The west Galicia margin (Spain) provides a model for passive continental margin evolution. During the Mesozoic, the continental crust of the margin experienced severa! episodes of extension. The main stage was during the Berriasian-late Aptian interval. The stretching of the lithosphere resulted in a) the thinning of the continental crust, testified by superficial extensional structures (normal faults, tilted fault blocks) and rapid subsidence, and b) the emplacement of mantle rocks (peridotite) at the continental rift axis. The crustal thinning and the final emplacement of peridotite onto the seafloor are explained by uniform, normal, simple shear of the continental lithosphere, following asthenosphere diapirism. The sedimentary response to the rifting process was the rapid deposition of coarse detrital sediments in the half grabens of the rift. The pre-rift sediments are platform carbonates, and the post-rift sediments are distal turbidites followed by pelagic sediments. To the south of the Bay of Biscay, the north Galicia and Asturias margin evolved as the Galicia passive margin until latest Cretaceous time. During the Paleocene-Eocene interval, it was converted into an active margin as a result of the Eurasian-lberian plate convergence and related southward subduction of the European plate beneath the lberian plate. A marginal trench and a tectonic accretionary prism developed at the plate boundary and the margin was shortened, deformed and eroded, becoming a subduction-related fold belt. Today it is the westward prolongation of the Pyrenean and Cantabric collisional chain. Therefore models accounting for the emerged part of the Pyrenees must also be constrained by offshore data.

All available seismic data have been used to establish a new structural map of the Galicia passive margin. The northsouth syn-rift normal faults that bound the tilted fault blocks are interrupted and/or slightly offset by a discrete pattern of transverse faults oriented N55°-N70° and N115°-N135°.

Zircon and apatite fission track ages were determined on granulites dredged along the Bay of Biscay margins. A sample from Ortegal Spur (Iberia margin) yielded 725 +/- 67 Ma (zircon). A sample from Le Danois Bank (Iberia margin) yielded 284 +/- 58 Ma (zircon), indicating post-Variscan cooling. Apatite from this sample gave 52 +/- 2 Ma, interpreted as final cooling after 'Pyrenean' thrust imbrication. Two other samples from Le Danois Bank have Early Cretaceous apatite ages (138 +/- 7 and 120 +/- 8 Ma), interpreted to result from exhumation during rifting. Finally, a granulite from Goban Spur (Armorican margin) gave 212 +/- 10 Ma (apatite), coinciding with a precursory rifting phase. Together with published radiometric results, these data indicate a Precambrian high-grade terrane at the site of the current margins. The distribution of the granulites on the seafloor reflects tectonic and erosional processes related to (a) Mesozoic rifting and (b) Early Tertiary incipient subduction of the Bay of Biscay beneath Iberia. "

The thinned continental crust of the west Galicia margin is bound by a belt of serpentinized peridotites ('peridotite ridge') lying about 300 km off the coast in the North Atlantic ocean. From this ridge, a gabbro and a chlorite rock were studied in an attempt to substantiate rift-related subcontinental magmatism, occurring prior to sea-floor spreading. U-Pb dating of 13 different zircon fractions yields a precise age of 122.1+/-0.3 Ma (2 sigma) for the emplacement of the chlorite rock protolith, from which more than 50% of Si and alkali-calc-alkali elements were lost during greenschist facies tectonometamorphism. Sr and Nd isotope signatures suggest that the gabbro and chlorite rock protoliths were derived from mantle sources that were moderately depleted in LILE, relative to a chondritic reservoir. No evidence for the presence of continental material in the magma source regions can be observed. From the new zircon age of 122.1 +/- 0.3 Ma, and the earlier determined Ar-39-Ar-40 of 122.0+/-0.6 Ma for amphibole from the same locality, it can be documented that magma formation, solidification and unroofing of the mantle rocks occurred during a short period of time of about 3.4 Ma, which means that the peridotite ridge detached from the continent and rose to the surface immediately after, or even coevally with mantle melting.

ABSTRACTDuring the continental rifting the upper mantle was unroofed, and the mantle rocks were transformed into serpentinite at the ocean‐continent transition of the west Galicia margin (Spain). The serpentinite layer, several km thick, extends probably eastwards, beneath the highly thinned continental crust of the margin.The serpentinite layer was recently imaged by seismic reflection. It is discontinuously and deeply layered. As serpentinized peridotite can have densities and seismic velocities comparable to those of the lower continental crust, we suggest that undercrusting by serpentinite can play a part in building the lower seismic crust in highly stretched continental rifted areas.

A normal-fault escarpment of the West Galicia Atlantic margin exposes an 800-m-thick section of weakly metamorphosed sandstone, dolomite, and volcaniclastic rocks. The microfauna and microflora from dolomitic layers indicate a shelf deposit of Late Devonian-early Carboniferous age. The series was probably deposited in a posttectonic basin developed on the Ossa Morena zone of the Iberian Variscides.

The western continental margin of the Iberian peninsular has the characteristic of a rifted non-volcanic continental margin with half-graben and tilted fault blocks seen in several places on multichannel seismic reflection profiles. The ocean-continent transition (OCT) is therefore expected to be where thinned continental crust and oceanic crust are juxtaposed, as elsewhere. The authors located the OCT off western Iberia in order to constrain the pre-lift fit of Iberia to North America. This fit is only marginally constrained by sea-floor spreading magnetic anomalies because the Cretaceous constant polarity interval is adjacent to the OCT. Thinned continental crust can be distinguished from oceanic crust by the nature of the lower crustal velocity structure. In 1986-1987, a series of seismic refraction profiles was shot across three parts of the Iberian Abyssal Plain, the OCT can be detected not only from seismic velocities but also by modeling magnetic anomalies. The chosen location of the OCT is consistent with the interpretation of subsequently acquired multichannel profiles. Off Galicia Bank, the OCT, recognized from seismic velocities and multichannel profiles, corresponds to a seabed peridotite ridge, which has been extensively sampled. In the Tagus Abyssal Plain, limited seismic data gives a less clear picture of themore » OCT.« less

There is a great similarity between the Galicia margin and the Aquitaine margin (i.e. the Aquitaine Basin and the North Pyrenean zone). In particular, the timing of the rifting as well as the resulting structures (exposure of perodotite, tilted fault blocks, normal and transverse faults, half grabens) are practically the same. This comparison leads to the interpretation that the northern side of the Pyrenean fold belt is inherited from the Mesozoic deep passive margin of Europe. The Cenozoic thrust sheets and reverse faults of the northern Pyrenees zone are tentatively interpreted as former rift structures (tilted blocks and listric faults) which were removed during the convergence of the Iberian and European plates during the Paleocene and Eocene.

Other| January 01, 1985 Exploration par submersible de la marge continentale au Nord-Ouest de l'Espagne Gilbert Boillot; Gilbert Boillot Author Univ. Pierre-et-Marie-Curie, dep. geodynam., FranceLab. geodynam., Villefranche sur Mer 06230, France Search for other works by this author on: GSW Google Scholar Dominique Temine; Dominique Temine Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Jacques-Andre Malod; Jacques-Andre Malod Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Raymond Capdevila; Raymond Capdevila Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Michel Cousin; Michel Cousin Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Pierre-Alain Dupeuble; Pierre-Alain Dupeuble Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Francisco Gonzalez-Lodeiro; Francisco Gonzalez-Lodeiro Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Michel Lamboy; Michel Lamboy Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Claude Lepvrier; Claude Lepvrier Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Juan R. Martinez-Catalan; Juan R. Martinez-Catalan Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Georges Mascle; Georges Mascle Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Carla Muller; Carla Muller Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Leo Pastouret; Leo Pastouret Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Josette Taugourdeau-Lantz; Josette Taugourdeau-Lantz Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Jean-Rene Vanney Jean-Rene Vanney Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Search for other works by this author on: GSW Google Scholar Author and Article Information Gilbert Boillot Author Univ. Pierre-et-Marie-Curie, dep. geodynam., FranceLab. geodynam., Villefranche sur Mer 06230, France Dominique Temine Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Jacques-Andre Malod Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Raymond Capdevila Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Michel Cousin Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Pierre-Alain Dupeuble Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Francisco Gonzalez-Lodeiro Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Michel Lamboy Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Claude Lepvrier Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Juan R. Martinez-Catalan Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Georges Mascle Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Carla Muller Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Leo Pastouret Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Josette Taugourdeau-Lantz Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Jean-Rene Vanney Author Univ. Pierre-et-Marie-Curie, dep. geodynam., France Publisher: Société Géologique de France First Online: 07 Mar 2017 Online Issn: 1777-5817 Print Issn: 0037-9409 GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique, Vandoeuvre-les-Nancy, France Bulletin de la Société Géologique de France (1985) I (1): 89–102. https://doi.org/10.2113/gssgfbull.I.1.89 Article history First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gilbert Boillot, Dominique Temine, Jacques-Andre Malod, Raymond Capdevila, Michel Cousin, Pierre-Alain Dupeuble, Francisco Gonzalez-Lodeiro, Michel Lamboy, Claude Lepvrier, Juan R. Martinez-Catalan, Georges Mascle, Carla Muller, Leo Pastouret, Josette Taugourdeau-Lantz, Jean-Rene Vanney; Exploration par submersible de la marge continentale au Nord-Ouest de l'Espagne. Bulletin de la Société Géologique de France 1985;; I (1): 89–102. doi: https://doi.org/10.2113/gssgfbull.I.1.89 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin de la Société Géologique de France Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Other| March 01, 1985 Observations geomorphologiques effectuees en plongees au Nord-Ouest de la peninsule iberique Jean-Rene Vanney; Jean-Rene Vanney Author Univ. Pierre et Marie Curie, Lab. Geol. Dyn., Paris 75230, France Search for other works by this author on: GSW Google Scholar F. Rojouan; F. Rojouan Author Search for other works by this author on: GSW Google Scholar D. Temine; D. Temine Author Search for other works by this author on: GSW Google Scholar J. A. Malod; J. A. Malod Author Search for other works by this author on: GSW Google Scholar Gilbert Boillot; Gilbert Boillot Author Search for other works by this author on: GSW Google Scholar Raymond Capdevila; Raymond Capdevila Author Search for other works by this author on: GSW Google Scholar M. Cousin; M. Cousin Author Search for other works by this author on: GSW Google Scholar Francisco Gonzalez-Lodeiro; Francisco Gonzalez-Lodeiro Author Search for other works by this author on: GSW Google Scholar C. Lepvrier; C. Lepvrier Author Search for other works by this author on: GSW Google Scholar Juan R. Martinez-Catalan; Juan R. Martinez-Catalan Author Search for other works by this author on: GSW Google Scholar G. Mascle; G. Mascle Author Search for other works by this author on: GSW Google Scholar Leo Pastouret Leo Pastouret Author Search for other works by this author on: GSW Google Scholar Author and Article Information Jean-Rene Vanney Author Univ. Pierre et Marie Curie, Lab. Geol. Dyn., Paris 75230, France F. Rojouan Author D. Temine Author J. A. Malod Author Gilbert Boillot Author Raymond Capdevila Author M. Cousin Author Francisco Gonzalez-Lodeiro Author C. Lepvrier Author Juan R. Martinez-Catalan Author G. Mascle Author Leo Pastouret Author Publisher: Société Géologique de France First Online: 03 Mar 2017 Online Issn: 1777-5817 Print Issn: 0037-9409 GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique, Vandoeuvre-les-Nancy, France Bulletin de la Société Géologique de France (1985) I (2): 153–159. https://doi.org/10.2113/gssgfbull.I.2.153 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jean-Rene Vanney, F. Rojouan, D. Temine, J. A. Malod, Gilbert Boillot, Raymond Capdevila, M. Cousin, Francisco Gonzalez-Lodeiro, C. Lepvrier, Juan R. Martinez-Catalan, G. Mascle, Leo Pastouret; Observations geomorphologiques effectuees en plongees au Nord-Ouest de la peninsule iberique. Bulletin de la Société Géologique de France 1985;; I (2): 153–159. doi: https://doi.org/10.2113/gssgfbull.I.2.153 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin de la Société Géologique de France Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Seismic reflection profiles and numerous pre-Neogene samples obtained from the continental margin off northern Spain provide a means to reconstruct its Mesozoic and Cenozoic evolution. During the Mesozoic, this evolution can be compared to that of the passive margins of the western Iberian peninsula and France (rifting during the Late Jurassic, transgression and deposition of “black shales” during the Early Cretaceous). These series have been tectonically deformed and emerged, together with their basement, during the latest Cretaceous and Eocene when the oceanic lithosphere from the Bay of Biscay underwent a limited (southward) subduction. Then the margin of northern Spain was again submerged during the late Paleogene and Neogene.

A new geological map of the English Channel is presented (1/1 000 000). In this work the authors recreate the structural evolution of the basin: from the Permian to the Jurassic ages, the English Channel is more like a 'demi-graben' placed on a continental rift. The faults of the graben were reactivated during the Tertiary following the compressions and extensions of the Pyrenean movements at that time.