Magmatic and tectonic evolution of the Alumine belt, Patagonian Batholith, Neuquen, Argentina

URRAZA, I.; GRECCO, L.; DELPINO, S.; ZENTILLI, M.

Québec

Congreso; GAC-MAC-SEG-SGA Annual Meeting; 2008

GAC-MAC-SEG-SGA

The Patagonian Batholith holds the key to understanding the Mesozoic tectonic development of the southern Andes.  The Alumine Batholithic Belt (ABB) constitutes the northern sector of the Patagonian Batholith.  Intercalated with magmatic rocks, outcrops of metamorphic basement are preserved; these are composed of schists, gneisses, amphibolites and scarce quartzose sandstones.  Andesites, tuffs and basalts overlying metamorphic and granitic rocks are also present.  The granitoids forming the ABB can be classified as: 1) quartz diorites (Pl+Qz+Bi+Opx±Cpx); 2) tonalites-granodiorites(Pl+Qz+Bi+Hbl+Cpx±Act); 3) granodiorite (Pl+Qz+Bi+Hbl-Act+Cpx); and 4) granites (Pl+Bt+Qz+Kfs±Act).  The geochemistry reveals a suite of I type metaluminous calcic rocks, characteristic of the Cordilleran Batholith, developed by subduction of oceanic lithosphere under the Jurassic - Cretaceous South American margin.  Pre-Mesozoic granitoids may be part of the complex, but remain undefined.  Three main regional lineaments have been recognized whose directions are: NE-SW, NW-SE and N-S.  These regional trends coincide with three groups of penetrative foliations affecting the rocks.  Based on petrographic-microstructural and mineral deformation analysis, at least two ductile deformation events were recognized in the rocks: one of high temperature (high amphibolite -granulite) and another of intermediate temperature. (greenschist- low amphibolite).  Argon-argon geochronology and geobarometry are being studied to develop a history of the batholith.