The geological composition of the hidden Wilhelm II Land in East Antarctica: SHRIMP zircon, Nd isotopic and geochemical studies with implications for Proterozoic supercontinent reconstructions

摘要

In this paper we present new U-Pb zircon age, Sm-Nd isotopic and chemical composition data for rocks cropping out in a few isolated nunataks in Wilhelm II Land in East Antarctica, namely Mirny oasis, Mt Brown and Gaussberg volcano, which contains xenogenic crustal material. These outcrops were subjects of geological investigations during the Soviet Antarctic Expedition of 1956-1957. Our data show that this region is underlain by a uniform crust which experienced a high-grade metamorphic event at ca 980-920 Ma, co-eval with the Rayner Orogeny in Kemp Land and the northern Prince Charles Mountains. Extensive indications of a ca 500 Ma event in coastal areas (granitoid intrusions in Mirny oasis and inherited zircons found in Gaussberg volcano), together with the lack of indications of this age in Mt Brown, point to a concentration of ca 500 Ma processes (roughly co-eval with the Prydz Orogeny) in the coastal part of Wilhelm II Land and their attenuation inland. We also determined a ca 1480 Ma age for a mafic magmatic protolith in Mt Brown which may be correlated with roughly co-eval orthogneiss in the Bunger Hills area. These observations suggest the conjugate positions of these crustal blocks in the early Mesoproterozoic and argue against a Cambrian suture running between them. In Gaussberg volcano a range of zircon Pb-206/U-238 ages of ca 320 Ma, ca 500 Ma, ca 980 Ma, and ca 2000-1800 Ma has been determined. The presence of ca 2000-1800 Ma zircons indicates involvement of mid-Palaeoproterozoic rocks in the structure of Wilhelm II Land. This argues for possible conjugation of this region with other East Antarctic blocks experienced the Palaeoproterozoic tectonic evolution and which have been considered to comprise the Mawson palaeocontinent. (C) 2014 Elsevier B.V. All rights reserved.