Assembly of the Armorica Microplate: A Strike-Slip Terrane Delivery? Evidence from U-Pb Ages of Detrital Zircons

Abstract

Detrital zircons separated from the Ordovician Armorican quartzite in the foreland of the Variscan belt of Iberia were dated by laser ablation inductively coupled plasma mass spectrometry. The age groups found correspond to Proterozoic and Archean crust formation events. The Proterozoic events reflected by zircon ages are Avalonian-Cadomian-Pan-African (550–800 Ma), Grenvillean-Sunsas (900–1300 Ma), and Eburnian-Transamazonian-Icartian (1800–2200 Ma). Archean zircon ages are comprised between 2500 and 2800 Ma (Central-Amazonian-Liberian events). The presence of Mesoproterozoic (Grenvillean) zircons in the Armorican quartzite, which was deposited in a shallow platform bordering the NW African craton (north Gondwana margin), suggests that the NW Iberian terrane drifted from the South American margin, where it was located during the Neoproterozoic, toward Africa. The drift of the Iberian block, likely achieved via transform faults, was arrested by its docking and amalgamation with the peri–NW African Neoproterozoic terranes, resulting in the birth of the Paleozoic Armorica Terrane Assemblage.