Australia: The Land Where Time Began
Antarctica – Early Opening, New Inferences and Consequences for the
The continental margins of Australia and Antarctica exhibit a very clear gravity anomaly on the satellite free-air gravity data. The detailed sinuosity seen in this first-order conjugate features are a perfect match for each other which suggests they are the signature of the initial continental breakup and mark the boundary between the continent and the ocean. Also, there is another, though weaker, pair of symmetrical gravity anomalies that have been identified oceanward. Considered as isochrones F and G, these anomalies have been dated tentatively to 128 Ma and 94 Ma. Over 3 sections of the margin precise reconstructions of pseudo-isochron F were achieved, which denoted the relative motion of Australia and East Antarctica, The Polda Block and East Antarctica, and Tasmania and West Antarctica. Tasmania and the Polda Block are transient microcontinents. Tasmania and Australia were reconstructed by Jacob & Dyment to align their linear eastern margin. When Australia, Tasmania and West Antarctica were reconstructed the eastern margin fitted a small circle with a radius of 15o with the western margin of the reconstructed Lord Howe Rise and Campbell Plateau, a transform motion between 128 Ma and 83 Ma is suggested. A gap between East and West Antarctica, that Jacob & Dyment suggest was probably filled by compressively deformed and thickened non-cratonic continental crust by the SW motion of East Antarctica and participation in the formation of the Transantarctic Mountains. It is suggested the initial extension between Australia and East Antarctica could possibly have been related to the formation of the Kerguelen hotspot, ~ 1000 km to the west. The style and localisation of both extensional and compressional deformations have probably resulted from the role played by the different rheology of cratons and orogenic terranes.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading