Evolution of the North Patagonian Andes and the adjacent continental massif: new impressions of Andean and pre-Andean tectonics

CINGOLANI, C.; DALLA SALDA, L.H.; HERVÉ, F.; MUNIZAGA, F. ; PANKHURST, R.J.; PARADA, M.A.; RAPELA, C.W.

Andean Magmatism and its Tectonic Setting-GSA Special Paper 265

Geological Society of America

Lugar: Boulder; Año: 1991; p. 29 - 44

The magmatic and tectonic evolution of northern Patagonia are reviewed, and new data are presented from a transect through the Andes between 39 and 42°S. Four main episodes of calc-alkaline granitoid magmatism are recognized: ca. 450 to 370 Ma, ca. 350 to 280 Ma, 220 to 200 Ma, and 180 to 10 Ma (Andean). Only the Andean structural trend is north-south, parallel to the coastline and prominent active strike-slip faults. The three older phases are all best developed within the stable continental region of the North Patagonian Massif, where they were emplaced under the control of north-northwest–south-southeast to northwest-southeast structural lineaments. Their outcrops can be traced into the Andes, and the two younger belts appear to emerge on the western side, in the Chilean Lake Region and the Nahuelbuta Mountains, respectively. Most of the older granitoids are geochemically more evolved and have higher initial 87Sr/86Sr ratios (typically 0.706 to 0.710) than Andean granitoids, indicating greater crustal involvement in their pedogenesis. Neither the structural relationships observed, nor details of the timing and geochemistry of plutonism, provide definite support for the hypothesis of a pre-Mesozoic allochthonous Patagonian terrane separated from the South American continent to the north by subducting ocean floor.