Tracing the Cadomian magmatism with detrital/inherited zircon ages by in-situ U–Pb SHRIMP geochronology (Ossa-Morena Zone, SW Iberian Massif)

Abstract

Keywords:Detrital/inherited zircon ages Cadomian magmatic arc Ediacaran Cambrian Northern Gondwana margin U-Pb SHRIMP geochronology on zircon extracted from a granite, a sandstone and a quartzite of the SW Iberian Massif (Ossa-Morena Zone), was used in order to investigate the contribution of Late Neoproterozoic (Cadomian) tectonothermal history to the crustal growth of northern Gondwana. The analysed Cambrian rocks were sampled along the southern margin of the Coimbra-Cordoba shear zone (Barquete granite and Crato sandstone), and within this shear zone (Ouguela quartzite). The Barquete granite yielded a crystallization age of 526 ± 4 Ma and evidence for Neoproterozoic and Paleoproterozoic inherited ages. The geochemical signature of the Barquete granite matches the igneous activity of the initial magmatic flooding of the Ossa-Morena Zone during the Early Cambrian. The petrography and geochemical signature of the Crato and Ouguela sandstones indicate that these clastic rocks were mainly derived from felsic igneous rocks. The youngest detrital zircon grain extracted from the Crato sandstone, dated at 552.7 ± 5.5 Ma, has a zircon overgrowth that yielded 532 ± 5.6 Ma. In the Ouguela quartzite, the youngest concordant age yielded 556.4 ± 5.7 Ma, but we also found a zircon overgrowth dated at 536.2 ± 5.6 Ma. The ages of the youngest detrital zircon in each sedimentary rock place an upper limit on the deposition age of Early Cambrian (c. 536-532 Ma). Four main Late Neoproterozoic age clusters at c. 640-638 Ma, c. 612-613 Ma, c. 590-585 Ma and c. 560 Ma were recognized in the populations of detrital zircons from both sandstones. These ages of zirconforming events seem to represent four successive thermal/magmatic pulses that overlap the Cadomian and Pan-African orogenies. These findings match other results published for the OMZ. Our U-Pb results show that detrital zircons in siliciclastic sediments and inherited zircon in granites are dominated by Neoproterozoic ages and few Paleoproterozoic and Archean ages. Those ages reported in the Ossa-Morena Zone rocks, together with a remarkable lack of Mesoproterozoic ages suggest that the clastic rocks in this peri-Gondwana basin were derived from the West African craton. The large population of Late Cryogenian and Ediacaran ages indicates denudation of the Cadomian basement during the Early Cambrian. A potential source for the detrital and inherited zircons found in this study is a long-lived magmatic arc that is only partly exposed in the SW Iberian Massif but is well represented in other peri-Gondwana regions. The large amount of Cadomian ages obtained in this study reinforces the idea that Cadomian magmatism played a significant role in the continental crustal growth history of Late Neoproterozoic uplift and erosion in Western and Central Europe (Cadomia).

Cadomian volcanosedimentary complexes across the Ediacaran–Cambrian transition of the Eastern Pyrenees, southwestern Europe

“…Cadomian orogenic events are differently recorded in the southwestern (Iberian Massif) and northeastern (North-, Central and South-Armorican Domains, Massif Central and Pyrenees) branches of the Variscan Ibero-Armorican Arc. A distinct angular discordance is 1 3 recorded in the Iberian Massif (except in the Central-Iberian Zone, interpreted as a back-arc setting; Bandrés et al 2002;Pereira et al 2011) and in the North-and Central Armorican Domains, whereas the Ediacaran-Cambrian transition is conformable in the inner margin of the eastern branch (Occitan Domain of the southern Massif Central; Álvaro et al 2014a, b;Pouclet et al 2017).…”

Potential sources of Ediacaran strata of Iberia: a review

“…Ediacaran strata of Iberia which are distributed across the Cantabrian Zone, West Asturian-Leonese Zone (CZ-WALZ), the Central Iberian Zone (CIZ) and the Ossa-Morena Zone (OMZ) (Figure 2) have been interpreted as representing arc-related basins (Eguíluz, Gil-Ibarguchi, Abalos, & Apraíz, 2000;Linnemann et al, 2008;Murphy, Eguiluz, & Zulauf, 2002;Pereira, Chichorro, Linnemann, Eguiluz, & Silva, 2006;Quesada, 1990aQuesada, , 1990bRodriguez-Alonso et al, 2004). These Ediacaran basins were filled with detritus mainly from the Cadomian magmatic arcs and also from other source areas located further towards North Gondwana inland such as the West African craton, the Trans-Saharan belt and more remote areas of the Saharan Metacraton and the Arabian-Nubian shield (Fernández-Suarez, Gutierrez-Alonso, & Jeffries, 2002;Fernandez-Suarez et al, 2013;Linnemann et al, 2008;Pereira et al, 2011;Pereira, Linnemann, et al, 2012).…”

Provenance Analysis of Lower Palaeozoic Siliciclastic Rocks of Southwestern Iberia (Ossa–Morena Zone): Distal Shelf Deposition on the North Gondwana Passive Margin

“…There are some Mesoproterozoic and Palaeoproterozoic ages and a few Archaean grains. The presence of Tonian zircons is distinctive when compared with the Ediacaran Série Negra succession and the Cambrian formations (Pereira et al 2011; this study). In the greywackes of the Terena Formation (Lower Devonian), the youngest detrital zircons found are Early Ordovician (ca.…”

“…550 to 400 Ma, the transition from an active margin with the formation of Neoproterozoic magmatic arcs (the Cadomian orogeny; Linnemann et al 2008;Pereira et al 2011Pereira et al , 2012 to a passive margin with the development of early Palaeozoic basins dominated by siliciclastic deposition on a distal shelf (Robardet and Gutierrez-Marco 2004) (Fig. 1).…”