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1.
Gallo D. G. Kidd W. S. F. Fox P. J. Karson J. A. Macdonald K. Crane K. Choukroune P. Seguret M. Moody R. Kastens K. 《Marine Geophysical Researches》1984,6(2):159-185
During the Fall of 1979, a manned submersible program, utilizing DSRV ALVIN, was carried out at the intersection of the East Pacific Rise (EPR) with the Tamayo Transform boundary. A total of seven dives were completed in the vicinity of the EPR/Tamayo intersection depression and documented the geologic relationships that characterize the juxtaposition of these types of plate boundaries. The young volcanic terrain of the EPR axis can be traced into and across the Tamayo Transform valley but becomes buried by sedimentary talus that is being shed from sediment scarps along the unstable sediment slope that defines the north side of the intersection depression. Within 4 km of the transform boundary, the dominant trend (000°) of the fissures and faults that disrupt the rise-generated volcanics is markedly oblique to the regional direction of sea floor spreading (120°). Since no evidence was found to suggest that these structures accommodate significant amounts of strike-slip displacement, they are taken to reflect a distortion of the EPR extensional tectonic regime by a transform generated shear couple. The floor of the Tamayo Transform valley in this area is inundated by mass-wasted sediment, and the principal transform displacement zone is characterized at the surface by a narrow (<1.5 km) interval of fault scarps in sediment that trends parallel with the transform valley. Extrapolated to the west, this zone links with zones of transform deformation investigated during earlier submersible studies (CYAMEX and Pastouret, 1981). Evidence of low-level hydrothermal discharge was seen at one locality on the EPR axis and at another 8 km west of the axis at the edge of the zone of transform deformation. 相似文献
2.
Study of ductile shear zones (Galicia, Spain) using texture goniometry and magnetic fabric methods 总被引：1，自引：0，他引：1
A joint magnetic and mica fabric study has been carried out on rocks from recognised shear zones in Galicia (Spain). The two main aims of the study are to determine strain gradients in a foliated material without any significant strain markers and to obtain a quantitative relationship between the magnetic susceptibility anisotropy ellipsoid and the mica fabric axes. The intensity parameters of the fabric on profiles intersecting the studied areas indicate the dominant influence of two major shear zones on the fabric development. The regional fabric shows less significant variations across minor (less developed) shear zones.The empirical relationship between magnetic fabric and strain reported by Rathore (1979, 1980) and Rathore and Henry (1982) is found to hold in the magnetic and mica fabrics comparison. The relationship found in this study is: 相似文献
3.
Pierre Choukroune Xavier Le Pichon Michel Seguret Jean-Claude Sibuet 《Earth and Planetary Science Letters》1973,18(1):109-118
The different hypotheses proposed for the creation of the Bay of Biscay are reviewed. New geological and geophysical data collected in the last two years in the Bay and in the Pyrenean domain give new insight into the tectogenesis of the Pyrenees. Geological data of the Pyrenean area provide tight constraints on the hypothesis of formation of the Bay. The most probable hypothesis is an opening by rotation of the Iberian Peninsula around a pole of rotation situated near Paris, which resulted in strike-slip motion along the North Pyrenean fault during the Upper Mesozoic. A progressive westward migration of the pole initiated in the late Cretaceous blocked the motion along the fault and led to the main Eocene tectogenetic Pyrenean phase. 相似文献
4.
P. Choukroune J. Francheteau B. Auvray J. M. Auzende J. P. Brun B. Sichler F. Arthaud J. C. Lepine 《Marine Geophysical Researches》1988,9(2):147-163
The results of 26 dives with the diving saucer Cyana in the Gulf of Tadjoura and Ghoubbet al Kharab (Republic of Djibouti) are presented. One can demonstrate that the sites of recent volcanism, tectonics and hydrothermal activity within the axial part of the Gulf of Tadjoura coincide with topographic highs trending at a high angle (azimuth 135°) with respect to the average trend of the axial trough of the Gulf (azimuth 080°). The highs owe their relief to both volcanism and normal faulting along a trend of 130–140°. Recent faulting on the bounding walls of the axial trough is also found along a trend of 130–140° where the faults interfere with another set of apparently older faults trending 070° parallel to the axial trough. Spacing between the active zones of the Gulf is regular and about 30 km. No evidence for transform faulting has been found, in contradiction to all previous kinematic models of the Gulf of Tadjoura. There is evidence that the presently active phase of opening associated with 130–140° faults is less than 0.7 my old and that there was an older phase associated with 070°–080° faults creating the main trough of the Gulf. The basaltic lavas created during the two phases have evolved from transitional to tholeiitic. 相似文献
5.
J. Francheteau H. D. Needham P. Choukroune T. Juteau M. Séguret R. D. Ballard P. J. Fox W. R. Normark A. Carranza D. Cordoba J. Guerrero C. Rangin Cyamex Scientific Team 《Marine Geophysical Researches》1981,4(4):345-379
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 gian 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. 相似文献
6.
Pierre Choukroune Jean Francheteau Roger Hekinian 《Earth and Planetary Science Letters》1984,68(1):115-127
Using the diving saucer “Cyana”, a portion of the East Pacific Rise between 12°38′ and 12°54′N has been studied and mapped. Four main zones are defined: (1) an active volcanic zone located in the central graben; the graben displays a variable relief along strike from less than 10 m up to 55 m and has an en-échelon pattern in plan view; (2) an active tectonic zone comprising the central graben and extending up to about 2 km from either side of the rise axis; (3) an inactive tectonic zone starting 2 km away from the axis and formed by discontinuous horst and graben type of structures; and (4) off-axis volcanoes (seamounts) located less than 20 km on either side of the rise axis. At 12°50′N, the active tectonic zone is extremely narrow and the mode of deformation is through fissuring in strong contrast with that observed in slow or intermediate rate ridges. The presence or absence of a magma reservoir at shallow depth explains the difference in the width of the active tectonic zone. The state of isostatic equilibrium or lack of equilibrium explains the different modes of deformation. 相似文献
7.
The deformation of two granitic massifs along a dextral wrench fault zone (the South Armorican Shear Zone) is examined at the sample and grain scales. We note that an association of continuous-discontinuous deformation mechanisms is responsible for the mylonitisation at the grain scale. The general characteristics of the deformation (strain, ellipsoid type, strain regime, non-coaxial model) and quartz fabrics measured in these mylonites at each of the mylonitisation stages described, are also discussed. 相似文献
8.
RésuméLe but de la présente étude est de caractériser la déformation récente subie par la Provence occidentale, située entre la nappe de Digne à l’est et la faille de Nîmes à l’ouest. Dans un premier temps, la déformation subie par un marqueur sédimentaire qui est à la fois le plus récent possible et le plus uniformément représenté dans la zone étudiée est considérée. Ce marqueur sédimentaire est le Miocène. La caractérisation de la déformation passe par l’étude de la localisation de celle-ci et donc par l’identification des structures actives responsables de la déformation du Miocène. Ces caractéristiques permettent d’estimer la quantité de raccourcissement total accumulé lors des derniers 20 millions d’années. Dans un deuxième temps, on distingue la part de la déformation postMiocène de cette déformation totale. Les marqueurs utilisés sont des surfaces et des objets géomorphologiques repères. Dans ce travail, nous montrons que la déformation en Provence a été de faible importance entre le Miocène et factuel et qu’elle est surtout produite au cours du Miocène. En conséquence, la déformation récente à actuelle est très difficile à localiser et à caractériser. 11 n’y a pas eu de déplacements post Miocène importants de part et d’autre de la faille de la Durance, pas plus d’ailleurs que le long de toutes les discontinuités majeures du domaine étudié. © 2000 Éditions scientifiques et médicales Elsevier SAS 相似文献
9.
H.D. Needham P. Choukroune J.L. Cheminee X. Le Pichon J. Francheteau P. Tapponnier 《Earth and Planetary Science Letters》1976,28(3):439-453
The Ardouko?ba Rift, subaerially exposed for ～12 km between the Ghoubbat-al-Kharab and Lake Asal in the French Territory of the Afars and Issas (northeast Africa), has intrinsic features and a regional setting consistent with arguments that it is the site of crustal accretion at approximately the same rate as that found along the rifted Mid-Oceanic Ridge (～2 cm/yr). The ～11 km wide Central Zone of the Ardouko?ba Rift has an internal relief of less than ～300 m and is set between step-like ridges standing up to 800 m above the deepest part of the rift. The lower inward-facing scarps of the Central Zone border a narrow Inner Floor. The Central Zone of the typically ～25–35 km wide oceanic Rift Valley can have a greater and rougher relief and has a width of ～8–16 km, but deep areas with an internal relief of <400 m have a maximum width that is about the same as that of the corresponding area in the Ardouko?ba Rift (～11 km). The width of the Inner Floor of the Ardouko?ba Rift varies from 2 to 5 km; in the oceanic Rift Valley the range is from less than 1 to ～9 km. Equivalence of tectonic and volcanic processes in the two settings has not been demonstrated; but a comparison of a segment of the Rift Valley in the FAMOUS area near 36°50′N in the Atlantic with the Ardouko?ba Rift encourages the tentative use of evidence from the latter to complement arguments about the pattern of vulcanism and scarp formation in the oceanic Rift Valley as a whole. The Inner Floor of the Rift Valley is the main site of horizontal extension without vertical displacements, of normal faulting that involves little or no accumulation of vertical offsets, and of constructional vulcanism, which may be further concentrated along narrow (～1 km wide) fissured zones. The normal faulting that disrupts and constrains more or less orderly growth of the Inner Floor may happen in such a way that the new graben that become new Inner Floors are laterally offset with respect to the middle line of the Rift Valley and to the axis of symmetry of a hypothetical block accounting for the central positive magnetic anomaly.Additional complexities may be introduced by syntectonic and post-tectonic vulcanism, and by normal fault displacement at any one time of young crust along only part of the distance between transform faults. Thus, although opening rate can always be equated in principle with total addition of new crust to the two plates, the assumption is suspect that the concept of spreading rate (rate of addition of crust to one plate or the other) can necessarily be applied precisely to the central part of the Rift Valley. In more general terms, the physical meaning of interpolated spreading rates on the time scale of magnetic anomalies is worth questioning. On evidence from the Rift Valley, the spreading rates need not reflect monotonic additions of new crust, and rocks of the same inferred age from opposite plates may not have the same composition. The problem is highlighted by the apparently symmetrical growth of the North Atlantic over long periods of time. 相似文献
10.
R. Hekinian J. Francheteau V. Renard R. D. Ballard P. Choukroune J. L. Cheminee F. Albarede J. F. Minster J. L. Charlou J. C. Marty J. Boulegue 《Marine Geophysical Researches》1983,6(1):1-14
A submersible study of a fast spreading (12 cm yr-1) Mid-Ocean ridge segment (East Pacific Rise near 12°50′ N) led to the discovery of intense hydrothermal activity. Twenty four sites with active vents and sixty inactive hydrothermal deposits were found within a narrow graben averaging about 300 m in width along a 20 km long segment of the ridge crest. The graben is floored with fresh basaltic sheet flows including collapsed pits or lava lake structures. From both deep towed camera stations and manned submersible observations, it is estimated that the average spacing between the ridge axis hydrothermal deposits averaging in size 10–50 m in diameter lies between 100 to 200 m. The hydrothermal deposits found in the central graben are believed to have formed rapidly (on the order of a few decades). Detailed investigations of one active site have enabled us to witness the growth of an active chimney which increased its height by 40 cm in 5 days i.e. 8 cm per day. Extensive hydrothermal deposits were discovered on an off-axis seamount located 6 km East of the ridge axis. The hydrothermal deposits found on both the ridge axis and on the seamount are similar in composition and consist essentially of zinc, copper and iron mineral phases. Chemical studies conducted on the venting fluids (320°C) showed that the concentration of the dissolved major metal ions (Fe, Mn, and Zn) is about 0.10–0.13 gl-1. If we accept an average flow rate of 10ls-1 based on visual observations the mass of metallic products spewing out from an active chimney must be about 100 kg per day. 相似文献