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Diamonds in Antarctica? Discovery of Antarctic kimberlites extends vast Gondwanan Cretaceous kimberlite province

Gregory M Yaxley1, Vadim S Kamenetsky2, Geoffrey T Nichols3, Roland Maas4, Elena Belousova3, Anja Rosenthal5 and Marc Norman1

1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
2 ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart TAS 7001, AUSTRALIA
3 GEMOC, Department of Earth & Planetary Sciences, Macquarie University, NSW 2109, AUSTRALIA
4 School of Earth Sciences, University of Melbourne, Victoria 3010, AUSTRALIA
5 Bayerisches Geoinstitut, University of Bayreuth, GERMANY

Kimberlites are a volumetrically minor component of the Earth’s volcanic record, but are of great importance as the major commercial source of diamonds and as the deepest samples of the Earth’s mantle. They were predominantly emplaced into ancient, stable regions of continental crust, known as cratons, from ≈2000 Ma to ≈10 ka ago but are also known from continental rifts and mobile belts. Kimberlites have been reported from all major cratons on all continents except for Antarctica. We report here the first bona fide Antarctic kimberlite occurrence, from the northern Prince Charles Mountains, emplaced as a result of reactivation of the Lambert Graben during rifting of India from Australia-Antarctica. The samples exhibit the textural, mineralogical and geochemical features typical of Group I kimberlites from more classical localities. The ages of the nPCM kimberlites, based on radiometric dating (120 Ma), overlap with many kimberlites and related rocks from other localities on the Gondwanan continents. This discovery extends a 135-115 Ma Gondwanan kimberlite province, for the first time, into Antarctica. The kimberlites’ emplacement reflects tectono-magmatic processes associated with Cretaceous rifting between the India and Antarctica-Australia.

Figure 1. A-C – plain light photomicrographs of the Antarctic kimberlites showing porphyritic texture, and two generations of olivine (fragmented and euhedral), olivine alignment, and olivine rimmed by oxide crystals (Ti-magnetite, Cr-spinel and perovskite). Olivine (ol) crystals are set in a fine- to coarse-grained groundmass, consisting of phlogopite (phl), calcite (cc), perovskite (pr), apatite and magnetite.  D – backscattered electron image of zoned olivine crystal with euhedral inclusions of high-Ca (Cpx) and low-Ca (Opx) pyroxenes in the resorbed core (sample 77082).