Phanerozoic Tectonic and Paleogeologic Evolution of Southern South America

URIEN, C. M., Instituto Tecnologico de Buenos Aires, Buenos Aires, Argentina, and J. J. ZAMBRANO, San Juan University, San Juan, Argentina

Before pre-Variscan time, southern South America had a quasicratonic nature. New structural alignments were overimposed due to Gondwana breakup and South Atlantic opening.

Phanerozoic tectonic history is divided as follows: (1) "Caledonian Geosyncline." Situated west of Brazilian shield and massives, consists of Cambrian to mid-Devonian clastics, carbonates, and intrusives. (2) Variscan Intracratonic Rifting and Foreland Basins. Alluvial and glaciolacustrine sediments accumulated in grabens and marine clastics accumulated in marginal basins along the western continental edge. Shallow clastic seas in intracratonic rifts were associated with glacial events. This period ends in Late Jurassic time (Gondwana breakup) with basaltic extrusions along rifting zones. (3) Inter Malm Taphogenesis. Basement fracturing and Proto-Atlantic opening took place and marine flooding advanced from the south. Along the western margin, a magmatic arc existed since Early Jurass c. The back-arc basins were filled by marine clastics and evaporites, alternating with acidic volcanics and making up the "Andine Geosyncline." Patagonia was covered by acidic volcanics. (4) Subhercynian Drifting. Sedimentary prisms were formed on the Atlantic margin. On the western margin, continental clastics were laid during the Middle and Late Cretaceous. Acidic extrusions and Andean batholith intrusion began during this time. (5) Laramic Flooding. An Atlantic transgression covered a great part of the extra-Andean region and Andean chains were formed. (6) Cenozoic Mountain Building. A new transgression expanded again over Argentine plains and Patagonia. New Andean uplifting phases, sub-Andean belt folding, and basement fracturing originated intermontane basins. Thick, alluvial, and p edmont sediments accumulated here. Marine circulation was established with a pattern similar to the present-day one.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)