GEOCHEMICAL CHARACTERIZATION AND EMPLACEMENT OF THE EARLY TRIASSIC FELSIC DYKE SWARMS, MENUCOS- LA ESPERANZA, NORTH PATAGONIAN MASSIF

MARTINEZ DOPICO, C.I.; LÓPEZ DE LUCHI, M. G.; MARQUEZ, E.; FRANCHESCHINIS, P; RAPALINI, A.E.; MIGUEZ, M.; COLAVITTO, B

Pto Madryn, Chubut

Congreso; XXI Congreso Geologico Argentino; 2022

Asociacion Geologica Argentina

Acidic dyke swarms are an exceptional expression of crustal extension as feeding channels for silica rich magmas in their way from the magmatic reservoirs throughout the upper crust. Evidence of extensional conditions from the Late Permian to Late Triassic can be tracked in the centre of the Massif, such as large shallow plutonic-volcanic complexes and volcanoclastic deposits (i.e. La Esperanza plutonic- volcanic complex, Martínez Dopico et al. 2019, Los Menucos basin, Luppo et al. 2018) and large W-E dextral strike-slip fault systems with kilometric displacements (i.e. Giacosa et al. 2007 Luppo et al. 2018). In the area of Estancia Cerro Piche, 45 km to the NW of Los Menucos (40º51´S, 68º5´E), three sets of rhyolitic dyke swarms (10-50 m-length; 0.5 to 3 m-width) were recognized, mainly W-E to WNW-ESE and NW-SE, and minor NE-SW. 2007). In Los Menucos area, the dyke swarm crosscuts Palaeozoic units, such as theCambrian metaclastic Colo Niyeu Formation (Martínez Dopico et al. 2017b), the andesitic and dacitic coulees correlated with the Collinao Dacite (Luppo et al. 2019), and sections of the rhyolitic to andesitic volcanic and volcaniclastic sequences of the Los Menucos Complex (Lema et al. 2008) which were dated at 257 ± 2 and 252 ± 2 Ma, respectively (Luppo et al. 2018). Similarly, 20 km to the north, in La Esperanza area, another E-W to minor SW-NE rhyolite dyke swarm intrudes the Collinao Dacite (253 ± 2 Ma; Luppo et al. 2019) and the epizonal leucogranites of the Calvo Granite (250 ± 2 Ma; Pankhurst et al. 2006) and older units of the La Esperanza plutonic-volcanic Complex (Martínez Dopico et al. 2019). The rhyolite dyke swarm was dated in La Esperanza area at 246 ± 2 and 244 ± 2 Ma (Pankhurst et al. 2006; Luppo et al. 2019).