Isotope characterization and estimated temperature of formation of calcite veins in ODP Sites 124-768 and 124-770 (Table 1)

Secondary carbonate minerals were recovered within the basalts at both ODP Sites 768 and 770 in the Sulu and Celebes seas. Petrographic and X-ray diffraction analyses indicate that the carbonates are calcites. Other alteration products recognized in the thin sections are smectites, iron oxides, and gypsum. The 13C values of carbonates from both sites range from 1.6 per mil to 2.3 per mil, which are indicative of inorganic carbonate formation with no contributions from 13C-depleted sources such as oxidized organic carbon or methane. The oxygen isotopes at Site 770 range from 30.8 per mil to 31.6 per mil, which indicates a pervasive circulation of cold seawater (9° to 12°C) during alteration of the Celebes Sea basalts. In contrast, carbonates associated with Site 768 basalts have less positive d18O values (21.0 per mil to 27.3 per mil). A lighter 18O isotopic signature indicates the formation of secondary calcite at either higher temperatures or in a system closed to seawater. The rapidly deposited pyroclastic flows at Site 768 would have limited water access to the crust very soon after its formation, which leads us to speculate that the carbonates in the Sulu Sea basalts were formed by isotopically modified fluids resulting from basalt alteration in a closed system.

Geochemistry of the oceanic crust from ocean drilling samples

This book presents new data on chemical and mineral compositions and on density of altered and fresh igneous rocks from key DSDP and ODP holes drilled on the following main tectonomagmatic structures of the ocean floor: 1. Mid-ocean ridges and abyssal plains and basins (DSDP Legs 37, 61, 63, 64, 65, 69, 70, 83, and 91 and ODP Legs 106, 111, 123, 129, 137, 139, 140, 148, and 169); 2. Seamounts and guyots (DSDP Legs 19, 55, and 62 and ODP Legs 143 and 144); 3. Intraplate rises (DSDP Legs 26, 33, 51, 52, 53, 72, and 74 and ODP Legs 104, 115, 120, 121, and 183); and 4. Marginal seas (DSDP Legs 19, 59, and 60 and ODP Legs 124, 125, 126, 127, 128, and 135). Study results of altered gabbro from the Southwest Indian Ridge (ODP Leg 118) and serpentinized ultramafic rocks from the Galicia margin (ODP Leg 103) are also presented. Samples were collected by the authors from the DSDP/ODP repositories, as well as during some Glomar Challenger and JOIDES Resolution legs. The book also includes descriptions of thin sections, geochemical diagrams, data on secondary mineral assemblages, and recalculated results of chemical analyses with corrections for rock density. Atomic content of each element can be quantified in grams per standard volume (g/1000 cm**3). The suite of results can be used to estimate mass balance, but parts of the data need additional work, which depends on locating fresh analogs of altered rocks studied here. Results of quantitative estimation of element mobility in recovered sections of the upper oceanic crust as a whole are shown for certain cases: Hole 504B (Costa Rica Rift) and Holes 856H, 857C, and 857D (Middle Valley, Juan de Fuca Ridge).

Chemistry of volcanic ash from Celebes and Sulu Sea Basins

During Leg 124, off the Philippines, volcanic material was recovered in deep-sea sediments dating from the late Oligocene in the Celebes Sea Basin, and from the early Miocene in the Sulu Sea Basin. Chemical and petrological studies of fallout ash deposits are used to characterize volcanic pulses and to determine their possible origin. All of the glass and mineral compositions belong to medium-K and high-K calc-alkaline arc-related magmatic suites including high-Al basalts, pyroxene-hornblende andesites, dacites, and rhyolites. Late Oligocene and early Miocene products may have originated from the Sunda arc or from the Sabah-Zamboanga old Sulu arc. Late early Miocene Sulu Sea tuffs originated from the Cagayan arc, whereas early late Miocene fallout ashes are attributed to the Sulu arc. A complex magmatic production is distinguished in the Plio-Quaternary with three sequences of basic to acidic lava suites. Early Pliocene strata registered an important activity in both Celebes Sea and Sulu Sea areas, from the newly born Sangihe arc (low-alumina andesite series) and from the Sulu, Zamboanga, and Negros arcs (high-alumina basalt series and high-K andesite series). In the late Pliocene and the early Pleistocene, renewal of activity affects the Sangihe-Cotobato arc as well as the Sulu and Negros arcs (same magmatic distinctions). The last volcanic pulse took place in the late Pleistocene with revival of all the present arc systems.

Miocene radiolarians of the Sulu Sea

Radiolarians are sporadic in sediments collected in the Sulu Sea during ODP Leg 124. Due to the generally poor preservation and low abundance of radiolarians in Sulu Sea sediments, no biostratigraphic datums are well defined, although three radiolarian zones are identified. Most samples containing radiolarians are pelagic or hemipelagic clays with varying proportions of volcanic ash. Detailed analysis of Sulu Sea radiolarians was limited to Miocene successions. Pliocene and Quaternary occurrences of radiolarians were noted but have not been zoned. The late middle Miocene of Sites 769 and 771 is represented by an assemblage of radiolarians (Diartus petterssoni Zone) that is entirely replaced by massive pyrite. This type of preservation develops only under anoxic conditions. The development of widespread anoxia in Sulu Sea waters in the late middle Miocene was probably the result of hydrologic isolation of basin waters, and may be associated with eustatic sea level fall over the silled basin. Upper lower Miocene pelagic and hemipelagic sediments that overlie pyroclastics and basalt flows in the Sulu Sea sites contain moderately to very poorly preserved radiolarians of the Calocycletta costata Zone. A thin unit of marine claystone was recovered from between the thick pyroclastics and basement rocks at Site 768. Radiolarians present in these claystones are rare and very poorly preserved. This radiolarian assemblage probably represents the C. costata Zone, although very poor preservation and low abundance make this interpretation equivocal. The radiolarian zones identified constrain the age of basin formation to late early Miocene or earlier.

Geochemistry and petrology of the volcanic rocks from the Sulu Sea

Major-, trace-, and rare-earth element analyses of the basaltic rocks recovered from the basement of the Sulu Sea and of lithic clasts from the pyroclastic unit representing the acoustic basement of the Cagayan Ridge, are presented. The major and trace elements were measured by X-ray fluorescence techniques, and rare-earth elements by instrumental neutron activation analysis. These data show that the Sulu Sea basalts are back-arc tholeiites and the lithic clasts are basalts, basaltic andesites, and andesites typical of volcanic arc suites erupted on continental crust. Petrogenetic modeling is used to show that the Sulu Sea basalts were derived from a heterogeneous mantle, probably representing subcontinental lithosphere, with contributions from a subduction component. The Sulu Sea is interpreted as a back-arc basin formed by rifting of an Oligocene to early Miocene volcanic arc leaving the Cagayan Ridge as a remnant arc. This event occurred during northward subduction of the Celebes Sea basement beneath the Oligocene to early Miocene arc.

Element analyses and isotopic composition of basalts from the western Pacific

New Sr- Nd- and Pb-isotopic and trace element data are presented on basalts from the Sulu and Celebes Basins, and the submerged Cagayan Ridge Arc (Western Pacific), recently sampled during Ocean Drilling Program Leg 124. Drilling has shown that the Sulu Basin developed about 18 Ma ago as a backarc basin, associated with the now submerged Cagayan Ridge Arc, whereas the Celebes Basin was generated about 43 Ma ago, contemporaneous with a general plate reorganisation in the Western Pacifc, subsequently developing as an open ocean receiving pelagic sediments until the middle Miocene. In both basins, a late middle Miocene collision phase and the onset of volcanic activity on adjacent arcs in the late Miocene are recorded. Covariations between 87Sr/86Sr and 143Nd/144Nd show that the seafoor basalts from both the Sulu and Celebes Basins are isotopically similar to depleted Indian mid-ocean ridge basalts (MORB), and distinct from East Pacifc Rise MORB, defining a single negative correlation. The Cagayan Arc volcanics are different, in that they have distinctly lower epsilon-Ne(T) for a given epsilon-Sr(T), compared to Sulu and Celebes basalts. In the 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, the Celebes, Sulu and Cagayan rocks all plot distinctly above the Northern Hemisphere Reference Line, with high Delta 7/4 Pb (5.3-9.3) and Delta 8/4 Pb (46.3-68.1) values. They define a single trend of radiogenic lead enrichment from Celebes through Sulu to Cagayan Ridge, within the Indian Ocean MORB data field. The data suggest that the overall chemical and isotopic features of the Sulu, Cagayan and Celebes rocks may be explained by partial melting of a depleted asthenospheric N-MORB-type ("normal") mantle source with isotopic characteristics similar to those of the Indian Ocean MORB source. This asthenospheric source was slightly heterogeneous, giving rise to the Sr-Nd isotopic differences between the Celebes and Sulu basalts, and the Cagayan Ridge volcanics. In addition, a probably slab-derived component enriched in LILE and LREE is required to generate the elemental characteristics and low Ne(T) of the Cagayan Ridge island arc tholeiitic and calcalkaline lavas, and to contribute to a small extent in the backarc basalts of the Sulu Sea. The results of this study confirm and extend the widespread Indian Ocean MORB signature in the Western Pacifc region. This signature could have been inherited by the Indian Ocean mantle itself during the rupture of Gondwanaland, when fragments of this mantle could have migrated towards the present position of the Celebes, Sulu and Cagayan sources.

GMRT observations of the group Holmberg 124: Evolution by tidal forces and ram pressure?

We report new radio continuum and 21 cm HI observations using the Giant Metrewave Radio Telescope (GMRT) of the group Holmberg 124 ( Ho 124) comprising four late-type galaxies, namely NGC 2820, Mrk 108, NGC 2814 and NGC 2805. The three galaxies, NGC 2820, Mrk 108 and NGC 2814 which are closely located in the sky plane have clearly undergone tidal interactions as seen from the various morphological tidal signatures and debris. Moreover we note various features in the group members which we believe might be due to ram pressure. In this paper, we describe four interesting results emerging from our observations: a) detection of the tidal radio continuum bridge at 330 MHz connecting the galaxies NGC 2820+ Mrk 108 with NGC 2814. The radio bridge was discovered at 1465 MHz by van der Hulst & Hummel ( 1985, A& A, 150, 17). We find that the bridge has a fairly steep spectrum with a spectral index alpha(S proportional to nu(alpha)) of - 1.8(-0.2)(+0.3) which is much steeper than the - 0.8 quoted by van der Hulst & Hummel ( 1985); b) detection of other tidal features like the tilted HI and radio continuum disk of NGC 2814, a HI streamer and a radio continuum tail arising from the south of NGC 2814. We also report the detection of a possible tidal dwarf galaxy in HI; c) sharp truncation in the HI distribution in the south of NGC 2820 and in the HI and radio continuum distribution in the north of NGC 2814. The optical disks in both the cases look undisturbed. As pointed out by Davis et al. ( 1997, AJ, 114, 613), ram pressure affects different components of the interstellar medium to varying degrees. Simple estimates of pressure in different components of the interstellar medium ( radio continuum, Ha and HI) in NGC 2820 indicate that ram pressure will significantly influence HI; d) detection of a large one-sided HI loop to the north of NGC 2820. No radio continuum emission or Ha emission is associated with the HI loop. We discuss various scenarios for the origin of this loop including a central starburst, ram pressure stripping and tidal interaction. We do not support the central starburst scenario since the loop is not detected in ionized gas. Using the upper limit on X-ray luminosity of Ho 124 (Mulchaey et al. 2003, ApJS, 145, 39), we estimate an upper limit on the intragroup medium (IGrM) density of 8.8 x 10(-4) cm(-3). For half this electron density, we estimate the ram pressure force of the IGrM to be comparable to the gravitational pull of the disk of NGC 2820. Since tidal interaction has obviously influenced the group, we suggest that the loop could have formed by ram pressure stripping if tidal effects had reduced the surface density of HI in NGC 2820. From the complex observational picture of Ho 124 and the numerical estimates, we suggest that the evolution of the Ho 124 group may be governed by both tidal forces due to the interaction and the ram pressure due to motion of the member galaxies in the IGrM and that the IGrM densities should not be too low (i.e. >= 4 x 10(-4)). However this needs to be verified by further observations.

Sapientia, 1977, Vol. XXXII, nº 124 (número completo)

Contenido: El subjetivismo historicista e irracionalista contemporáneo / Octavio N. Derisi – El ser en Santo Tomás y en la Fenomenología / Vicente O. Ciliberto – La Palabra / Octavio N. Derisi – Ética, teología y religión / Victorino Rodríguez – El poeta del Santísimo Sacramento / Sisto Terán – Notas y comentarios -- Bibliografía

Diário da Constituinte [gravação de vídeo] : [programa n. 124]

Os constituintes do Norte e Nordeste querem mais recursos para as suas regiões. Querem o aumento de dois para cinco por cento de recursos destinados aos órgãos de desenvolvimento regional. Rubem Branquinho (PMDB-AC) relata sobre as diferenças regionais de desenvolvimento e cita o potencial do Estado do Acre. Geraldo Fleming (PMDB-AC) acredita que a proposta de 5% seja aprovada na Comissão de Sistematização da Assembleia Nacional Constituinte (ANC). Asdrubal Bentes (PMDB-PA) também defende maiores recursos para o desenvolvimento da Amazônia, tal como ocorreu na Constituição de 1946. Na sessão O Povo Pergunta, cidadã quer saber o que muda no ensino. Paulo Almada (PMDB-MG) responde que a Constituinte tem soluções para melhorar a assistência do Estado ao ensino universitário e ao ensino de primeiro grau. Bernardo Cabral (PMDB-AM), após conversa com Afonso Arinos (PFL-RJ), fala com a imprensa e afirma que o anteprojeto até agora é o resultado dos trabalhos das comissões temáticas e que só em agosto apresenta seu substitutivo. Demonstrou também seu posicionamento favorável ao parlamentarismo e pretende diminuir o número de artigos da Constituição. União estável de um homem com uma mulher será reconhecida como família. Além disso, o casamento religioso também terá efeito legal e o Estado deverá facilitar a celebração do casamento civil. Cid Carvalho (PMDB-MA) esclarece que é inovador o conceito de família que está prevalecendo no projeto de Constituição.