ETERNALLY DIVIDED: POSSIBLE MANTLE ORIGINS FOR LONG-LIVED BASIN DIVISIONS

How do the thermal and mechanical properties of the mantle affect the structural evolution of the overlying crust? Phanerozoic rift basins that develop on the flanks of Archean cratons, such as those offshore northwest Australia, may have sub-basins underlain by either Archean sub-continental lithospheric mantle (SCLM) or younger, more dense mantle. As typical Archean, Proterozoic and Phanerozoic SCLM differ in density, geothermal gradient and buoyancy, we test the hypothesis that adjacent regions of continental crust can display different deformation styles and subsidence patterns during rifting if they are underlain by SCLM of differing ages. We present numerical simulations where an Archean/Proterozoic craton and adjacent Phanerozoic lithosphere with realistic geothermal gradients and densities are extended. We also test the effect of varying strain-rate and the orientation of the interface between the different types of SCLM. Preliminary results indicate that any interface between SCLM of different ages will localize strain in the overlying crust over long timescales during rifting. This may help explain long-lived “border” faults that form the boundaries of sub-basins or basins. Preliminary results also indicate that strain tends to be more concentrated in continental crust atop Phanerozoic SCLM, whereas the adjacent continental crust underlain by an Archean craton is less deformed.