Adding pieces to the puzzle: Episodic crustal growth and a new terrane in the northeast Yilgarn Craton, Western Australia

Abstract

New geological mapping and geochronology in the northeast Yilgarn Craton has changed our geological understanding of this region. The Yilgarn Craton had previously been divided into a series of terranes, with the easternmost Eastern Goldfields Superterrane separated from the Youanmi Terrane, which forms the core of the protocraton, by the Ida Fault zone. The Eastern Goldfields Superterrane was subdivided into the western Kalgoorlie, central Kurnalpi, and eastern Burtville terranes, with the latter, easternmost terrane the focus of the new field mapping and geochronology. Four main episodes of greenstone crustal growth have been recognised in the northeast Yilgarn Craton: ca 2970–2910 Ma, ca 2815–2800 Ma, 2775–2735 Ma, and ca 2715–2630 Ma. Rather than a single Burtville Terrane, as previously proposed, the distribution of greenstone magmatism reveals a previously unrecognised young (<2720 Ma) Yamarna Terrane in the northeast corner of the craton. The Yamarna Terrane is separated from the older (>2735 Ma) redefined Burtville Terrane by the Yamarna Shear Zone, which is now regarded as a terrane boundary. The correlation of lithologies and ages of magmatism in the northeast Yilgarn Craton with the rest of the craton indicates that the Burtville Terrane has affinities with the Youanmi Terrane that forms the nucleus of the craton, whereas the Yamarna Terrane has affinities with the Kalgoorlie Terrane in the west of the Eastern Goldfields Superterrane.The Burtville and Youanmi terranes shared a common history from ca 2970 Ma until ca 2720 Ma, when regional extension accommodated deposition of the Kambalda Sequence in the Kalgoorlie Terrane. It appears that extension also occurred along the Yamarna Shear Zone after ca 2720 Ma, accommodating the deposition of greenstones in the Yamarna Terrane. Like the Kalgoorlie and Kurnalpi Terranes, the Yamarna Terrane contains inherited zircon and local older rocks. This suggests that the ca 2720 Ma extension did not result in widespread rifting and the formation of extensive oceanic crust. Rather, there was thinning of older crust that extended right across the current Yilgarn Craton.