Thursday March 7, 12:15pm

Mr. Ian Russell

Regional Skill Area Coordinator for ExxonMobil Exploration Company
 

Tectonic & Volcanic History of the Carnarvon Terrace  
 

Abstract

The under-explored Carnarvon Terrace, part of the offshore Carnarvon Basin, represents one of the remaining frontier areas on the northwest Australian margin. We have interpreted 6,700km of seismic profiles covering an area of 23,750km2 for assessing the tectonic and volcanic evolution of this area. Our data suggest a multiphase history of faulting and sediment accumulation in which major bounding faults were active during the Late Triassic and Early Jurassic. A major phase of uplift and erosion affected both the Bernier Platform and the Exmouth Sub-basin shortly before the breakup between Greater India and Australia prior to 130 Ma. Widespread lower Cretaceous sills, dykes and a large intrusion in the Exmouth sub-basin, and the offshore Wallaby and Zenith plateaus, provide evidence for syn- and post-rift volcanism. Whether or not the observed volcanism was due to a mantle plume is important for assessing the thermal and uplift/subsidence history of the area. Mantle convection modelling based on our global plate model and mantle density heterogeneities suggests that the St. Paul hotspot moved southward through time by several hundred kilometers, similar to the Kerguelen hotspot. The reconstructed position of the St. Paul hotspot would have been underneath the Indian Plate, not the Australian margin. Therefore, we reject the mantle plume hypothesis for the formation of this volcanic margin. The observed lower Cretaceous uplift of the Bernier Platform and Exmouth subbasin may rather represent flexural rift-shoulder uplift, and the observed volcanism may have been driven by small-scale convection due to the juxtaposition of thick and thin lithosphere along the transform margin south of the Bernier Platform. Our approach illustrates how conventional exploration tools can be used jointly with geodynamic modelling to constrain the tectonic and volcanic history of sedimentary basins.