Provenance of Late Palaeozoic sediments of the Patagonian palaeo-Pacific margin (southernmost Chile and Argentina)

Augustsson C, Bahlburg H.

Abstract

In this provenance study of late Palaeozoicmetasediments of the Eastern Andean MetamorphicComplex (EAMC) along the south Patagonian proto-Pacific margin of Gondwana, the palaeogeologicalsetting of the continental margin in Devonian-Carboniferousand Permian times is reconstructed. Thestudy is based on detrital heavy mineral contents,chemical compositions of tourmaline grains, and wholerock element and Nd-Sr isotopic compositions. Elementand isotopic compositions reveal that Devonian-Carboniferous metaturbidites deposited before thedevelopment of a Late Carboniferous-Permian magmaticarc along the margin were mainly fed from felsic,recycled, old continental rocks. The last recyclingphase involved erosion of metasediments that wereexposed in Patagonia. Feeder systems to the basin cuteither through epidote-rich or garnet-rich metasediments.In Permian time, EAMC metaturbidites weredeposited next to the evolving magmatic arc and werederived from felsic, crustal rocks. Two provenancedomains are recognised. The metasediments of thenorthern one are chemically similar to those of theDevonian-Carboniferous metasediments. This domainwas fed from the metasedimentary host rocks of themagmatic arc. The southern domain probably was fedfrom the arc proper, as indicated mainly by the dominanceof metaplutonic lithic fragments, abundantdetrital biotite, and the major element composition ofthe metasediments.