During last years, the authors of this paper have been developing field works focusing essentially on the Volcano-Stratigraphy, Geomorphology, and Structural Geology of Madeira Island. These preliminary studies have shown that the importance of the tectonic faulting of Madeira was clearly underestimated in the past. On the other hand, the preliminary results of the analysis of SPOT satellite imagery (Project CORINE, published by CNIG) at the 1/50,000 scale, allowed the identification of more than one hundred very well defined tectonic lineaments, longer than 1 km, totalling an accumulated length of 450 km. Some of these lineaments were validated in the field and represent the surface trace of faults. These preliminary works lead to a geological multi-disciplinary study of Madeira Island. A project for the Autonomous Region was submitted in order to elaborate a complete cartography program (to be presented at the 1/50,000 scale) that will be developed in the next three years.
The Madeira Archipelago, that includes Madeira, Porto Santo, Desertas and Selvagens Islands, presents a volcanic nature and is located in the oceanic portion of the African plate. It is located near the south-western termination of the large seamounts and volcanic paleo-ridges alignment extending from the Iberian Peninsula shelf to almost 1000 km to the southwest. On the basis of its spatial orientation, it has been proposed that this belt of volcanoes could represent a hotspot track (Morgan 1981). The main island - Madeira -, located at 32°N, 17°W, represents 90% of the total area of the archipelago. In this region the lithosphere is 130 Ma old and is approximately 100 km thick. Uchupi et al. (1976) put it in evidence the existence of an underwater relief, rising 1.800 m from the abyssal plain and trending NE-SW, which is usually designated as Madeira Rise. The aligned group of seamounts, of which the most important are the volcanic structures of Madeira and Porto Santo at the southwestern tip of this mega structure, form the Madeira-Tore Rise. Consequently, Madeira is younger than Porto Santo Island, 40 km to northeast, where the exposed lavas are dated from 18.8 to 10.2 Ma (Ferreira et al. 1988). Firstly suggested by Mata (1996), the hypothesis that some of the geomorphologic linear patterns, materialized by alignments of volcanic cones with constant orientations, should represent alignments of great tectonic importance (Zoback 1992) in Madeira Island, was later confirmed and validated through systematic field studies (Fonseca et al. 1998a, b). The multi-disciplinary works in this island, herein described, were initiated in 1996. The geological/geomorphological interpretation studies, were based on: a) Analysis of SPOT satellite image at the 1/50,000 scale (CNES-SPOT IMAGE) obtained in the scope of the "Portuguese-French Cooperation Project- CORINE Land Cover - Madeira Island", and published by the National Centre for Geographical Information (CNIG), State Secretary for Science and Technology and by the Ministry for Planning and Administration of the Territory, and b) Mapping and air photo interpretation performed on selected key places, of the observable tectonic accidents, larger structures, geomorphology and volcano-stratigraphy.
