Cadomian/Pan-African consolidation of the Iberian Massif assessed by its detrital and inherited zircon populations : is the ~610Ma age peak a persistent Cadomian magmatic inheritance or the key to unravel its Pan-African basement?

Abstract

Acknowledgement. Martim Chichorro is grateful for the funding provided by GeoBioTec (UIDB/04035/2020). We acknowledge the support of Portuguese Fundação para a Ciência e a Tecnologia (FCT) through PhD grant SFRH/BD/138791/2018 to João Lains Amaral. This work was funded by the FCT I.P./MCTES through national funds (PIDDAC) - UIDB/50019/2020 to Telmo M. Bento dos Santos via IDL - Instituto Dom Luiz. Geopark Naturtejo is also gratefully acknowledged for long-term logistic support. Insightful comments, suggestions and corrections provided by Josep Maria Casas and an anonymous reviewer are kindly acknowledged. Finally, the authors would like to express their gratitude to the Guest Editor

This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (~120Ma sedimentary record), the main systematic peak occurs at ~610Ma, followed by peaks at typical Cadomian ages (~590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (~590-550Ma) but, once again, a remarkably consistent Pan-African ~610Ma peak occurs. In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M'Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the lateEdiacaran sediments of the Ossa Morena Zone and the Central Iberian Zone. Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed-system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, to separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircon during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.