GEOCHEMISTRY OF THE YAMINUÉ METAIGNEOUS COMPLEX

LÓPEZ DE LUCHI, M.G.; RAPALINI, A.E.; MARTÍNEZ DOPICO, C.I.; RAPELA, C.W.; PANKHURST, R.J.

Córdoba

Congreso; XIX Congreso Geológico Argentino; 2014

Asociación Geológica Argentina- UNC- UNRC

The Yaminué MetaIgneous Complex (YIC) (Rapalini et al. 2013 and references therein which extends south ofRamos Mexía station (40º30?05??S-67º15?42??W) down to the Yaminué village (40º57?03?S?-67º10?27??W), is a780 km2 sheeted orthogneissic complex. Foliated equigranular or porphyritic biotite- and scarce biotiteamphibolegranitoids are interlayered with locally coarse grained foliated equigranular or porphyric biotitemuscoviteleucogranite. Undeformed N to NNE trending leucogranitic dykes are present in the south. The hostof the Yaminué MetaIgneous Complex is represented in the south by marble plus scarce amphibolites. A steeplydipping NNW mylonite belt controls this contact. In the north the host rock is a metaclastic biotite-plagioclasemuscovitegneiss with detrital? ages of ca 380 Ma (Tohver et al. in prep). Based on ages and lithology wepropose to separate the Yaminué MetaIgneous Complex in three sectors: northern, central and southern. TheYaminué MetaIgneous Complex in the northern sector forms WNW-ENE shallowly NE (in few cases SW)dipping sheet like bodies of a coarse to medium grained porphyritic biotite (±amphibole) granodiorite and biotitemonzogranite (López de Luchi et al. 2010) that are separated by sub-concordant sheets of a fine-grainedequigranular to porphyritic leucogranite and some pegmatite dykes. In the central sector coarse to mediumgrained biotite (±amphibole) tonalite to granodiorite are interlayered with biotite-muscovite leucogranite. In bothsectors titanite is common even in samples lacking amphibole. In the southern sector sheeted units which exhibita dominant N to NNE S2 penetrative planar fabric and shallowly dip to the east or west, are made up by coarse tomedium grained porphyritic biotite granodiorite-monzogranite interlayered with a highly deformed mediumgrainedto pegmatoid equigranular to porphyritic muscovite-biotite leucogranite which in some layers containsgarnet (López de Luchi et al. 2010). Sub-concordant sheets of mostly finer grained biotite tonalite orthogneissare observed. For many years this unit was considered of Precambrian age based on low quality radimetricdating for rocks located in the central part (see López de Luchi et al. 2010 for details). Basei et al. (2002)calculated U-Pb conventional zircon ages of 305±31, 281± 29, 276±11 Ma and 244±14 Ma, for rocks located inthe central and southern parts. New accurate SHRIMP dating allowed to recognize Ordovician ages for thesouthern sector (Rapalini et al. 2013), Permian-Late Permian for the granodiorite and tonalite of the centralsector (Chernicoff et al. 2013, Pankhurst et al. 2014) and Early Triassic ages for the granodiorite of the northernsector (Tohver et al. in prep).8 new samples of the Yaminué MetaIgneous Complex were analyzed for whole-rock major- and trace elementsat Activation Laboratories (Canada). This new data are combined with published data from Varela et al. (2005and Pankhurst et al. (2014)All the studied samples are I-type granitoids that can be separated in each sector in two groups based on SiO2content of 70.5%. All the studied granitoids are enriched in LILE (large ion lithophile elements) compared toHFSE (high field strength elements), which is a general characteristic of calc-alkaline granitoids.Rocks with SiO2 lower than 70.5 % are I-type metaluminous to slightly peraluminous with A/CNK