Abstract

MARTINEZ DOPICO, Carmen I.; LOPEZ DE LUCHI, Mónica G.; WEMMER, Klaus  and  RAPALINI, Augusto E.. Chemical composition of biotite and hornblende and cooling ages as indicators of the emplacement conditions of the La Esperanza Plutonic Complex (Upper Permian), North Patagonian Massif. Rev. Asoc. Geol. Argent. [online]. 2013, vol.70, n.1, pp.3-15. ISSN 0004-4822.

La Esperanza Plutonic Complex crops out in the northern part of the North Patagonian Massif in the Upper Paleozoic magmatic belt of northern Patagonia. This magmatic complex is mainly composed of 273 Ma biotite and amphibole bearing (Prieto Granodiorite) or biotite bearing (Donosa Granite) granitoids. In this study, biotite and amphibole mineral compositions are used to describe the nature of the granitic magma and to estimate the pressure and temperature at which these plutons were emplaced. Based on biotite chemistry, La Esperanza Plutonic Complex represents a calc-alkaline magma with a trend of increasing peraluminosity, which could be related to a transitional orogenic to anorogenic setting. Emplacement pressures for Prieto Granodiorite vary between 0,6 and 2,0 kbar, with higher values in an inequigranular facies which crops out to the east of La Esperanza locality. Hornblende-Plagioclase thermometer yields emplacement temperatures ranging from 630 to 790ºC at high oxygen fugacity conditions. These results, combined with good qualitycooling ages, propose a shallow emplacement in an elevated thermal regime that might have lasted from Middle Permian to Permotriassic times.

Keywords : La Esperanza Plutonic Complex; Biotite; Hornblende; Thermobarometry; Permian.

        · abstract in Spanish     · text in Spanish     · Spanish ( pdf )