LA FORMACIÓN DEL CONTINENTE SUDAMERICANO

RAPELA, C.W.

Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales de Buenos Aires

ACADEMIA NACIONAL DE CIENCIAS EXACTAS FÝSICAS Y NATURALES

Lugar: Buenos Aires; Año: 2008 vol. 60 p. 25 - 31

0365-1185

The amalgamation of the South American continent. This work is a review ofrecent geochronological research aimed to unravel the origin and processes that leaded to the amalgamation of southern South America. Ages obtained in ancient granític rocks using the U-Pb SHRIMP (Sensitive High Resolution Ion Microprobe) methodology, precise the age range and geographical distribution of two old continental blocks, of 2000-2260 Ma and 1000-1270 Ma respectively. The older block is the Río de la Plata Craton, which in Argentina only outcrop in the Sierras de Tandil and in Martín García Island. Dating of samples recovered from deep boreholes below the Chaco- Pampean plains indicate ages between 2088-2189 Ma, within the range ofthose in Tandil, indicating a W and NW sub-surface extension of 500-600 km of the Río de la Plata Craton. A complex oblique collision ofthe 1000-1270 Ma block against the western edge ofthe Río de la Plata Craton occurred at 530-430 Ma, heralded the final amalgamation of the Gondwana supercontinent. Widely apart outcrops ofthe 1000-1270 continental blocks occur in the Sierras Pampeanas of La Rioja and San Juan, the San Rafael Massif in Mendoza and low-altitude minor outcrops in the province of La Pampa. Similar studies carried out in old granitic rocks of Patagonia, suggest that a block composed of southern Patagonia and the Antarctic Penmsula joined later to Gondwana, during a 335-314 Ma Carboniferous continental collision. .The formation of the South American plate at 130 Ma, after the breakup and dispersalThe formation of the South American plate at 130 Ma, after the breakup and dispersal ofGondwana, included remnants ofthe two old blocks that collided at 530 Ma, which are the bulk of the continental crust of southern Brazil,-Uruguay and the ~entral and northern sectors of Argentina and Chile.