Trace element and isotope constraints on crustal anatexis by upwelling mantle melts in the North Atlantic Igneous Province: an example form the Isle of Rum, NW Scotland

Sr and Nd isotope ratios, together with lithophile trace elements, have been measured in a representative set of igneous rocks and Lewisian gneisses from the Isle of Rum in order to unravel the petrogenesis of the felsic rocks that erupted in the early stages of Palaeogene magmatism in the North Atlantic Igneous Province (NAIP). The Rum rhyodacites appear to be the products of large amounts of melting of Lewisian amphibolite gneiss. The Sr and Nd isotopic composition of the magmas can be explained without invoking an additional granulitic crustal component. Concentrations of the trace element Cs in the rhyodacites strongly suggests that the gneiss parent rock had experienced Cs and Rb loss prior to Palaeogene times, possibly during a Caledonian event. This depletion caused heterogeneity with respect to 87Sr/86Sr in the crustal source of silicic melts. Other igneous rock types on Rum (dacites, early gabbros) are mixtures of crustalmelts and and primarymantle melts. Forward Rare Earth Element modelling shows that late stage picritic melts on Rum are close analogues for the parent melts of the Rum Layered Suite, and for the mantle melts that caused crustal anatexis of the Lewisian gneiss. These primary mantle melts have close affinities to Mid-Oceanic Ridge Basalts (MORB), whose trace element content varies from slightly depleted to slightly enriched. Crustal anatexis is a common process in the rift-to-drift evolution during continental break-up and the formation of Volcanic Rifted Margins systems. The ‘early felsic–later mafic’ volcanic rock associations from Rum are compared to similar associations recovered from the now-drowned seaward-dipping wedges on the shelf of SE Greenland and on the Vøring Plateau (Norwegian Sea). These three regions show geochemical differences that result from variations in the regional crustal composition and the depth at which crustal anatexis took place

Hart boven Hard op een kruispunt

Hart boven Hard nam in september 2014 een vliegende start en ontpopte zich al gauw tot de motor voor een hernieuwde politisering van het middenveld. De beweging bestaat ondertussen meer dan twee en half jaar. Op 7 mei staat alweer een volgende Grote Parade gepland. Vandaag staat Hart boven Hard echter op een kruispunt en krijgt de beweging met interne spanningsvelden te maken, die het zal moeten overwinnen om een gamechanger te zijn

Quantifying garnet-melt trace element partitioning using lattice-strain theory: New crystal-chemical and thermodynamic constraints

Many geochemical models of major igneous differentiation events on the Earth, the Moon, and Mars invoke the presence of garnet or its high-pressure majoritic equivalent as a residual phase, based on its ability to fractionate critical trace element pairs (Lu/Hf, U/Th, heavy REE/light REE). As a result, quantitative descriptions of mid-ocean ridge and hot spot magmatism, and lunar, martian, and terrestrial magma oceans require knowledge of garnet-melt partition coefficients over a wide range of conditions. In this contribution, we present new crystal-chemical and thermodynamic constraints on the partitioning of rare earth elements (REE), Y and Sc between garnet and anhydrous silicate melt as a function of pressure (P), temperature (T), and composition (X). Our approach is based on the interpretation of experimentally determined values of partition coefficients D using lattice-strain theory. In this and a companion paper (Draper and van Westrenen this issue) we derive new predictive equations for the ideal ionic radius of the dodecahedral garnet X-site,

Geochemistry of the Quaternary alkali basalts of Garrotxa (NE Volcanic Province, Spain): a case of double enrichment of the mantle lithosphere

The area of Garrotxa (also known as the Olot area) represents the most recent (700,000–11,500 y) and better preserved area of magmatic activity in the NE Volcanic Province of Spain (NEVP). This region comprises a suite of intracontinental leucite basanites, nepheline basanites and alkali olivine basalts, which in most cases represent primary or nearly primary liquids. The geochemical characteristics of these lavas are very similar to the analogous petrologic types of other Cenozoic volcanics of Europe, which are intermediate between HIMU, DM and EM1. Quantitative trace element modeling, suggests derivation from an enriched mantle source by degrees of melting that progressively increased from the leucite basanites (,4%) to the olivine basalts (,16%). However, the relatively more variable Sr–Nd–Pb isotope signature of the magmas suggests the participation of at least two distinct components in the mantle source: (1) a sublithospheric one with a geochemical signature similar to the magmas of Calatrava (Central Spain) and other basalts of Europe; and (2) an enriched lithospheric component with a K-bearing phase present. The geochemical model proposed here involves the generation of a hybrid mantle lithosphere source produced by the infiltration of the sublithospheric liquids into enriched domains of the mantle lithosphere, shortly before the melting event that generated the Garrotxa lavas. The available geological data suggest that the first enrichment event of the mantle lithosphere under the NEVP could be the result of Late Variscan mantle upwelling triggered by the extensional collapse of the Variscan orogen during the Permo-Carboniferous. By Jurassic/Cretaceous time, large-scale NNE-directed sublithospheric mantle channeling of thermally and chemically anomalous plume material was placed under the Iberian Peninsula and Central Europe. However, the geodynamic conditions in the NEVP did not favor magmatism, which could not take place until the Cenozoic after extension started. This favored the second enrichment event of the mantle lithosphere by entrainment and storage of liquids generated in the sublithospheric plume material. After a relatively short period of time, as extension progressed, it triggered melting in the enriched portions of the mantle lithosphere during the Quaternary, generating the Garrotxa volcanism.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Photoinduced effects and light emission in Ga-La-S:Pr/sup 3+/ glass

Acces full text: https://doi.org/10.1109/SMICND.2003.1251363The absorption and radiation spectra of Ga-La-S-O glasses with fixed cation ratio Ga/La=0.7/0.3 and two oxygen content 0.65 Wt % and 2.95 Wt % were studied for two Pr/sup 3+/ doping levels of 0.1 and 1.0 Wt %. Presence of oxygen induces blue shift of the fundamental absorption edge and results in lowering of the low-energy components of the Pr/sup 3+/ absorption bands. The glasses show bright luminescence due to Pr/sup 3+/ ion emission similar to that in other glasses. The effect of oxygen on the luminescence spectra is determined by decreasing of host glass self-absorption of the short-wavelength bands, which became visible with oxide content growing