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An aeromagnetic survey and a gravity/GDS transect over the admiralty mountains region: Field activities
No full textSr-Nd isotopes and geochemistry of recent lavas from Mt. Etna (Italy): Inferences on mantle sources
No full textSr-Nd-Pb-He-O Isotope and Geochemical Constraints on the Genesis of Cenozoic Magmas from the West Antarctic Rift
No full textThe West Antarctic Rift System (WARS) represents one of the major active continental extension zones on Earth. The Ross Sea coast in northern Victoria Land (NVL) is littered with alkaline rift-related igneous products (Middle Eocene-Present). This study characterizes the nature of the magma source involved in the rift process through geochemical-isotopic investigation of Cenozoic basalts from NVL, and provides important constraints for the reconstruction of the tectono-magmatic evolution of the Ross Sea region-WARS. The chemical compositions of the basalts (Miocene-Present) display major and trace element characteristics typical of ocean island basalts (OIB), with strong enrichment in the most incompatible elements. Whole-rock isotopic compositions are in the range 0.7028-0.7034 for (87)Sr/(86)Sr, 0.5129-0.5130 for (143)Nd/(144)Nd (epsilon Nd(t) similar to 4.8-6.7), 19.3-19.7 for (206)Pb/(204)Pb, 15.4-15.6 for (207)Pb/(204)Pb and 38.7-39.3 for (208)Pb/(204)Pb, suggesting a HIMU-like (high U/Pb) signature of the mantle source. Determinations of (3)He/(4)He on crushed olivine yielded values between 5.7 and 7.2 times the atmospheric ratio, similar to the lithospheric mantle and in the range of mid-ocean ridge basalts (MORB). The delta(18)O(ol) of olivine separates varies from 4.92 to 5.53% and is positively correlated with Fo content. Integration of our geochemical and isotope data with available geological, geophysical and geochronological data has led to the following reconstruction. The differences in the oxygen isotope values principally reflect the involvement of a heterogeneous mantle source and/or the assimilation of variable amounts of hydrothermally altered crustal rocks from the volcanic edifices. The (3)He/(4)He data allow us to exclude a plume-driven model to explain the continuing rifting process. Based on the evidence of metasomatic processes, we propose a model to generate the mantle source(s) of the Cenozoic basaltic melts of the NVL. This is sublithospheric mantle metasomatized during an amagmatic extensional event that affected the WARS in the Late Cretaceous. During Eocene-Oligocene times, mantle flow warmed the mantle at the edge of the thick Antarctic lithosphere, and the reactivation of old translithospheric discontinuities promoted mantle melting and the rise of magmas as plutons and dyke swarms. From the Late Miocene to Present, the continuing craton-directed mantle flow led to normal faulting of the rift shoulder, which favoured the rise of magmas to build up large volcanic edifices
Vapor-buffered volcanic activity of southern Italy and mantle degassing
No full textWidespread mantle degassing is active in many areas of Earth, contributing to volcanic and seismic processes. The Italian territory is invested dramatically by deep degassing, at both volcanic and non-volcanic sites, with huge punctual as well as diffuse emissions of carbon dioxide. The pery-thyrrenian area of southern Italy is the place where these emissions are accompanied by active volcanism.
A global look at melt inclusions from southern Italian volcanoes, particularly from the Campanian volcanic district, suggests that these volcanoes produce magmas under nearly common fluid buffered conditions that initiate in the litospheric mantle. Although the role and nature of components added to the mantle source is as debated as the mantle source itself, volcanic volatiles and the ensemble of petrologic evidences promote the prevailing hypothesis involving the subduction of a continental crust and/or oceanic sediments carrying both pelagic and non-pelagic fractions. The observed extended mantle degassing suggests that volcanism is an ‘occasional’ consequence that pierces the surface at some preferential degassing sites, depending on connected geological structures, including veined mantle paths, and regional stress conditions. Despite these complexities, magma fluxes can be still used to test simple hypotheses on the homogeneity of the volatile source metasomatising the local mantle
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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