Publication Name: The Sedimentary Basins of WA
Authors: R. Dietmar M?ller, Dona Mihut and Stephanie Baldwin
Publication Volume: 2
Date Published: December 1998
Number of Pages: 29
Reference Type: Book Section
Abstract:
Satellite altimetry has revolutionised our knowledge of the tectonic structure of the ocean floor and the continental shelves where ship data are sparse. We have used existing and new ship magnetic, bathymetric and seismic data with satellite derived gravity data to develop a revised model of Mesozoic continental breakup and sea-floor spreading in the Perth, Cuvier, Gascoyne and Argo abyssal plains. Based on this data set, we identified the boundary between continental and oceanic crust (COB), fracture zones, and traces of propagating rifts. In our model sea-floor spreading in the Gascoyne and Cuvier abyssal plains starts in the Lower Valanginian (136.2 Ma), 3.7 My earlier than previously interpreted. Combined with a model for the dispersal of Gondwanaland, our results imply that a shear zone between the southern and the northern part of Greater India is required to accommodate their relative motion between 136 and 99 Ma. A major plate tectonic event occurred at the Albian/Cenomanian boundary ( -99 Ma), when the spreading direction between India and Australia changed from northwestsoutheast to north-south. An event at about 61 Ma (magnetic anomaly 27) in the Early Paleocene isrecorded in the Tasman Sea and in the southeast Indian and Pacific oceans as a change in spreading direction. Analysis of the tectonic history of 108 wells shows widespread anomalous subsidence or uplift on the North West Shelf at both times. The magnitude and location of the anomalous subsidence and uplift indicate that the 99 Ma event locally resulted in renewed lithospheric extension, whereas the 61 Ma event may reflect elastic buckling of the lithosphere. Both events may have originated from the stepwise subduction of the Neo-Tethyan Ridge, first north of India at 99 Ma and then north of Australia at 61 Ma. In the Miocene/Pliocene almost the entire North West Shelf from the Carnarvon Basin to the Timor Sea underwent accelerated subsidence, which started as early as 20 Ma in some areas, and reached magnitudes of more than 500 m up to 1000 km away from the Timor Trough. These observations cannot be explained by foreland basin loading, but are likely the result of a complex evolution of compressive intraplate stresses following the recent breakup of the Indo-Australian Plate into the Indian, Australian and Capricorn plates.