Descrição
Detrital zircons from Devonian and Carboniferous synorogenic flysch deposits occurring in an
imbricate stack have been dated by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS)
to: (1) obtain a maximum depositional age to constrain the maximum age limit for thrusting of exotic
terranes in the NW Iberian Massif; (2) correlate the zircon age populations with published ages in nearby
units to establish their possible source areas. The maximum depositional ages are Late Devonian for rocks
high in the structural nappe pile (Gimonde Formation), in accordance with palynomorph dating, and around
the Devonian–Carboniferous boundary for structurally lower samples (San Vitero Formation). Used in
conjunction with previously published ages, the new ages are interpreted in terms of the advance of the thrust
system responsible for the emplacement of exotic terranes upon the Iberian autochthon during the Variscan
collision. Early Variscan zircon population ages indicate the exotic terranes as the source of synorogenic
sediments, whereas their scarcity suggests derivation from the Iberian autochthon. One of the samples
analysed lacks Variscan detrital zircons; this feature, together with the absence of an Early Palaeozoic zircon
age population, puts into question its synorogenic character and suggests that the sample may be representative
of the preorogenic parautochthon.
; Fernández-Suárez, Javier 
