Lead isotopic evidence for deep crustal-scale fluid transport during granite petrogenesis

Abstract

Lead isotopic compositions are reported for K-feldspars from the Bega and Berridale batholiths in the Paleozoic Lachlan Fold Belt (LFB) of southeastern Australia. In marked contrast to the wide range in initial Nd (ε{lunate}Nd = +3 to -9.2), the feldspars exhibit an extremely limited variation in Pb isotopic composition with 206Pb 204Pb of 18.14 to 18.18, 207Pb 204Pb of 15.58 to 15.63 and 208Pb 204Pb of 38.04 to 38.21. This variability is less than that observed in modern intra-oceanic island arcs such as the Marianas. Despite the very limited range of Pb isotopic compositions, there are still good correlations with ε{lunate}Nd values as well as between single-stage Pb-Pb and TNd model ag..