The Ocean-Continent Transition of Western Iberia

WHITMARSH, R. B., P. R. MILES, and L. M. PINHEIRO, Institute of Oceanographic Sciences Deacon Laboratory, Wormley, Surrey, United Kingdom, G. BOILLOT, Universite Pierre et Marie Curie, Villefranche-sur-Mer, France, and M. RECQ, Universite de Bretagne Occidentale, Brest, France

The western continental margin of the Iberian peninsular has the characteristics 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. We located the OCT off western Iberia in order to constrain the pre-rift 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 efraction profiles was shot across three parts of the Iberian margin from Galicia Bank to the Tagus Abyssal Plain. In the Iberia Abyssal Plain, the OCT can be detected not only from seismic velocities but also by modelling 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 the OCT.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)