Superimposed tectonic events at 2450 Ma, 2100 Ma, 900 Ma and 500 Ma in the North Mawson Escarpment, Antarctic Prince Charles Mountains

Abstract

The North Mawson Escarpment, in Antarctica's Prince Charles Mountains, forms part of a Palaeoproterozoic crustal complex which separates Archaean cratonic material to the south from Early Neoproterozoic and Early Palaeozoic metamorphic belts to the north. It consists of nappe-like masses of grey gneiss and metasupracrustal rocks that were subjected to repeated ductile deformation under upper amphibolite to lower granulite facies metamorphic conditions. In this paper, we report zircon U-Pb dating results that constrain the principal tectonothermal events to the periods 2490-2420 Ma, 2180-2080 Ma, 940-880Ma and 530-490 Ma. The magmatic precursors of volumetrically important grey gneiss were produced, and reworked at least partly, during the 2490-2420Ma and 2180-2080Ma events. The superimposition of these events is clearly documented by U-Pb ages from several composite zircons. The formation of associated metasupracrustals, possibly in a passive margin setting, occurred between the 2490-2420Ma and 940-880Ma events. Both grey gneiss and metasupracrustals were subsequently reworked during the 940-880Ma and 530-490Ma events, corresponding to the superposition of both the Rayner and Prydz Belts onto Palaeoproterozoic lithosphere of the Lambert Complex. Transposition and peak metamorphism preceded the intrusion of leucogranite dykes at 905Ma and, based on metamorphic zircon growth at around 930Ma in metapelitic schist, are related to the Rayner orogeny. It is suggested that the North Mawson Escarpmentwas assembled to most coastal regions of the Antarctic sector between 45 grades and 80 gradesE by at least 900 m.y. ago.