Early archaean narryer gneiss complex, Yilgarn Craton, Western Australia

Abstract

An outline is given of the Narryer Gneiss Complex that forms the northwest part of the Yilgarn Craton. It consists of two major groups of quartzo-feldspathic gneiss: Meeberrie gneiss mainly derived from ∼ 3680 Ma monzogranite, and Dugel gneiss derived from ∼ 3400 Ma syenogranite and monzogranite. The gneisses contain inclusions of an ∼ 3730 Ma layered gabbro-anorthosite intrusion called the Manfred Complex and are tectonically interleaved with metasedimentary rocks, mainly quartzite and banded iron formation. The complex was deformed and metamorphosed in granulite facies about 3350-3300 Ma ago. The gneiss complex is in tectonic contact with a granite-greenstone terrain that forms most of the Yilgarn Craton. These terrains were juxtaposed, intruded by sheets of granite, intensely deformed and metamorphosed about 27002600 Ma ago. The Narryer Gneiss Complex is a substantial addition to known areas of early Archaean crust. In contrast to most previously described terrains of this antiquity, it is largely derived from granite, it is devoid of metavolcanic rocks, and metasedimentary rocks are predominantly siliceous. The latter contain detrital zircons with U-Pb ages of 4275-4000 Ma, far older than any known terrestrial rocks. These features all suggest the former presence of a substantial amount of very old sialic crust (> 3700 Ma) and that remnants of it may still survive in this vast complex.