THE EDIACARAN-PERMIAN DETRITAL ZIRCON RECORD IN THE NORTHERN MARGIN OF GONDWANA (IBERIA): TRACING ACCRETION, DISPERSION AND COLLISION INVOLVING ENIGMATIC TERRANES

The north Gondwanan passive margin sequence of the Iberian Massif is one of the most complete and well-studied Ediacaran-Paleozoic sections in the world. Detrital zircon U-Pb age analysis of 20 samples spanning each geologic time period from the Ediacaran through Permian have provided a consistent set of group ages, mainly Ediacaran-Cryogenian (ca. 0.55-0.8 Ga), Tonian-Stenian (0.85-1.2 Ga), Paleoproterozoic (ca. 1.8-2.2 Ga) and Archean (ca. 2.5-3.3 Ga), with large variations in relative age proportions recording provenence variations over 300 My. Detrital zircon data 1) record the transition from active volcanism of the Cadomian-Avalonian arc to stable platform following the separation of Avalonian terranes and the opening of the Rheic Ocean, and 2) track the exhumation of different rock suites over the course of Variscan orogeny and the development of the Ibero-Armorican Arc. Variations in detrital zircon populations through the Paleozoic reflect changes in source areas and/or variation inproportions of recycled sediments along the northern Gondwanan margin. A high proportion (up to ca. 55%) of Tonian-Stenian age zircons in Ordovician, Silurian and Devonian sedimentary rocks that could not have been sourced via recycling from the underlying strata may provide record of an otherwise unpreserved Tonian-Stenian arc terrane largely exposed within the NE African realm (in or around the Arabian Nubian shield) throughout the Paleozoic. The Ediacaran to Permian clastic sedimentary rocks of NW Iberia and their detrital zircon populations are witness to a complete Wilson cycle from the Ediacaran subduction to the creation of an ocean basin (the Rheic) by break-off along an older suture (Ediacaran arc-continent accretionary boundary), widening of the (Rheic) ocean basin from the Ordovician through the Early-Middle Devonian, initiation of convergence and closure of the Rheic beginning in Middle-Late Devonian times, collision, exhumation, and finally formation of the Ibero-Armorican oroclinal arc and related lithospheric delamination.