Neoproterozoic deformation in the Radok Lake region of the northern Prince Charles Mountains, east Antarctica; evidence for a single protracted orogenic event

Ion microprobe dating of structurally constrained felsic intrusives indicate that the rocks of the northern Prince Charles Mountains (nPCMs) were deformed during a single, long-lived Neoproterozoic tectonic event. Deformation evolved through four progressively more discrete phases in response to continuous north-south directed compression. In the study area (Radok Lake), voluminous granite intrusion occurred at similar to 990 Ma, contemporaneous with regionally extensive magmatism, peak metamorphism, and sub-horizontal shearing and recumbent folding. Subsequent upright folding and shear zone development occurred at similar to 940 Ma, while new zircon growth at similar to 900 Ma constrains a final phase of deformation that was accommodated along low-angle mylonites and pseudotachylites. This final period of deformation was responsible for the allochthonous emplacement of granulites over mid-amphibolite facies rocks in the nPCMs. The age constraints placed on the timing of deformation by this study preclude the high-grade reworking of the nPCMs as is postulated in some of the recent literature. Furthermore, 990-900 Ma orogenesis in the nPCMs is at least 50 Myr younger than that recognised in other previously correlated Grenville aged orogenic belts found in Australia, east Africa and other parts of the Antarctic. This distinct age difference implies that these belts are probably not correlatable, as has been previously suggested in reconstructions of the supercontinent Rodinia. (C) 2000 Elsevier Science B.V. All rights reserved.