International Geologiical Congress - Oslo 2008

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STT-06 Marine and continental fold and thrust belts

 

Pulsed south-westerly migration of the Zagros deformation front during the Miocene-Recent: Seismic evidence from the Persian Gulf

 

Caroline Burberry, Imperial College London (United Kingdom)
Christopher A-L Jackson, Imperial College London (United Kingdom)
John W Cosgrove, Imperial College London (United Kingdom)
JianGuo Liu, Imperial College London (United Kingdom)
 

 

The Zagros Simply Folded Belt (ZSFB) is a spectacular example of an actively deforming mountain belt, formed by the ongoing collision of Arabia and Eurasia. Typically, the deformation front of this orogen is placed at the NE margin of the Persian Gulf. However, recent work suggests that basement deformation extends considerably further south-westwards into the Arabian basement. In addition, the locations of recent earthquake epicentres in the Persian Gulf imply that the deformation front is actively migrating to the SW. The migration of the terrestrial deformation front has been investigated using remote sensing of fold morphology and drainage alteration, and the spatial distribution of frontal structures has been mapped. These data indicate a model for deformation within the ZSFB that includes episodes of footwall collapse, combined with the process of serial folding above intermediate detachments in the cover succession.
Interpretation of marine 2D seismic data, offshore from Bushehr and to the east of the Kazerun fault trace, reveals the presence of subtle compressional structures in the basin, a further 75 km basinward from the inferred location of the Zagros deformation front. Two types of compressional deformation are observed; (i) inversion of a salt-diapir-related extensional fault and partial expulsion of the associated syn-kinematic hangingwall fill and (ii) long-wavelength (16 km), low-amplitude (60 ms TWTT) folds. Deformation of two major unconformities tentatively dated as Late Cretaceous/Early Tertiary in age, combined with growth strata geometries implies that maximum activity on these structures was during the Early Miocene. In addition, detailed mapping of growth strata packages indicates a prolonged period of growth. Distinct thickening of these packages NE towards the hinterland implies loading from the Zagros Frontal Fault with relatively rapid deformation and associated subsidence. Furthermore, the presence of salt in this region implies that the salt decollement extends further SW than current mapping suggests.
The identification of compressional structures within the Persian Gulf suggests that the Zagros deformation front location cannot be defined by the spatial extent of large-scale, onshore structures and is considerably further SW than the presently accepted position. The distance of the observed compressional structures in the Persian Gulf from the previously inferred deformation front further implies that deformation in the Zagros orogen is not occurring by serial folding alone, but by combined ductile and brittle faulting processes.

 

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