Elements and isotopic measurements of magmatic rock samples from ODP Hole 104-642E

Trace element and isotopic signatures of magmatic rock samples from ODP Hole 642E at the Vøring Plateau provide insight into the interaction processes of mantle melt with crust during the initial magma extrusion phases at the onset of the continental breakup. The intermediate (basaltic-andesitic) to felsic (dacitic and rhyolitic) Lower Series magmas at ODP Hole 642E appear to be produced by large amounts of melting of upper crustal material. This study not only makes use of the traditional geochemical tools to investigate crust-mantle interaction, but also explores the value of Cs geochemistry as an additional tool. The element Cs forms the largest lithophile cation, and shows the largest contrast in concentration between (depleted) mantle and continental crust. As such it is a very sensitive indicator of involvement of crustal material. The Cs data reinforce the conclusion drawn from isotopic signatures that the felsic magmas are largely anatectic crustal melts. The down-hole geochemical variation within ODP Hole 642E defines a decreasing continental crustal influence from the Lower Series into the Upper Series. This is essential information to distinguish intrinsic geochemical properties of the mantle melts from signatures imposed by crustal contamination. A comparison with data from the SE Greenland margin highlights the compositional asymmetry of the crust-mantle interactions at both sides of the paleo-Iapetus suture. While Lower Series and Middle Series rocks from the SE Greenland margin have isotopic signatures reflecting interactions with lower and middle crust, such signatures have not been observed at the mid-Norwegian margin. The geochemical data either point to a dissimilar Caledonian crustal composition and/or to different geodynamic pre-breakup rifting history at the two NE Atlantic margin segments.

Procedimientos servianos de lectura acerca de los certámenes fúnebres en Eneida V : La naumaquia (vv. 104-285)

La figura de Servio y su comentario a la obra virgiliana constituye la summa opera de la tradición escolar tardoantigua; su importancia reside porque es el resultado de numerosas estratificaciones que recogen diversos abordajes exegéticos. Al tratarse de un comentario ?continuo?, los Commentarii servianos comprenden un conjunto de saberes que examinan la obra literaria desde la perspectiva histórica y de todo aquello que se relacionaba con esta. A partir de esta mirada lectora, la comunicación se centrará en el análisis que Servio realiza sobre la naumaquia del libro V de la Eneida (vv. 104-285), donde el texto base expone una secuencia narrativa caracterizada por epicismos homéricos y pos-homéricos que el gramático desarticula, privilegiando aspectos como el lingüístico, retórico, fabuloso y histórico-arqueológico. Asimismo, se comprobará que el certamen virgiliano constituye un pretexto para instalar un nuevo contexto que garantice la continuidad del sistema burocrático imperial

Organic geochemistry of ODP Leg 104 holes

The Leg 104 organic geochemistry program consisted of monitoring (a) hydrocarbon gases, (b) organic and inorganic carbon, and (c) parameters resulting from Rock-Eval pyrolysis at three sites on the Voring Plateau. The results amplify some of those obtained earlier on Deep Sea Drilling Project (DSDP) Leg 38. In a regional sense there is an inverse correlation between amounts of hydrocarbon gas and organic carbon. For example, significant concentrations of methane are present only at Site 644 in the inner part of the plateau where organic carbon contents are always less than 1%; in contrast, at Site 642 on the outer plateau, methane concentrations are very low (ppm range) whereas amounts of organic carbon approach 2%. Only at Site 644 are the environmental conditions such that methanogenesis is an active diagenetic process. Because of the importance of routine gas analyses to the Ocean Drilling Program (ODP), a procedure was devised to improve the use of Vacutainers for collection of gas samples. Comparison of methods for determining organic carbon showed that at Sites 643 and 644 Rock-Eval TOC could be used as a measure of organic carbon, but not at Site 642. Although no liquid or solid hydrocarbons were encountered at any of the sites, a catalog of potential organic geochemical contaminants was developed in anticipation of such a discovery.