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Victoria Land Basin

I-Terror Rift-

I-Terror Rift-

late Cenozoic intrusives possible Beacon Supergroup rocks

Fig. 5.16. Profile A across the Eastern Basin (after Hinz and Block, 1983). Major unconformities are marked with interpreted ages. Profile B across the Central Trough (after Hayes and Davey, 1975). Profile C across the Victoria Land Basin (after Cooper and Davey, 1985).

late Cenozoic intrusives possible Beacon Supergroup rocks

Fig. 5.16. Profile A across the Eastern Basin (after Hinz and Block, 1983). Major unconformities are marked with interpreted ages. Profile B across the Central Trough (after Hayes and Davey, 1975). Profile C across the Victoria Land Basin (after Cooper and Davey, 1985).

Iselin Bank, which lies between the eastern and western Ross Sea continental margins, is continental in character (Hayes and Davey, 1975). It forms part of a structural boundary between the east and west Ross Sea (the line of basement highs from the ice shelf ot Iselin Bank) and may also have existed in pre-Tertiary times as it coincides with the junction of the New Zealand and Australian continental blocks in Gondwana reconstructions (e.g., Grindley and Davey, 1982).

The Campbell Plateau

The Campbell Plateau is a continental margin plateau laying to the southeast of New Zealand (Fig. 5.17) at a depth of about 1,000 m. The basement rocks underlying the south and west Campbell Plateau at Campbell Island and in drillholes (Fig. 5.17) comprise schists similar to the Palaeozoic schists and gneisses of the Transantarctic Mountains and Tasmania (Anderton et al., 1982). During the Early to Mid Mesozoic, deep sedimentary deposits developed seaward of these Gondwana coast sequences. The associated volcanics and accreted ophiolites occurring in these thick flysch sequences indicate the existence of a convergent subducting margin during Permian and Jurassic times. Exposures of this partially- to fully-metamophosed belt of geosynclinal fore-arc sediments are known in the Southern Alps of New Zealand, Marie Byrd Land, Ellsworth Land and the Antarctic Peninsula. They constitute basement rocks on the northern Campbell Plateau and on the Chatham Rise.

New Zealand started to rift from Antarctica in the Mid Cretaceous, thinning the crust and giving rise to deep grabens forming a number of large depocentres parallel to the axes of rifting (Fig. 5.17). Bounty Trough was initiated as a rift valley at this time, separating Campbell Plateau from the Chatham Rise, but subsequently failed to spread. Five main basins occur on the Campbell Plateau (Fig. 5.17). The Great South Basin is the largest and most complex with a fault-controlled northwestern margin and with southwestern and southeastern flanks formed by sediments thinning and onlapping on to shelving basement. The central part of the basin contains sediments up to 8 km thick and mainly Mid Cretaceous to Eocene in age.

The Pukaki Trough (the Pukaki Basin and the Pukaki Embayment), an elongate trough of sediments which runs off the southern corner of the Great South Basin, and the Campbell Embayment, which extends eastwards from near Campbell Island, both contain in excess of 3.5 km of sediments (Sandford, 1980). Most of the sediments are older than Palaeocene, and there has been little local subsidence since that time. The arcuate Campbell Basin, at the southwest corner of the Campbell Plateau, contains a maximum sediment thickness in excess of 2 km, mostly of pre-Middle Palaeocene age.

The commencement of drifting and the formation of new oceanic crust that occurred about 85 Ma B.P. is marked by an unconformity in the sedimentary layers and a change from non-marine to marine or restricted marine sedimentation as the land surface sank. By uppermost Cretaceous-Palaeocene, a full marine transgression covered the Campbell Plateau with the far offshore areas starved of sediments.

During the Mid Miocene (15 Ma B.P.), the Kaikoura Orogeny commenced. Oblique convergence at the Indian-Pacific plate boundary through New Zealand led to the uplift of the Southern Alps providing a source for the significant amounts of Mio-Pliocene sediments which accumulated in northern coastal areas. Further offshore, shelf and deep-water carbonates have predominated with minor Mio-Pliocene volcanism in scattered localities.

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