High-spatial-resolution SM-ND & U-PB and LU-HF & U-PB isotope geochemistry of monazite and zircon in the Old Woman- Piute Batholith, California

Abstract

The Old Woman-Piute Range Batholith (OWPB) in the Mojave Desert of south-eastern California is a suite of metaluminous and peraluminous Cretaceous granites that intrudes Proterozoic basement. The peraluminous Sweetwater Wash, Painted Rock and North Piute plutons were sampled to investigate geochemical heterogeneity. Zircon and monazite crystals were analysed for U–Pb & Lu–Hf and U–Pb & Sm–Nd isotopes, respectively, using the high-spatial resolution and the recently developed Laser Ablation Split Stream (LASS) approach. Inherited cores are widespread in zircon, limited in monazite, and yield U-Pb ages that range from 1800-1400 Ma, consistent with regional Proterozoic crustal building events. Zircon and monazite rims give a range of crystallisation ages between 70–75 Ma. The OWPB shows a large range in εHfi and εNdi in both inherited and magmatic populations, a characteristic that is derived primarily from the Proterozoic crustal source, but also influenced by the partial dissolution and preservation of inherited grains.