%0 Journal Article
%T Ages and geochemistry of Mesozoic-Eocene back-arc volcanic rocks in the Ays¨¦n region of the Patagonian Andes, Chile
%A Miguel A. Parada
%A Alfredo Lahsen
%A Carlos Palacios
%J Revista geol¨®gica de Chile
%D 2001
%I Scientific Electronic Library Online
%X Eighteen new radiometric ages (fourteen 40Ar-39Ar, four K-Ar), combined with previously published ages, confirm the existence of three main extensional back-arc volcanic events, previously defined by stratigraphic relationships, in Chilean Patagonia (Ays¨¦n region). These three events developed during the Middle Jurassic -Early Cretaceous (160-130 Ma). Cretaceous (114-75 Ma), and Eocene (55-46 Ma). Based on distinct geochemical data and Sr-Nd isotopic characteristics of the back-arc volcanic rocks collected north and south of 46¡ã30'S, two Mesozoic-Eocene magmatic domains are recognized: Northern Magmatic Domain (NMD) and Southern Magmatic Domain (SMD). Most analyzed basalts and intermediate volcanic rocks of the NMD have alkaline affinities and depleted to slightly depleted Sr-Nd isotopic values similar to those derived from an asthenosphere-dominated source. The SMD mafic volcanic rocks have a subalkaline character and more enriched Sr-Nd isotopic signatures, comparable to those derived from a lithospheric source. The felsic volcanic rocks of the SMD have lower eNd values and slightly higher initial 87Sr/86Sr ratios than the NMD felsic rocks, suggesting a larger crustal contribution in the magma sources. The geochemical and isotopic distinction between NMD and SMD felsic rocks could be influenced by the presence of Paleozoic metamorphic rocks as basement of the volcanic rocks of the SMD. Moreover, the compositional distinction between basalts of both domains may correspond to differences in magnitude of extension, the NMD being the one where the extension would have been greater and, consequently, the lithosphere thinner Edades y geoqu¨ªmica de las rocas volc¨¢nicas del trasarco del Mesozoico-Eoceno en la regi¨®n de Ays¨¦n de los Andes patag¨®nicos, Chile. Diez y ocho nuevas edades radiom¨¦tricas (catorce 40Ar-39Ar, cuatro K-Ar) junto con las ya publicadas confirman la existencia de tres eventos volc¨¢nicos (previamente definidos por relaciones estratigr¨¢ficas) en la Patagonia chilena (Regi¨®n de Ays¨¦n) durante el intervalo Mesozoico-Eoceno: Jur¨¢sico Medio-Cret¨¢cico temprano (160-130 Ma), Cret¨¢cico (114-75 Ma) y Eoceno (55-46 Ma). Sobre la base de las caracter¨ªsticas geoqu¨ªmicas e isot¨®picas de Sr y Nd de las rocas volc¨¢nicas estudiadas, se pueden reconocer dos dominios magm¨¢ticos Mesozoico-Eoceno: Dominio Magm¨¢tico Norte (DMN) y Dominio Magm¨¢tico Sur (DMS). Los basaltos y rocas intermedias del DMN tienen afinidades alcalinas y valores isot¨®picos de Sr-Nd deprimidos a moderadamente deprimidos similares a aquellos derivados de una fuente dominada por material as
%K Volcanismo de trasarco
%K Edades 40Ar-39Ar
%K Fuente magm¨¢tica
%K Extensi¨®n cortical
%K Patagonia Chilena
%K Back-arc volcanism
%K 40Ar-39Ar ages
%K Magma source
%K Crustal extension
%K Chilean Patagonia
%U http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082001000100002