Mariano Yenes

Granite emplacement in orogenic compressional conditions: the La Alberca–Béjar granitic area (Spanish Central System, Variscan Iberian Belt)

Abstract The La Alberca–Bejar granitic area comprises a set of intrusions of Upper Carboniferous to Lower Permian age located in the hinterland of the Variscan belt of western Spain. Gravity data, anisotropy of magnetic susceptibility, and microstructural studies carried out in the granitoid and its country rocks indicate that the granitoids of this region have tabular and inverted drop shapes and show sub-horizontal magmatic fabrics and SW–NE lineations. The granitoid bodies were intruded episodically, with single intrusive pulses recorded by deformation in the country rocks. All intrusive events took place during D 3 compressive stage, in the core of large D 1 anticlines, and are not related to structures in the country rock. A syn-orogenic emplacement model for granite intrusion in such conditions is proposed. The proposed model implies the activity of coeval emplacement mechanisms and room generation.

Characterization of serpentinites to define their appropriate use as dimension stone

Abstract Many questions arise when considering the appropriate use of building stones such as serpentinites. The commercial names of these rocks, collectively grouped as ‘Green marbles’, have no correspondence to their actual mineralogy, geochemistry and/or physical characteristics. Serpentinite being the hydrated product of an ultramafic parent rock and not a metamorphic product of limestone as implied by the term ‘marble’. However, the serpentinites most widely used for ornamental purposes come from India (e.g. Rajasthan Green, Emerald Green) and in these the original mineralogy has been almost completely converted into carbonates. By contrast, serpentinites from elsewhere (e.g. Vermont Verde Antique from the USA and Verde Pirineos from Spain) do preserve some of their original mineralogy. The different physical and chemical behaviour of carbonates and serpentine minerals can result in significantly different behaviour of commercial building stones. Thus, carbonates are resistant to weathering but suffer from acidic cleaning agents in interior use; whereas serpentinites, with a high content of talc, used on external faces undergo an increase in volume and a consequent rapid degradation. Accurate and precise characterization of serpentinites, including information on their mineralogy and geochemistry (including major, trace and volatile elements together with oxygen isotopes), in conjunction with their physical properties, would enable architects to select the appropriate interior or exterior use of these handsome building stones.

Shallow foundations on expansive soils: a case study of the El Viso Geotechnical Unit, Salamanca, Spain

Construction on expansive soils can generally be resolved using piles. Where shallow foundations are used in these materials, the swelling pressure should be determined and the foundations designed to provide a greater pressure to counteract this. Clearly, it will also be necessary to determine the capacity of the ground to take this load. The paper discusses the bearing capacity of unsaturated expansive soils for a given suction value and notes the bearing capacity was increased by 26% when the effect of suction was taken into account. However, an increase in the water content would cause a decrease in suction and hence a decrease in the bearing capacity.RésuméLa construction sur sols gonflants peut généralement être réalisée à l’aide de pieux. Là où des fondations peu profondes sont mises en œuvre dans ces matériaux, la pression de gonflement devrait être déterminée et les fondations dimensionnées pour apporter une pression supérieure permettant de contrebalancer celle-là. Clairement, il est aussi nécessaire de déterminer la capacité du terrain à supporter ce chargement. L’article discute de la capacité portante de sols gonflants non saturés présentant une valeur de succion donnée et note que la capacité portante est augmentée de 26% quand les effets de la succion sont pris en compte. Cependant, une augmentation de teneur en eau entraînerait une diminution de la succion et de ce fait de la capacité portante.

Serpentinites from Cabo Ortegal (Galicia, Spain): a search for correct use as ornamental stones

Abstract Different varieties of serpentinites present at Cabo Ortegal were studied. For many years, the ‘Verde Pirineos’ type has been quarried and sold commercially, but its physical characteristics do not fulfil the requirements for its use as an ornamental stone. ‘Piedra de Doelo’ is the local name for a serpentinite that has been quarried and used for many centuries in a large number of historical buildings distributed throughout the area. The preservation status of the rock is very poor and the stone is severely affected by weathering. A third variety, similar to the ‘ophicalcite’ described in the literature, is currently under investigation with a view to studying the possibility of the resumption of serpentinite quarrying. Although serpentinites are commercially known as ‘green marbles’, Galician serpentinites do not fulfil the mineral requirements to be described as such. Study of the characteristics of serpentinites, including their mineralogy, may offer a clue to the correct use of Galician serpentinites.