2.8 Ga Subduction-related magmatism in the Youanmi Terrane and a revised geodynamic model for the Yilgarn Craton

Abstract

New studies in the central and southern parts of the Murchison Domain in the Youanmi Terrane, western Yilgarn Craton, reveal previously unidentified igneous rock types in addition to boninitic occurrences similar to those found in the northern part of the domain. New results also allow for a re-assessment of a volcanic suite previously described as examples of a “Karasjok type” of komatiite. The rocks are most plausibly examples of arc picrites, specifically of the type found in ophiolite settings. In addition to boninitic rocks and picrites, this study identified remobilized olivine-cumulate rich lavas that resemble examples found in the Troodos and Othris ophiolites. Examples of REE enriched high magnesium andesites exhibit pronounced high field strength element depletions on normalized plots combined with mantle-like Nb/Zr ratios. The rocks chemically resemble Phanerozoic examples of enriched boninites and their signatures are distinct from those typically attributed to crustal contamination of mantle plume magmas. Intrusions of the ∼2792 Ma Warriedar Suite have compositions analogous to those of post-Archean Alaskan Intrusive complexes and were likely derived from subduction-modified sub-cratonic mantle. The new observations can be accounted for in a geodynamic scenario involving subduction along the western Yilgarn margin at ∼2800 Ma. Similarities with the contemporaneous Superior Province raise the possibility that the nuclei of the two cratons were closely associated at this time. © 2019 Elsevier B.V.