The Makran Accretionary Prism: Tectonics and Sedimentation Interplay on an Active Margin

Raymi Castilla and Nadine Ellouz
IFP, 92500 Rueil Malmaison, France

The Makran accretionary prism is a 350 km wide thrust belt associated to the northward verging subduction of the Arabian plate under Eurasia. Three-quarters of the belt crop out between the Irani-Pakistani coast (south) and the Jaz Murian and Hamun depressions (north). The remaining quarter is offshore, and it embodies the frontal and most active part of the prism. Two distinct areas can be recognized in this offshore portion. The western area where structures are mostly cylindrical, east-west oriented and regularly spaced, and the eastern one with strongly arched, irregularly spaced structures. This non-standard behaviour, in contrast to the more classical coulomb wedge model, is studied here using a twofold approach.
Firstly, multi-channel seismic reflection lines and high-definition bathymetry, acquired in 2004 during the CHAMAK cruise, are used to characterize the deformation processes associated to the development of this accretionary prism. Secondly, laboratory modelling of wedges with heterogeneous rheology (brittle and ductile) gives useful insights on the behaviour of natural compressive wedges. Thickness of ductile levels relative to brittle ones together with deformation rates control the order of thrusts nucleation and the shortening accommodation within the wedge. Sedimentary processes associated to active margins are also included in the models to study the interactions between deformation and sedimentation on these kind of settings. The in-detail study of piggyback basins along the Makran slope shows the complex history of these interactions with multiple periods of enhanced deformation over sedimentation and vice versa.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece