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| Registros recuperados: 30 | |
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| Hekinian, Roger; Rosendahl, Br; Cronan, Ds; Dmitriev, Y; Fodor, Rv; Goll, Rm; Hoffert, M; Humphris, Se; Mattey, Dp; Natland, J; Petersen, N; Roggenthen, W; Schrader, El; Srivastava, Rk; Warren, N. |
| Relatively thick (up to 15 m) hydrothermal deposits from the southern flank of the Galapagos spreading center were drilled on a crust of about 0.62 myr old (magnetic age), during Leg 54 of the "Glomar Challenger" in the central Eastern Pacific Ocean. A stratigraphic sequence of ferrobasalt, pelagic oozes, and hydrothermal deposits of green clay-rich material and Fe-Mn concretions were recovered. The green clay-rich material (Fe-Si type of smectite) is also found interlayered between the pelagic ooze and filling veins, veinlets and vesicles in the drilled basement rocks. The low transitional metal content (Cu < 150 ppm). Ni < 100 ppm and Co < 200 ppm) and the nature of the green clay-rich material from the Galapagos deposits make them comparable to... |
| Tipo: Text |
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| Ano: 1978 |
URL: http://archimer.ifremer.fr/doc/1978/publication-5254.pdf |
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| Hekinian, Roger; Bideau, Daniel; Francheteau, Jean; Cheminee, Jean-louis; Armijo, Rolando; Lonsdale, Peter; Blum, Norbert. |
| The Hess Deep, a rifted oval-shaped depression located east of the Galapagos Triple Junction at the tip of the Cocos-Nazca ridge (about 101-degrees-W, 2-degrees-N), was explored in 1988 during 21 submersible dives. A total of 11 dives were devoted to the exploration of the E-W trending Intrarift ridge (15 km in length, 3000-5400 m in depth) north of the Hess Deep depression. The Intrarift ridge represents, an outcrop of recent (1 m.y.) crustal and subcrustal material created at the axis of the East Pacific Rise (EPR), and emplaced during the lithospheric extention responsible for the westward propagation of the Cocos-Nazca rift (Francheteau et al., 1990). The lithospheric block has undergone cataclastic deformation and was dislocated by tectonic activity... |
| Tipo: Text |
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| Ano: 1993 |
URL: http://archimer.ifremer.fr/doc/00193/30391/29225.pdf |
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| Hekinian, Roger; Bonte, P.; Dupley, P.l.; Blanc, P.l.; Jehano, C.; Labeyrie, L.; Dupleyssis, J.c.. |
| THE Sierra Leone Rise, located in the east equatorial Atlantic, forms a discontinuous chain of seamounts as shallow as 2 km extending with a general NE-SW trend from near the Sierra Leone Coast of Africa, to the St Paul fracture zone near the Mid-Atlantic Ridge (Fig. 1). The origin of this feature has remained a topic of discussion. Sheridan et al. have hypothesised that the Sierra Leone Rise is a volcanic structure formed at the beginning of the opening of the Atlantic in the early Cretaceous period. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1979 |
URL: http://archimer.ifremer.fr/doc/1979/publication-5259.pdf |
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| Rosendahl, Bruce R.; Hekinian, Roger; Natland, James H.; Warren, Nick; Petersen, Nikolai; Roggenthen, William; Briqueu, Louis. |
| The Pacific phase of IPOD ocean crust drilling was initiated with Leg 54, the region targeted for study by the Ocean Crust Panel being survey area PT-4 (Figure 1) (and Plate 1 [in back pocket]) north of the Siqueiros fracture zone on the western flank of the East Pacific Rise (EPR). The original purpose of this leg was to establish a type section for fast-spreading, nonrifted crust by direct sampling with stratigraphic control. We anticipated that this section would serve, in part, as a standard of comparison for other type sections, such as the Mid-Atlantic Ridge (MAR). [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1980 |
URL: http://archimer.ifremer.fr/doc/1980/publication-5325.pdf |
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| Francheteau, Jean; Choukroune, P.; Hekinian, Roger; Le Pichon, Xavier; Needman, H.d.. |
| Data from rock-dredging have often been used to infer that oceanic fracture zones provide a 'window' into layers of the oceanic crust lying at a depth below the surface that is approximately equivalent to the vertical offset of the fracture zone, and thus permit the reconstruction of a crustal stratigraphy for the whole of acoustic layer 2 (commonly considered to have an average thickness of ~2 km) and in some interpretations for the upper part of layer 3. Alternatively, it has been suggested that fracture zones are preferential sites of serpentinite mega-dykes differing in composition from layer 3 but containing inclusions of the third layer. The published data indicate that basalts and basaltic rubble are abundant in fracture zones and on analysis do not... |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1976 |
URL: http://archimer.ifremer.fr/doc/1976/publication-5109.pdf |
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| Hekinian, Roger. |
| THE Walvis Ridge is a non-continuous aseismic feature in the south-eastern Atlantic Ocean with a general trend north-east/ south-west. Close to the principal interruptions of the ridge is a north-south topographiç lineation shown on Simpson's map (Fig. 1). The ridge appears to be attached at its northeast end to the shelf of Angola and South-west Africa and at its south-west end to the east flank of the Mid-Atlantic Ridge through two volcanic islands, Tristan da Cunha and Gough (Fig. 1). These two islands are made up of recent alkalibasalt-trachyte suite². . The geology of the Walvis Ridge has remained relatively unknown. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1972 |
URL: http://archimer.ifremer.fr/doc/1972/publication-5124.pdf |
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| Boucault, H.; Hekinian, Roger. |
| Dredged rocks from an area of about 15 km² within the inner floor and on the adjacent walls of the Rift Valley were collected. Based on petrographic and chemical data, four types of basaltic rocks were recognized: (1) picritic basalts with olivine xenocrysts, Ti02 inf 0.6%, K20 inf 0.l%, (2) olivine basalts with olivine megacrysts, Ti02=0.8-1.5%, K20=0.1-0.2%, (3) highly phyric and moderately phyric plagioclase basalts with megacrystic plagioclase, Ti02 inf 1.3%, K20 inf 0.3%, and (4) pyroxene basalts with pyroxene > plagioclase, Ti02=0.8-1%, K20=0.2-0.4%. The Cr and Ni having high partition coefficients show different variation trends for each type of rock and their values decrease continuously as crystallization proceeds within each type of basalt. It... |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1974 |
URL: http://archimer.ifremer.fr/doc/1974/publication-5460.pdf |
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| Hekinian, Roger; Stoffers, Peter; Devey, Colin; Ackerman, Dietrich; Hemond, Christophe; O'Connor, John; Binard, Nicolas; Maia, Marcia. |
| Exploration of the Foundation Volcanic Chain (33 degrees S-131 degrees W; 37 degrees S-111 degrees W) revealed the existence of different magmatic provinces with relation to their geological settings. (1) The Pacific-Antarctic Ridge (PAR) is made up of several en echelon segments where both glassy midocean ridge basalts (MORBs) with low incompatible elements (K2O<200 ppm, Zr<120 ppm and Ce <20 ppm) as well as andesites and dacites have erupted, (2) Oblique Ridges located up to 300 lan from the PAR axis are topped with seamounts made up essentially of transitional (T) and enriched (E) MORBs with intermediate incompatible elements (K2O=0.11-0.40 %, Zr=70-140 ppm and Ce=15-30 ppm), (3) the Foundation Seamounts (FS) consisting essentially of isolated... |
| Tipo: Text |
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| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00336/44707/44913.pdf |
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| Sichler, Bertrand; Hekinian, Roger. |
| The St. Paul Fracture Zone (FZ) in the equatorial Atlantic is interrupted by three intratransform ridge (ITR) spreading centers. A detailed magnetic survey, corrected for the diurnal variations using a moored magnetic station, six submersible dives, and three bottom-towed video camera tracks provide data on the most eastern ITR (0degrees37'N, 25degrees27'W). Visual observations and submersible sampling displayed a high ultramafic/volcanic ratio, supporting the assumption that the ITR is in a magmatically starved state. Volcanics were mainly found on the rift valley floor from 4700 to 4000 m and as a thin cap (<160 m) on the top of the eastern rift crest (2700 m). Most of the rift walls consist essentially of serpentinized peridotites and gabbros. The... |
| Tipo: Text |
Palavras-chave: Magnetic anomaly; Equatorial Atlantic; Stochastic inversion. |
| Ano: 2002 |
URL: http://archimer.ifremer.fr/doc/00000/10223/9585.pdf |
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| Hekinian, Roger; Fevrier, M.. |
| Deep-sea hydrothermal deposits from the accreting plate boundaries of the Rift valley in the gulf of Aden of the Galapagos spreading center of the Rift valley on the Mid-Atlantic Ridge near 26° North and from Transform fault "A" on the Mid-Atlantic Ridge near 37° North are studied and compared. Two main types of products are found occurring in all these areas.1 ) Dark-brown Fe-Mn concretions made up essentially of todorokite and birnessite and 2) A variegated clay-rich material composed mainly ol Fe-Si-rich smectite.In general the textural appearance, the mineralogy and the chemistry of the hydrothermal maicrial from the various localities are similar. Secondary alteration products found in basaltic rocks are compared with the clay-rich material from the... |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1979 |
URL: http://archimer.ifremer.fr/doc/1979/publication-5265.pdf |
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| Hekinian, Roger; Thompson, Geoffrey. |
| New chemical analyses and a review of published data show that there is a compositional diversity between volcanics of basaltic composition found in the M.A.R. rift valley, M.A.R. transform faults and aseismic ridges. The basaltic rocks from, the M.A.R. transform faults are less mafic (depleted in olivine content) than those from the M.A.R. rift valley. The transform fault basalts have a higher range of TiO2 content (1-4%), of Fe2O3 + FeO content (8-14%) and a lower range of Cr content (50-500 ppm) and Ni content (50-300 ppm). The volcanics from aseismic ridges around the world are considered to be the more felsic types of the two provinces. They have a higher range of variation for their TiO2, and Fe203 + Fe0 (1.6-5% ; 9-15% ; respectively) and a lower... |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1976 |
URL: http://archimer.ifremer.fr/doc/1976/publication-5011.pdf |
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| Francheteau, Jean; Needman, David; Choukroune, Pierre; Juteau, Thierry; Seguret, Michel; Ballard, Robert D.; Fox, Jeffery; Normark, William; Carranza, Arturo; Cordoba, Diego; Guerrero, José; Rangin, Claude; Bougault, Henri; Cambon, Pierre; Hekinian, Roger. |
| Massive zinc, copper and iron sulfide ore deposits have been found at the axis of the East Pacific Rise. Although several investigators had predicted their presence on the deep-ocean floor, there was no supporting observational evidence. The East Pacific Rise deposits represent an appealing modern analogue of Cyprustype ores associated with ophiolitic rocks on land. They contain up to about 29% zinc metal and up to at least nearly 3% metallic copper. Their discovery will provide a new focus for deep-sea exploration, leading to new assessments of the concentration of noble metals in the upper layers of the oceanic crust. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1978 |
URL: http://archimer.ifremer.fr/doc/1978/publication-5388.pdf |
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| Bideau, Daniel; Hekinian, Roger. |
| Small-scale distribution of basaltic compositions along the mid-ocean ridge crests suggests that the magmatic processes are sensitive to spatial and temporal fluctuations related to proximity of ridge hot spots, changes in spreading rate, thermal boundary effects associated with ridge offsets, off-axis volcanoes and ridge propagators, and variations in magma supply through time. A detailed sampling of the East Pacific Rise (EPR) axis, near 13 degrees N, revealed that complex basalt compositional variations unrelated to morphology and structure occur both on the ridge axis and on nearby off-axis seamounts. This small-scale heterogeneity is attributed to successive magmatic cycles separated by periods of quiescence (amagmatic phases) where each cycle... |
| Tipo: Text |
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| Ano: 1995 |
URL: http://archimer.ifremer.fr/doc/00258/36974/35516.pdf |
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| Prevot, Michel; Lecaille, Alain; Hekinian, Roger. |
| Comparison of magnetic properties of pillow basalts from the Rift Valley (FAMOUS area) and from the Crest Mountains (site 332 of DSDP Leg 37) of the Mid-Atlantic Ridge near 37°N shows that major differences in magnetic structure and properties of the oceanic crust occur between these two sites. Mean effective intensity of magnetization of the pillow basalt layer drops from 1.4 x 10 ² emu cm (4 A m ) at the axis to about 0.4 x 10 ² emu cm (4 A m at site 332). While the magnetic anomaly over the spreading center may be accounted for by a magnetized layer less than 500 m thick, deeper seated material contributes to the magnetic anomalies over the Crest Mountains. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1979 |
URL: http://archimer.ifremer.fr/doc/1979/publication-5250.pdf |
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| Hekinian, Roger; Chaigneau, M.; Cheminee, J.l.. |
| During the 1972 Midlante* cruise of the RV Jean Charcot to survey a limited area of the rift valley south of the Azores, a dredge (CH-DR11) was taken at a depth of 1,360 fathoms in a depression near the foot of the eastern wall at latitude 36° 49.3' N and longitude 33° 15' W. Two types of rocks were recognized from their structure and their degree of weathering. One type is "slab-like" rock, 2 to 13 cm in diameter and 1 to 2 cm thick (Fig. la and b). The other type of rock consists of oval glassy pebbles (1 to 5 cm in diameter, Fig. 1c) which were observed to jump and explode, one or two at a time, for 3 d after the dredge haul was emptied on to the deck of the ship. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1973 |
URL: http://archimer.ifremer.fr/doc/1973/publication-5155.pdf |
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| Chaigneau, M.; Hekinian, Roger; Cheminee, J.l.. |
| Magmatic gases extracted and analysed from basaltic rocks collected in the FAMOUS area near 36° 50' N in the Atlantic ocean show that the total amount of gas included in the samples varies between about 500 pprn to 1600 ppm. The main gaseous phases included in the various types of basalts consist of CO2 (270-700 ppm), CO (150-800 ppm), HCI (100-1000 ppm), H2 (0-50 ppm), SO2 (up to 175 ppm), N2 (up to about 213 ppm) and traces of hydrocarbons (up to about 24 ppm). The relative amount of CO, CO2 and SO2 varies with both the degree of crystallinity of the rock and with fractional crystallization and/or fractional melting.The glassy margin of pillow lavas have a higher CO/C02 ratio than the more crystalline interior. The most fractionated rocks of the series... |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1980 |
URL: http://archimer.ifremer.fr/doc/1980/publication-5266.pdf |
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| Bellaiche, G.; Cheminee, J.l.; Francheteau, Jean; Hekinian, Roger; Le Pichon, Xavier; Needham, H.d.; Ballard, R.d.. |
| THE Rift Valley of the Mid-Atlantic Ridge, within which lies a segment of the accreting plate boundary between Africa and North America, is well defined between 36°40'N and 36°55' N. It is about 30 km wide and 1.5 km deep in that area (Fig. 1). This small portion of the rift, WSW of the Azores, was chosen as the primary target of the French-American Mid-Oceanic Undersea Survey (FAMOUS) programme, and many surface ship studies have heen conducted already. We report here preliminary results of seven dives into the deepest part of the Rift Valley that were made by the bathyscaphe Archimède during the summer of 1973. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1974 |
URL: http://archimer.ifremer.fr/doc/1974/publication-5443.pdf |
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| Registros recuperados: 30 | |
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