|
|
|
| Registros recuperados: 30 | |
|
|
| 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 |
|
| Ano: 1995 |
URL: http://archimer.ifremer.fr/doc/00258/36974/35516.pdf |
| |
|
| |
|
| |
|
|
| Cheminee, J-l; Hekinian, Roger; Talandier, J; Albarede, F; Devey, C W; Francheteau, Jean; Lancelot, Y. |
| The Teahitia-Mehetia hot spot region located in the southeastern extension of the Society Islands chain, near 18 degree S-148 degree W, consists of several active volcanoes. The distribution of recent volcanic activity correlates with seismic epicenters, and covers an area of more than 1,000 km super(2). Intermittent volcanic activity has given rise to large (> 1,000 m high) and small (< 500 m high) edifices composed of various types of flows. Several recent volcanic events have produced a suite of alkalic rocks ranging from ankaramites, through alkali basalts to trachy-phonolites. The presence of altered MORB-like tholeiites on one small seamount suggests that a different mantle source material was involved in forming some of the crust in this hot... |
| Tipo: Text |
|
| Ano: 1990 |
URL: http://archimer.ifremer.fr/doc/00268/37896/35977.pdf |
| |
|
| |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
|
| Natland, James H.; Rosendhal, Bruce; Hekinian, Roger; Dmitriev, Yuri; Fodor, Ronald V.; Goll, Robert M.; Hoffert, Michel; Humphris, Susan E.; Mattey, David P.; Peterson, Nikolai; Roggenthen, William; Schrader, Edward L.; Srivasiava, Ramesh K.; Warren, Nick. |
| The Galapagos mounds sea-floor hydrothermal system is at least 300,000 years old and once produced manganese-poor sediments, which nearly blanketed the area of the present mounds field. Present-day mound deposits are limited manganese-rich exposures, suggesting that the system has changed from rock- to water-dominated and has diminished in intensity with time. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1979 |
URL: http://archimer.ifremer.fr/doc/1979/publication-5382.pdf |
| |
|
|
| 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 |
|
| Ano: 1978 |
URL: http://archimer.ifremer.fr/doc/1978/publication-5254.pdf |
| |
|
|
| Hoffert, M; Perseil, A; Hekinian, Roger; Choukroune, P; Needham, Hd; Francheteau, J; Le Pichon, X. |
| Deep-sea hydrothermal deposits were observed, mapped and sampled in situ with the submersible "Cyana" in the Famous area of the Mid-Atlantic Ridge.Two neighbouring fields, each covering an area of about 600 m2, are associated with low, E-W trending sediment-covered ridges that lie at a depth of about 2 700 m close to the axis of Transform Fault "A".In each field the deposits are thicker (up to about 1 m) close to the small, fissure-like vents through which they were evidently delivered. Despite their heterogeneous composition, their mineralogical and chemical variations have an orderly pattern.The principal constituents are a green clay-rich material, and Fe-Mn oxides in the form of black concretions. The relative abundances of these products vary with... |
| Tipo: Text |
|
| Ano: 1978 |
URL: http://archimer.ifremer.fr/doc/1978/publication-5216.pdf |
| |
|
|
| 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 |
| |
|
|
| 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 |
|
| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00336/44707/44913.pdf |
| |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
|
| Hekinian, Roger; Bideau, Daniel; Hebert, Réjean; Niu, Yaoling. |
| The Garrett transform is characterized by recent (zero age) volcanic activity located within the active tectonic domain of the transform valley at depths greater than the 3500 m. This intratransform volcanic activity contributed to the formation of constructional edifices forming ridges (>300 m in height) and small mounds (<20 m in height) built near slivers of serpentinized peridotites. The erupted lavas are depleted mid ocean ridge basalts (MORBs) with low ratios of K/Ti (0.02-0.11), Zr (30-100 ppm), Y (18-50 ppm), and (La/Sm)(N) (0.25-0.60). Their more depleted nature and smaller range of variability for the compatible elements (Ni=70-180 ppm, Mg#=0.58-0.71, where Mg# is the magnesium number (=Mg+2/Mg+2+Fe+2)) are the main points of difference... |
| Tipo: Text |
|
| Ano: 1995 |
URL: http://archimer.ifremer.fr/doc/00259/36975/35515.pdf |
| |
|
| |
|
|
| 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 |
| |
|
|
| Francheteau, Jean; Needham, H.d.; Choukroune, P.; Juteau, T.; Seguret, M.; Ballard, R.d.; Fox, P.j.; Normark, W.; Carranza, X; Cordoba, D.; Guerrero, J.; Rangin, C.; Bougault, Henri; Cambon, Pierre; Hekinian, Roger. |
| Massive ore-grade zinc, copper and iron sulphide deposits have been found at the axis of the East Pacific Rise.Although their presence on the deep ocean-floor had been predicted there was no supporting observational evidence. The East Pacific Rise deposits represent a modern analogue of Cyprus-type sulphide ores associated with ophiolitic rocks on land.They contain at least 29% zinc metal and 6% metallic copper.Their discovery will provide a new focus for deep-sea exploration, leading to new assessments of the concentration of metals in the upper layers of the oceanic crust. [NOT CONTROLLED OCR] |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1979 |
URL: http://archimer.ifremer.fr/doc/1979/publication-5278.pdf |
| |
|
|
| Hekinian, Roger; Rosendahl, Bruce R.; Natland, James H.. |
| Two distinct sedimentary facies produced by sea-floor hydrothermal activity were cored during Deep Sea Drilling Project Leg 54. The first is equivalent to the typical basal iron- and manganese-rich, clayey mud recovered at many DSDP sites. It was sampled as a dispersed component throughout the cores taken in small sediment ponds in several sites within 120 km of the East Pacific Rise at 9°N. We infer that this component was originally deposited as iron hydroxides dispersed from high-temperature vents over the axial magma chamber of the East Pacific Rise. In the sediments, the iron hydroxides have reacted diagenetically with siliceous microfossil tests and detrital clays to form K- and Fe-rich clays with variable SiO(2)/Fe(2)O(3) and... |
| Tipo: Text |
Palavras-chave: Histoire Ifremer. |
| Ano: 1980 |
URL: http://archimer.ifremer.fr/doc/1980/publication-5328.pdf |
| |
| Registros recuperados: 30 | |
|
|
|
