The Amery Oasis, Northern Prince Charles Mountains
The Amery Oasis of the northeastern Prince Charles Mountains is a deglaciated area located at the approximate point where the Lambert Glacier merges with the Amery Ice Shelf. It is bordered to the west by the Loewe, Manning and McLeod Massifs, to the east by Jetty Peninsula, comprising the Else and Kamenistaya Platforms and McKelvey Ledge, and to the south by Flagstone Bench which is itself bounded by a tributary of the Lambert Glacier. The main feature of this area is Beaver Lake, a 50 km long, 25 to 30 km wide ice-covered lake occupying the centre of the oasis. Although Beaver Lake is located approximately 250 km from the open waters of Prydz Bay, it is situated at sea level and subject to tidal influxes beneath the Amery Ice Shelf. Radok Lake, a smaller lake situated within the McLeod Massif to the southwest, is the deepest (~350m) known lake on the Antarctic continent and the only known freshwater lake to host a floating ice tongue glacier, the Battye Glacier. Radok Lake drains into Beaver Lake via the fluvially cut, 6 km long, Pagodroma Gorge, the eastern half of which hosts an estuarine environment as a result of backwash from fluctuating water levels in Beaver Lake.
In the Amery Oasis region, basement Precambrian metamorphic rocks, representing part of the Proterozoic mobile belt of the East Antarctic Shield, are only exposed along the western side of Radok Lake and on the northeastern side of Beaver Lake, the latter along the Kamenistaya and Else Platforms of Jetty Peninsula. These basement rocks are considered to derive from both igneous and sedimentary precursors, and to have undergone a low to medium pressure granulite facies metamorphic event, accompanied by at least two deformational episodes, at ~1000ma. Subsequent retrograde metamorphism produced amphibolite facies mineral assemblages and was accompanied by at least one episode of folding.
The remainder of the Amery Oasis area is dominated by the Amery Group sedimentary succession, comprising late Paleozoic to early Mesozoic fluviatile strata which are thought to be down-faulted against the basement metamorphic rocks along the NNE-trending Amery Fault. This fault is inferred to pass through Radok Lake and forms the western boundary of the Beaver Lake Sub-graben, a western extension of the Lambert Graben system. Glacigene deposits of Cenozoic or younger age also occur in this area, forming an irregularly distributed cover sequence, up to 400m thick, of semi-lithified tillite, the Pagodroma Tillite, which is thought to be predominantly Miocene or Pliocene in age.
Both the Proterozoic and Paleozoic strata in the Amery Oasis area are intruded by Mesozoic (140 to 150ma) alkaline mafic and ultramafic intrusive bodies which host a range of mantle xenoliths, including garnet and spinel lherzolites, garnet-free dunites, harzburgites and wehrlites.
Simplified geological map of the Amery Oasis area, northern Prince Charles Mountains, East Antarctica (from Cantrill et al., 1995).
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