Magnetic fabrics and cooling age of the Permian La Esperanza Plutonic Complex.

MARTINEZ DOPICO, CARMEN; WEMMER, KLAUS; RAPALINI, AUGUSTO E.; LOPEZ DE LUCHI, MÓNICA

Neuquén

Congreso; 18 congreso Geológico Argentino; 2011

Asociación Geológica Argentina

  La Esperanza Plutonic Complex (LEPC) is located 60 Km to the N-NW of Los Menucos town in the Río Negro Province, north of North Patagonian Massif (NPM), Argentina. LEPC was first studied by Llambías and Rapela (1984), who divided the complex in three facies whose extension and precise chronology is not completely defined (Rapela and Llambías 1985; Pankhurst et al., 1992). It comprises: a) the Prieto Granodiorite, a biotite-hornblende equigranular to inequigranular granitoid dated by U-Pb SHRIMP in zircon in 273±2 Ma (Pankhurst et al., 2006); b) the Giménez Granite, an equigranular to porphyritic granite and c) the Donosa Granite (DGr), a megacrystic biotite-rich granite, which was originally dated using the Rb-Sr method in ~250 Ma (cooling age) by Rapela et al. (1988), and interpreted from field observations as intruding the Gimenez Granite and Prieto Granodiorite (Llambías and Rapela, 1984). A younger pluto-volcanic unit, the Dos Lomas Complex (DLC), is interpreted to be the eruptive counterpart of the LEPC and is mainly composed of dacitic and rhyolitic domes and ignimbrites (264±2Ma, 246±2 Ma) and high-silica two mica leucogranites (250±2Ma, Pankhurst et al., 2006).  LEPC intrudes the very low grade metasedimentary rocks of the Early Cambrian (?) Colo Niyeu Formation and is unconformably overlain by DLC.  Previous geological and geochemical studies performed by Rapela and Llambías (1985) and Rapela and Caminos (1987) indicate that the granitoids and volcanic rocks are late to post-tectonic with calk-alkaline to alkaline affinities. Geochemical and loosely geochronological evidence might indicate a possible correlation between these rocks and the Navarrete plutonic and Treneta volcanic complexes that crop out further east around Valcheta area