Active Margins, Part 4—Makran Fold Belt, Profile N 1804
P. Lehner, H. Doust, G. Bakker, P. Allenbach, J. Gueneau, 1983. "Active Margins, Part 4—Makran Fold Belt, Profile N 1804", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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Profile N 1804 across the offshore part of the Makran fold belt in the northern Gulf of Oman was selected to show the structure of an accretionary wedge produced by subduction of a basement covered with thick sediments.In the framework of global tectonics, the Gulf of Oman is interpreted as the second largest oceanic gap (next to the Sunda arc) in the collision front between Eurasia and the Gondwana continents. This gap is interpreted as a remnant of the Tethys, between India and Arabia. The Makran fold belt represents the accretionary wedge of a subduction complex, which extends from the base of the continental slope of Pakistan and Iran to the northern border of Baluchistan.
There is no direct evidence for the age of the basement below the Gulf of Oman and its oceanic nature is not yet fully confirmed. All available data from regional geology and offshore seismic, however, suggest that the oceanic basement ranges in age from Late Cretaceous to early Tertiary. It is covered with 4 to 6 km (2.5 to 3.7 mi) of flat and level sediments.
The top of the basement can be traced on seismic below the accretionary wedge of folded and overthusted sediments in the Pakistan slope approximately as far as the shelf edge, where it is observed at a depth of around 15 km (9.3 mi).
Evidence from earthquake seismic indicates that crustal subduction takes place further inland below the Hamon-Rud basin in northern Baluchistan, a fore-arc basin in front of the Tertiary volcanic arc.In contrast to the rather chaotic accretionary prisms of the Java and Japan trenches, seismic sections across the frontal part of the Makran fold belt show an orderly set of overthrusts and thrustfolds which resemble the Canadian foothills type. Moving away from the thrust front in a landward direction, the anticlinal ridges become narrower and diapiric, and the synclines grow wider and deeper.
Based on the age of the volcanics in northern Baluchistan, it is assumed that subduction began in Eocene time. Line N 1804 indicates continuous deformation into Recent times. Individual thrusts produce elongated ridges with a local relief often in excess of 1,000 m (3,281 ft). Undisturbed, ponded sediments in synclinal areas are very thin. The reflection band about 1 sec below the seabed is interpreted as gas hydrate, a common feature in subsea fold belts.