Mass estimates and morphometric meassurements of Discoaster species and Sphenolithus from Ceara Rise ODP Site 927

Mass estimates for Late Miocene and Pliocene (8.6-3.25 Ma) Discoaster species and Sphenolithus are determined using samples of the equatorial Atlantic (Ceara Rise: ODP Site 927). Based on morphometric measurements, 3D computer models were created for 11 Discoaster species and their volumes calculated. From these, shape factors (ks) were derived to allow calculation of mass for different-sized discoasters and Sphenolithus abies. The mass estimates were then used to calculate the contribution of nannofossils to the total nannofossil carbonate. The discoaster contribution ranges from 10% to 40%, with a decreasing trend through the investigated interval. However, our estimates of total nannofossil carbonate from size-corrected abundance data are consistently 30-50% lower than estimates from grain-size measurement; this suggests that data based on mass estimates need to be interpreted with caution.

Estudio de algunas problemáticas políticas a partir de parámetros de análisis de la geografía actual

El presente artículo intenta abordar el estudio de algunos de los principales problemas que nos presenta, a diversas escalas, la política actual, ateniéndonos a sus implicancias espaciales y a partir de diversos parámetros ofrecidos en los últimos tiempos por la ciencia geográfica. La propuesta se apoya en bases teóricas desarrolladas a partir de los enunciados de Emmanuel Wallerstein y Peter Taylor acerca de un sistema mundial estructurado como una economía-mundo, basada en el modo de producción capitalista. Por otra parte, intenta formular una explicación teórica acerca de la dinámica experimentada por los territorios sobre la base de la mecánica de dicho sistema mundial. A partir de estos postulados, se propone el análisis de algunos de los principales fenómenos emanados del estudio anterior y sus implicancias espaciales, como las actuales relaciones de poder en el sistema, la subsistencia de factores de poder tradicionales (el Estado-nación, las configuraciones culturales de base étnica) y la aparición de nuevos (la constitución de bloques y asociaciones supranacionales, los nuevos movimientos sociales, las nuevas formas de participación local), la importancia de los discursos hegemónicos y contrahegemónicos en la construcción de las representaciones simbólicas y de los medios de información en dichos procesos o el nuevo cuadro de las identidades e hibridaciones culturales a partir de la movilidad de la población.

Estudio de algunas problemáticas políticas a partir de parámetros de análisis de la geografía actual

El presente artículo intenta abordar el estudio de algunos de los principales problemas que nos presenta, a diversas escalas, la política actual, ateniéndonos a sus implicancias espaciales y a partir de diversos parámetros ofrecidos en los últimos tiempos por la ciencia geográfica. La propuesta se apoya en bases teóricas desarrolladas a partir de los enunciados de Emmanuel Wallerstein y Peter Taylor acerca de un sistema mundial estructurado como una economía-mundo, basada en el modo de producción capitalista. Por otra parte, intenta formular una explicación teórica acerca de la dinámica experimentada por los territorios sobre la base de la mecánica de dicho sistema mundial. A partir de estos postulados, se propone el análisis de algunos de los principales fenómenos emanados del estudio anterior y sus implicancias espaciales, como las actuales relaciones de poder en el sistema, la subsistencia de factores de poder tradicionales (el Estado-nación, las configuraciones culturales de base étnica) y la aparición de nuevos (la constitución de bloques y asociaciones supranacionales, los nuevos movimientos sociales, las nuevas formas de participación local), la importancia de los discursos hegemónicos y contrahegemónicos en la construcción de las representaciones simbólicas y de los medios de información en dichos procesos o el nuevo cuadro de las identidades e hibridaciones culturales a partir de la movilidad de la población.

Estudio de algunas problemáticas políticas a partir de parámetros de análisis de la geografía actual

El presente artículo intenta abordar el estudio de algunos de los principales problemas que nos presenta, a diversas escalas, la política actual, ateniéndonos a sus implicancias espaciales y a partir de diversos parámetros ofrecidos en los últimos tiempos por la ciencia geográfica. La propuesta se apoya en bases teóricas desarrolladas a partir de los enunciados de Emmanuel Wallerstein y Peter Taylor acerca de un sistema mundial estructurado como una economía-mundo, basada en el modo de producción capitalista. Por otra parte, intenta formular una explicación teórica acerca de la dinámica experimentada por los territorios sobre la base de la mecánica de dicho sistema mundial. A partir de estos postulados, se propone el análisis de algunos de los principales fenómenos emanados del estudio anterior y sus implicancias espaciales, como las actuales relaciones de poder en el sistema, la subsistencia de factores de poder tradicionales (el Estado-nación, las configuraciones culturales de base étnica) y la aparición de nuevos (la constitución de bloques y asociaciones supranacionales, los nuevos movimientos sociales, las nuevas formas de participación local), la importancia de los discursos hegemónicos y contrahegemónicos en la construcción de las representaciones simbólicas y de los medios de información en dichos procesos o el nuevo cuadro de las identidades e hibridaciones culturales a partir de la movilidad de la población.

Major element concentrations in spinel, olivine and pyroxene from peridotites of ODP Hole 210-1277 of the Newfoundland margin

Serpentinized spinel peridotites of the Newfoundland margin drilled during ODP Leg 210 at Site 1277 have preserved, relic mineral compositions similar to the most depleted abyssal peridotites worldwide and different from those of the conjugate Iberian margin. The samples are derived from mass flows containing clasts of peridotite and gabbro and from in-situ basement, and are mostly mylonitic cpx-poor spinel harzburgites with Cr-rich spinels (Cr#0.35-0.66). Melting of the Newfoundland mantle occurred in the spinel peridotite field and probably exceeded the cpx-out phase boundary for some samples. Using proposed spinel peridotite melting models and experimentally derived phase diagrams, the Newfoundland harzburgites can be modeled as a residue after extraction of 14 to 20-25% melting. Basalts that are interleaved with mass flow deposits on top of the peridotite basement resemble normal to transitional mid-ocean ridge basalt. This, together with the unusually high Cr# of some spinel harzburgites suggest that the formation of basalts and partial melting of the underlying peridotite are not cogenetic. Among mantle samples some of the Newfoundland harzburgites approach mineral compositions of the Bay of island ophiolite and ophiolites from Japan that represent peridotites formed in an arc-setting. Thus, the peridotites drilled at Site 1277 may represent inherited (Caledonian or older) subarc mantle that was exhumed close to the ocean floor during the rifting evolution of the Atlantic. Compared to the spinel harzburgites from Newfoundland, the peridotites from the conjugate Iberian margin are, on average, less depleted and provide evidence for local equilibration in the plagioclase stability field. This can either be explained by an inherited, primary, Ca-richer composition of the Iberia peridotite, or, alternatively, by local melt impregnation and stagnation during continental rifting, and thus refertilizing previously depleted (arc-related) peridotite.

Lithogeochemical and isotope (Rb-Sr, Sm-Nd, Pb-Pb whole rock and Lu-Hf zircon) composition of samples from the Shackleton Range, East Antarctica

Three distinct, spatially separated crustal terranes have been recognised in the Shackleton Range, East Antarctica: the Southern, Eastern and Northern Terranes. Mafic gneisses from the Southern Terrane provide geochemical evidence for a within-plate, probably back-arc origin of their protoliths. A plume-distal ridge origin in an incipient ocean basin is the favoured interpretation for the emplacement site of these rocks at c. 1850 Ma, which, together with a few ocean island basalts, were subsequently incorporated into an accretionary continental arc/supra-subduction zone tectonic setting. Magmatic underplating resulted in partial melting of the lower crust, which caused high-temperature granulite-facies metamorphism in the Southern Terrane at c. 1710-1680 Ma. Mafic and felsic gneisses there are characterised by isotopically depleted, positive Nd and Hf initials and model ages between 2100 and 2000 Ma. They may be explained as juvenile additions to the crust towards the end of the Palaeoproterozoic. These juvenile rocks occur in a narrow, c. 150 km long E-W trending belt, inferred to trace a suture that is associated with a large Palaeoproterozoic accretionary orogenic system. The Southern Terrane contains many features that are similar to the Australo-Antarctic Mawson Continent and may be its furthermost extension into East Antarctica. The Eastern Terrane is characterised by metagranitoids that formed in a continental volcanic arc setting during a late Mesoproterozoic orogeny at c. 1060 Ma. Subsequently, the rocks experienced high-temperature metamorphism during Pan-African collisional tectonics at 600 Ma. Isotopically depleted zircon grains yielded Hf model ages of 1600-1400 Ma, which are identical to Nd model ages obtained from juvenile metagranitoids. Most likely, these rocks trace the suture related to the amalgamation of the Indo-Antarctic and West Gondwana continental blocks at ~600 Ma. The Eastern Terrane is interpreted as the southernmost extension of the Pan-African Mozambique/Maud Belt in East Antarctica and, based on Hf isotope data, may also represent a link to the Ellsworth-Whitmore Mountains block in West Antarctica and the Namaqua-Natal Province of southern Africa. Geochemical evidence indicates that the majority of the protoliths of the mafic gneisses in the Northern Terrane formed as oceanic island basalts in a within-plate setting. Subsequently the rocks were incorporated into a subduction zone environment and, finally, accreted to a continental margin during Pan-African collisional tectonics. Felsic gneisses there provide evidence for a within-plate and volcanic arc/collisional origin. Emplacement of granitoids occurred at c. 530 Ma and high-temperature, high-pressure metamorphism took place at 510-500 Ma. Enriched Hf and Nd initials and Palaeoproterozoic model ages for most samples indicate that no juvenile material was added to the crust of the Northern Terrane during the Pan-African Orogeny but recycling of older crust or mixing of crustal components of different age must have occurred. Isotopically depleted mafic gneisses, which are spatially associated with eclogite-facies pyroxenites, yielded late Mesoproterozoic Nd model ages. These rocks occur in a narrow, at least 100 km long, E-W trending belt that separates alkaline ocean island metabasalts and within-plate metagranitoids from volcanic arc metabasalts and volcanic arc/syn-collisional metagranitoids in the Northern Terrane. This belt is interpreted to trace the late Neoproterozoic/early Cambrian Pan-African collisional suture between the Australo-Antarctic and the combined Indo-Antarctic/West Gondwana continental blocks that formed during the final amalgamation of Gondwana.

Accumulation, velocities, fluxes and mass balance of glacial tributaries to the Lambert Glacier-Amery Ice Shelf system, Antarctica

By incorporating recently available remote sensing data, we investigated the mass balance for all individual tributary glacial basins of the Lambert Glacier-Amery Ice Shelf system, East Antarctica. On the basis of the ice flow information derived from SAR interferometry and ICESat laser altimetry, we have determined the spatial configuration of eight tributary drainage basins of the Lambert-Amery glacial system. By combining the coherence information from SAR interferometry and the texture information from SAR and MODIS images, we have interpreted and refined the grounding line position. We calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from Radarsat three-pass interferometry together with ice thickness data interpolated from Australian and Russian airborne radio echo sounding (RES) surveys and inferred from ICESat laser altimetry data. Our analysis reveals that three tributary basins have a significant net positive imbalance, while five other subbasins are slightly positive or close to zero balance. Overall, in contrast to previous studies, we find that the grounded ice in Lambert Glacier-Amery Ice Shelf system has a positive mass imbalance of 22.9 ± 4.4 Gt/a. The net basal melting for the entire Amery Ice Shelf is estimated to be 27.0 ± 7.0 Gt/a. The melting rate decreases rapidly from the grounding zone to the ice shelf front. Significant basal refreezing is detected in the downstream section of the ice shelf. The mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates.