P. Schmoldt, PhD - MTNet - DIAS

7. Geology of the Iberian Peninsula
Layer
Depth of lower Velocity (km/s)
boundary (km) P-wave S-wave
Interpretation
Sediments 3.0 3.3 2.50 Tertiary and Mesozoic sediments
Crystalline 5 - 9 5.9 - 6.1 3.48 Low grade Palaeozoic metamorphic
basement
rocks (mostly shale and quartzite)
Intermediate 23 - 25 6.2 - 6.3 3.58 Igneous and metamorphic rocks
crust
(Migmatites,
granodiorite)
quartz-monozite, and
Lower crust 30 - 33 6.7 - 6.8 3.90 Igneous and metamorphic rocks
(granodiorite, diorite, and granulites)
Uppermost
mantle
... 8.0 - 8.2 4.4 - 4.5 Ultramafic rocks
Tab. 7.2.: Crustal layer thickness and seismic velocity below the Tajo Basin in proximity of the Iberian Massif, according to Banda
et al. [1981]. Values for shear wave velocity and sedimentary layer are taken from Díaz and Gallart [2009]. Data were observed
using seismic reflection and wide-angle profile, interpreted with reflectivity and ray-tracing methods (depth of uppermost mantle not
resolved in this work).
7.3.2. Previous geophysical studies in the region
Previous geophysical studies, in particular MT, have been focussed on the area of the
Pyrenees and the Betics Chain with their alpine orogeny (see Sec. 7.2); see Korja [2007]
for a summary of MT investigations in Europe. Central Spain has been mainly the subject
of near-surface research and has remained comparatively neglected in terms of deepprobing
investigations, meaning that our study breaks new ground. An extensive literature
search, however, did yield a number of studies providing information that are used
to construct initial subsurface models and to contrast results of the PICASSO Phase I
investigation (cf. Chap. 10). Results from this body of work are briefly presented here
divided into groups of methods, followed by a summary of key aspects most relevant for
the PICASSO Phase I project.
Seismic reflection
The crust–mantle interface beneath the Iberian Peninsula was investigated by Banda et al.
[1981] and, recently, by Díaz and Gallart [2009] using a compilation of seismic sounding
profiles. The authors derive a Moho depth between 30 km and 33 km, which deepens
towards the SE and NE corners, coinciding with the locations of the Betic mountain chain
and the Pyrenees – Iberian Chain respectively (Fig. 7.18). Additionally, wide-angle
profiles interpreted with reflectivity and ray-tracing methods reveal two first-order discontinuities
in the crust below the Tajo Basin region [Díaz and Gallart, 2009](Fig. 7.20).
Accordingly, the authors divide the crust into three layers, i.e. upper crust (including sedimentary
layer and crystalline basement), intermediate crust, and lower crust (associated
with the Variscan basement of the Iberian Massif); respective values of seismic velocities
152