PhD presented by Isabel Prudêncio. 1993, 233 p.

Abstract
Chemical and mineralogical changes during the alteration of continental basaltic rocks from central and southern Portugal, specially the Lisbon volcanic complex, were studied. The main purposes of this work were: (1) to study the chemical and mineralogical processes during the alteration of basaltic rocks; and (2) to contribute to the knowledge of the rare earth elements behaviour in the surface environment under temperate climate (mediterranean type).

Weathering is the predominant alteration process of the basaltic rocks from central and southern Portugal. The processes are similar to those found in temperate climates with dry and wet seasons. Smectites are the dominant clay minerals found in the fraction<2µm and interstratified minerals are rare. In general, haloisites occur in the top and medium parts of the profiles and dominate in the higher lands, whlist smectites dominate in the lower lands. The smectites formed in Algarve have higher Na content and lower Mg content than the smectites formed in the Lisbon region, which may explain the presence in the fraction<2µm of analcime in the south and palygorskite in the central Portugal. These differences may be due to climatic differences (higher aridity in algarve). Supergenic calcite, sometimes associated with palygorskite and smectites, occurs filling fissures and vacuoles of basaltic rocks. In some cases supergene epigenesis by calcite was found. The results obtained for the rare earths in the weathering profiles showed that in temperate climates these elements can be mobilized, fractionated, transported and reprecipitated in favorable conditions. The rare earths behaviour under mediterranean climate seems to be similar to the behaviour of these elements in tropical regions.

Further, contact Profª. Drª. Maria Amália Braga.