1 research outputs found
Crustal Seismic Structure beneath Portugal (Western Iberia) and the role of Variscan Inheritance
Mainland Portugal comprises most of theWestern portion of the Iberian Peninsula, in a geodynamic setting associated
with the Africa-Eurasia plate boundary. The crustal structure in Portugal is the result of a complex assemblage
history of continental collision and extension with most of the surface is covered by rocks dating to the Variscan
orogeny, the coastal ranges dominated by Mesozoic structures and Mesocenozoic basins covering partially the
mainland.
The impact and extension of this complex tectonic in the structure of the Iberian Lithosphere is still a matter of
discussion, especially in its western part beneath Portugal. The existing knowledge relating the observed surface
geology and lithospheric structures is sparse and sometimes incoherent, the relation between shallow and deep
structures and their lateral extension still widely undetermined. Some questions still pertinent are the role and influence
of the several tectonic units and their contacts in the present tectonic regime and in the stress field observed
today, and the relation between the anomalous seismicity and associated crustal deformation rates with the inherited
structure from past orogenies.
In this study we present the results of a local earthquake tomographic study, performed to image this complex
crustal structure down to 20 km depth. The relocation of the onshore seismicity recorded in the period 2000-2014
with the new 3D model allows cleansing some of the alignments and their correlation with some of the main active
structures in Portugal enabling for the first time to correlate a large number of tectonic features to the small
magnitude seismicity pattern. The seismicity distribution also displays a complex pattern, mainly reflecting the
interaction between inherited Variscan structures with more recent fault systems created during the rifting stages
of the Atlantic and diapir magmatic intrusions.
The complex history of the assemblage of the crust beneathWestern Iberia is well-marked in the final models. The
arcuate shape of the Ibero-Armorican Arc can be perceived over the general pattern of the Vp and Vp/Vs anomalies
and the heterogeneity observed on the surface geology are clearly marked in the tomograms. Other significant
features are the low Vp values associated with the Mesocenozoic rocks outcropping in the Lusitanian and Algarve
basins, and the low Vp and high Vp/Vs values of the sedimentary cover of the Lower-Tagus and Sado Basin.Publication supported by FCT- project UID/GEO/50019/2013 - Instituto Dom LuizPeer Reviewe