Meso-Neoproterozoic sources for the Andean mobile belts

RAPELA, C.W., .PANKHURST, R.J. Y FANNING, C.M.

Punta del Este, Uruguay

Congreso; V South American Symposium on Isotope Geology; 2006

Facultad de Agronomía y Facultad de Ciencias de la Universidad de la República

 Identifying sources and growth mechanisms of the mobile belts in SW Gondwana is fundamental, as this sector is one of the best world examples of continental growth by lateral accretion. Recent U-Pb SHRIMP studies coupled with Nd isotope systematics in the Rio de la Plata Craton (RPC), Eastern Sierras Pampeanas (ESP) and Patagonia raise important constraints on sediment sources during evolution of the margin. Primitive Palaeoproterozoic sequences mostly in the range 2.050–2.260 Ma are characteristic of the Rio de la Plata Craton, which extends from the Atlantic to at least 63ºW in the province of Cordoba. Cambrian low-grade metasediments in northern Patagonia show few detrital zircons of  ~ 2000 Ma,  in detrital populations formed at large by 540–620 Ma and c. 1000 Ma. Early and Late Palaeozoic sediments of central, southern and eastern of Patagonia, including those forming the basement of the southern Andes, do not show evidence of Paleoproterozoic sources similar to the RPC. Remarkably, nor do most ESP metasediments record zircon provenance in the interval c. 2065–2235 Ma, but display peak TDM model ages in the interval 1600–1700 Ma. As in Patagonia, the ESP are dominated  by detrital peaks at 560–680 Ma and 960–1090 Ma, indicating that Pacific growth of the South American continent was derived from “Grenville-age” and  “Brazilean” Meso–Neoproterozoic sources.