STRUCTURE OF THE CRUST IN THE SCHISTOSE DOMAIN OF GALICIA-TRAS-OS-MONTES (NW IBERIAN PENINSULA)

Two seismic refraction/wide-angle reflection experiments were carried out in 1982 in the northwest of the Iberian Peninsula, one in Galicia (Spain), and the other in the north of Portugal. The joint interpretat ion of four of these profiles is discussed in this paper. Travel time and amplitude information have been used. The four resulting crustal m odels show similar characteristics with regard to the number of layers and the thickness of the crust (30 km), and differences in the distri bution of P-wave velocities. A low-velocity layer of 5.7 km . s-1 has been found in the north of Galicia at a depth between 5 and 10 km, whi ch could establish a lower border to the Ordenes Massif, discarding th e possibility of a deep rooting of the Massif and favoring the hypothe sis of an alloctonous emplacement. In the central part of the studied area, the middle crust shows a P-wave velocity of 6.2-6.4 km . s-1 at a depth between 10 and 23 km. In the southern part, outside the Galici a-Tras-os-Montes zone, the velocity of P-waves varies from 6.0 to 6.2 km - s-1 at a depth between 7 and 19 km. In the lower crust, the veloc ity of P-waves increases from 6.6 to 7.1 km . s-1 under the Ordenes Ma ssif and from 6.8 to 7.2 km . s-1 in the central part of Galicia; in t he north of Portugal a constant velocity value of 6.8 km - s-1 has bee n found. The lower crust in the area of the Ordenes Massif is characte rized by a lamellar structure. In the uppermost mantle P-waves propaga te with a velocity of 8.1-8.2 km . s-1 in the Galicia-Tras-os-Montes z one, while in the southern part P-wave velocity varies from 8.2 to 8.3 km . s-1. The Moho presents itself as a first-order discontinuity. Th e results obtained in this study are comparable with those obtained fo r other Hercynian areas of the Iberian Peninsula.