The interaction of the Pacific-Farallon spreading centers with the North American convergent margin off Baja California, Mexico, supposedly ceased at 12 Ma, when plate convergence and seafloor spreading stopped. We propose a new geodynamic evolution based on full bathymetry coverage and magnetic profiles from 23°N to 27°N (Famex cruise of the R/V L'Atalante, April 2002). The data unveil a major clockwise rotation of the Pacific-Farallon spreading direction, starting ca. 14 Ma, that formed a series of short spreading centers that became extinct ca. 8–7 Ma. We suggest that the transcurrent motion between the Pacific and North America along Baja California was accommodated by seafloor spreading and oblique convergence along the trench. This change in spreading direction was followed by a concomitant progressive demise of both Pacific-Farallon seafloor spreading and Farallon–North America subduction that are attributed to the break-off of the Farallon slab. This also resulted in the opening of a trench-parallel slab window beneath Baja California

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During the FAMEX cruise of the R/V L'Atalante (April 2002), swath bathymetry and seismic profiles were recorded along the Baja California margin from 23° to 27°N. The upper‐slope of the margin exhibits active faulting of recent sediments along the Tosco‐Abreojos fault system (TAFS). Flower structures evidence strike‐slip motion along the TAFS. Right lateral strike slip faulting, associated in places with small extensional features, are consistent with present‐day slip and extension rates predicted along the TAFS. The TAFS thus belongs to the western active boundary of a Baja California Block yet not totally transferred to the Pacific plate.

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Découvrez plus de documents accessibles gratuitement dans Archimer Article No 51 5 Contribution C.O.B. No 701 La biellette danakile : un modèle pour l'évolution géodynamique de PAfv par BERTRAND SICHLER .Ifou clCs.-Ciiiématique. Horst. Rift, Limite plaque. Rotation continentale. Pal6omagnbtisme. Djibouti. Dépressioii Afar (Danakil). R4sitnii. = L e s données géologiqurs et géophysiques existant actuellement en Afar et aux alentours permettent de penser que la trrtoriique des plaques peut s'appliquer daiis cette région, en introduisant pour certaines parties du puzzle la notion de poiiits d'srticiilation. Le bloc danakil serait, daiis ce conlexte, considéré conime une piece niobile, articulée au Nord. sur la plaque nubienne supposée nxr. dans la région de Zula et au Sud sur la plaqiie arabe dans la zone de Bab el hlaiideb. Cette hjpothese de biell~ttr perniet de passer du rift d~ 1'Erta .\le au rift de la Mer rouge sans faille transfornianle et d'expliquer de nombreux traits niorpliologiques de l'Afar. La durbe de vie d'une telle birllrtte est liniitée, des signes de faiblesse existent. e t on peut s'attendre, à ternie, a une rupture de la piece pile-nisine ou plus vraiscniblablenirnt d r l'articulation Nord. De tels nibcaiiisnies peuvent rendre coiiiple. dans divers océans. de certaines structures obliques anorniales coninie le Banc de Rockall en Atlantique Sord-Est, le plateau de Voringe en Mer de Norvège ou le plateau des Baléares en !déditerranée. , The danakil crank-orm : a mode1 for th. geodynamic evolution of the a Afar triangle m Absrrari.-Geological and geophysical data now available in Afar and neighbouring areas suggest tliat plate tectonics is usable in this area if one acrepts. for sniiie parts of the puzzle the notion of hinge poiiits. In this context. the Danakil bloc can be considered as a nioviiig piece hiiiged in the North to the Nubian plate wliich is assuiiied Io be fixed, and Iiinged in the South to the Arabian plate in the Bab el ifaiideb area. This hypotliesis of a Danakil crank-ariii allors one Io juiiip froni the Erta Ale rift to the Red Sea rift without the need for a traiisforiii fault and to explaiii soine morphological features of the Afar. The life of siich a crankarni is short and il exliibits zones of crustal reakness and in the future the crank-arm itself, or niore probably the northern hinge point niust rupture. Sucli a Iiypntliesis can explain the occurrence in the oceans or oblique abnormal structures like Rockall bank iii the Nurth-E a d-\Ilantic, Voring plateau in tho Norvegian & ! a and the Baleares plaleau In the Mediterranean Sea.