Single-zircon dating by step-wise Pb evaporation: Comparison with other geochronological techniques applied to the Hercynian granites of Corsica, France

Abstract

The Corsican Batholith provides an opportunity to test the single-zircon evaporation technique developed by B. Kober for Hercynian times. In this paper we attempt to clarify the method of calculating²⁰⁷Pb^*/²⁰⁶Pb^* ages and errors. The significance of the²⁰⁷Pb^*/²⁰⁶Pb^* ages are discussed with particular reference to the determination of the crystallization age of plutons. Zircon morphology is clearly an important criterion in selecting grains for analysis. Geological relations in the example that we are using are firmly established, enabling discussion of the²⁰⁷Pb^*/²⁰⁶Pb^* model age in the light of previous age determinations using other methods (RbSr,⁴⁰Ar/³⁹Ar and conventional UPb).

We interpret the well-defined322±12-Ma²⁰⁷Pb^*/²⁰⁶Pb^* age as the time of the crystallization of the U₁, MgK rocks. This is in good agreement with RbSr ages of the younger units U_2a and U_2b (312±9and290±6Ma, respectively).

Lead model ages on single-zircon crystals can be very precise and can give geologically more meaningful ages than those given by other methods, including the bulk-fraction conventional UPb method. The problem of episodic loss of radiogenic Pb can be avoided, making the grain concordant, and inherited grains or cores are easily detected.