Tholeiitic and high‐Mg mafic/ultramafic sills in the Eastern Goldfields Province, Western Australia: Implications for tectonic settings

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Abstract
Layered and differentiated mafic/ultramafic sills are an important component of greenstones in the Eastern Goldfields Province and can be grouped into tholeiitic and high‐Mg associations. These associations can be further subdivided according to geochemical parameters and order of crystallization of the main mineral phases. The distribution of sills is consistent with models that envisage the Kalgoorlie Terrane (abundant komatiitic and MORB‐like tholeiitic volcanics and intrusive equivalents) as an ancient continental margin basin. Although mafic volcanic rocks and sills encompass a similar range of compositions, chemostratigraphic trends for sills in the Ora Banda domain oppose those of the enclosing volcanic rocks. Plagioclase‐rich (leucodolerite) sills in the Melita area (Gindalbie Terrane) have alumina‐rich, TiO2‐poor compositions comparable to island‐arc tholeiites and were derived by partial melting of an enriched mantle source. The geochemistry and distribution of sills is not compatible with a simple, craton‐scale plume model for the formation of the greenstone belts.