摘要：

Plate reconstruction models for the rifting and spreading between Australia and East Antarctica continue to be poorly constrained prior to 50 Ma, due to an historical paucity of magnetic anomaly data close to the margins and a slow initial spreading rate. Published reconstructions result either in large overlaps between the South Tasman Rise and Antarctica, or in the partial misfitting of conjugate magnetic anomalies. Utilizing the new1- minute gravity grid by Sandwell and Smith, we have identified several NW-SE oriented small-offset fracture zones on the conjugate Australian and East Antarctic plates which display a bend to N-S oriented spreading at around Chron 22/21 time, suggesting a major plate reorganization at that time. Previous plate reconstructions for Australia-Antarctica match the Leeuwin Fracture Zone (eastern side of the Naturaliste Plateau) with the Vincennes fracture zone (eastern side of the Bruce Rise), which results in reconstructions where the Naturaliste Plateau is located to the north of the Bruce Rise, as well as in a major plate reorganization at around Chron 34, which does not correspond to a time of regional or global plate reorganization. Juxtaposition of the Naturaliste Plateau to the north of the Bruce Rise is problematic due to the identification of M-series magnetic anomalies which likely reflect Antarctic-India separation. Using a NW-SE direction of motion for separation prior to Chron 22/21, the Naturaliste Fracture Zone (western side of the Naturaliste Plateau) matches with the Vincennes Fracture Zone, resulting in reconstructions that place the Naturaliste Plateau to east of the Bruce Rise. Plate reconstructions using this revised direction for pre-chron21 motion between Australia and Antarctica show reduced amounts of overlap between the South Tasman Rise and Cape Adare and provide improved constraints on motion between East and West Antarctica and global plate circuit closure.

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