Tectonic history of Antarctic seafloor in the Australia-New Zealand-South Pacific sector: implications for Antarctic continental tectonics

Abstract

We review the seafloor spreading record of plate motions adjacent to the Antarctic continent during and after Cretaceous separation of the New Zealand and Australia continental fragments from Antarctica. The earliest seafloor in this region (c. 95-83 Ma) records separation of Australia from Antarctica and separation of the Lord Howe rise from eastern Australia. At this time, continental extension occurred between the Campbell Plateau/Chatham Rise and Marie Byrd Land with oblique subduction of Phoenix plate fragments (Aluk and Bellingshausen) beneath the West Antarctic margin from c. 125ºW to at least 90ºW. Seafloor spreading started first (Chron 34, before 83 Ma) in the mouth of the rift, between the Chatham Rise and the Bellingshausen plate, and later (Chron 33, c. 79 Ma) between the Campbell Plateau and Marie Byrd Land, joining the Tasman sea ridge to the southwest Pacific spreading centre. Subsequent tectonic events include: (1) <50 km of rifting of the seafloor adjacent to Marie Byrd Land along the northeast-trending Iselin trough, east of the Iselin Bank, from Chrons 27 to 24 (61-55 Ma); (2) propagation of the southeast Indian Ridge between the south Tasman Rise and Victoria Land to join the Tasman Sea spreading centre by Chron 27 (61 Ma); (3) capture of the Bellingshausen plate by West Antarctica by about Chron 27; (4) 150-180 km of separation between East Antarctica and West Antarctica (Iselin Bank) centred on the NNW-trending Adare trough between Chrons 18 and 9 (40-27 Ma). These observations predict, first, that the West Antarctic margin at 125ºW was the site of a triple junction from at least 84 to 61 Ma, with Phoenix plate annihilation and expected tectonics of West Antarctica in many ways analogous to breakup of the Farallon plate and its effects on western North America. Second, northern Victoria Land may exhibit unique tectonics compared to elsewhere along this part of the Antarctic margin because it lay in a continental strike-slip regime, sliding against continental crust of the Australia plate (western south Tasman Rise) until Eocene time. Finally, the 150+ km of Oligocene seafloor formed at the Adare Trough implies a significant extensional event of this age farther south in the Ross Sea, in agreement with results from recent drilling at Cape Roberts hole CRP-3.

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