Multiple early Paleozoic volcanic events at the northern Gondwana margin: U-Pb age evidence from the Southern Variscan branch (Sardinia, Italy)

In Sardinia, one of the southernmost remains of the European Variscan belt, a crustal section through different Gondwanan paleodomains is largely preserved. Laser ablation ICP-MS U-Pb ages on undoubtedly igneous sites of the zircons were determined on the Lower Palaeozoic volcanic rocks, constrained by defined field relationships, thus evidencing three subsequent volcanic events:I.Intermediate and felsic (491.7 \ub1 3.5\ua0Ma \uf7 479.9 \ub1 2.1 Concordia ages) transitional volcanic rocks embedded within a Cambro-Ordovician terrigenous succession, that occurs with continuity in external and inner nappes, bounded to the top by the Sardic unconformity.II.This Cambrian-Lower Ordovician succession is cut by calc-alkalic rhyodacites, which yielded a Concordia age of 465.4 \ub1 1.4\ua0Ma, confirming their pertinence to the huge, bimodal Mid-Ordovician arc volcanism, commonly interpreted as the widespread marker of the Rheic ocean subduction.III.Alkalic metaepiclastites in the external nappe, within the post-Caradocian transgressive sequence, dated at 440 \ub1 1.7\ua0Ma, likely related to rifting and collapse of the Mid-Ordovician volcanic arc. In the reshaped Lower Palaeozoic stratigraphy of Sardinia, the timing of the early steps of the Variscan Wilson cycle can be inferred. \ua9 2009 International Association for Gondwana Research