Composición química de biotita y hornblenda y edades de enfriamiento como indicadores de las condiciones de emplazamiento del Complejo Plutónico La Esperanza (Pérmico Superior), Macizo Norpatagónico

MARTÍNEZ DOPICO, C.; LÓPEZ DE LUCHI, M. G.,; WEMMWE, K.; RAPALINI, A.E.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2013 vol. 70 p. 3 - 15

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 Ranch. Hornblende-Plagioclase thermometer yields emplacement temperatures ranging from 630 to 790ºC at high oxygen fugacity conditions. These results, combined with good quality-cooling ages, propose a shallow emplacement in an elevated thermal regime that might have lasted from Middle Permian to Permotriassic times.