INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Jurassic Cooling ages on granitoids of the NE sector of the North Patagonian Massif
LÓPEZ DE LUCHI, M.G.; MARTÍNEZ DOPICO, C.I.; RAPALINI, A.E.; WEMMER, K.
Rio de Janeiro
Congreso; Gondwana 14. Reuniting Gondwana: East meets West; 2011
The main event of penetrative ductile deformation in the NE corner of the North Patagonian Massif was considered to be bracketed between the Late Carboniferous and the Early Permian (Rapalini et al., 2010, and references therein).The arc and collisional stages would be represented by the Late Carboniferous meta-igneous Yaminué Complex (YC) (Basei et al., 2002, López de Luchi et al, 2010) whereas the post-collisional stages would correspond to the undeformed Late Paleozoic Navarrete Plutonic Complex (Caminos, 2001, Pankhurst et al., 2006). Triassic-Early Jurassic magmatism is represented by the Treneta Plutono-Volcanic Complex from which the undeformed 188± 3 Ma Flores Granite (FG) represents the epizonal granitic plutonism (Pankhurst et al. 1993). Two new Early Jurassic K-Ar ages on muscovite of two pegmatitic miaroles of an undeformed fine grained facies of the FG were calculated on samples V27b and V8E which yielded 188.2±2.9Ma and 193.3±4.5 Ma respectively. On the other hand, three muscovite K-Ar cooling ages were obtained for foliated granitoids of the YC. In the northern sector an age of 198.2±2.2 Ma was calculated from muscovite defining the planar fabric (Val55) of a medium to coarse grained leucogranite. In the central part, muscovite booklets of pegmatitic miaroles of a foliated leucogranite dyke (V69) yielded an age of 190.1±2.0 Ma, while in the southern parts of the complex, muscovite from a coarse grained Grt-Ms foliated leucogranite (V79-1) yielded an age of 182.4±2.9 Ma. In the northern outcrops NW foliation in the leucogranite is discordant respect to the main WNW trending fabric of the host which is locally folded around an ENE trending axis. In the central part, the NW foliation of the leucogranitoids is also discordant respect to the main NNW trending fabric of the YC, whereas in the south the SE planar fabric of the leucogranite is apparently concordant with that of the host. The obtained cooling ages display a youngering pattern towards the south which is accompanied by a change in the orientation of the planar fabric. Regional folding along NE-SW axes and associated mylonitization were described as resulting from a NW directed compression by von Gosen (2003), whereas Sato et al. (2004) identified a Jurassic deformational episode represented by the syn-kinematically emplaced 186±9Ma El Sótano Granodiorite on the Atlantic shore of Río Negro Province with a WNW trending foliation. The new cooling ages confirm the early Jurassic age of the fine grained facies of the undeformed Flores granite which is coetaneous with neighbouring magmatic units emplaced or affected during a Jurassic deformational event bracketed between around 198 and 182 Ma. This event was apparently related with a NW to WNW directed compression in the NE North Patagonian Massif.