Estudi estratigràfic i estructural del Cambroordovicià de la zona dels ''pics alts'' d'Andorra: (Valls del Coma-Pedrosa i del Pla de l'Estany)

(CAT) L'àrea dels "pics alts" d'Andorra està constituïda essencialment per roques d'edat cambroordoviciana que s'inclouen dins de l'anomenat Massís de la Pallaresa, del qual formen part pràcticament totes les roques que afloren al nord-oest del país. Aquest massís i la resta d'unitats estructurals que conformen la geologia andorrana estan incloses en la Zona Axial pirinenca, la qual constitueix l'aflorament de l'antiga serralada Varisca de la cadena pirinenca. Les roques que constitueixen aquest basament, junt amb la seva cobertura mesozoica, es veuran involucrades en la posterior deformació Alpina que durant el Terciari va donar lloc a l'orogènia pirinenca (serralada Pirinenca). (ENG) The Comapedrosa and Pla de l'Estany valleys study area is located in the northwest of Andorra. This area is comprised of rocks from he Cambro-Ordovician and Upper Ordovician age, which are included in the Pallaresa Dome. The creation of a new 1:25000 scale geological map of this area has allowed us to differentiate three units in the Cambro-Ordovician serie and to recognize for the first time in this area the Cava, Estana and Ansovell formations of Upper Ordovician age. Moreover, we have identified outcrops of the volcanic rocks inserted into the Cambro-Ordovician serie. The country observations make clear a foliation (S1) in the northern part of this area that is associated with the north-verging folds. In the whole study area an axial planar foliation (S2) associated with upright or south-verging folds is identified. However, where the S1 foliation is very well developed, the S2 foliation hasn't been found. The structures associated with S1 and the folds associated with S2 are affected by thrusts with NE-SW and E-W trend.