Tourmaline Granites of the Conlara Metamorphic Complex

LÓPEZ DE LUCHI, M.G.; IANIZZOTTO, N.F.; MARTÍNEZ DOPICO, C.I.; CERREDO, M.E.

Neuquén

Congreso; XVIII Congreso Geológico Argentino; 2011

Asociación Geológica Argentina

The Ordovician Los Alanices granite (Fig. 1), originally defined by Ulacco and Ramos (2001), consists of muscovite granites (MsG) and muscovite-tourmaline leucogranites (MsTG) (Fig. 1) and belongs to the low-temperature muscovite leucogranites of the Ordovician granodiorite–granite suite (OGGS; peraluminous calcic to calc-alkaline granodiorite–monzogranites) of the Sierra de San Luis (López de Luchi et al., 2007). K-Ar muscovite cooling age of 420±9 Ma was calculated for the MsTG whereas muscovite from the near El Peñón muscovite leucogranite (SHRIMP U/Pb zircon age of 497±8 Ma) yielded 439±10 Ma (López de Luchi et al., 2007 and references therein). Magmatic to high temperature solid-state deformation argues for an early Famatinian syn-kinematic emplacement for the MsG (López de Luchi et al., 2007 and references therein). MsTG exhibits clear-cut contacts against the fine grained biotite-muscovite schists of the host Conlara Metamorphic Complex (López de Luchi et al, 2007) and is located at the southernmost sector of the Los Alanices pluton. MsTG is a fine to medium grained leucogranite characterized by up to 4% tourmaline plus muscovite, scarce biotite and in some cases reddish pink garnet. Tourmaline is euhedral to subhedral with dark olive green cores and olive green or brown rims: it may be included in or associated with biotite. Apatite and garnet are abundant whereas zircon is rare as accessory phases. The NNE trending foliation which results from the high-temperature solid-state overprint of the MsG is weakly developed in the MsTG. Major and trace elements were analysed for three samples of the MsTG facies of the Los Alanices pluton (Fig.2). These granites are peraluminous (A/CNK=1.10 to 1.15) highly fractionated, calc-alkaline rocks (Fig 2a) with low phosphorus content (