Morphotectonics and mechanics of the central Makran accretionary wedge offPakistan

Swath bathymetry images and 3.5 kHz data acquired during RV Sonne cruise 12 3 in autumn 1997 are the base for analysing the morphology and deformation styles of the huge Makran accretionary wedge. The continental slope off Pak istan is characterised by three morphological provinces: (a) The lower slop e is built of a sequence of imbricate thrust slices which form long and nar row accretionary ridges with Ranks locally as steep as 20 degrees and betwe en 10 degrees and 20 degrees on average, while the regional slope is only 1 -2 degrees, (b) the nearly flat mid-slope terrace is present in the central east part of the margin, narrows significantly towards the east, and is ab sent east of 63 degrees 45' and (c) the upper slope up to the shelf has a r egionally uniform slope as steep as about 8 degrees and comprises a very ro ugh topography with many gullies and canyons and evidence for mass wasting. Two meandering canyons crossing the entire margin down to the abyssal plai n at about 63 degrees 15'-63 degrees 30', can be correlated with onshore ri vers. They have been formed by episodic erosion through turbidity Rows and are characterised by erosional and depositional portions. Sinuosity of the canyons is exclusively caused by the accretionary ridges functioning as obs tacles for flow to be directly downhill. Application of Coulomb rheology to the frontal part of the Makran Wedge implies that the mid-level decollemen t is intrinsically extraordinary weak with a great strength contrast to the overlying sediments. Comparison with Nankai, Cascadia, and the Western Med iterranean Ridge reveals new insights in the parameters controlling the sha pe of an accretionary wedge and the role of a mid-level decollement. (C) 20 01 Elsevier Science Ltd All rights reserved.