Ordoviclan Cambrian sadlmenl thickness in km strike slip fault (Greal South Basin] 175"

Fig. 5.17. Campbell Plateau. Bathymetry - light line. Drillholes reaching metamorphic basement - filled circles. Metamorphic basement geology shown for offshore region. Heavy dashed line marks northeastern limit of high temperature -high pressure metamorphic basement. Major sedimentary basins of Campbell Plateau. Sediment thickness in kilometres (modified after Sandford, 1980). Dashed line marks the major strike slip faults along the northeast margin of Great South Basin (Mercator projection).

Sedimentary sequences within the Bounty Trough show mainly pelagic sedimentation during the Early-Mid Cenozoic, when there was a very low relief in the adjacent landmass, followed by more turbiditic sedimentation resulting from uplift of the adjacent South Island since the Mid Miocene (Kaikoura Orogeny), as indicated by results from DSDP site 594 (Kennett et al., 1986).

The South Tasman Rise

The East Tasman Plateau and South Tasman Rise (Fig. 5.18) are probably subsided continental crust that fragmented during the initial separation of Australia from Antarctica. DSDP site 281 (Kennett et al., 1975a) sampled a quartz mica schist basement, possibly a correlative of the Palaeozoic schist found in Tasmania. The plateau and rise are separated from the narrow continental shelf and steep upper continental slope of Tasmania by troughs. The northern portion of the South Tasman Rise shows flanking horst and graben structures with a central platform region and sediments up to 3 km thick but of unknown age on the flanks.

Fig. 5.18. Bathymetry of the South Tasman Rise and East Tasman Plateau. DSDP sites 280 and 281 marked by solid circles (Mercator projection).

Post break-up deposition commenced in the Late Eocene (DSDP site 281) (Kennett et al., 1975a). The East Tasman Plateau has been poorly surveyed but it is probably continental. Oceanic basement abuts its eastern margin with no marginal rift suggesting a transcurrent rather than extensional margin.

Macquarie Island

Macquarie Island is part of the ridge crest of the Macquarie Ridge which forms the Indian-Pacific plate boundary from New Zealand to the triple junction at about 60°S, 160°E (Fig. 5.7). It is elongate parallel to the ridge and extends over an area of about 170 km2. It is formed of fault-bounded blocks of basic extrusive rocks and associated sediments characteristic of deposition on the ocean floor at water depths of about 2,000-4,000 m (Varne et al., 1969) and represents a faulted section through oceanic crust (Varne and Rubenach, 1972).

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