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Normal and transform faults originally formed at a spreading-centre can be reactivated in diffuse plate boundary zones and in areas of lithospheric flexure such as at peripheral bulges to subduction zones. Using new seismic reflection profiles and modeling, we investigate how the original oceanic fabric is reactivated in the simple case of fault perpendicular compression. In the Central Indian Basin, well-oriented normal paleofaults were reactivated with reverse motion at the very onset of deformation (9 Ma) but only a small subset remained active past similar to 7 Ma, suggesting that most of the densely spaced small-offset faults were abandoned while deformation localized onto fewer faults with larger spacing. We find a similar evolution using a 2D finite element code of lithospheric shortening using a pseudoplastic rheology. Weak zones, 3 km-spaced and 30-40% weaker than the surrounding material, are introduced to simulate the fabric formed at the ridge axis. We show that reactivation and selective abandonment require strain weakening followed by strain-rate weakening once a maturation threshold is reached. A maturation fault slip of less than 50 m is needed to produce a fault network similar to that in the Central Indian Ocean.

Normal and transform faults originally formed at a spreading-centre can be reactivated in diffuse plate boundary zones and in areas of lithospheric flexure such as at peripheral bulges to subduction zones. Using new seismic reflection profiles and modeling, we investigate how the original oceanic fabric is reactivated in the simple case of fault perpendicular compression. In the Central Indian Basin, well-oriented normal paleofaults were reactivated with reverse motion at the very onset of deformation (9 Ma) but only a small subset remained active past similar to 7 Ma, suggesting that most of the densely spaced small-offset faults were abandoned while deformation localized onto fewer faults with larger spacing. We find a similar evolution using a 2D finite element code of lithospheric shortening using a pseudoplastic rheology. Weak zones, 3 km-spaced and 30-40% weaker than the surrounding material, are introduced to simulate the fabric formed at the ridge axis. We show that reactivation and selective abandonment require strain weakening followed by strain-rate weakening once a maturation threshold is reached. A maturation fault slip of less than 50 m is needed to produce a fault network similar to that in the Central Indian Ocean.

Normal and transform faults originally formed at a spreading-centre can be reactivated in diffuse plate boundary zones and in areas of lithospheric flexure such as at peripheral bulges to subduction zones. Using new seismic reflection profiles and modeling, we investigate how the original oceanic fabric is reactivated in the simple case of fault perpendicular compression. In the Central Indian Basin, well-oriented normal paleofaults were reactivated with reverse motion at the very onset of deformation (9 Ma) but only a small subset remained active past similar to 7 Ma, suggesting that most of the densely spaced small-offset faults were abandoned while deformation localized onto fewer faults with larger spacing. We find a similar evolution using a 2D finite element code of lithospheric shortening using a pseudoplastic rheology. Weak zones, 3 km-spaced and 30-40% weaker than the surrounding material, are introduced to simulate the fabric formed at the ridge axis. We show that reactivation and selective abandonment require strain weakening followed by strain-rate weakening once a maturation threshold is reached. A maturation fault slip of less than 50 m is needed to produce a fault network similar to that in the Central Indian Ocean.