Devonian magmatism in the accretionary complex of southern Chile

HERVE, F.; CALDERÓN, M.; FANNING, C.M; PANKHURST, R.J.; FUENTES, F.; RAPELA, C.W.; CORREA, J.; QUEZADA, P. ; MARAMBIO, C.

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

Lugar: Londres; Año: 2016

0016-7649

Abstract: Supposed or potential Devonian igneous rocks in the accretionary complex of southern Chile were investigatedusing sensitive high-resolution ion microprobe U?Pb dating of zircon, with Hf- and O-isotope analyses of selected grains. Agesof 384 ± 3 and 382 ± 2 Ma are confirmed for two igneous bodies (another having been previously dated at 397 ± 1 Ma). Detritalzircon ages in the host rocks, some associated with Devonian marine fossils, indicate maximum possible sedimentation ages ofc. 330 ? 385 Ma. Devonian ages of 391 ± 10 and 374 ± 3 Ma for plutonic rocks at the western edge of the North PatagonianMassif are somewhat older than those of orthogneisses in the western flank of the Andes near Chaitén (361 ± 7 and 364 ±2 Ma). O and Hf isotopes indicate that the Devonian intrusions in the accretionary complex crystallized from mantle-derivedmagmas, whereas those in the North Patagonian Massif show a strong crustal influence, corresponding to oceanic andcontinental margin subduction environments of magma genesis, respectively. Devonian zircon provenance in the accretionarycomplex was from the North Patagonian Massif and not from the mantle-derived intrusions, suggesting that the accretionarycomplex formed an integral part of the Gondwana margin during Devonian?Carboniferous times.