Tectonic and neotectonic implications of a new basement map of the Lower Tagus Valley, Portugal

Abstract

a b s t r a c t a r t i c l e i n f oIn this paper we present a new basement (defined here as Paleozoic, Precambrian and Mesozoic igneous rocks) map of the Lower Tagus Valley area. This map is a contribution to the understanding of the structural evolution of the top of the basement in the Lower Tagus Valley area during the Mesozoic and Cenozoic Eras. The map was produced using aeromagnetic, well, seismic reflection and geological outcrop data. It shows unprecedented details of the geometry of the basement rock's surface with higher resolution and covers a larger area than the previous basement map of the study area. In spite of an estimated average error of 200 m in depth and an horizontal resolution of 4 km, our map not only reproduces with accuracy several well known basement structures but it also emphasizes previously unknown features. Major basement faults were inferred from large depth variations at the top of the basement, magnetic 2D Euler deconvolution and horizontal gradient analysis and are compatible with surface geological structures, well data and hydrogeological information. Implications to the geodynamic evolution of the SW European Variscides and consequences to Meso-Cenozoic tectonics are discussed. The correlation of the basement structures with instrumental seismicity is carried out and their neotectonic activity is discussed on the basis of existing geological outcrop data.

New data on the chronology of the Vale do Forno sedimentary sequence (Lower Tejo River terrace staircase) and its relevance as a fluvial archive of the Middle Pleistocene in western Iberia

“…Choffat, 1907;Bensaúde, 1910;Freire de Andrade, 1933;Cabral et al, 2003Cabral et al, , 2004Cabral et al, , 2013Ribeiro, 1988, 1989;Cabral, 1995Cabral, , 2012Vilanova and Fonseca, 2004;Carvalho et al, 2008Carvalho et al, , 2014Martins et al, 2009;Besana-Ostman et al, 2012). This is expressed as a regional scale tectonic lineament concealed by Holocene sediments.…”

Tectonic evolution of an intraplate basin: the Lower Tagus Cenozoic Basin, Portugal

“…, wells, faults derived from the seismic reflection interpretation and basement faults recently derived by Carvalho et al . (). These faults also affect the Meso‐Cenozoic sediments, as we can see in the Euler deconvolution solutions presented in the bottom panel of Fig.…”

Ground-Motion Simulation in the Lower Tagus Valley Basin

“…(CABRAL et al 2003). Some of the major fault zones that control the evolution of the LTCB are hidden, because of the presence of the sedimentary layer (CABRAL et al 2003(CABRAL et al , 2004CARVALHO et al 2006CARVALHO et al , 2014; geophysical methods are, thus, of fundamental importance in their recognition. The seismic reflection method, combined with well data, has been used for many decades (usually in association with the oil industry) to study the stratigraphy and tectonic evolution of sedimentary basins, including the Lower Tagus/Lusitanian Basin.…”

“…1 seismic reflection and well data (CARVALHO et al 2014) for the areas where these data were available; and 2 potential-field data for the areas with no seismic coverage. Figure 1 shows the location of the study area, situated in the central Portuguese mainland and the seismicity of the area.…”