(Table 1) Results of pore water analyses, including boron content and boron isotope ratios

Drilling a transect of holes across the Costa Rica forearc during ODP Leg 170 demonstrated the margin wedge to be of continental, non accretionary origin, which is intersected by permeable thrust faults. Pore waters from four drillholes, two of which penetrated the décollement zone and reached the underthrust lower plate sedimentary sequence of the Cocos Plate, were examined for boron contents and boron isotopic signatures. The combined results show dilution of the uppermost sedimentary cover of the forearc, with boron contents lower than half of the present-day seawater values. Pore fluid "refreshening" suggests that gas hydrate water has been mixed with the sediment interstitial water, without profoundly affecting the d11B values. Fault-related flux of a deeply generated fluid is inferred from high B concentration in the interval beneath the décollement, being released from the underthrust sequence with incipient burial. First-order fluid budget calculations over a cross-section across the Costa Rica forearc indicate that no significant fluid transfer from the lower to the upper plate is inferred from boron fluid profiles, at least within the frontal 40 km studied. Expulsed lower plate pore water, which is estimated to be 0.26-0.44 km3 per km trench, is conducted efficiently along and just beneath the décollement zone, indicating effective shear-enhanced compaction. In the upper plate forearc wedge, dewatering occurs as diffuse transport as well as channelled flow. A volume of approximately 2 km3 per km trench is expulsed due to compaction and, to a lesser extent, lateral shortening. Pore water chemistry is influenced by gas hydrate instability, so that it remains unknown whether deep processes like mineral dehydration or hydrocarbon formation may play a considerable role towards the hinterland.

Pleistocene Mass Transport Deposits Off Barbados Accretionary Prism (Lesser Antilles)

Two Pleistocene mass transport deposits (MTDs), with volumes of thousands of km(3), have been identified from multi-channel seismic data in the abyssal plain at the front of the Barbados accretionary prism. Estimated sediment volumes for these MTDs are likely underestimated due to limited seismic coverage. In this work, we suggest that these MTDs are comparable in size to large submarine landslides as reported in the literature. These MTDs lie on the vicinity of two major oceanic ridges, the Barracuda Ridge and the Tiburon Rise. It is also suggested in this work that the MTDs come from seismicity associated with the formation of the Barracuda Ridge or the Barbados accretionary prism; however, triggering mechanisms involved in their formation remain uncertain. The present study discusses the potential causal factors accounting for the formation of these MTDs.

Análisis del discurso del grupo guerrillero movimiento 19 de abril (M-19) a la luz de la teoría sobre el discurso de Teun Van Dijk (1974-1990)

El tema central de la presente monografía es mostrar la relación entre el discurso del movimiento 19 de abril (M-19) y sus acciones cometidas en el periodo de 1974 a 1990, a partir, de la explicación y aplicación de la teoría sobre el discurso de Teun Van Dijk, enfatizando en los conceptos de acción, contexto e ideología. Se analizaron los discursos hechos por el grupo guerrillero, relacionándolos con varias de sus acciones, lo que permitió ver cómo el discurso del M-19 al igual que su ideología cambiaron a través del tiempo; convirtiéndose, además, en un medio para justificar las acciones, dado que se pudo observar una concordancia entre las declaraciones, las palabras, y los actos políticos y revolucionarios del movimiento.