Abstract

MENEGATTI, Nilda D; MASSAFERRO, Gabriela I; FERNANDEZ, María I  and  GIACOSA, Raúl E. Geología y geoquímica de los cuerpos básicos alcalinos al sur de los lagos Musters y Colhué Huapí, cuenca del golfo San Sorge, Chubut. Rev. Asoc. Geol. Argent. [online]. 2014, vol.71, n.4, pp.484-499. ISSN 0004-4822.

In the region of Colhué Huapí and Musters lakes, south central province of Chubut, crop out Eocene-Pleistocene igneous alkaline basic bodies which corresponds to stocks, sills, lopoliths and dikes structures. In this paper, we present the results of the survey conducted in the Cerros Negro, Cresta-Puricelli, Guacho, Solo, San Bernardo, Cresta-Leones-Trompete and Tumba del Indio, located south of Sarmiento town. Lithological and textural varieties allowed to classify the rocks as gabbro, nepheline monzogabbro, nepheline syenite, basalt and basanite, being gabbro the predominant variety. On the basis of their shape and size, the presence of textural gradients and zeolites among others, the outcrops studied were characterized as intrusives bodies emplaced at high crustal levels (< 1 km). Most of the analyzed samples are basic with a SiO2 content between 44 % and 48 %. They are characterized by the high Fe2O3 (10.66-14.67 %), TiO2 (1.23-3.37) and alkalis (3.35-5.91 %) content. The patterns of the normalized diagrams are typical of intraplate alkaline basalts compatible with an OIB type with garnet present source without subducted plate or crustal contamination. The steep slope of the normalized REE (La/Yb = 10.2- 22.4) points out relatively low degrees of partial melting. An extensional environment for the emplacement of these bodies is suggested by the structural analysis which is coherent with the geochemical characteristics.

Keywords : Alkaline intrusives; Basic; Patagonia; Cenozoic magmatism.

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