U-Pb chronology on accessory minerals of the Velay anatectic dome (French Massif Central)

The U-Pb chronology of zircon, monazite and apatite from three samples of granite and gneiss from the S edge of the Velay dome has been studied. The earlier of two migmatization stages is constrained at 314 + or - 5 m.y. by the U-Pb data on abraded monazite from the leucosome part of a paragneiss; the later migmatization has been dated with monazites from the cordierite-bearing Velay granite at 301 + or - 5 m.y. Monazites from the paragneiss and the Velay granite even after an abrasion process are still discordant in the concordia diagram, and monazite from the third sample, an orthogneiss, reveal an unusual pattern with a reverse discordia. Zircons in each case demonstrate inheritance; even for the Velay granite where zircon fractions define a normal discordia pattern, single grain analyses reveal the presence of inherited lead. The apatites in all three samples yield an age of 289 + or - 5 m.y., which is interpreted as a cooling age during the uplift of the Velay region.