Petrology and geochemistry of sedimentary Unit III of ODP Hole 135-840B

The sedimentary sequence recovered at Site 840, on the Tonga frontal-arc platform, is 597.3 m thick and is subdivided into three lithostratigraphic units. The lowermost, late Miocene Unit III is 336.8 m thick and consists of a sequence of volcaniclastic mass-flow deposits (predominantly turbidites) interbedded with pelagic/hemipelagic deposits. Unit III was deposited in the forearc basin of the Lau volcanic arc, probably on a slope dominated by mass flows that built eastward from the ridge front and across the forearc. Upward through the unit a thinning and fining of individual turbidites takes place, interpreted to reflect a reduced sediment supply and a change from large to smaller flows. Decreasing volcanic activity with time is inferred from a decrease in coarse-grained volcaniclastic content in the upper part of the unit. The majority of the turbidites show the typical Bouma-type divisions, although both high- and low-density turbidity currents are inferred. High-density turbidity currents were especially common in the lower part of the unit. Geochemical analyses of detrital glass lie mainly in the low-K tholeiite field with a compositional range from basalt to rhyolite. A coherent igneous trend indicates derivation from a single volcanic source. This source was probably situated on the rifted part of the Lau-Tonga Ridge, within the present Lau backarc basin. The initial opening of the Lau Basin may have been around 6.0 m.y. ago. The onset of more extensive rifting, approximately 5.6 m.y. ago, is reflected in an increase in the silica content of volcanic glass. At the boundary toward Unit II, at approximately 5.25 Ma, an influx of thicker bedded and coarser grained volcaniclastic material is interpreted to reflect increasing volcanism and tectonism during the final breakup of the Lau-Tonga Ridge.

Sistema de identidad y diseño editorial de la revista Zero

El proyecto responde a la necesidad de la revista Zero, la cual difunde la cultura musical en Mendoza, de competir en el mercado local. Basándose en estos requerimientos, se diseña una identidad joven y pregnante. Así mismo se diagrama el interior de la misma, y se construye una estética que resulte atrayente al público consumidor.

Chemistry of igneous rocks from, the Celebes Sea basement

Major and trace elements, mineral chemistry, and Sr-Nd isotope ratios are reported for representative igneous rocks of Ocean Drilling Program Sites 767 and 770. The basaltic basement underlying middle Eocene radiolarianbearing red clays was reached at 786.7 mbsf and about 421 mbsf at Sites 767 and 770, respectively. At Site 770 the basement was drilled for about 106 m. Eight basaltic units were identified on the basis of mineralogical, petrographical, and geochemical data. They mainly consist of pillow lavas and pillow breccias (Units A, B, D, and H), intercalated with massive amygdaloidal lavas (Units Cl and C2) or relatively thin massive flows (Unit E). Two dolerite sills were also recognized (Units F and G). All the rocks studied show the effect of low-temperature seafloor alteration, causing almost total replacement of olivine and glass. Calcite, clays, and Fe-hydroxides are the most abundant secondary phases. Chemical mobilization due to the alteration processes has been evaluated by comparing elements that are widely considered mobile during halmyrolysis (such as low-field strength elements) with those insensitive to seafloor alteration (such as Nb). In general, MgO is removed and P2O5 occasionally enriched during the alteration of pillow lavas. Ti, Cs, Li, Rb, and K, which are the most sensitive indicators of rock/seawater interaction, are generally enriched. The most crystalline samples appear the least affected by chemical changes. Plagioclase and olivine are continuously present as phenocrysts, and clinopyroxene is confined in the groundmass. Textural and mineralogical features as well as crystallization sequences of Site 770 rocks are, in all, analogous to typical mid-ocean-ridge basalts (MORBs). Relatively high content of compatible trace elements, such as Ni and Cr, indicate that these rocks represent nearly primitive or weakly fractionated MORBs. All the studied rocks are geochemically within the spectrum of normal MORB compositional variation. Their Sr/Nd isotopic ratios plot on the mantle array (87Sr/87Sr 0.70324-0.70348 with 143Nd/144Nd 0.51298-0.51291) outside the field of Atlantic and Pacific MORBs. However, Sr and Nd isotopes are typical of both Indian Ocean MORBs and of some back-arc basalts, such as those of Lau Basin. The mantle source of Celebes basement basalts does not show a detectable influence of a subduction-related component. The geochemical and isotopic data so far obtained on the Celebes basement rocks do not allow a clear discrimination between mid-ocean ridge and back-arc settings.

En la prensa y en la guerra v sabe en qué filas se me ha de encontrar siempre : La campaña en el ejército grande de Sarmiento en el contexto de su polémica con Alberdi

La Campaña en el Ejército Grande aliado de Sud América de Sarmiento, puede pensarse como el texto que, de manera más fuerte y directa, reclama de Alberdi su compromiso en un debate. Se trata de un texto que, a partir de una serie de maniobras ancladas en textualidades de tipos diversos, instaura el polemos en el intento de legitimar un modelo de Nación, como así también la subjetividad adecuada para llevar adelante tal proyecto. El "desvío" de Alberdi, su nueva colocación cercana a Urquiza, pone en crisis el diagrama anterior trazado sobre el ideologema civilización versus barbarie. En su acercamiento a Urquiza, Alberdi revela lo inestable de un equilibrio fundado y sostenido sólo por la permanencia de Rosas en el poder. Corrido Rosas de la escena, los diques de contención se abrieron haciéndose visibles los puntos de fuga. El movimiento de Alberdi desestabiliza las certezas porque se trata de una operación de un alto valor semiótico. En última instancia, lo que se pone en juego en esta polémica mediante el uso de muy variados géneros de discurso es la disputa de dos sistemas interpretativos en pugna por acceder al lugar de la hegemonía. El espacio de la civilización se transforma, de este modo, en el teatro de operaciones de la lucha por imponer un sistema de reconfiguración de significados