Abstract
Strain analysis is made of the primary cleavage fabric in Precambrian and Palaeozoic psammites outcropping in a Northeastem area of the Iberian Range. The calculated total finite strain shows a decrease in the strain towards the highest part of the stratigraphic sequence. Rocks with a high proportion of matrix show oblate o uniaxial ellipsoids. Rocks with a very low proportion of matrix show slightly prolate ellipsoids or with an axial relation nearly l. These features have allowed to state an evolutive sequence in the cleavage development, defined by two main stages: Stage of embrionic cleavage, characterized by oblate ellipsoids whose x strain axis is nearly horizontal in rocks with a high proportion of matrix, coexisting with quarzitic rocks, with show prolate ellipsoids, whose x strain axis is nearly vertical. Stage of well developed cleavage, showing oblate ellipsoids whose x strain axis is nearly vertical.
Highlights
Se realiza la cuantificación de la deformación asociada a la esquistosidad en samitas precámbricas y paleozoicas, aflorantes en la rona nororiental de la Cordillera Ibérica
Strain analysis is made of the primary cleavage fabric in Precambrian and Palaeozoic psammites outcropping in a Northeastem area of the Iberian Range
Rocks with a very low proportion of matrix show slightly prolate ellipsoids or with an axial relation nearly l. These features have allowed to state an evolutive sequence in the cleavage development, defined by two main stages: Stage of embrionic cleavage, characterized by oblate ellipsoids whose x strain axis is nearly horizontal in rocks with a high proportion of matrix, coexisting with quarzitic rocks, with show prolate ellipsoids, whose x strain axis is nearly vertical
Summary
Se realiza la cuantificación de la deformación asociada a la esquistosidad en samitas precámbricas y paleozoicas, aflorantes en la rona nororiental de la Cordillera Ibérica. Estas técnicas parten de la base de que los marcadores tienen propiedades fisicas semejantes a las del volumen total de la roca y de que los límites de los clastos son puramente geométricos. El contraste de ductilidades entre los c1astos y la matriz, determina que la deformación no sea homogénea y que el valor del' elipsoide no se corresponda con el del total de la roca (De Paor, 1980). Freeman y Lisie (1987), analizando la influencia de las formas de los cantos en conglomerados y el contraste de competencias con la matriz, indican que la magnitud de la deformación y la relación de carácter prolat%blato será mayor cuando los marcadores constituyen volumétricamente una pequeña fracción de la roca. Aplicando estas técnicas en rocas samíticas paleozoicas y precámbricas, hemos intentado realizar una aproximación cuantitativa de la deformación interna en el área estudiada e interpretar su relación con el desarrollo de las estructuras
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