Journal Article

A Rare Glimpse of Paleoproterozoic Sub‐Arc Mantle: The Ussuit Peridotite, West Greenland

Zha, X., Szilas, K., Waterton, P., Gong, B., McIntyre, T., Pearson, D. G., Li, L.

2025

Overview

Mantle residues beneath Archean cratonic nuclei have been extensively studied, whereas less attention has been given to the mantle lithosphere beneath Proterozoic mobile belts that link these nuclei. Rare mantle tectonites within tectonic mélanges of Paleoproterozoic mobile belts provide information important to understanding the broader processes involved in the construction of the cratonic mantle lithosphere. Here we present mineral compositions, bulk‐rock major, trace, and platinum group elements, Re‐Os isotopes, and olivine oxygen isotopes from a Paleoproterozoic mantle tectonite in West Greenland–the Ussuit peridotite. The Ussuit peridotite was emplaced in the crust during the Nagssugtoqidian orogeny between 1,870 Ma and 1,775 Ma and preserves primary melt depleted characteristics that reflect >30% melting, for example, Al2O3 < 0.4 wt.%, Ti < 10 ppm, Lu/Yb > 0.25, and Mg #s up to 93. Cryptic signatures of hydrous melting, for example, spinel Cr #’s >65, Os/Ir ratios between 0.3 and 6, and supramantle olivine δ18O values, suggest that the high degree of melt depletion was partly inherited from a forearc or sub‐arc melting environment. Re‐Os isotopic systematics show melt depletion occurred at ∼2 Ga overlapping the juvenile oceanic arc crust that hosts the peridotites. This age coincides with a peak in the global production of juvenile cratonic lithosphere. Furthermore, the global Paleoproterozoic cratonic mantle has strong geochemical similarities with the Ussuit peridotites. It is suggested that subduction zone peridotites form key components of the Paleoproterozoic cratonic lithospheric mantle, creating a viscous, buoyant mantle lithosphere that contributed to the long‐term stability of the greater cratonic masses. Plain Language Summary The continental lithosphere formed over much of the Earth's history through the aggregative accretion of lithospheric fragments to “Archean cratonic nuclei.” Today, these nuclei are extant and formed >2.5 billion years ago and provide stable, above sea‐level platforms for continental growth. They have been extensively studied but little is known about the sutures and underlying mantle lithosphere holding together the cratonic nuclei of our modern continents. In this study, new geochemical and geochronological data are presented on a fragment of the mantle lithosphere—the Ussuit peridotite—that is hosted in a ∼1.8 Ga cratonic suture. The data imply that, like the Archean cratonic mantle lithosphere, the Ussuit peridotite formed via high degrees of mantle melting, >30%. More cryptic data imply that the rocks formed in the deep mantle portions of a volcanic oceanic arc. Geochemical and geochronological comparisons between the Ussuit peridotite and global, temporally related mantle peridotites are likewise similar. This implies that processes of melt depletion in the Ussuit peridotite may have been globally active at that time. As such, the lithospheric mantle underlying these ca. 1.8 Ga sutures may have components formed via similar processes to those of the Ussuit peridotite, shedding light on how our continental lithosphere grew through time. Key Points New geochemical and isotopic data shed light on the age and origin of a Paleoproterozoic orogenic peridotite—The Ussuit peridotite Re‐Os isotopic constraints indicate the Ussuit peridotite formed via melting of juvenile asthenospheric mantle around 2 Ga The new data suggest that Ussuit peridotite formed in an arc environment and coincident with a period of continental growth globally ca. 2 Ga

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Accretion / Components / cratonic mantle lithosphere / Depletion / Geochemistry / Geochronology / Lithosphere / mantle melting / Melting / Mineral composition / Nucleus / Olivine / orogenic peridotite / Orogeny / Oxygen isotopes / paleoproterozoic / Peridotite / Platinum / Precambrian / Rocks / Subduction / Subduction zones / Sutures / Systematics