Sr and Nd isotopic investigations towards the origin of feldspar megacrysts in microgranular enclaves in two I-type plutons of the Lachlan Fold Belt, southeast Australia

Abstract

New Sr and Na isotopic cata are presented for several large feldspar crystals occurring in microgranular enclaves in the Swifts Creek and Bricle Track biutons, along with analyses of their host enclave grounamass and adjacent granitoid. In the Swifts Creek Pluton several previous studies have concluded that the microgranular enclaves represent admixed, more mafic and more primitive magmas, and new data presented here confirm that. Felaspar megacrysts in the microgranular enclaves have Sr and Nd isotopic signatures that are distinct from the surrounding enclave ground-mass and from other enclaves in the pluton and therefore cannot have crystallised in situ. Isotopic compositions of these feld..