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Rift to drift transition in the southwest Australian deepwater Mentelle Basin




Guerzon, Emmanuel, author
Harry, Dennis, advisor
Stright, Lisa, committee member
Scalia, Joseph, IV, committee member

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The Mentelle Basin is a deepwater polyphase basin located off of the southwest margin of Australia that formed during Late Jurassic and Early Cretaceous breakup of Gondwana. It is underlain by highly extended continental crust and is bordered to the west by less extended crust forming the Naturaliste Plateau, and to the east by the Yalingup Shelf and Perth Basin beneath the continental shelf and coastal plain. The purpose of this study is to characterize the depositional, subsidence, and tectonic histories of the Mentelle Basin during the syn-rift to post-rift transition period. We use seismic reflection data and boreholes drilled by the Deep Sea Drilling Project and International Ocean Discovery Program (IODP) to map three horizons and intermittent volcanic features within this > 134 Ma to 126 Ma period. The youngest horizon mapped was the top of Lithostratigraphic Unit 5 (LSU5) at IODP Site U1513, which corresponds with the lower Aptian age (126 Ma) when rifting on this part of the margin ended and seafloor spreading began between Greater India and Australia west of the Naturaliste Plateau. Also mapped was a reflector encountered at the top of the basalt pile in IODP Hole U1513D at the western edge of the Mentelle Basin. The oldest horizon mapped is the Valanginian Unconformity that lies below this basalt pile and corresponds with breakup and the onset of seafloor spreading on the Perth Abyssal Plain further north. Isochore maps and two depth structure maps generated from these horizons illustrate the subsidence history and structural and magmatic evolution of the Mentelle Basin during breakup. Syn-rift magmatism in the Mentelle Basin was more widespread than previously thought. While earlier studies deemed the western half of the Mentelle Basin magmatic, the eastern extent of magmatism was unknown. Seismic correlation of the basalt reflector at Site U1513 indicates the Naturaliste Plateau basalts extended eastward to the eastern flank of the Mentelle Basin. Younger flows 2 – 20 km wide and occasional volcanic cones ranging from 0.5 – 2.5 km wide are imaged in the western half of the basin to the toe of the eastern slope. These younger volcanic features were emplaced between the late Valanginian through the start of the Aptian age. Basalt flows and some volcanic features in the basin are interpreted to have been exposed and weathered at or above sea level around the time of emplacement before subsequent burial by a marine transgression. The Mentelle Basin began to subside prior to the Naturaliste Plateau (> 134 Ma) as rifting occurred between India and Australia-Antarctica. Once final breakup occurred and seafloor spreading began west of the Naturaliste Plateau, both the Mentelle Basin and Naturaliste Plateau subsided to bathyal depths beginning around 126 Ma.


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