Quantitative compositional mapping and estimation of P-T conditions in a mylonitic amphibolite from Laguna Témpanos, North Patagonian Andes basement (Bariloche Complex)

FRANCO D. BIANCHI ; JUAN CRUZ MARTÍNEZ ; SERGIO H. DELPINO; VANESA S. ARAUJO; FERNANDA GUIMARÃES

Bahía Blanca

Congreso; 14° Congreso de Mineralogía, Petrología Ígnea y Metamórfica, y Metalogénesis; 2023

Outcrops of metasedimentary rocksbetween the Jacob Lake (Refugio San Martin) and the Témpanos Lake, 16 km southof Bariloche city in the North Patagonian Andes, were recently studied indetail and included as part of the Bariloche Complex (Oriolo et al. 2019).Three deformation events were identified into the undifferentiated metapeliticlithologies of this area. Amphibolite was indicated as a different lithotype ofthe complex with two dissimilar textures; coarse and fine-grained amphibolites (García-Sansegundoet al. 2009). The presence of minor amphibolite bodies inside metapelites ofthe Gutiérrez Lake area (10 km southeast) is mentioned by the latter authors.In the present contribution, we study a metamorphicrock from the Témpanos Lake composed of a centimeter-scale interlayering ofgarnet-bearing metapelite and fine-grained amphibolite, which belongs to the contactof a larger, boudinaged amphibolite of around one meter thick. The layering isdepicted at thin section scale as two domains. One is formed by ribbon-quartz,garnet, myrmekitic plagioclase, fine-grained biotite, apatite and ilmenite. Theother domain is composed of elongated, fibrous amphibole crystals whichsurround composite plagioclase and quartz porphyroclasts (also with myrmekite),with minor titanite, ilmenite and apatite. Chlorite, sericite and epidotealteration is usually overprinting both described mineral assemblages.