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

- Basement map produced by constrained magnetic modeling, seismic reflection and well data.
- Obtained map has improved resolution and covers a larger area then previous map.
- Magnetic Euler deconvolution and horizontal gradient confirm NW-SE and NE-SE basement faults.
- Some of obtained unknown fault zones are corroborated by geological outcrop data.
- These faults have instrumental seismicity associated and are very probably active.

In 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.