Seismic reflection images of intraplate deformation, central Indian Ocean, and their tectonic significance

Abstract

, which is at the lower end of predictions from plate motions, but significant enough to recognize this area as a diffuse plate boundary. The formation of long-wavelength basement undulations and the reactivation of fracture zones and ridge-parallel fault fabrics are linked in a unified tectonic model driven by the high level of intraplate compressive stress in the area. There is little evidence from the seismic profiles for intraplate deformation starting before the widespread unconformity dated as 7 Ma.

Crustal fault reactivation facilitating lithospheric folding/buckling in the central Indian Ocean

“…Geoid and free-air gravity anomalies contour maps also exhibit undulating character (Figs 1 and 3), correlating with oceanic basement undulations. Folding axes appear to be discontinuous and even seem to undergo rotation across old fracture zones (Bull, 1990;Bull and Scrutton, 1992). The offset of undulations across the fracture zones is consistent with N-S compression.…”

“…The main objective is to investigate the role of crustal fault reactivation as a potential perturbation mechanism. In the central Indian Ocean Basin, undulations of oceanic basement and, if present, sedimentary cover (Figs 2 and 3) trend E-W to NE-SW, with an amplitude of 1-2 km and a wavelength that increases from less than 100 km in the south to more than 300 km towards the north, averaging around 200 km (Weissel et al, 1980;Zuber, 1987;Neprochnov et al, 1988;Bull and Scrutton, 1992). The increase in wavelength is possibly related to the northward increase in age from 40 to 70 Ma of the oceanic lithosphere, and the associated increase in flexural rigidity (McAdoo and Sandwell, 1985).…”

“…Some of the basement faults on the seismic profiles seem to penetrate the entire crust and possibly into the subcrustal lithosphere. Bull and Scrutton (1992) suggest that these faults may nucleate in the upper mantle at the brittle-ductile transition and propagate upwards, reactivating the ridge-parallel fault fabric in the oceanic crust. These geometrical characteristics, together with other factors, have led to the interpretation that the faults result from the reactivation of the oceanic structural fabric that originated at the midocean spreading centres (Bull, 1990).…”

Large fault fabric of the Ninetyeast Ridge implies near‐spreading ridge formation

“…Older sediment fill implies that the larger troughs were initially formed at the time of ridge construction or shortly thereafter. Some of these faults are active and it is likely that intraplate deformation has reactivated existing faults here as it has in the adjacent Central Indian Basin [Bull and Scrutton, 1992]. [15] The second observation is that fault extension and trends are consistent with a spreading ridge origin.…”

Fault populations and their relationship to the scaling of surface roughness

“…In order to compare these results to the simulation, the program was altered so that the apparent movement on the faults was reverse. Two fault populations were used, mirroring the results of Bull and Scrutton [ 1992] The simulation was made with a bi-fractal fault population with D values of 1.9 and 1.0, with maximum values of 900 and 150 respectively. The graphs were then analyzed to give two fractal dimensions, in the same way as the natural section was analyzed (see Figure 10).…”