The Makran Accretionary Prism — Pakistan — Shortening, Gravity-Driven Tectonics & Fluid Migration Processes

Nadine Ellouz-Zimmermann, Raymi Castilla y Chacon, Jeremie Ferrand, Alain Prinzhoffer, Anne Battani, and Eric P. Deville
Geology-geochemistry-geophysics, IFP, Rueil-Malmaison cedex, France

The Makran accretionary prism results from the continuous subduction of the Arabian/Indian plates below the Afghan block microplates formerly accreted on Eurasia. Subduction started during Cretaceous time, and the tectonic accretionary prism developed south to southeastward. From new nannoplancton datings, we show that the trench was progressively filled by erosion products, either coming from Himalayas since Eocene times and conveyed by Paleo-Indus River, or by a diffuse hydrographic net (since Middle Miocene times).

Based on field data and new bathymetric and seismic data acquired in 2004 during the CHAMAK survey, regional sections have been analyzed. Their internal structure is characterized by:(1) a basal décollement level located within Paleogene or Cretaceous series, which deepens progressively from 6-8 km at the deformation front down to 11-12 km depth onshore; (2)a complex tectonic style depending both on the lithology controlled by regional and/or local depositional environment, and the sedimentary rates; and (3) a local disconnection between surface and deep structures,above disharmonic late Miocene slope series, where deep overpressure conditions developed. Linked with these pressure cells at depth, fluid and mud mobilization processes develped. At the surface, a spectacular "belt" of mud volcanoes outlined this processes onshore in the Coastal Range, but also offshore where high sedimentary rates and regional shortening combined to generate overpressure regime, below the platform.

Geochemical studies on waters and gas, giving a thermogenic signature on 3 samples, from mud volcanoes and seepages and from long cores (from Calypso piston core of Marion Dufresne II on BSR), we propose a conceptual model of the architecture of the structural traps-reservoirs system and on the fluid.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery