Age, Inheritance, and Uplift History of the Old Woman-Piute Batholith, California and Implications for K-Feldspar Age Spectra

Abstract

Ion probe U-Pb zircon analyses yield a crystallization age of $$74 \pm 3 Ma$$ for both peraluminous and metaluminous plutons within the Old Woman-Piute batholith. These analyses reveal that about 50% of the zircons from the peraluminous Sweetwater Wash granite are restitic. Inherited zircons from this batholith yield ages ranging from older than 1800 Ma to ~1100 Ma, and most are similar in age to Proterozoic igneous rocks in the eastern Mojave Desert. $$^{40}Ar/^{39}Ar$$ hornblende ages from the metaluminous granodiorite are $$73 \pm 2 Ma$$, and mica ages from both plutonic series are $$70 \pm 2 Ma$$. K-feldspar age spectra yield age gradients with initial steps between 60 and 67 Ma and rise to plateau ages of $$70 \pm 2 Ma$$. Several K-feldspars from the granodiorite yield elevated "plateau" ages after 50% $$^{39}Ar$$ released that result from excess argon. Uplift rates as high as 4 mm/yr between 74 and 70 Ma are required by the narrow age range for all minerals.