Multiple early Paleozoic volcanic events at the Northern Gondwana Margin : U-Pb evidence from the southern Variscan Branch (Sardinia Italy)

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±3.5 Ma÷479.9±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±1.4 Ma, 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±1.7 Ma, 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.