La estructura y la evolución metamórfica en un corte comprendido entre Carballiño y Forcarei: área esquistosa de Galicia central.

Abstract

[Resumen] La sección de Carballiño-Forcarei se sitúa en una zona clave, para establecer las relaciones tectónicas y metamórficas entre las grandes unidades que componen la cordillera. Las microestructuras de la D2, dominante en la zona, muestran una variación gradual a través de los sectores Inferior y Central en el tipo de foliación, el tamaño de las micas que forman la S2' yen los pliegues D2. El sector de Forcarei muestra un salto brusco, en estas características, con respecto al sector Central. En la base del Grupo de Forcarei existe una deformaci6n más intensa con bandas de cizalla y rocas de falla que explican el salto brusco en las estructuras D2• .Las lineaciones nos indican que la extensión máxima, durante la Dz tiene una posición N-S. Los ejes de los pliegues Fi, en el sector Central, menos deformado, se generaron con una posición que formaba ángulos altos con la dirección N-S, Yrotaron hasta alcanzar un paralelismo con esta direcci6n de máximo estiramiento. Existe un salto metamórfico con superposición de la zona del granate (Forcarei) sobre la clorita (Paraño). Este se explica por un cabalgamiento sinmetamórfico que da lugar a evoluciones distintas para la parte inferior (prograda) y superior (retrograda).

[Abstract] The Carballiño-Forcarei section is located, due to the distance to the thermal domes, in a good position to study the structural and metamorphie relationships between the allochthonous mafic, gneissic and ultramafic units belong to the complex and the lower metasedimentary units, that together foem the most internal part of the Hercynian belt in NW Spain. The structure consist in asymetric closed fold 0 3 affecting the main foliation S2 with only a locally developed axial plain cleavage. With the analysis of the S2' a gradual variation from N-S and subhorizontal , axis in the Lower sector to E-W in the Central (less deformed) sector can be seen. This variation which is realised throught folds with curved hinges lying in the S2 planes, is explained by the orientation of original E-W folds axis (F21), to the direction of maximum finite extension marked by mineral stretching lineation in schist and granitic rocks during O2. In the upper sector O2fold axis become N-S and subhorizontal always lying in the S2 planes. A variation in mica grain size and in the stage of development of the S2 crenulation can also be observed. To the base of the Upper sector (Forcarei Group) extensional crenulation cleavage and fault rocks originated in the fragil-ductil transition has been recognised. A metamorphic contrast between the Upper sector (garnet zone) and the Central (chlorite zone) was detected and explained by a sinmetamorphic thrust, wich influence the thermal structure of the zone, causing a retrograde path (in T) for the allochthonous unit of Forcarei and prograde for the lower authocthonous (Nogueira and Paraño Groups). Granitic bodies and dikes are locally weakly deformed by the last stages of subhorizontal shearing of the second deformation phase.