Metasedimentary and metaigneous protoliths in Cushamen formation. Rio Chico area, Rio Negro province

CERREDO, M.E.; LOPEZ DE LUCHI, M.G.

Neuquén

Congreso; 18 Congreso Geológico Argentino; 2011

Universidad del Comahue

The metamorphic series of CF is made up of metasedimentary and metaigneous rocks; magmatic additions accompanied the entire CF evolution since the pre-metamorphic stage. Near Río Chico bimodal volcanism emplaced in the CF sedimentary basin is represented by rare thin dikes and layers of dacitic and basaltic composition (López de Luchi et al., 2002). Variably foliated tonalitic to leucogranitic rocks (ranging from pegmatite through aplite textures) occurring as sheets, veins and dykes within the metamorphic series have been reported for the whole CF belt. The metamorphic series display a complex structural evolution characterized by several deformation phases (Franzese et al., 1992; Cerredo, 1997; Cerredo et al., 2002; Giacosa et al., 2004; von Gosen, 2009). The two older deformations, D1 and D2, produced foliations and have been recognized in the whole CF belt and interpreted as part of the prograde metamorphic evolution, whereas the later D3 and D4 phases have only been reported for the northern areas (from Comallo to Río Chico) and interpreted to accompany the retrograde, uplift path of CF (Cerredo and López de Luchi, 1998; von Gosen, 2009). Several episodes of synkynematic and intertectonic magmatic additions accompanied the D1-D3 evolution of CF (Giacosa et al., 2004, López de Luchi and Cerredo, 2008, Von Gosen, 2009). The metamorphic series of CF underwent a medium-pressure regional metamorphism; it is regionally dominated by upper greenschist to amphibolite facies mineral assemblages (Cerredo and López de Luchi, 1998; Cerredo et al., 2002; Giacosa et al., 2004; von Gosen, 2009), except for the restricted exposures of Cañadón Chacay Huarruca, Río Chico area (41º 42´S/ 70º 33´W, Río Negro province) where lower greenschist facies have been reported (Cerredo 1997).