Evolution of the Antarctic Continental Margins (Paleoceanographic Mapping Project Progress Report No. 31-1287)
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With the exception of the Pacific facing margin of West Antarctica between Thurston Island and the tip of the Antarctic Peninsula, all of the continental margins of Antarctica are either rifted passive margins or sheared transform margins. The exception was a convergent margin where subduction was active from prior to the breakup of Gondwanaland until very recently. Starting in the southwestern Weddell Sea which rifted as part of a back -arc basin connected with back-arc spreading in the Rocas Verdes Basin of southern South America during the Middle to Late Jurassic ( -170 Ma), the continental margins of Antarctica seem to young clockwise. A sheared margin along the Explora Escarpment between 25°W and 10°W connected the southwestern Weddell Sea rifting with contemporaneous rifting in the Mozambique Basin. This resulted in a Middle Jurassic rifted passive margin along Dronning Maud Land. East of the Gunnerus Ridge at 35°E, Sri Lanka and India rifted off of Antarctica sometime between 129 Ma and 118 Ma. Rifting between Australia and Antarctica, stretching in the Ross Sea Embayment and rifting between the Campbell Plateau--Chatham Rise and Marie Byrd Land, all started about 95±5 Ma. The convergent margin on the Pacific margin of the Antarctic Peninsula stopped active subduction in the west at about 50 Ma, with the most recent subduction about 5 Ma off the South Shetland Islands. The only presently active continental margin on the Antarctic Continent is a short section of left lateral transform fault along the tip of the Antarctic Peninsula. Very young volcanism in the Ross Sea region may indicate that a new continental margin is in the initial stages of formation.