%0 Journal Article
%T Lan¨ªn volcano (39.5¡ãS), Southern Andes: geology and morphostructural evolution
%A Luis E. Lara
%A Jos¨¦ A. Naranjo
%A Hugo Moreno
%J Revista geol¨®gica de Chile
%D 2004
%I Scientific Electronic Library Online
%X Lan¨ªn volcano is a compound stratocone, mainly effusive, made up by four units defined through morphological criteria. The first unit represents an ancient volcano; the youngest three units form the present stratocone built since the Middle-Late Pleistocene. Compositionally, volcanic rocks from Lan¨ªn Volcano are mainly basalts/basaltic andesites and dacites with scarce intermediate types. Postglacial pyroclastic deposits are also silicic and confirm a sharp bimodality of the magmas. Major oxides and REE patterns suggest a low-pressure magmatic evolution dominated by fractional crystallization of plagioclase and orthopyroxene with extraction of olivine, clinopyroxene and magnetite without complex interactions. The effusive eruptive cycles would be controlled by a short residence in a shallow magma chamber with rapid and coeval evacuation of dacites and basalts. In recent eruptions, viscous magma would have sealed the central conduit inducing the lateral drainage of basalts and, possibly, the partial collapse of the upper part of the cone. Nevertheless, the most active degradational processes are those related to the ice-cover condition of the present stratocone. The singular evolution of Lan¨ªn volcano, geochemically and morphologically intermediate between the monogenetic cones and the stratovolcanoes of the Villarrica-Lan¨ªn chain, could be related to its distance to the trench which causes low degree of partial melting in the source and the ascent of small batches of magma that would be stored in an ephemeral magma chamber El volc¨¢n Lan¨ªn (39,5¡ã), Andes del sur: geolog¨ªa y evoluci¨®n morfoestructural. El volc¨¢n Lan¨ªn es un estratovolc¨¢n compuesto, predominantemente efusivo, para el que se han definido cuatro unidades seg¨²n criterios geomorfol¨®gicos. La primera de ellas representa restos de una estructura ancestral; las tres siguientes constituyen el edificio volc¨¢nico actual construido esencialmente desde el Pleistoceno Medio-Superior. Composicionalmente, las rocas volc¨¢nicas del volc¨¢n Lan¨ªn corresponden, principalmente, a basaltos/andesitas bas¨¢lticas y dacitas subordinadas con escasas variedades intermedias. Los dep¨®sitos pirocl¨¢sticos post glaciales muestran tambi¨¦n composiciones sil¨ªceas y confirman una estricta bimodalidad composicional de los magmas. Los patrones de tierras raras y elementos mayores indican una evoluci¨®n magm¨¢tica de baja presi¨®n controlada por fraccionamiento de plagioclasa y ortopiroxeno con extracci¨®n de olivino, clinopiroxeno y magnetita, sin interacciones complejas. Los ciclos volc¨¢nicos efusivos ser¨ªan controlados por un red
%K Estratovolc¨¢n
%K Geoqu¨ªmica
%K Morfoestructura
%K Magmatismo bimodal
%K Andes del Sur
%K Stratovolcano
%K Geochemistry
%K Morphostructure
%K Bimodal magmatism
%K Southern Andes
%U http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082004000200004