Geología del sector de Lolco, cordillera andina de la IX Región, Chile

Abstract

The studied area is located in the chilean Andes Range between latitudes 38°05' - 38°25'S. and 71°18' - 71°43' Long. W. Five rocks units are recognized: Villucura Volcanic Complex: it is probably of continental origin and Cretacicage. Lancu Beds: andesitic rocks of continental origin and assigned to the Lower Tertiary. Lolco Formation: sedimentary and volcanic secuence of continental origin ranging from Eocene to Miocene divided in three members: Lower member: sedimentary clastic rocks with abundant fossil flora. Middle member: tuffs rocks. Upper member: sedimentary calcareous and clastics rocks with fossil fishes. Cerro Canasto Volcanics: andesitic rocks of continental origin assigned to the Pliocene-Pleistocene. Tolhuaca-Lonquimay Volcanic Group: complex of modern strato-volcanos with mainly basaltic lavas of continental origin, ranging Pliocene-Holocene. Intrusive bodies: Banos del Lolco stock: granites and in less proportion granophyres assigned to the Upper Cretaceous-Eocene. Piedras Blancas Ring Dyke: porphyric rocks of andesitic composition and probable Miocene-Pleistocene age. Techtonically the Lolco area has suffered comprensive and extensive regional stress. The first ones are responsable of the units and the second ones are reflected on the alinments and/or fault systems that controle the main water courses of the area and the inter-glacial and post-glacial volcanic centers.