Geoquímica del basamento de la Puna Austral y Cordillera Oriental.

BECCHIO, R.; LUCASSEN, F.,; FRANZ, G.; VIRAMONTE, J. G.; KASEMAN, S

Buenos Aires

Congreso; X. Congreso Latinoamericano de Geología; 1998

AGA. SEGEMAR. Universidad de Buenos Aires

Metamorphic conditions of high temperature and relatively low pressure were found in the early Pz high grade rocks in the whole area of investigation. Low T - high P metamorphism is absent. The general age of metamorphism is Pampean with 525 - 500Ma. The age data are in good agreement with data from south - eastern Sierras Pampeanas the latter show-ing a similar type of metamorphism with similar or slightly higher P and T (Rapela et al., 1998). A history of subduction and collision as invoked south of ca 27° (Rapela et al., 1998 and ref. therein) could not be proven for our transect. The tectonic setting was probably different in the north: the ~500 Ma Mobile Belt extends from the Pacific Coast to the east (Fig.9) and obducted ocean floor is absent. Accretion of exotic terranes north of the Argentine Precordillera is unlikely, however, the Silurian thermal overprint at Sierra de Quilmes could be related to the advent of the Arg. Precordillera. The early Pz meta-morphic rocks and contemporaneous granitoid intrusions have very similar isotopic compositions (our data; Damm et al., 1990, 1994; Rapela et al., 1998) and the major process of crustal formation is recycling of Proterozoic basement. Juvenile additions to the crust are negligible. Unrecycled Proterozoic basement seems restricted to Peru and Bolivia