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Bathymetry: Features and Hypsography
Published in Yeqiao Wang, Coastal and Marine Environments, 2020
Heidi M. Dierssen, Albert E. Theberge
The bathymetry of each of the five ocean basins varies considerably (Figure 18.4). Ridges and rises associated with seafloor spreading can be found in all five of the ocean basins. As mapped in the 1800s,[1] the Mid-Atlantic Ridge extends from the north of Iceland to the Southern Ocean boundary. Wide continental shelves (<200 m depth) are visible along much of the western Atlantic Ocean. The vast Pacific Ocean contains mostly broad expanses of deep ocean floor including abyssal hills, chains of seamounts, and lineal scars of great fracture zones. Prominent bathymetric features also occur along the margins of the Pacific Ocean. The Pacific Ocean is bounded by the “Ring of Fire” consisting primarily of subducting plates on the western, northern, and eastern margins with deep trenches and considerable earthquakes and volcanic activity. The southern boundary is defined by the Pacific–Antarctic Ridge and the southern portion of the East Pacific Rise. The Indian Ocean is crossed by ridges and volcanic island structures where the African, Indian, Australian, and Antarctic crustal plates all converge. With the exception of Western Australia, the Indian Ocean has limited continental shelf area. In contrast, the Arctic Ocean represents the shallowest of ocean basins and is characterized by broad expansive deep (500 m) shelves and shallow seas. The Southern Ocean also contains deep continental shelves (500 m), large expanses of abyssal plains, and prominent ridge features bordering the Pacific, Atlantic, and Indian Oceans.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
The eastern margin of Eastern Gondwana has been more complex, dominated since the Paleozoic by subduction zones of varying polarity, back-arc basins, rifting events resulting in ribbons of continental crust outboard of the margin, including Zealandia (Mortimer et al., 2017, 2019), ridge creations and jumps, and transform fault developments. From ca 400 to 130 Ma, the Phoenix Plate was subducting along the eastern margin of Gondwana (Matthews et al., 2016; Müller et al., 2016), followed by the Pacific and then Hikurangi plates (Wright et al., 2016). Subsequently, a number of smaller, dominantly oceanic plates have developed and been partly subducted along this margin. Subduction accompanied the commencement of spreading between Australia and Zealandia at ca 90 Ma, that included the component continental fragments of the latter, such as the Lord Howe and Chatham rises, Challenger and Campbell plateaus, and New Zealand (e.g. Jordan et al., 2020; Nelson & Cottle, 2018). By 70 Ma, the Tasman Sea ridge connected through to ridges between Antarctica and the Pacific, and from ca 62 to 52 Ma, Zealandia was on a separate plate from that including Australia and Antarctica, consequent to the propagation of spreading from the Tasman to Coral seas, and linkage with microplate boundaries in the southwestern Pacific. At ca 50 Ma, the Tasman Sea ridge ceased spreading, resulting in the recombination of Zealandia and Australia in the same plate. By 35 Ma, the Pacific–Antarctic Ridge connected through to the Australia–Antarctic ridge, thereby completing the isolation of Antarctica and fragmentation of the major continents that formed Gondwana. From ca 80 Ma to the present, the Pacific Plate has subducted along the eastern margin of the Australian and bordering plates. A complex series of arc and reararc development has occurred with the formation of troughs (e.g. New Caledonia), back-arcs (Lau-Havre Trough, South and North Fiji basins) and continental ribbons (Crawford et al., 2003; Schellart & Spakman, 2012). A subduction polarity reversal developed consequent to the arrival at ca 8 Ma of the Ontong Java Plateau at the Vitiaz Trench, outboard of the Solomons and New Hebrides arcs (Petterson et al., 1999). A subduction zone is in an early stage of development south of New Zealand along the Puysegur Trench (Gurnis et al., 2019).