Structural, Metamorphic and Uplift History of the Prince Charles Mountains

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From the abstracts of two of the referenced papers:

The low-temperature (ie less than ~120 degrees C) thermal history of the East Antarctic Shield has been assessed by apatite fission-track analysis of 42 Precambrian outcrop samples. Fission-track ages for these samples range from 466 plus or minus 20 Ma to 153 plus or minus 3 Ma and mean track lengths vary from 14.4 plus or minus 0.11 micrometres to 12.41 plus or minus 0.17 micrometres. The variability in the relationship between apatite fission track age and mean track length in data from various geographical regions suggests differences in styles of cooling during the Phanerozoic. Samples from the continental margin east of Prydz Bay are inferred to have cooled during the late Palaeozoic and early Mesozoic, between ~300 and 200 Ma, while samples from the Prince Charles Mountains and from the continental margin west of Prydz Bay are inferred to have cooled more recently in the Mesozoic, at ~150 Ma. Evidence for cooling during the Mesozoic at ~150 Ma is attributed to exhumation associated with the early stages of Gondwana break-up. Cooling during the late Palaeozoic and early Mesozoic may have been associated with an earlier phase of aborted rifting. These preliminary apatite fission track data suggest that the Lambert Graben has had an important influence on the Phanerozoic exhumation history of the East Antarctic Shield, with the region to the west of the Lambert Graben showing the greatest amount of uplift and erosion related to the early stages of Gondwana break-up.

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Thermobarometric studies on various granulite facies along the Prydz Bay coast, East Antarctica (73 degrees - 79 degrees E, 68 degrees - 70 degrees S), show that, at around 1100 Ma, during a late Proterozoic orogeny, the rocks of the Larsemann Hills suffered a lower pressure metamorphic peak than the surrounding areas. Along the Prydz Bay coast, the rocks affected by this event include parts of the Vestfold Hills block plus all of the Rauer Group, the Larsemann Hills and the Munro Kerr Mountains. The dykes in the south-west corner of the Vestfold Hills were recrystallized during this event with little deformation at temperatures not quite as high as in the areas further south-west (650 degrees C, 6.5 kbar), the Rauer Group was metamorphosed at 800 degrees C and 7.5 kbar, the Larsemann Hills at 750 degrees C and 4.5 kbar, and the Munro Kerr Mountains probably at around 850 degree C and 5 kbar. Retrograde equilibration in the different areas occurred during decompression to about 10 km depth in all areas, followed by isobaric cooling at this depth.

This paper shows that the peak metamorphism in the Larsemann Hills occurred at a pressure which is too low to have been the consequence of thermal relaxation of overthickened crust with normal mantle heat flow. Although other areas in Prydz Bay were metamorphosed at sufficiently high pressures so that their decompression paths are not inconsistent with a continental collision model, the inferred pre-metamorphic peak histories and the requirement of consistency with the Larsemann Hills, make it unlikely that collision followed by erosion-driven decompression is an appropriate model. We suggest that the thermal regime of the crust in the Larsemann Hills region was controlled by a perturbation in the asthenosphere, with magma invasion of the crust. We suggest that the 500 Ma event, represented in Prydz Bay by granitic outcrops at Landing Bluff and by several K/Ar ages from the Larsemann Hills area, was responsible for the final excavation of the terrane.

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Progress Code: completed

Statement: Values provided in temporal and spatial coverage are approximate only.