Development of En-Echelon Folds above the Offshore Extent of the Minab Fault, Makran Accretionary Complex, Offshore Iran
The Makran Accretionary Complex (MAC), Iran and Pakistan, is a fold-thrust system bound by the Murray Ridge and Ornach Nal Fault to the east and the Minab Fault System (MFS) to the west. It is c. 1000 km wide and the frontal c. 125 km of the system is submerged beneath the Gulf of Oman. We use 2D seismic reflection data to investigate the structural style and evolution of the offshore, Iranian segment of the MAC. Overall, the MAC is characterised by laterally continuous, north-dipping thrust faults, which are overlain by south-verging, non-cylindrical, fault-propagation folds.
Two principal structural domains are identified; (i) an inner domain, located immediately offshore, which is characterised by normal faults in the lower sequence and E-W-striking, thrusts and fault-propagation folds in the upper sequence and (ii) an outer domain, close to the deformation front, which is dominated by E-W-striking thrusts and fault-propagation folds that affect the entire sequence.
Immediately offshore from the onshore trace of the MFS, the MFS itself is not imaged, suggesting that the structure does not continue offshore or that its offshore expression is too subtle to be imaged by seismic data. Instead, the structures in domain (i) are intensely thrusted, with reactivation on the normal faults. The thrusts and associated folds in domain (ii) trend NW-SE and, in contrast to the laterally-continuous structures that characterise the rest of domain (ii), folds in this location are only c. 20 km long and have a wavelength of c. 5 km.
Similar shallow-level fold structures are observed
above the offshore extent of the Kazerun Fault, western Iran. Neither these
folds, nor the structures offshore from the MFS can be adequately described by
a flower structure model, implying that this model has limited applicability in
strongly mechanically layered sequences. In the examples above, the cover
sequences are decoupled from the major basement fault and flower structures do
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California