The prominent example of compression of oceanic lithosphere in the Central Indian Ocean south of the Indian peninsula does not occur where recent models for the state of stress in the Indo-Australian plate predict maximum horizontal compressive stress. The Afanazy-Nikitin seamount group, which was erupted in Late Cretaceous of Early Teritary time, is centrally located in the region where deformation is best developed. We suggest that critical wavelength components in the deflection caused by the emplacement of these seamounts were preferentially amplified when north-south directed compression was applied to the northern part of the Indo-Australian plate in the late Miocene. To test this hypothesis, we develop simple one- and two-dimensional models for compression of a thin elastic plate overlying an inviscid fluid, where the plate contains a preexisting deflection. The ≥2 km peak-to-trough amplitude and 200 km average wavelength characteristics of the broad-scale crustal deformation and the observed east-west trending pattern of free-air gravity anomalies are best matched in the modeling with an applied horizontal compression of 1.5--2.0¿1013 N m-1, and a plate with an effective elastic thickness of 10--15 km at the time of compression.

In addition, the lithosphere is particularly susceptible to deformation by horizontal compression if seawater initially filled the deflection due to seamount emplacement, but Bengal Fan sediment fills the additional deflection caused by compression. The value of effective elastic thickness determined for the deformed lithosphere is about a factor of 2 less than values obtained from flexure of comparably aged lithosphere beneath seamounts and at trenches (≈20--30 km). We attribute this to plastic yielding at the top and bottom of the lithosphere in response to horizontal loading. We determine a north-south shortening rate of ~1 mm yr-1 from the amplitude of horizontal compression, the width of the deformed region, and the time interval over which the deformation has occurred. This shortening rate is similar to estimates determined from present-day plate motion studies. ¿American Geophysical Union 1990