Helena Sant'Ovaia

Characterization of soils from the Algarve region (Portugal): A multidisciplinary approach for forensic applications

The Algarve is located at a very short distance from North Africa, in Southern Portugal, and as one of the most touristic regions of Portugal, it is accessible by air, land and sea. It is very susceptible to many illegal activities, such as illegal migration, drug trafficking, kidnapping, and murder, among others. Therefore, an Algarve soils database for forensic purposes is being conducted with the conjunction of geological and palynological methodologies on soils characterization, since this is of fundamental importance to assess reliable evidence on forensic investigations. In this study, the properties of soils from several proximate sites from the Algarve were investigated, namely: (i) colour determined by spectrophotometry; (ii) particle size distribution determined by laser granulometry; (iii) low-field magnetic susceptibility by a susceptibility meter; and (iv) pollen content using a light microscope. Finally, a hierarchical cluster analysis was applied to ascertain the capacity of the different soil properties for discrimination between samples. The study reveals the utility of geobotanical techniques for forensic discrimination of soils. Even though some similarities between some of the samples were found, each one presented a combination of colour, particle size distribution, magnetic susceptibility and pollen features that enable the determination of a fingerprint expected to reveal a specific site for future selection of coastal search areas in the Algarve region.

Composite-laccolith emplacement of the post-tectonic Vila Pouca de Aguiar granite pluton (northern Portugal): a combined AMS and gravity study

The Vila Pouca de Aguiar granite pluton, emplaced during the latest event of the Variscan orogeny of northern Portugal, is here subjected to a detailed study that combines magnetic fabric measurements and gravity modelling of its shape at depth. This laccolith, less than 1 km in thickness over ≈60% of its outcrop area, appears to be fed from its northern area, through narrow conduits, up to 5 km deep, belonging to a set of Y-shaped valleys that almost perfectly correspond to the local Regua-Verin fault-system identified in the geological maps. A normal petrographical zonation, already identified geologically, appears to be rather progressive, although a gradient in magnetic suceptibility magnitude in-between the two main magma types is evidenced. It is suggested that the first to be emplaced and the least evolved granite type (Vila Pouca de Aguiar Granite) upwelled from the local, NE-trending fault-zone, acting as a dyke, and formed a thin sill where NE-directed magma flow was dominant, at least close to the floor. The more evolved granite type (Pedras Salgadas Granite), located just above the main feeder zone, and deeply rooted at the intersection beween underlying faults, is at the centre of a remarkably regular concentric distribution of the foliation trajectories. They may reflect the late doming of the laccoliths northern part, coeval with a slight E-W extension of the inflating magma reservoir, as marked by the E-W-trending lineations. Along with ubiquitous magmatic to near-magmatic microstructures and particularly low anisotropy magnitudes, such patterns can be entirely explained by magma movement within its inflating reservoir. This composite laccolith, during emplacement of which no interference with the regional strain pattern can be recorded, is therefore considered as typical of post-tectonic emplacement.