Chemistry of gabbroic rocks of ODP Hole 118-735B

We present results of a microprobe investigation of fresh and least-deformed and metamorphosed gabbroic rocks from Leg 118, Hole 735B, drilled on the east side of the Atlantis II Fracture Zone, Southwest Indian Ridge. This rock collection comprises cumulates ranging from troctolites to olivine-gabbro and olivine-gabbronorite to ilmenite-rich ferrogabbros and ferrogabbronorites. As expected, the mineral chemistry is variable and considerably expands the usual oceanic reference spectrum. Olivine, plagioclase, and clinopyroxene are present in all the studied samples. Orthopyroxene and ilmenite, although not rare, are not ubiquitous. Olivine compositions range from Fo85 to Fo30, while plagioclase compositions vary from An70 to An27. Mg/(Mg + Fe2+) of clinopyroxene (mostly diopside to augite) varies from 0.88 to 0.54. Mg/(Mg + Fe2+) of orthopyroxene varies from 0.84 to 0.50. These minerals are not significantly zoned. All mineralogical data indicate that fractional crystallization is an important factor for the formation of cumulates. However, sharp contacts, interpreted as layering boundaries or intrusion margins, suggest polycyclic fractionation of several magma batches of limited volumes. Calculated compositions of magmas in equilibrium with the most magnesian mineral samples at the bottom of the hole represent fractionated liquids through separation of olivine, plagioclase, and clinopyroxene at moderate to low pressures (less than 9 kb). Crystallization of orthopyroxene and ilmenite occurs in the most differentiated liquids. Mixing of magmas having various compositions before entering the cumulate zone is another mechanism necessary to explain extremely differentiated iron-rich gabbros formed in this slow-spreading ridge environment.

Investigations on volcanic rocks in sediment core CRP-3 from the Ross Sea, Antarctica

The petrography, mineralogy and geochemistry of volcanic and subvolcanic rocks in CRP-3 core have been examined in detail in order to characterise and to compare them with volcanic and subvolcanic rocks cropping out in the Victoria Land area, and to define the clast provenance or to establish possible volcanic activity coeval with deposition. Clasts with sizes ranging from granule to boulder show geochemical and mineralogical features comparable with those of Ferrar Supergroup rocks. They display a subalkaline affinity and compositions ranging from basalts to dacite. Three different petrographic groups with distinct textural and grain size features (subophitic, intergranular-intersertal, and glassy-hyalopilitic) are recognised and are related to the emplacement/cooling mechanism. In the sand to silt fraction, the few glass shards that have been recognised are strongly altered: however chemical analyses show they have subalkalic magmatic affinity. Mineral compositions of the abundant free clinopyroxene grains found in the core, are less affected by alteration processes, and indicate an origin from subalkaline magmas. This excludes the presence, during the deposition of CRP-3 rocks of alkaline volcanic activity comparable with the McMurdo Volcanic Group. Strong alteration of the magmatic body intruded the Beacon sandstones obliterates the original mineral assemblage. Geochemical investigations confirm that intrusion is part of the Ferar Large Igneous Province.

Organic facies and hydrocarbon potential at DSDP Leg 64 Holes

The sediments from the Gulf of California are potentially good sources for oil and gas. They are rich in organic carbon (av. = 1.9%). Sediments from the margins of the Gulf are rich in oil-prone marine-amorphous organic matter. Sediments from Guaymas Basin contain the same material plus abundant subordinate amounts of gas-prone terrestrially derived organic matter. The enrichment of all of these sediments in marine-amorphous components reflects deposition in a highly productive and oxygen-poor water mass. The sediments are thermally immature, except for those altered by hydrothermal activity or by the intrusion of sills. These sediments are extensively cooked and may have lost their potential for hydrocarbon generation.

Elemental and isotope compositions of lipids, kerogens and asphaltenes from samples of DSDP Hole 41-368

The thermal effects of three (one major and two minor) Miocene diabase intrusions on Cretaceous black shales from DSDP site 41-368 have been analyzed. A concentration gradient was observed, especially for the hydrocarbons, decreasing towards the major intrusion and between the three sills. The thermally-altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally-derived pristane over phytane. whereas, the unaltered sediments contained no elemental sulfur, and more phytane than pristane. A maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill. Two classes of molecular markers were present in this bitumen suite. The first was sesqui-, di- and triterpenoids and steranes. which could be correlated with both terrigenous and autochthonous sources. They were geologically mature and showed no significant changes due to the thermal stress. The second class was found in the altered samples, which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds. These compounds were derived from pyrolytic reactions during the thermal event. Kerogen was isolated from all of these samples, but only traces of humic substances were present. The H/C, N/C, d13C, d34S and dD all exhibit the expected effects of thermal stress. The kerogen becomes more aromatized and richer in 13C, 34S and D in the proximity of and between the sills. Maturation trends were also measured by the vitrinite reflectance and electron spin resonance, where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity. The effects of in situ thermal stress on the organic-rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills.

Chemical and strontium isotopic compositions of interstitial waters from sediments of ODP Site 135-841

The depth variations in the major chemical components dissolved in interstitial waters from the Tonga margin (ODP Site 841) are much more pronounced than those usually observed in deep-sea sediments. The extensive alteration of volcanic Miocene sediments to secondary minerals such as analcime, clays, and thaumasite forms a CaCl2-rich brine. The brine results from a high exchange of Ca to Na, K, and Mg and an increase in Cl concentrations due to removal of H2O from the fluid during the authigenesis of hydrous minerals. The formation of thaumasite could have partly controlled the concentration of dissolved SO4, HCO3, and Ca in the Miocene sediments. The strontium isotopic signature of the interstitial water suggests that alteration of the volcanic Miocene sediments occurred a long time after sedimentation. A transient diffusion model indicates that molecular diffusion was not prevented by lithologic barriers and that the formation of secondary minerals in the Miocene sediment occurred over a short period of time (e.g.,intrusion of andesite sills and dikes into the Miocene sediments.

Isotopic geochemistry of granitoids in the Jinshajiang suture zone, SW China

The Jinshajiang suture zone, located in the eastern part of the Tethyan tectonic domain, is noticeable for a large-scale distribution of Late Jurassic to Triassic granitoids. These granitoids were genetically related to the evolution of the Paleo-Tethys Ocean. The Beiwu, Linong and Lunong granitoids occur in the middle zone of the Jinshajiang Suture Zone, and possess similar geochemical features, indicating they share a common magma source. SIMS zircon U-Pb dating reveals the Beiwu, Linong and Lunong granitic intrusions were emplaced at 233.9±1.4 Ma (2 sigma), 233.1 ±1.4 Ma (2 sigma) and 231.0±1.6 Ma (2 sigma), respectively. All of these granitoids are enriched in abundances of Si (SiO2 =65.2-73.5 wt.%), and large-ion-lithophile-elements (LILEs), but depleted in high-field-strength-elements contents (HFSEs, e.g., Nb, Ta, Ti). In addition, they have low P2O5 contents (0.06-0.11 wt.%), A/CNK values ([molecular Al2O3/(CaO+Na2O+K2O)], mostly<1.1) and 10000Ga/Al ratios (1.7-2.2), consistent with the characteristics of I-type granites. In terms of isotopic compositions, these granitoids have high initial 87Sr/86Sr ratios (0.7078-0.7148), Pb isotopic compositions [(206Pb/204Pb)t=18.213-18.598, (207Pb/204Pb)t=15.637-15.730 and (208Pb/204Pb)t=38.323-38.791], zircon d18O values (7. per mil-9.3 per mil) and negative eNd(t) values (-5.1 to -6.7), suggesting they were predominantly derived from the continental crust. Their Nb/Ta ratios (average value=8.6) are consistent with those of the lower continental crust (LCC). However, variable ?Hf(t) values (-8.6 to +2.8) and the occurrences of mafic microgranular enclaves (MMEs) suggest that mantle-derived melts and lower crustal magmas were involved in the generation of these granitoids. Moreover, the high Pb isotopic ratios and elevated zircon d18O values of these rocks indicate a significant contribution of the upper crustal composition. We propose a model in which the Beiwu, Linong and Lunong granitoids were generated under a late collisional or post-collisional setting. It is possible that this collision was completed before Late Triassic. Decompression induced mantle-derived magmas underplated and provided the heat for the anatexis of the crust. Hybrid melts including mantle-derived and the lower crustal magmas were then generated. The hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rocks assimilation. Such three-component mixing magmas source and subsequent fractional crystallization could be responsible for the formation of the Beiwu, Linong and Lunong granitoids.

Paleomagnetic of igneous rocks of ODP Leg 114

A paleomagnetic study was made of 12 samples of trachytic basalt from the base of ODP Hole 698A on the Northeast Georgia Rise (southwest Atlantic) and four samples of andesitic basalt and nine samples of volcanic breccia from the base of ODP Hole 703A on the Meteor Rise (southeast Atlantic). The magnetic intensities of the Hole 703A samples are anomalously low, possibly reflecting alteration effects. The mean magnetic intensity of the Hole 698A samples is high, and compatible with the model of Bleil and Petersen (1983) for the variation of magnetic intensity with age in oceanic basalts, involving progressive low-temperature oxidation of titanomagnetite to titanomaghemite for some 20 m.y. followed by inversion to intergrowths of magnetite and other Fe-Ti oxides during the subsequent 100 m.y. These results support the interpretation of the Hole 698A basalts as true oceanic basement of Late Cretaceous age rather than a younger intrusion. Well-defined stable components of magnetization were identified from AF and thermal demagnetization of the Hole 698A basalts, and less well-defined components were identified for the Hole 703A samples. Studies of the magnetic homogeneity of the Hole 698A basalts, involving harmonic analysis of the spinner magnetometer output, indicate the presence of an unevenly distributed low-coercivity component superimposed on the more homogeneous high-coercivity characteristic magnetization. The former component is believed to reside in irregularly distributed multidomain magnetite grains formed along cracks within the basalt, whilst the latter resides in more uniformly distributed finer magnetic grains. The inclination values for the high-coercivity magnetization of five Hole 698A basalt samples form an internally consistent set with a mean value of 59° ± 5°. The corresponding Late Cretaceous paleolatitude of 40° ± 5° is shallower than expected for this site but is broadly compatible with models for the opening of the South Atlantic involving pivoting of South America away from Africa since the Early Cretaceous. The polarity of the stable characteristic magnetization of the Site 698 basalts is normal. This is consistent with their emplacement during the long Campanian to Maestrichtian normal polarity Chron C33N.

Paleomagnetism and bedding orientations at DSDP Sites 87-582, 87-583 and 87-584

Paleomagnetic measurements of sediment samples provide the magnetostratigraphy at Deep Sea Drilling Sites 582, 583, and 584 in the Nankai Trough and the Japan Trench. Drastic changes in the rate of sediment accumulation are documented by the magnetostratigraphic and biostratigraphic correlations. The changes in the accumulation rate correspond to the supply of sediments and variations in the accretionary process, which are directly related to the tectonic cycles in the geologic evolution of the Japanese island arc. Faults and folds within the drilled sedimentary sequences are oriented by paleomagnetic declination. Their directions and stress patterns are related to the relative plate motion along the trough and trench. The original remanent magnetization of the sediment was modified and remagnetized in the tectonic process of accretion by physical deformation, faulting, and intrusion of dewatering veinlets.

Pulperos rurales: entre la vida privada y la pública

Este trabajo estudia la vida privada del pulpero rural de la campaña de Buenos Aires y las actividades que desarrolla cuando no se encuentra frente a su negocio. A través del análisis de testamentos e inventarios de pulperos rurales de Buenos Aires de fines del siglo XVIII y principios del XIX el estudio intenta penetrar en la intimidad y en las actividades alternativas que desempeñaban. El trabajo logra comprobar la existencia de un espacio protegido de la intromisión pública. Si bien la frontera que separaba ambos territorios muchas veces aparecía desfigurada, el espacio privado ha sido conquistado en mayor o menor medida por el pulpero rural. Con ello este artículo cuestiona la visión de rusticidad general que envolvía a la vida en la campaña y ubica a los pulperos dentro de los sectores medios que poblaban la campaña.

Biopoder en los cuerpos

En las últimas fechas, los estudios de biopolítica y biopoder se han elevado significativamente. Es un asunto antiguo, presente en la filosofía griega y en su realidad. Es la vieja discusión de la relación y la intromisión de la política en la vida y la superación del Estado de naturaleza. La actualidad de la biopolítica se refleja en las dimensiones que adquiere la tecnología y en el asedio de los poderes globales contra la democracia. El cuerpo humano, entidad visible y externa, resiente toda clase de intervenciones y sujeciones encaminadas a la individualización y al establecimiento de una realidad totalitaria. La Biopolítica y la Tanatopolítica se entrelazan al administrar la vida y la muerte en una realidad escalofriante donde la técnica introduce el artificio más allá de lo natural. El cuerpo humano como zona fronteriza de lo natural y lo artificial expresa los alcances del post-humanismo. Una cultura física más equilibrada ayudaría a contener la deshumanización tan extendida, que reduce y degrada lo corporal a la vez, mientras los poderes someten, discriminan, intervienen a través de cuerpos cada vez más dóciles

Pensando con demonios entre los comuneros de Castilla : El diablo y la revuelta de las Comunidades (1520-1521)

Entre los siglos XII y XVII el diablo fue uno de los protagonistas de la cultura europea, incrementándose, a la vista de las personas de dichos siglos, su intervención en el mundo. Su participación era asociada a múltiples sucesos, como las catástrofes naturales, la creación de las herejías o la dirección de una secta de brujos y brujas que pretendía destruir a la cristiandad. Luego de considerar la figura del diablo como rebelde en la tradición cristiana, este artículo se ocupa de la intrusión del demonio en la revuelta de los comuneros de Castilla (1520-1521): muchos de los contemporáneos vincularon a los rebeldes con los estereotipos normalmente relacionados con la actividad diabólica, desde presencia de demonios entre los mismos a la utilización de la magia demoníaca por algunos de los líderes comuneros. De esta manera, se analiza lo que podrían llamarse los usos políticos de la demonología. Frente a la incredulidad de las autoridades inquisitoriales españolas respecto del estereotipo del sabbat, se percibe aquí otro diablo amenazante: el organizador de revueltas contra la monarquía. Finalmente, se incorpora al rebelde entre la galería de "otros" demonizadas por la cultura europea medieval y renacentista

Pulperos rurales: entre la vida privada y la pública

Este trabajo estudia la vida privada del pulpero rural de la campaña de Buenos Aires y las actividades que desarrolla cuando no se encuentra frente a su negocio. A través del análisis de testamentos e inventarios de pulperos rurales de Buenos Aires de fines del siglo XVIII y principios del XIX el estudio intenta penetrar en la intimidad y en las actividades alternativas que desempeñaban. El trabajo logra comprobar la existencia de un espacio protegido de la intromisión pública. Si bien la frontera que separaba ambos territorios muchas veces aparecía desfigurada, el espacio privado ha sido conquistado en mayor o menor medida por el pulpero rural. Con ello este artículo cuestiona la visión de rusticidad general que envolvía a la vida en la campaña y ubica a los pulperos dentro de los sectores medios que poblaban la campaña.

Biopoder en los cuerpos

En las últimas fechas, los estudios de biopolítica y biopoder se han elevado significativamente. Es un asunto antiguo, presente en la filosofía griega y en su realidad. Es la vieja discusión de la relación y la intromisión de la política en la vida y la superación del Estado de naturaleza. La actualidad de la biopolítica se refleja en las dimensiones que adquiere la tecnología y en el asedio de los poderes globales contra la democracia. El cuerpo humano, entidad visible y externa, resiente toda clase de intervenciones y sujeciones encaminadas a la individualización y al establecimiento de una realidad totalitaria. La Biopolítica y la Tanatopolítica se entrelazan al administrar la vida y la muerte en una realidad escalofriante donde la técnica introduce el artificio más allá de lo natural. El cuerpo humano como zona fronteriza de lo natural y lo artificial expresa los alcances del post-humanismo. Una cultura física más equilibrada ayudaría a contener la deshumanización tan extendida, que reduce y degrada lo corporal a la vez, mientras los poderes someten, discriminan, intervienen a través de cuerpos cada vez más dóciles