Abstract
Osmium isotopes, whole rock and mineral geochemical data from peridotite xenoliths from two Miocene McMurdo Volcanic Group cinder cones in the Transantarctic Mountains (TAM) in Southern Victoria Land, Antarctica, reveal that the underlying mantle preserves evidence for major mid-Proterozoic lithosphere formation despite the crust being dominated by late Neoproterozoic-Ordovician (~0.65–0.47 Ga) rocks. The Hooper Crags xenolith suite is dominated by harzburgites with highly refractory olivine Mg# (up to 92.3) and depleted bulk rock major and platinum group element + Re abundances, with 187Os/188Os ratios indicating depletion in the mid-Proterozoic. Pipecleaner Glacier xenoliths, 18 km distant, are lherzolites with olivine Mg# (<91) and fertile major and platinum group element abundances, with Os isotope abundances defining an aluminochron that also indicates mid-Proterozoic depletion. Although exposed crust along this portion of Antarctica reveals only minor evidence for Proterozoic magmatism, the major episode of lithosphere formation indicated by the Os isotope data is supported by published bulk rock Sm-Nd isotope and zircon εHf mantle model ages of Neoproterozoic to Ordovician plutonic rocks. The heterogeneous circum-cratonic mid-Proterozoic mantle under Southern Victoria Land has therefore persisted on a Ga timescale, including through the formation and destruction of Rodinia and Gondwana supercontinents as well as extensive crustal melting and emplacement of the Ferrar large igneous province. This longevity may be due to the thick (>250 km) East Antarctic Craton lithosphere shielding the immediately adjacent circum-cratonic mantle from being affected by convective asthenosphere-driven erosion. This contrasts with mantle lithosphere accreted distally to the East Antarctic Craton (represented by the now-detached Zealandia continent), which did not attain extreme thickness and has therefore been more susceptible to tectonic reworking and lateral translation.