterogeneities. Melting of two mantle materials, one isotopically more depleted and similar to the Depleted Mantle (DM) and the other with more radiogenic Pb-isotope ratios comparable to a mantle with high U/Pb ratio (HIMU), accounts for the isotopic and trace element composition of the Pliocene–Quaternary magmas of Gran Canaria. Geochemical variations show that the Pliocene–Quaternary mantle source is compositionally and lithologically heterogeneous and supports the presence of a silica-deficient pyroxenite mantle component. The contribution of the pyroxenite component in the generation of the Roque Nublo and Post-Roque Nublo magmas is estimated to be in the range from 50 to 70%. Trace element ratios support mixing between the two mantle components (pyroxenite veins in a peridotite matrix) which obscure the original chemical and isotopic composition of these two end-members.This research was funded by the Spanish Ministry of Education and Science through projects CGL2004-04039BTE and PB96-0243.This research was funded by project PI2002/148 from the Canarian Government.It was carried out in the framework of the Consolidated Research Group PEGEFA (Refs. SGR-2005-795 and SGR-2009-972), funded by AGAUR-DURSI, Catalan Government.It was carried out in the framework of the Consolidated Research Group GEOVOL Research Group, Universidad de Las Palmas de Gran Canaria (Spain).Peer reviewe

Groundwater hydrogeochemistry of Trikala municipality, central Greece

Sixty-four samples from the groundwater resources of Trikala municipality, central Greece, were collected during two periods (2006 and 2007) and analyzed for physico-chemical parameters (temperature, pH, specific electrical conductivity, and total dissolved solids), major ions (Ca2+, Cl-, HCO (3) (-) , K+, Mg2+, Na+, NO (3) (-) , SO (4) (2-) ), and several potentially toxic elements (Al, B, Ba, Br, Ca, Ce, Cl, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Nd, Ni, P, Pb, Rb, S, Sc, Si, Sn, Sr, U, V, Y, Zn). European Council directives and USEPA guidelines were used to assess the water quality. The results indicate that all samples are fresh water, suitable for human consumption. All basic ions and physico-chemical parameters have average concentrations below their recommended optimum limits with the exception of electrical conductivity, for January 2007, and nitrate for October 2006 and January 2007 sampling periods. This exceedance is the result of dissolution of minerals such as calcite and dolomite that are present in the surrounding rocks and the application of fertilizers, respectively. Lead is the only element with an average value that exceeds the recommended EC guideline, while special attention should be paid to one borehole (T9) which has elevated NO (3) (-) values which may pose a risk to human health