LATE JURASSIC-EARLY CRETACEOUS RIFTING ON THE SOUTHWEST AUSTRALIAN CONTINENTAL MARGIN: RESULTS FROM IODP EXPEDITION 369

Western Australia is bordered by a rifted continental margin formed during opening of the East Indian Ocean in Late Jurassic through Early Cretaceous time as Greater India rotated counterclockwise away from Australia and Antarctica during the breakup of East Gondwana. International Ocean Discovery Program Expedition (IODP) 369 drilled four boreholes on the southwestern part of the margin in the deep water Mentelle Basin. The drilling results, coupled with seismic reflection data, show the southwestern Australian continental margin remained coupled to Greater India following breakup and the onset of seafloor spreading to the north in the Perth Abyssal Plain at 134 Ma. The Mentelle Basin and adjacent Naturaliste Plateau continued to extend until 129 Ma, when seafloor spreading was established west of the Naturaliste Plateau and Greater India became completely separated from Australia. Breakup on the Perth Abyssal Plain portion of the margin was accompanied by basaltic volcanism in the western Mentelle Basin and on the Naturaliste Plateau. A detrital volcaniclastic succession above the basalts records erosion and re-working of the basalts in shallow water during the period between the onset of seafloor spreading in the Perth Abyssal Plain and to the west of the Naturaliste Plateau. Rapid sedimentation is interpreted to indicate thermal subsidence of the plateau in Late Cretaceous, after seafloor spreading was well established. Limited sedimentation and subsidence occurred further inboard in the Mentelle Basin during this time. Renewed subsidence and sedimentation in the Mentelle Basin during Paleogene time is attributed to extension between Australia and Antarctica, culminating on breakup on the southern margin of the NP/MP at X Ma. The Naturaliste Plateau was relatively unaffected by this final phase of extension between Australia and Antarctica.