Neoproterozoic palaeogeography of the Cadomia and Avalon terranes: constraints from detrital zircon U–Pb ages

Abstract

Detrital zircons from three Neoproterozoic sandstone units from the Cadomia terrane of northern France and the Channel Islands yield ages in three broad groups: late Neoproterozoic (650–600 Ma), early Palaeoproterozoic (2.4–2.0 Ga) and Archaean (>2.5 Ga). The lack of Mesoproterozoic zircon crystals, combined with the high abundance of grains between 2.20 and 2.00 Ga, corresponds closely to the ages of exposed rocks in the West Africa Craton, and thus it is suggested that Cadomia was in close proximity to West Africa by c . 580 Ma. In contrast, the main age groups of detrital zircon from the Neoproterozoic Avalon terrane are Mesoproterozoic and there is a distinct gap of ages between 2.40 and 2.05 Ga. These significant differences suggest that the two terranes were in different locations relative to major Gondwanan cratons in latest Neoproterozoic time.

Heavy-mineral, mineral-chemical and zircon-age constraints on the provenance of Triassic sandstones from the Devon coast, southern Britain

“…Given that their sources lay to the south on the basis of a variety of other provenance indicators, most notably the presence of fossiliferous pebbles of Armorican aspect, the dominance of the late Neoproterozoic group indicates that the Cadomian basement (as found, for example, in the Channel Islands and northern France) was the main source. The Cadomian granitoid basement rocks are believed to have formed in two phases from ~615 Ma to ~540 Ma (Samson et al, 2005). U-Pb zircon dating of the Cadomian granitoids of La Hague, Normandy, indicates two phases of magmatism, an earlier one between 620 Ma and 608 Ma and a later one between 583 Ma and 572 Ma (Samson et al, 2005).…”

U–Pb zircon ages (SHRIMP) for Cadomian and Early Ordovician magmatism in the Eastern Pyrenees: New insights into the pre-Variscan evolution of the northern Gondwana margin

“…In recent years, the development of isotopic geochemistry and the improvement in geochronological methods have made great strides in the reconstruction of the Cadomian orogen and its geodynamic evo lution and in the transition of the Cadomian to the Variscan cycle in the European realm (e.g., Stampfli et al, 2002;Linnemann et al, 2004;Samson et al, 2005;Gerdes and Zeh, 2006). In this regard, the Iberian Massif has played a major role for three main reasons: (i) good pre servation of pre-Variscan sediments, unaffected or affected by very low grade metamorphism, (ii) fairly complete stratigraphic sequences with thick Precambrian series, and (iii) the presence of volcanic and plutonic rocks emplaced in several stratigraphic levels at different times and with diverse geochemical signatures (Nagler et al, 1995;Femandez Suarez et al, 1998;Valladares et al, 2002;Bandres et al, 2004;Rodrtguez-Alonso et al, 2004;Silva and Pereira, 2004;Dlaz Garda, 2006 and references therein).…”

A new, high precision U–Pb date from the oldest known rocks in southern Britain

“…Alternative palaeogeographic reconstructions (e.g. Samson et al 2005;Strachan et al 2007) suggest that Avalonia was further around the Gondwanan margin, adjacent to the Amazon Craton, during Late Neoproterozoic times. This region is in part distinguished from the West African Craton by the presence of Mesoproterozoic belts ranging from around 1.6 to 1.0 Ga in age (e.g.…”