Original paper

Lead inheritance phenomena related to zircon grain size in the Variscan anatectic granite of Ax-les-Thermes (Pyrenees, France)

Delaperrière, Eric; Respaut, Jean-Patrick

European Journal of Mineralogy Volume 5 Number 2 (1993), p. 341 - 352

49 references

published: Apr 27, 1993
manuscript accepted: Nov 27, 1992
manuscript received: Jul 3, 1992

DOI: 10.1127/ejm/5/2/0341

BibTeX file

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Abstract The Ax-les-Thermes granite is a Variscan leucogranite of anatectic origin, intrusive into the gneisses of the Axial Zone of the Pyrenees. We studied this granite using the U-Pb method on zircon fractions and the direct-evaporation single-zircon-grain method. In the concordia diagram, the experimental points define two arrays, depending on the size of the zircon grains: a reverse discordia for the coarse zircons and a normal discordia for the fine ones. However the ages obtained with these discordias (at 350 and 370Ma) are inconsistent with previous Rb-Sr dating at 300 Ma and with field evidence for a syn- to late-Variscan intrusion (ca. 300 Ma). This exceptional pattern may be caused by a combination of different processes including the coexistence of relict and newly crystallized zircons and involving inheritance of old radiogenic lead and various stages of lead loss


U-Pb geochronologyzirconlead inheritanceanatexis granite