SEISMIC STRUCTURE OF THE NORTHERN CONTINENTAL-MARGIN OF SPAIN FROM ESCIN DEEP SEISMIC PROFILES

By the end of the Carboniferous, the crust of the continental shelf in northwestern Spain was made up of deeply rooted structures related to the Variscan collision. From Permian to Triassic times the tectonic s etting had changed to mainly extensional and the northern Iberian cont inental margin underwent rifting during Late Jurassic-Early Cretaceous times, along with sea-floor spreading and the opening of the Bay of B iscay until the Late Cretaceous. Subsequently, the northern Iberian ma rgin was active during the north-south convergence of Eurasia and Iber ia in the Tertiary. A multichannel seismic experiment, consisting of t wo profiles, one north-south (ESCIN-4) crossing the platform margin of fshore Asturias, and another (ESCIN-3) crossing the platform margin to the northwest of Galicia, was designed to study the structure of the northern Iberian margin, The ESCIN-4 stacked section reveals inverted structures in the upper crust within the Le Danois Basin. North of the steep continental slope, ESCIN-4 shows a thick sedimentary package fr om 6 to 9.5 s, two-way travel time (TWT). Within this latter package, a 40-km-long, north-tapering wedge of inclined, mainly south-dipping r eflections is thought to represent a buried, Alpine-age accretionary p rism. In the north western part of the ESCIN-3 (ESCIN-3-1) stacked sec tion, horizontal reflections from 6.5 to 8.5 a correspond to an undist urbed package of sediments lying above oceanic-type basement. In this part of the line, a few kilometres long, strong horizontal reflection at 11.2 s within the basement may represent an oceanic Moho reflection . Also, a band of reflections dips gently towards the southeast, from the base of the gently dipping continental slope. The part of ESCIN-3 line that runs parallel to the NW-Galicia coast (ESCIN-3-2), is charac terized by bright, continuous lower crustal reflections from 8 to 10 a . Beneath the lower crustal reflectivity, a band of strong reflections dips gently toward the southwest from 10 to 13.5 s. The part of ESCIN -3 that parallels the northern margin (ESCIN 3-3), shows goad reflecti vity in all levels, Upper crustal reflections image the sedimentary fi ll of probable Mesozoic to recent basins, Mid-crustal reflectivity is characterized by dipping reflections until 8 s that are probably relat ed to compressional Variscan features. The lower crustal level shows ' layered' reflections between 8 and 12 s. Dipping reflections are found below the continental Moho.