Abstract
The continental margin off the Makran coast of Iran and Pakistan is an excellent example of active deformation of sediments at a compressive plate boundary. Seismic reflection profiles across the margin suggest that relatively flat-lying sediments from the Oman abyssal plain are being scraped off the Arabian plate and accreted onto the Eurasian plate in a series of tightly folded sediment ridges aligned parallel to the coast. The most active folding appears to be occurring in the southernmost of the ridges, where it has formed a frontal fold up to 750 m high, with a width of 3–4 km. Filling of the basins between the ridges with later sediment becomes progressively more complete towards the north, and produces a smooth continental shelf near the coast, where the ridges are completely buried by sediment. Evidence for the possible presence of northward-dipping thrust faults which uplift the ridges towards the coast is seen in the consistent back-tilting of the sediments in the inter-fold basins. Below the abyssal plain to the south of the folded zone the sediments are divided by a prominent reflector, horizon A, into an upper group of flat-lying beds that overlie strata which dip gently to the north. A sharp velocity increase occurs across this horizon. The deepest observable reflector, horizon B, is seen as a series of diffraction hyperbolae which dip conformably northwards at about 1°. Velocity determinations from refraction and variable-angle reflection stations over the abyssal plain indicate a thick pile of low-velocity material which is probably sediment lying above horizon B. The material directly below horizon B has a velocity of 4.5 ± 0.2km/s and is probably volcanic in origin.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call