The Napier Complex of Enderby and Kemp Lands is predominantly composed of gneisses metamorphosed at ca. 2.8 Ga and/or ca. 2.5 Ga at high to ultra-high temperature (Harley et al., 2019). Protolith ages up to 3.75 Ga are recorded, with a few zircon ages approaching 4.0 Ga in felsic orthogneiss of the Tula Mountains at Mount Sones and Gage Ridge (Harley et al., 2019, Kusiak et al., 2013) and east of Tula Mountains at Mount Jewell and Budd Peak (Król et al., 2020) in Enderby Land and in adjacent Kemp Land at Aker Peaks (Belyatsky et al., 2011, Kusiak et al. 2021). The relationship between these isolated outcrops of Eoarchean crust is little understood and the aim of this study is to determine the extent of ancient crust across the Napier Complex in order to shed new light on the source and conditions prevailing on the early Earth. Geochemical diversity is demonstrated in Eoarchean protoliths from the Tula Mountains, where they can be subdivided into Y-HREE-Nb-Ta depleted and undepleted groups (Krol et al., 2020, 2022). Medium to high-pressure melting of basaltic crust can account for Y-HREE-Nb-Ta depletion in granitoids, whereas undepleted granitoids can be generated by low-pressure melting. The lack of a simple correlation between protolith age and geochemical type is an indication that magmatism throughout the Archean involved different sources and processes, including re-melting and recycling of crustal components, rather than just the formation of juvenile crust. The identification of Eoarchean crust in both Enderby and Kemp Lands, at localities ca. 300 km apart, may indicate that ancient crust is widespread throughout the complex. Most likely the Napier Complex represents a composite of continental crust formed at different times during the Archean that was assembled as late as 2.5 Ga.

Reference(s)

Belyatsky, BV, Rodionov, NV, Antonov, AV, Sergeev, SA, 2011, Doklady Earth Sciences, 438, 770-774.

Harley, SL, Kelly, N., Kusiak, MA, 2019, Earth's Oldest Rocks, Elsevier, pp. 865-897. 

Król, P, Kusiak, MA, Dunkley, DJ, Wilde, SA, Yi, K, Lee, S., Kocjan, I. 2020, Gondwana Research, 82, 151-170. 

Król, P, Kusiak, MA, Dunkley, DJ, Wilde, SA, Yi, K, Whitehouse, MJ, Lee, S, Harley, SL, 2022. Precambrian Research 370: 106530. 

Kusiak, MA, Dunkley, DJ, Wilde, SA, Whitehouse, MJ, Kemp, AIS, 2021. Gondwana Research, 93: 227-241. 

Kusiak, MA, Whitehouse, MJ, Wilde, SA, Dunkley, DJ, Menneken, M, Nemchin, AA, Clark, C, 2013, AJS, 313, 933-967.