Geoloby of the Cerra Fitz Roy area,province oSSanta Gruz. The surveyed Cerro Rtz Roy area (73"15'-72"50' W Long., 4S1'25'-49'17'S Lat., southernmost Andes) is located between the Electrico River to the north and the Tune1 River to tire south, and limited to the east by the Las Vueltas R i h r and to the west by the Campo Sur del IIielo Patagbnico. The stratigraphy record starts with Devonian-Carboniicrous leptametamorphic sedimentary rocks of the Bahia La Lancha Formation, which are unconEomably overltyed by conglomerates of the Arroyo de la Mina Formation, a basal unit of the Jurassic volcano-sedimentary El Cluemado Complex. A low angle unconformity separates this Complex from thc Early Cretaceous black pelites of the Rio Mayer Formation. Miocene Fitz Itoy Granite intrudes the whole column. Overthrusting of the Jurassic voleanics that acted like a rigid body over thc Cretaceous pelites that derormed plastically with an intcnse folding, indicates a strong tectonic overprint. Thc later intrusion of the granites generates a contact aureole that attains amphibolite grade. A younger extensional tectonic is responsible for the gravitational faulting. ~l x ill-defined sinistral E-W strike-slip f~ulting associatnd to the Mackena andviedrna inegastructures is recognized.
Characterization o f the Fitz Roy granite, province o f Santa Cruz, Argentina. The Miocene aged Fitz Roy granite is located at 73" 4' W and 49" 16' S in the province of Santa Cruz, Argentina. It is a 45 kin2 stock of ovoidal section, being its major axes of approximately 16 km EW and 9 km NS direction. Its character is epizonal, and zonal in its transversal sense facies. A marginal dark microdioritic facies and a main graniticgranodioritic facies are clearly seen. The box is made up of leptomorphytes of the Paleozoic Formation Bahia de la Lancha, vulcanogenic Jurassic rocks of the Complejo el Queinado and Cretaceous sedimentites of the Rio Mayer Formation. Both facies are chalcoalkalines of medium to high potassic alkalinity. The dioritic facies is alumina infrasaturated, whereas the granitic main facies presents meta and peraluminous saturation terms.Key words: Fitz Roy pluton, geochemistry, Patagonia, Argentina. Ramos et al. (1982) mencionan pequedos stocks, de edad miocena, que afloran a lo largo del borde este del Batolito Patagbnico, de composicibn calco-alcalina a alcalina, entre ellos el del Fitz Roy y otros como el San Lorenzo y el Paine; estos cuerpos estarian desconectados superficialmente del Batolito Patag6nico.El Batolito Patag6nico esta expuesto desde 10s 39" hasta 10s 56" de latitud sur, siendo el tipo de roca dominante la tonalita (Wells, 1979, in Ramos et al., 1982. Se&n una transecta a 10s 45" de latitud S, este se puede dividir en tres grupos: las rocas basicas occidentales, las centrales intermedias y las acidas orientales, que presentan en general una tendencia calcoalcalina (Ramos et al., 1982). El emplazamieto del Batolito Patag6nico se vincula a1 ciclo magmatic0 Patagonidico en el que se reconocen tres fases diastr6ficas: una inicial de caracter tensional que produce un extenso vulcan i s m~, una oroghnica que controla el emplazamiento del Batolito Andino y una p6stuma posiblemente tensional en el Senoniano .A1 este de la Cordillera se encuentran una serie de plateaux de basaltos alcalinos, correspondientes a diferentes pulsos de actividad durante el Eoceno, Mioceno superior, Plioceno y tambihn durante el Cuaternario. Un analisis detallado de estos eventos puede leerse en Ramoset al. (19821, Ramos & Kay (1992) y Kay (2002), entre otros.En la actualidad el magmatismo estk representado por varios aparatos volc~nicos, el mas pr6ximo a la zona objeto de este estudio es el Volcan Lautaro ubicado en el Hielo Patagbnico, en territorio chileno, a la latitud del lago San Martin.En la Patagonia extraandina un importante vulcanismo basico, plateaux basalticos, de asociaci6n alcalina, comenz6 en el Cretacico superior con un mfiximo en el Mioceno superior e inferior. El magma original estaria localizado a grandes profundidades en el inanto, en contraposici6n a 10s basaltos que estan cerca de la cordillera, de una asociacibn tholeitica v alcalina, 10s cuales se habrian originado a profundidades mas someras. Los datos de inclusiones ultramaficas y maficas sugieren que 10s basaltos, aun 10s u...
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