Mantle and crustal sources in the genesis of late-hercynian granitoids (NW Portugal) : geochemical and Sr-Nd isotopic constraints

Large volumes of granitoids were emplaced in the Hercynian Central Iberian Zone during the last ductile deformation phase (D3, 300-320 Ma). The biotite-rich granitoids are the most abundant: (1) syn-D3 granodiorites-monzogranites (313-319 Ma) with calc-alkaline and aluminopotassic affinities; (2) late-D3 granodiorites-monzogranites (306-311 Ma), related to subalkaline and aluminopotassic series. These granitoids are associated with coeval gabbro-norite to granodiorite bodies and/or mafic microgranular enclaves. Both granitoids and basic-intermediate rocks show petrological, geochemical and isotopic evidence of interaction between felsic and mafic magmas. The mantle-derived melts, represented by shoshonitic gabbro-norites, were probably derived from an enriched and isotopically homogeneous source (Srl = 0.7049 to 0.7053, eNd= -2.1 to -2.5). In some syn- and late-D3 plutons there are evidences of essentially crustal granites, represented by moderately peraluminous monzogranites of aluminopotassic affinity. They have similar Nd model ages (1.4 Ga) but different isotopic compositions (Srl = 0.7089 to 0.7106, eNd= -5.6 to -6.8), revealing a heterogeneous crust. Potential protoliths are metasedimentary (immature sediments) and/or fclsic meta-igneous lower crust materials. Large amounts of hybrid magmas were generated by the interaction of these coeval mantle- and crust-derived liquids, giving rise to slightly peraluminous monzogranites/granodiorites of calc-alkaline and subalkaline affinities, which display more depleted isotopic compositions than the crustal end-members (Sr, = 0.7064 to 0.7085, eNd = -4.4 to -6.2). Petrogenetic processes involving mingling and/or mixing and fractional crystallization (at variable degrees) in multiple reservoirs are suggested. A major crustal growth event occurred in late-Hercynian times (305-320 Ma) related to the input of juvenile mantle magmas and leading to the genesis of composite calc-alkaline and subalkaline plutons, largely represented in the Central Iberian Zone.Financial support was provided by FCT (project PRAXIS 2/2.1/391/94), France-Portugal Scientific Cooperation Programs and by the University of Minho

A study exploring learners' informal learning space behaviors, attitudes, and preferences

What makes a successful informal learning space is a topic in need of further research. The body of discourse on informal space design is drawn from learning theory, placemaking and architecture, with a need for understanding of the synergy between the three. Findings from a longitudinal, quantitative and qualitative study at Sheffield Hallam University, explore learners' behaviours, attitudes and preferences towards informal learning spaces in higher education, within and outside of the context of the academic library. The learning spaces study contributes to the discourse on informal learning spaces design by producing a typology of nine learning space preference attributes which address aspects of learning theory, placemaking and architecture. The typology can be used to evaluate existing spaces and inform redevelopment of informal learning spaces in higher education institutions. Implementing the typology will be subject to localised conditions, but at Sheffield Hallam University the key conclusions have included developing a portfolio of discrete, interrelated learning environments, offering spaces with a clear identity and encouraging students to translate their learning preferences into space selection

Le magmatisme basique hercynien et post-hercynien du Système central espagnol: essai de caractérisation des sources mantelliques

Les manifestations du magmatisme basique dans le Système central espagnol s’étalent de façon sporadique sur une période de 140 Ma. Les données géochimiques suggèrent des sources mantelliques variables pour les cinq suites magmatiques reconnues. Une contribution crustale significative est mise en évidence dans les magmas Gb1 à Gb3, mis en place en liaison avec l’orogénèse hercynienne. Elle témoigne de processus d’hybridation intracrustal et/ou du recyclage de matériaux d’origine continentale dans le manteau. En revanche, le magmatisme post-collisionnel ultérieur montre une empreinte crustale négligeable dans la suite lamprophyrique alcaline Gb4, extraite d’un réservoir source de type OIB. La suite tholéiitique Gb5 pourrait témoigner d’un manteau source métasomatisé par un composant d’origine crustale [ABSTRACT] Hercynian and post-Hercynian basic rocks from the Spanish Central System: estimates of Central Spain subcontinental mantle. Basic magmatism in central Spain occurred sporadically during a long period of ca. 140 Ma. The geochemical data on representative samples from the five igneous episodes show that different mantle reservoirs were tapped. Crustal involvement (via recycling in mantle sources or by hybridization at emplacement levels) was important in the basic magmas related to the Hercynian orogeny (Gb1 to Gb3 suites). Samples occurring as later dykes have signatures ranging from OIB-like values (Gb4 alkaline lamprophyres) to those of a formerly enriched subcontinental lithospheric mantle (tholeiites Gb5

U–Pb isotopic ages and Hf isotope composition of zircons in Variscan gabbros from central Spain: evidence of variable crustal contamination

Ion microprobe U–Pb analyses of zircons from three gabbroic intrusions from the Spanish Central System (SCS) (Talavera, La Solanilla and Navahermosa) yield Variscan ages (300 to 305 Ma) in agreement with recent studies. Only two zircon crystals from La Solanilla massif gave slightly discordant Paleoproterozoic ages (1,848 and 2,010 Ma). Hf isotope data show a relatively large variation with the juvenile end-members showing ɛHfi values as high as +3.6 to +6.9 and +1.5 to +2.9 in the Navahermosa and Talavera gabbros, respectively. These positive ɛHfi values up to +6.9 might represent the composition of the subcontinental mantle which generates these SCS gabbros. This ɛHfi range is clearly below depleted mantle values suggesting the involvement of enriched mantle components on the origin of these Variscan gabbros, and is consistent with previous whole-rock studies. The presence of zircons with negative ɛHfi values suggest variable, but significant, crustal contamination of the gabbros, mainly by mixing with coeval granite magmas. Inherited Paleoproterozoic zircons of La Solanilla gabbros have similar trace element composition (e.g. Th/U ratios), but more evolved Hf-isotope signatures than associated Variscan zircons. Similar inherited ages have been recorded in zircons from coeval Variscan granitoids from the Central Iberian Zone. Granitic rocks have Nd model ages (TDM) predominantly in the range of 1.4 to 1.6 Ga, suggesting a juvenile addition during the Proterozoic. However, Hf crustal model ages of xenocrystic Proterozoic zircons in La Solanilla gabbro indicate the presence of reworked Archean protoliths (TDM2 model ages of 3.0 to 3.2 Ga) incorporated into the hybridized mafic magma