Mineralogy and textures of metagabbros and ultramafic related rocks from La Huerta and Valle Fértil Ranges, Western Pampean Ranges, San Juan, Argentina

CASTRO DE MACHUCA, BRÍGIDA; CONTE-GRAND, ALICIA; MEISSL, ESTELA; PONTORIERO, SANDRA; RECIO, OLGA; SUMAY, CELINA

Buenos Aires

Congreso; VI Congreso de Mineralogía y Metalogenia (6º MINMET); 2002

Asociación Mineralógica Argentina (AMA) - Universidad de Buenos Aires

The eastern flank of La Huerta and Valle Fértil hills, Western Pampean Ranges, San Juan province, Argentina, mainly consists of metaigneous dioritic to granodioritic rocks that intruded the Proterozoic basement in the Early-Middle Ordovician (Famatinian Orogeny). Small bodies of metagabbro and related ultramafic rocks, up to a few hundred meters across, are present in minor amounts. Two-pyroxene metagabbros display well preserved igneous textures and mineralogy comprising Mg-Ca rich minerals: Pl(An100-75)+Opx(En82-76Fs18-23Wo0-1)+Cpx(Wo50-46En44-47Fs6-8)±Ol(Fo83-75)±Spl±Ilm±Mag. Abundant coronas composed of Ol-Opx-Cpx-Pl were developed at Ol-Pl boundaries. In this study, coronitic texture is interpreted to be the result of slow cooling of the mafic-ultramafic bodies under high-amphibolite to lower-granulite metamorphic conditions. The peak of metamorphism in the area coincided with corona formation and was related to the Famatinian intrusive activity. Later, the metagabbros were locally cut by narrow ductile shear-zones associated with mylonitization.