Probe and SIMS investigation of clinopyroxene inclusions in chromites from the Troodos chromitites (Cyprus): Implications for dunite–chromitite genesis

Chromite ores formation is still a debated topic and, in this study, detailed analyses of major, minor elements by EMPA and Rare Earth Elements (REE) by SIMS, were performed on silicate inclusions detected in chromite grains of chromitite pods, enveloping dunites and on clinopyroxene of lherzolitic host rock of well known Trodoos chromite ores. Results show the complexity of relationships among lithologies that reflects the subtlety of genetic events and of chromite ore occurrence.Analyses of textural and chemical features have led to a better understanding of the chromite ore genetic process, that is related to a supra-subduction geodynamic setting where partial melting processes were overlapped by metasomatic events.Metasomatism, that marks the general genetic context, is characterized by the presence of a hydrated boninitic melt that favors the precipitation of chromite ores. Chromite ores, typical of ophiolite complexes and usually enveloped by dunite are, in this case, characterized by the presence of two different types of dunites whose geochemical differences are reflected by olivine mineral chemistry and by different REE patterns of analyzed clinopyroxenes. Such geochemical marks, related to different magmatic and metasomatic events, could be a main key for location of fertile or barren dunites in terms of chromite ore occurrence in the field.     

The distribution of megabenthic, invertebrate epifauna in the Balearic Basin (western Mediterranean) between 400 and 2300 m: Environmental gradients influencing assemblages composition and biomass trends

The distribution of megabenthic epifauna (invertebrates) in the Balearic Basin (western Mediterranean) has been analyzed at depths between 427 and 2265 m after compiling samplings performed in 1985–1992 and 2007–2008 with an OTSB-14 bottom trawl. 84 epibenthic taxa of invertebrates (excluded decapod crustaceans) were collected. Epibenthic assemblages were organized in five groups (n-MDS analyses) as a function of increasing depth: upper slope assemblage, U, hauls between 427 and 660 m; middle slope assemblages M1 and M2, hauls between 663–876 m and 864–1412 m, respectively; lower slope assemblages L1 and L2, hauls between 1488–1789 m and 1798–2265 m, respectively). We found significant differences in assemblage composition between all depth-adjacent pairs of groups. Trends in the distribution of biomass vs. depth and within assemblages varied when hauls taken over insular were compared to those over mainland slopes. Over insular slopes we found (n-MDS) only four distinct depth assemblages, with significant differences between all depth-adjacent group pairs, except between L1 and L2. Over the mainland slope, two peaks of biomass situated at U (427–660 m) and at L1 (1488–1789 m) were clearly identified, attributable to the echinoid Brissopsis lyrifera and holothurian Molpadia musculus at U and to the synallactid holothurian Mesothuria intestinalis at L1. The distribution of biomass vs. depth on insular slopes did not follow this pattern, showing no significant biomass peak below 1000 m and a total biomass an order of magnitude lower than adjacent to the mainland. After compiling available environmental data over the mainland slope off Barcelona, we found coincidence between the peak biomass of Mesothuria intestinalis and: i) a significant increase of labile OM (%OrgC, C/N, hydrolizable aminoacids–EHAA, and the EHAA/THAA-total hydrolizable aminoacids-ratio) over 1600 m; and ii) an increase of turbidity and T at 1500–1600 m in February 2008. We suggest that such OM inputs must likely be associated to the formation of nepheloid layers close to submarine canyons, probably associated with oceanographic processes in deep water masses in the area. This would explain why aggregations of M. intestinalis were linked to the mainland part of the Balearic basin, with highest densities located south of canyons. If hotspots of biomass as cited here for M. intestinalis are regulated by factors such as river inputs, both natural climatic changes (e.g. changes in rainfall regimes) and human impact (e.g. river damming) may affect deep-Mediterranean communities below 1000 m.