The spatial and temporal evolution of strain during the separation of Australia and Antarctica

[1] A re-evaluation of existing onshore and offshore gravity, magnetic, seismic reflection, and well data
from the Australo-Antarctic margins suggests that magmatism and along-strike lithospheric heterogeneities
have influenced the localization of initial rifting. The 3-D crustal architecture of the Australian and
Antarctic margins, which formed during multiple rifting episodes spanning 80 Myr, reveal local
asymmetries along strike. Rift structures from the broad, late Jurassic (165–145 Ma) rift zone are partially
overprinted by a narrower, mid-to-late Cretaceous rift zone (100 Ma), which evolved in highly extended
crust. This late-stage rift zone is located within a region of heterogeneous crust with faults that cut late synrift
strata, interpreted as a continent ocean transition zone. This late stage transitional rift is populated by
seismically identified rift-parallel basement highs and intracrustal bodies with corresponding positive
Bouguer gravity and magnetic anomalies. These undrilled features can be interpreted as exposures of
exhumed mantle rocks, lower crustal rocks and/or as discrete magmatic bodies. Our results suggest that
strain across an initially broad Australo-Antarctic rift system (165–145 Ma) migrated to a narrow rift zone
with some magmatism at 100–83 Ma. Breakup did not occur until 53 Ma within the eastern Bight-Wilkes
and Otway-Adelie margin sectors, suggesting a west to east propagation of seafloor spreading. The
prolonged eastward propagation of seafloor spreading processes and the increased asymmetry of the
Australian-Antarctic margins coincides with a change from rift-perpendicular to oblique rifting processes,
which in turn coincide with along-strike variations in cratonic to Palaeozoic lithosphere