The Annandagstoppane Granite, East Antarctica: Evidence for Archaean Intracrustal Recycling in the Kaapvaal-Grunehogna Craton from Zircon O and Hf Isotopes

Abstract

The Grunehogna Craton (GC, East Antarctica) is interpreted as part of the Archaean Kaapvaal Craton of southern Africa prior to Gondwana breakup. The basement of the GC is exposed only within a small area comprising the dominantly leucocratic Annandagstoppane (ADT) S-type granite. The granite (and hence the craton) has been dated previously only by Rb–Sr and Pb–Pb mica and whole-rock methods. Here, the crystallization age of the granite is determined to be 3067 ± 8 Ma by U–Pb dating of zircon. This age is coeval with that of granitoids and volcanic rocks in the Swaziland and Witwatersrand blocks of the Kaapvaal Craton. Inherited grains in the ADT granite have ages of up to 3433 ± 7 Ma, and are the first evidence of Palaeoarchaean basement in Dronning Maud Land. The age spectrum of the inherited grains reflects well-known tectono-magmatic events in the Kaapvaal Craton and forms important evidence for the connection of the GC to the Kaapvaal Craton for at least 2·5 billion years and probably longer. Whole-rock chemistry and zircon O isotopes demonstrate a supracrustal sedimentary source for the granite, and Hf model ages show that at least two or three crustal sources contributed to the magma with model ages of ∼3·50, ∼3·75 and possibly ∼3·90 Ga. The 3·1 Ga granites covering ∼60% of the outcrop area of the Kaapvaal–Grunehogna Craton played a major role in the mechanical stabilization of the continental crust during the establishment of the craton in the Mesoarchaean. Combined zircon Hf–O isotope data and the lack of juvenile additions to the crust in the Mesoarchaean strongly suggest that crustal melting and granite formation was caused by the deep burial of clastic sediments and subsequent incubational heating of the crust. Intracrustal recycling of this type may be an important process during cratonization and the long-term stabilization of continental crust.