The Famatinian granitoids of the southwestern sector of Sierra de San Luis: Classification and geothermometry

Abstract

Several plutons belonging to an old magmatic arc are recognized in the southwestern of the Sierra de San Luis. They are emplaced in metamorphic rocks of greenschist to lower amphibolites facies, and interpreted as pre-ocloyic, older than 460 Ma, within the Famatinian orogenic cycle. The mapping, petrographic study, and chemical microanalysis in feldspars, have enabled a classification of the plutonics roks of the area and have revealed part of the history of cooling and emplacement of the different facies. Also, the chemical microanalysis in feldspars shows that there is great variation in the An content of plagioclase in the mafic series, in comparison with those ofthe felsic series, indicating a variation in the range of temperatures from 1100° to 748° C respectively, and a probably different origin of magmas. The data were modeled and adjusted to existing theoretical diagrams of isothermsfor the system or-ab-an, and for an internal pressure of H₂O 5000 bars (pseudo-isobaric system)