Source variability in a single graniticpluton : Example from the St SylvestreLeucogranite complex

International audienceThe Upper carboniferous Variscan St Sylvestre Leucogranite Complex(SSLC), located in the western Massif Central (Limousin, France) iscomposed of four main granitic facies : a biotite-only facies (Brame),a two-mica facies (St Sylvestre) ; a coarse grained two-mica facies (StGoussaud) ; a fine grained two-mica facies (Châteauponsac) emplacedas sills within the Brame facies.We studied magmatic and inherited zirconsusing U/Pb datations and Lu/Hf isotopic signature. Even thoughsome zircons present cases of lead loss and/or common lead, concordantmagmatic ages provide overlapping ages for each different faciesbetween 3283 and 3273 (St Sylvestre facies) and 3203 Ma (Châteauponsac).The Brâme facies confirms an existing age of 3243 Maand zircons from the St Goussaud facies gives a Discordia with a upperintercept at 32713 Ma. Inherited zircons and Hf isotopes revealdifferences of sources between the facies. Despite age uncertainties onsingle zircon, a eHf(t) vs. time diagram reveals different patterns foreach granitic facies. The Model ages (TDM2) for the differentiationof crustal to the depleted mantle provide a range from 1.0 to 2.5 Gafor each phase. However, the ages of inherited zircon recorded by eachphase argue in favour of different sources. The Brâme and Châteauponsacfacies would be related to a source with rather homogeneous U/Pbages only ranging between 500 and 540 Ma. On the contrary, the StSylvestre facies provide a significantly wider range of inherited agesbetween 480 and 660 Ma. Unfortunately the St Goussaud facies doesnot provide sufficiently good data to be interpreted in a similar way.These results may suggest that the St-Sylvestre leucogranitic complexis produced from the melting of a heterogeneous Cadomian crust mostlycomposed of orthogneiss derived from a granitic protolith of Cambrianage and Paragneisses derived from sediment deposited in a Cadomianbasin collecting crustal material formed between Brioverian and Cambrian