Constraining the Tectonic Evolution of the Perth Abyssal Plain

Two microcontinents, the Batavia Knoll and Gulden Draak Knoll, remained undiscovered in the Eastern Indian Ocean, ~1600 km west of the Perth Basin, until dredging in 2011 recovered continental basement rocks. New Ar-Ar dates from recovered gabbro-basalt samples and fossil assemblages from sandstone samples, combined with magnetic anomalies and swath bathymetry from the Perth Abyssal Plain, constrain the history of rifting and seafloor spreading along the western Australian continental margin. These data illustrate that the age of cessation of spreading in the Perth Abyssal Plain and synchronous micro-continent rifting occurred at 102 +/- 0.5Ma. At this time, the India-Australia plate boundary jumped westwards, isolating the two micro-continents from the passive margin of eastern Greater India. Shallow marine conditions persisted on the micro-continents even during the final stages of continental breakup, likely via dynamic support from the Kerguelen plume. The new model much more accurately constrains the time dependence of the progression of the mid-ocean ridge along the continental Wallaby/Zenith Plateau region to the north of the Perth Abyssal Plain, which has implications for understanding heat flow in this region.Many micro-continents were formed in the Indian Ocean during Gondwana breakup, including the Seychelles, Elan Bank, parts of the Kerguelen Plateau, and Mauritius/Mascarene Plateau and failed micro-continents such as the Naturaliste Plateau. 
Typically, micro-continent formation occurs from passive margins <25 Myr old.Rifting of the Batavia and Gulden Draak microcontinents, however, occurred from a relatively mature (~34Myr old) passive Indian continental margin, and with an apparent absence of syn- or post-rift volcanism. These unusual conditions lead us to suggest that rifting of these micro-continents was aided by the dramatic change in plate motions between India and the co-joined Australia-Antarctica in conjunction with weakening of the continental lithosphere by the Kerguelen plume. Geochemical analyses of basalts recovered from the Dirck Hartog Ridge confirm the interpretation of this feature as an extinct mid-ocean ridge, although the unusually high bathymetric relief of this feature is suggestive of compressive reactivation following the cessation of spreading in this region, possibly driven by the dramatic change in plate boundary forces associated with the change in relative plate motions between India and Australia.