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Discussion papers
https://doi.org/10.5194/se-2018-137
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2018-137
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Dec 2018

Research article | 18 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

Linked thick to thin – skinned inversion in the central Kirthar Fold Belt of Pakistan

Ralph Hinsch1, Chloé Asmar1, Muhammad Nasim2, Muhammad Asif Abbas2, and Shaista Sultan2 Ralph Hinsch et al.
  • 1OMV Upstream, Exploration, Vienna, 1020, Austria
  • 2OMV (Pakistan) Exploration GmbH (subsidiary of United Energy Group Limited), Islamabad, Pakistan

Abstract. The Kirthar Fold Belt is part of the lateral collision zone in Pakistan linking the Makran accretionary wedge with the Himalaya orogeny. The region is deforming very obliquely, nearly parallel to the regional S-N plate motion vector, indicating strong strain partitioning. In the central Kirthar Fold Belt, folds trend roughly N-S and their structural control is poorly understood. In this study, we use newly acquired 2D seismic data with pre-stack depth migration, published focal mechanisms, surface and subsurface geological data as well as structural modelling with restoration and balancing to constrain the structural architecture and kinematics of the Kirthar Fold Belt.

The central Kirthar Fold Belt is controlled by Pliocene to recent inversion of Mesozoic rift related normal faults. Focal mechanisms indicate dip-slip faulting on roughly N-S trending faults with angles in the order of 45°, which are too steep for newly initiated thrust faults. The hinterland of the study area is primarily dominated by strike slip faulting. The inverting faults do not break straight through the thick sedimentary column of the post-rift and flexural foreland; rather the inversion movements link with a series of detachment horizons in the sedimentary cover, progressively imbricating the former footwall of the normal fault. Due to the presence of a thick incompetent upper unit (Eocene Ghazij shales) these imbricates develop as passive roof duplexes. Finally, the youngest footwall shortcut links with a major detachment and the deformation propagates to the deformation front, forming a large fault-propagation fold. Shortening within the studied sections is calculated to be on the order of 20%.

The central Kirthar fold belt is a genuine example of hybrid thick- and thin-skinned system in which the paleogeography controls the deformation. The locations and sizes of the former rift faults controls the location and orientation of the major folds. The complex tectonostratigraphy (rift, post rift, flexural foreland) alone with the strong E-W gradients defines the mechanical stratigraphy, which in turn controls the complex thin-skinned deformation.

Ralph Hinsch et al.
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Short summary
We use surface and geophysical subsurface data to constrain the structure and evolution of the central Kirthar Fold belt, a mountain belt on the western margin of the Indian plate in Pakistan. It can be shown, that the extension phase prior to the collision of India with Asia has a major impact on how the rocks deform today. The inherited structures in the crystalline basement reactivate in opposite sense and complexly deform the sedimentary rocks that have deposited before collision.
We use surface and geophysical subsurface data to constrain the structure and evolution of the...
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