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  • Data  (244)
  • 1980-1984  (244)
Collection
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Years
Year
  • 1
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Cyamex Scientific Team; Francheteau, Jean; Needham, H D; Choukroune, P; Juteau, Thierry; Séguret, Marie J M; Ballard, R D; Fox, P J; Normark, William R; Carranza, A; Cordoba, D; Guerrero, Gerardo; Rangin, Claude (1981): First manned submersible dives on the East Pacific Rise at 21�N (project RITA): General results. Marine Geophysical Research, 4(4), 345-379, https://doi.org/10.1007/BF00286034
    Publication Date: 2019-01-14
    Description: A submersible study has been conducted in February - March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera - Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of giant size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.
    Type: Dataset
    Format: text/tab-separated-values, 21 data points
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  • 2
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Juteau, Thierry; Eissen, Jean-Philippe; Francheteau, Jean; Needham, David; Choukroune, P; Rangin, Claude; Séguret, Marie J M; Ballard, R D; Fox, P J; Normark, William R; Carranza, A; Cordoba, D; Guerrero, J (1980): Homogeneous basalts from the East Pacific Rise at 21° N: seady state magma reservoirs at moderately fast spreading centers. Oceanologica Acta, 3(4), 487-503, http://archimer.ifremer.fr/doc/00323/43430/
    Publication Date: 2019-01-14
    Description: Forty basaltic rocks collected by submersible during the Cyamex expedition (1978) on the East PacifIc Rise at 21°N, a moderately fast spreading segment (6 cm/year opening rate) of the mid-ocean ridge, consist of angular pillow fragments and glass buds, sheet-flow slabs and samples of columnar pillars standing in collapsed fossillava pools. Most of the rocks are from the crestal are a of the Rise. The collection shows a striking petrographic homogeneity wh en compared with the range of basalts found on other segments of midocean ridges: olivine-phyric, or highly plagioclase-phyric rocks, so common in the slowspreading Famous are a in the Atlantic, are absent. All samples are typical lowpotassium oceanic tholeiites with a limited fractionation trend. Pillow-lavas, thin and thick sheet-flows cannot be distinguished by their major element compositions, as in the Galapagos rift which has the same spreading rate as the EPR at 21°N. Further, ferrobasalts have been described from the Galapagos rift, but do not appear in the Cyamex rocks. In the Cyamex area, olivine and plagioclase are the main silicate phases, and clinopyroxene is absent. In the pillows and sheet-flow samples, four generations of olivine and plagioclase crystals are distinguished. Samples from the fossillava pools are aphyric. The corresponding magma batches are presumed to have migrated rapidly through the magma chamber, and to have been extruded in large volumes, possibly during episodes ofhigh instantaneous opening rate. Fe-Ni and Fe-Cu-rich sulphide phases are common in an lava types as massive globules scatterred through the glass, or as microglobules decorating the walls of empty vesicles. Palagonite and Fe-Mn oxide thicknesses across the strike of the Rise indicate relative ages compatible with successive extrusions at the Rise axis.
    Type: Dataset
    Format: text/tab-separated-values, 108 data points
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  • 3
    Publication Date: 2019-04-16
    Description: Five sites were drilled along a transect of the Walvis Ridge. The basement rocks range in age from 69 to 71 m.y., and the deeper sites are slightly younger, in agreement with the sea-floor-spreading magnetic lineations. Geophysical and petrological evidence indicates that the Walvis Ridge was formed at a mid-ocean ridge at anomalously shallow elevations. The basement complex, associated with the relatively smooth acoustic basement in the area, consists of pillowed basalt and massive flows alternating with nannofossil chalk and limestone that contain a significant volcanogenic component. Basalts are quartz tholeiites at the ridge crest and olivine tholeiites downslope. The sediment sections are dominated by carbonate oozes and chalks with volcanogenic material common in the lower parts of the sediment columns. The volcanogenic sediments probably were derived from sources on the Walvis Ridge. Paleodepth estimates based on the benthic fauna are consistent with a normal crustal-cooling rate of subsidence of the Walvis Ridge. The shoalest site in the transect sank below sea level in the late Paleocene, and benthic fauna suggest a rapid sea-level lowering in the mid-Oligocene. Average accumulation rates during the Cenozoic indicate three peaks in the rate of supply of carbonate to the sea floor, that is, early Pliocene, late middle Miocene, and late Paleocene to early Eocene. Carbonate accumulation rates for the rest of the Cenozoic averaged 1 g/cm**2/kyr. Dissolution had a marked effect on sediment accumulation in the deeper sites, particularly during the late Miocene, Oligocene, and middle to late Eocene. Changes in the rates of accumulation as a function of depth demonstrate that the upper part of the water column had a greater degree of undersaturation with respect to carbonate during times of high productivity. Even when the calcium carbonate compensation depth (CCD) was below 4400 m, a significant amount of carbonate was dissolved at the shallower sites. The flora and fauna of the Walvis Ridge are temperate in nature. Warmer-water faunas are found in the uppermost Maastrichtian and lower Eocene sediments, with cooler-water faunas present in the lower Paleocene, Oligocene, and middle Miocene. The boreal elements of the lower Pliocene are replaced by more temperate forms in the middle Pliocene. The Cretaceous-Tertiary boundary was recovered in four sites drilled, with the sediments containing well-preserved nannofossils but poorly preserved foraminifera.
    Type: Dataset
    Format: text/tab-separated-values, 30 data points
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  • 4
    Publication Date: 2019-04-30
    Type: Dataset
    Format: text/tab-separated-values, 12 data points
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  • 5
    Publication Date: 2019-04-16
    Type: Dataset
    Format: text/tab-separated-values, 19 data points
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  • 6
    Publication Date: 2019-04-16
    Type: Dataset
    Format: text/tab-separated-values, 164 data points
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  • 7
    Publication Date: 2019-04-16
    Type: Dataset
    Format: text/tab-separated-values, 82 data points
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  • 8
    Publication Date: 2019-04-16
    Type: Dataset
    Format: text/tab-separated-values, 22 data points
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  • 9
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Ryabchikov, I D; Babansky, A D; Dmitriev, Yuri I (1982): Genesis of calc-alkaline magmas: Experiments with partial melting of mixed mediments and basalts from the Middle America Trench, southern Mexico Transect. In: Watkins, JS; Casey Moore, J; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 66, 699-702, https://doi.org/10.2973/dsdp.proc.66.132.1982
    Publication Date: 2019-02-13
    Description: It is widely accepted that the calc-alkaline magmatism of active continental margins is caused by the melting of ocean crust in subduction zones, which in turn is due to the interaction of lithospheric plates (Dickinson, 1970; Fitton, 1971; Green, 1972). In particular, the Neogene-Quaternary magmatism of Central America is considered to be the result of the subduction of the Cocos Plate under the continent of North America in the zone of the Middle America Trench (Pichler and Weyl, 1973; Stoiber and Carr, 1974). Recent investigations (Magaritz et al., 1978; Stern, 1974) show that the direct melting of ocean crust basalts does not result in the formation of calc-alkaline magmas, and the models of the generation of these melts would not be complete without taking into account both the processes of magmatic differentiation and their interaction with the sialic material of ocean and continental crust.
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 10
    Publication Date: 2019-07-25
    Type: Dataset
    Format: text/tab-separated-values, 392 data points
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