Rb‐Sr, Sm‐Nd and Pb‐Pb geochronology of ancient gneisses from Mt Narryer, Western Australia

Abstract

New Rb‐Sr, Sm‐Nd and Pb‐Pb data are presented from banded gneisses in the Mt Narryer region of the Western Gneiss Terrain, together with Rb‐Sr and Sm‐Nd data from cross‐cutting granite sheets. The Meeberrie Gneiss, which previously gave a Rb‐Sr isochron age of 3348 + 43 Ma and an initial ratio of 0.7037 + 0.0005, has given a Pb‐Pb age of 3357 ± 70 Ma, whilst an additional suite of the same gneisses collected to the SW of the original samples gives a Rb‐Sr age of c. 3100 Ma with an initial ratio of c. 0.705. Deformed sheets of recrystallized granite which intrude the Meeberrie Gneiss give a Rb‐Sr age of 2579 + 122 Ma with an initial ratio of 0.7143 ± 0.0092. Sm‐Nd analyses on samples of the Meeberrie Gneiss give T_CHUR ages of 3710 ±30 Ma and 3620 + 40 Ma, which support the previously determined model age of 3630 ± 40 Ma. An additional T_CHUR of 3540 ± 30 Ma for a sheet of Dugel Gneiss within the Meeberrie Gneiss coincides with a previously reported value of 3510 ± 50 Ma for another sample of the Dugel Gneiss. Two cross‐cutting granite sheets give T_CHUR ages of 3120 ± 30 Ma and 3070 ± 40 Ma. The geochronological data in this paper support and extend the isotopic evidence previously reported from the banded gneisses of the Mt Narryer region, and confirm that the Western Gneiss Terrain is the oldest known major segment of sialic crust in the Yilgarn Block, Western Australia.