Paleozoic terranes of the central Argentine‐Chilean Andes

TLDR

Accreted terranes are key to orogenesis, prompting searches for allochthonous fragments along South America’s western and southern margins. We present stratigraphic and petrologic data from Chile and Argentina (29°–33°S) to demonstrate that several major terranes were accreted during the Paleozoic. We describe three lower‑middle Paleozoic terranes—Pampeanas, Precordillera, and Chilenia—detailing their lithology, stratigraphy, and tectonic setting. Carboniferous strata show the terranes were sutured into South America by the Devonian, and Permo‑Carboniferous interactions mirrored the modern Andean margin with eastward subduction, accretionary prism formation, and arc magmatism migrating from Chile to western Argentina.

Abstract

The recognition of accreted terranes and their importance in orogenesis has spurred the search for allochthonous fragments along the western and southern margins of South America. Here we present stratigraphic and petrologic data from Chile and Argentina between 29° and 33°S latitude that demonstrate the “suspect” nature of several major terranes, which we infer to have been accreted during the Paleozoic. Three lower‐middle Paleozoic terranes are described (from east to west): (1) the Pampeanas terrane, a Cambrian‐Devonian magmatic and metamorphic province built on late Precambrian basement at the margin of South America, (2) the Precordillera terrane, a Cambrian‐Devonian shelf‐slope‐oceanic basin assemblage bounded by mélanges on both sides and bearing many stratigraphic similarities to the lower‐middle Paleozoic of the Northern Appalachians, and (3) the “Chilenia” terrane, which has largely been obliterated by late Paleozoic magmatism and metamorphism. The distribution of Carboniferous continental, deltaic, and marine strata demonstrates that these three terranes were sutured together and part of South America by the end of the Devonian. Subsequent Permo‐Carboniferous plate interactions more closely resembled the modern Andean margin, with eastward subduction, accretionary prism formation, and minor terrane emplacement exposed along the present coast of Chile and eastward migrating arc magmatism from the present coast of Chile to western Argentina.