Prydz Bay

Prydz Bay near the Australian station of Davis comprises an Archaean terrain, the Vestfold Hills Block, that formed and stabilised around 2500 Ma ago, and a younger ~500Ma mobile belt that is identified in outcrops along the eastern coast of Prydz Bay, namely in the Rauer Group, Brattstrand Bluffs, Larsemann Hills and Bolingen Islands. Both the Vestfold Hills Block and the Prydz Bay terrains preserved evidence of at least five major periods of crustal accretion and high-grade deformation.

Archaean components in the Rauer Group, are 300-700 Ma older than the Vestfold Hills Block, indicating a separate Archaean evolution of both terrains. Juxtaposition occurred around 2500 Ma ago, because both terrains preserve evidence of a similar sequence of Palaeoproterozoic to Mesoproterozoic intrusive and shearing events that can be correlated across the boundary of the mobile belt. From this correlation it is inferred that a period of high-grade metamorphism affected the mobile belt sometime between 1750-1380 Ma. The tectonic significance of this event is not clear.

The evolution of Prydz Bay from 1250 Ma to 500 Ma can be explained in terms of an extended extensional-compressional tectonic cycle that led to the formation of the mobile belt. Emplacement of N-S dykes in the Vestfold Hills Block around 1245 Ma was coeval with the opening and infill of a sedimentary basin along the axis of the later mobile belt. This was followed by the emplacement of 1000 Ma old felsic to intermediate intrusives, which could have been generated during initial closure of the sedimentary basin.

Early Palaeozoic tectonism at approximately 500 Ma (generally referred to as the Pan African Event) formed a belt of high-grade rocks that can be correlated from Prydz Bay into the southern Prince Charles Mountains. The Prydz Bay mobile belt is characterised by families of composite progressive structures that can be grouped on the basis of a common lineation direction and sense of non-coaxial flow. Two main structural regimes occur in the mobile belt; early structures are characterised by E-plunging lineations, compression, relatively high metamorphic pressures (12-6 kbar) and decompression textures related to 20-25 km uplift, later structures are characterised by SW-plunging lineations, extension, lower metamorphic pressures (6-3 kbar) and uplift to 10 km or less, followed by cooling. Both structural regimes formed in response to E-W compression resulting in N-S extensional collapse of the upper crust.