Provenance of the Variscan Upper Allochthon (Cabo Ortegal Complex,NW Iberian Massif)

Abstract

This study focuses on the provenance of the uppermost unit of the Upper Allochthon of the Variscan belt with combined U–Pb and Lu–Hf zircon (LA-ICPMS) and Sm–Nd whole-rock analyses. This unit is represented in the Cabo Ortegal Complex (NW Iberia) by the metasiliciclastic Cariño Gneisses which overlap ophiolitic units that represent perigondwanan oceanic domains. The data set indicates a maximum depositional age of c. 510 Ma and a c. 1.73 Ga Sm–Nd model age, typifying a late or post Pan-African (or Cadomian) and Eburnean events, which entailed abundant input of juvenile material involving broad mixing with older crustal sources. The Mesoproterozoic activity is scarce and scattered and therefore unlikely to represent a major crust generation pulse in the source area of the siliciclastic unit. The data set also records an Archean orogenic pulse in its source area followed by a long lasting crust reworking process, where the Eburnean juvenile materials intruded. These data are interpreted asindicative of a WestAfrica Craton provenance, wherethe siliciclasticseries from whichthe Cariño Gneisses are derived were probably deposited in a back-arc type basinwhere detritus wasmostly sourced by the continent rather than the magmatic arc.