MAMIL CHOIQUE GRANITOIDS AT THE SOUTHWESTERN CORNER OF THE NORTHPATAGONIAN MASSIF, ARGENTINA MAGMATISM AND METAMORPHISM ASSOCIATED WITH A POLYPHASIC EVOLUTION

CERREDO, M.E.; LÓPEZ DE LUCHI, M. G.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Año: 1998 vol. 11 p. 499 - 515

0895-9811

Petrological and structural features of the metamorphic  Cushamen Formation (CF), and igneous units Tunnel Tonalites (TT) and  Mamil Choique Granitoids (MCG) displaying polyphasic tectonics in the  Rio Chico-Mamil Choique area, southwestern corner of North Patagonian  Massif (NPM) are studied. A medium pressure regional metamorphism is  described for metapelites of CF which were later intruded by TT and  the widespread MCG. Magmatism comprising TT-MCG is calcalkaline with a  metaluminous-peraluminous trend. MCG include two magmatic series  controlled by differences in oxygen fugacity, fluid interaction and  crystallization dynamics. Four deformational phases have been  recognized. Regional relationships among  metamorphism-deformation-magmatism agree with what is to be expected  from a collisional setting with peak metamorphic conditions being  synchronous or shortly after the second deformation and with magmatism  postdating regional metamorphism. This would be consistent with the  deep seated magmatism interpreted from crystallization sequences in  the epidote bearing TT and MCG. TT and MCG could be adscribed to the  same tectonothermic event since their primary magmatic foliations are  overprinted by D3 subsolidus deformation. MCG Rb-Sr age, either  Ordovician/Silurian or Carboniferous, would reflect an emplacement  event and would set a lower chronological constrain for D3. In this  connection, that age could bracket a crustal thickening event.