Potential Field Imaging of Salt and Basement Structures in the Southern Zagros Foreland Basin

Abstract

The blind and exposed salt domes in the Fars Arc of the south-eastern Zagros Fold and Thrust Belt, are rooted in the Precambrian–Early Cambrian Hormuz Salt, which deposited over a Precambrian crystalline basement. To define the subsurface blind salt domes and examine the influences of the basement morphology on the distribution of the salt domes and their impact on hydrocarbon accumulation, we used high–resolution terrestrial magnetic and gravity data. Applying various derivative–based filters on the Bouguer gravity anomalies we identified seven blind salt domes. From those, two have characteristic topographic implications and another three have been also imaged by the earlier seismic studies. A low Bouguer anomaly with a prominence sharp variation limits the western extent of the overlying allochthonous Late Oligocene–Early Miocene Fars Salt layer. The horizontal derivative of the Bouguer anomaly highlights a distinctive lineament in the south of the Bander–e–Lengeh anticline, which is interpreted as the effect of the Fars Salt layer on folding and faulting propagation. The magnetic anomalies were not effective for detecting blind salt domes due to the presence of highly magnetised crystalline basement rock fragments within salt domes, yielding an unexpected non-zero susceptibility value similar to the surrounding sedimentary layers. This indicates the influence of crystalline basement dynamics on salt tectonism in the study area. The N–S trend of the long-wavelength magnetic anomaly of the Hendurabi Lineament extends east of the study area and reflects a basement structure. The integrated E–W gravity–magnetic forward modelling implies an N–S trending horst–graben structure in the crystalline basement, which controls the thickness of the Hormuz salt and possibly the distribution of salt domes.