Rigid and Non-rigid Plate Reconstruction of the East Africa and Antarctic Continental Margins
Nguyen, Luan Chan 1988-
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The Early Jurassic separation of Antarctica from Africa plays an important role in our understanding of the dispersal of the Gondwana supercontinent. Previously proposed reconstruction models often contain overlaps and gaps in the restored margins that reflect difficulties in accurately delineating the continent-ocean boundary (COB) and determining the amount and distribution of extended continental crust. This study focuses on the evolution of the African margin adjacent to the Mozambique Basin and the conjugate margin of Antarctica near the Riiser Larsen Sea. A complete break-up history involving both seafloor spreading and continental rifting has been investigated. New satellite-derived gravity data have been used to trace the orientations and landward limits of fracture zones in the study area. A 3-D gravity inversion has produced a crustal thickness model that reliably quantifies the extent and amount of stretched crust. Information on crustal thickness along with the identification of magnetic isochrons reveal COBs that are located significantly closer to the coasts of Africa and Antarctica than previously recognized. Correlation of both fracture zone azimuths and magnetic isochrons in addition to the identified COBs over the conjugate margins suggest Antarctica began drifting away from Africa at approximately 171 Ma in a roughly SSE direction. Of several scenarios examined to determine the crustal character of the Beira High, the preferred model assigns it an oceanic origin and suggests that it may be a conjugate feature of the southern Astrid Ridge in Antarctica. An areal balancing method that involves restoring the crust to a uniform pre-rift thickness has been used to perform the non-rigid reconstruction. This restoration has been carried out for both a non-volcanic and volcanic margin with magmatic underplating. Based upon the results, Africa underwent extension of 65-105 km while Antarctic crust was stretched by 90-190 km. Both margins reveal a trend of increasing extension from east to west. Various models tested to determine the direction of extension during rifting suggest that Antarctica underwent a counter-clockwise rotation with respect to Africa during the period between 186-171 Ma.