Newly-recognised Continental Fragments Rifted from the West Australian Margin

• Main Authors: Williams, SE, Whittaker, J, Muller, RD
• Format: Conference Object
• Language: English
• Published: RE Solutions Resource & Energy Services P/L 2013
• Subjects: Earth Sciences; Geology; Tectonics; Indian; Antarc*
• Online Access: https://www.aime.com.au/__novadocuments/44419?v=635258742235770000; http://ecite.utas.edu.au/86220

The southwest Australian margin formed at the nexus ofrifting and breakup between India, Australia and Antarcticain the Early Cretaceous. Studying the basin evolution alongthis margin has been hampered by a lack of data from theoffshore Perth Abyssal Plain (PAP), and from the conjugateGreater Indian margin, which was highly deformed duringcollision with Eurasia. Here, we present new data (magneticanomaly profile data, swath bathymetry, and dredgesamples) constraining the evolution of the PAP, collectedduring voyage ss2011/v06 of the RV Southern Surveyor inlate 2011.The Batavia Knoll (BK) and Gulden Draak Knoll (GDK)are two prominent, previously unsampled bathymetricfeatures located >1600 km offshore Australia that have beenassumed to be igneous features. Successful dredges on thewestern flanks of both knolls recovered continental basementrocks, revealing that both knolls are microcontinents. Weuse quantitative analysis of shiptrack magnetic profilescombined with satellite gravity anomalies to estimate theextent and spatial variation in thickness of the continentalcrust. Sediment thickness estimates are made using depths tomagnetic sources for shiptrack profiles.The geophysical data provide evidence for basin structureswithin the knolls of a similar scale to those imaged withinother fragments of stretched continental crust such as theNaturaliste Plateau. Interpretation of previously unidentifiedM-series anomalies in the Perth Abyssal Plain, combinedwith dredge data, support a reconstruction model where theBK and GDKs are microcontinents that initially rifted withGreater India during breakup with Australia at ~130 Ma. Asseafloor spreading ceased in the PAP at about 105100 Ma,a westward ridge jump led to the rifting of the BK and GDKfrom Greater India.