Precambrian History of the Pacific Mantle Domain: New Constraints from Woodsreef and Port Macquarie Serpentinized Spinel Harzburgites of the New England Orogen, Australia.

This article focuses on the petrographic, geochemical, and isotopic study of serpentinized spinel harzburgite mantle rocks from the early Cambrian Weraerai ophiolite mélange in the New England Orogen, eastern Australia, which represent fragments of the Paleo-Pacific oceanic lithosphere. Analyses indicate these mantle peridotites formed by 20–30% anhydrous partial melting at pressures ≥3 GPa and temperatures >1400°C, consistent with a mantle plume environment, likely related to supercontinent Nuna’s breakup and Rodinia’s assembly between 1.4 and 1.1 billion years ago. Two subgroups of samples were identified based on highly siderophile element (HSE) and osmium (Os) isotope data: a normal-Os group yielding melt depletion ages of 1.4–1.1 Ga, and a low-Os group showing evidence of Os loss through post-melting processes. The study suggests that this Mesoproterozoic depleted mantle domain was recycled into the Paleo-Pacific oceanic lithosphere formed around 530–505 Ma and later accreted to East Gondwana, highlighting mantle heterogeneity and plume-related processes in early Paleozoic oceanic lithosphere formation.