Revista de la Asociación Geológica Argentina
versión On-line ISSN 1851-8249
BROGIONI, N.; PARRINI, P. y PECCHIONI, E.. Petrology of the pre-deformational arc magmatism in the Cordón de El Realito and in the northern zone of the La Escalerilla pluton, Sierra de San Luis. Rev. Asoc. Geol. Argent. [online]. 2005, vol.60, n.3, pp. 495-512. ISSN 1851-8249.
The pre-deformational Late Cambrian to Early Ordovician arc-magmatism of the Sierra de San Luis forms several outcrops of which Cordón de El Realito and La Escalerilla pluton are the most extensive. High-K calcalkaline magmas intrude low- to medium-grade metasedimentary rocks in both areas. The oldest event is represented by arc-type, metaluminous Pl+Bt+Ep±Hbl±Kf granodiorites, tonalites and scarce diorites, carrying numerous enclaves of gabbroic to monzodioritic composition. Chemical abundances and evolutionary trends of these rocks correlate well with those of the metaluminous arcsequence of Sierras de Chepes and Los Llanos in La Rioja province. The youngest event consists of peraluminous and collisionrelated Kf+Pl+Ms±Bt±Grt, leucocratic monzogranites, intruding the arc-sequence. The monzogranites do not appear to be generated as a result of differentiation from the metaluminous sequence, although both magmatic suites are part of the Famatinian subductionrelated arc. The peraluminous magmatism displays the typical vertical evolutionary trend of felsic peraluminous granitoids and is interpreted as derived mainly from partial melting of Ms-metapelites and greywackes. Some geochemical abundances and HREE patterns of the La Escalerilla stock are probably controlled by differences in the source. The Famatinian regional metamorphism and shearing strongly modified the arc-sequence rocks fabrics. However, the magmatic rocks preserved their whole chemical signatures except for the most basic members of the series which display spreading in evolutionary trends and increased peraluminosity. The pre-deformational peraluminous melts in both areas are clearly distinct from those of some syn-kinematic Ms±Bt±Grt leucogranitoids which crop out in the Eastern Basement Complex of the Sierra.
Palabras clave : Pre-deformational; Arc-magmatism; San Luis; Cordón de El Realito; La Escalerilla stock; Metaluminous; Peraluminous felsic.