INGEIS   05370
INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
artículos
Título:
Li bearing granitoids of the Sierra de Mamil Choique, southwest Northpatagonian Massif
Autor/es:
LÓPEZ DE LUCHI, M.G.; MARTÍNEZ DOPICO, C.I.; RAPALINI, A.E.; CERREDO, M.E.
Revista:
BOLLETTINO DI GEOFISICA TEORICA ED APPLICATA
Editorial:
ISTITUTO NAZIONALE DI OCEANOGRAFIA E DI GEOFISICA
Referencias:
Lugar: Trieste; Año: 2013 vol. 54 p. 283 - 286
ISSN:
0006-6729
Resumen:
Lithium bearing granites at the SW sector of North Patagonian Massif (NPM) are represented by La Pintada Granite (LPG) which comprises a group of medium to fine grained leucomonzogranites and monzogranites and associated pegmatoids that crops out in the central and northeastern corner of the Sierra de Mamil Choique (SMC). LPGintrudes with clear cut contacts the Permian HuenchuquilGranodiorite (HG) facies of the Mamil Choique Granitoids. In this contribution we present a revised chemical characterization of the La Pintada Granite together with a new Rb-Sr isochron and propose its genetic link with the Li-bearing pegmatoids that crops out around Pto. Huenchuquil (Fig. 1) first described by Sesana (1968).The Permian La Pintada Granite was originally defined by Dalla Salda et al. (1994) as corresponding to the granites of the eastern half of the Sierra de Mamil Choique. López de Luchi and Cerredo (1997, 2008)redefined this unit and considered that it comprises scattered outcrops of white to light pinkish medium to fine grained garnet-leucomonzogranites and monzogranitesin the northern part of the central area and along the northeastern border of the Sierra de Mamil Choique. The monzogranite-leucomonzogranitein which pegmatoid veins or pods are present, crops out in the NE corner of the SMC in a series of rounded hills. Towards the central part of the Sierra granitoids became subordinated to widespread pegmatoids that appear either as veins or as apparently flat-laying sills or stocks intruding the HuenchuquilGranodiorite facies. Granites(M=4-6) are medium- to fine-grained equigranular or pophyroidand are composed of plagioclase, quartz, microcline, white mica ± biotite, garnet, opaque minerals. Brittle deformation is occasionally observed. Plagioclase (An10-An26) occurs both as subhedral zonal phenocrysts set in a fine-grained groundmass and as anhedral crystals in the equigranular facies; perthitic microcline appears both as an interstitial phase and as anhedral ameboidal phenocrysts. Quartz is euhedral to subhedral, shows undulose extinction. Primary muscovite is subhedral it occurs and contains inclusions of quartz, zircon and very scarce apatite. Microstructural evidence indicates that lepidolite replaces muscovite and occurs as large late crystallization undeformed plates, sometimes accompanied by scarce chloritized biotite. Li2O contents ca. 4.76% was measured in some cases. Pinkish small, (less than 0,3mm) inclusion-free garnet crystals in low modal amounts (