Area Balanced Crustal Cross-Section across the NW Zagros Belt and Late Cretaceous Arabian Margin Reconstruction: Shortening and Deformation Sequence

Vergés, Jaume ¹; Saura, E. ¹; Casciello, E. ¹; Fernàndez, M. ¹; Villaseñor, A. ¹; Jiménez-Munt, I. ¹; Garcìa-Castellanos, D. ¹
(1)Group of Dynamics of the Lithosphere - GDL, Barcelona, Spain.

New area balanced and restored cross-sections are constructed across the NW Zagros Fold Belt in Lurestan in Iran integrating new geological observations and local and global geophysical datasets. The balanced cross-section is pinned in the Mesopotamian foreland (non-deformed Arabian crust) near the Iraq-Iran border at 20 km to the south-west of the Mountain Frontal Flexure. The top of the area balanced corresponds to the near top Sarvak Formation (main HC reservoir, Late Cretaceous in age at around 90 Ma). This level together with the Oligocene-Miocene Asmari level (main Tertiary HC reservoir) show a fairly continuous outcrop along the study transect. The base of the Arabian crust is defined in recently published receiver functions results showing deepening of the Moho from about 42 km in the non-deformed crust to 56 km below the inner regions of the Zagros. The present boundary between Arabia and Eurasia plates is defined by new seismic tomographic sections displaying a sharp contact, dipping about 50° to the north-east separating a relatively fast lithosphere in the south-west (Arabia) and a slow and warmer lithosphere beneath Iran. These four limits constrain a crustal area of 10,800 km² that is used to determine the restored structure of the Arabian margin before compression.

The quantified reconstruction of the Arabian margin during Late Cretaceous times assumes area conservation through compressive deformation. In addition, the Arabian margin is divided in 6 different tecto-sedimentary domains according to their sedimentary facies and paleobathymetries and assuming Airy isostasy. Using these constraints we reconstruct an Arabian margin that extent about 169 km further to the north-east of the present position of the Main Reverse Fault (MRF), which is considered the actual boundary between Arabia and Iran.

The direct comparison between balanced and restored cross-sections indicates a much larger shortening than previously calculated using field data only. The Arabian basement rocks shortened ~149 km (39%). Interestingly, the Arabian cover rocks shortened about ~180 km (47%), which include all compressive events from Late Cretaceous obduction through Miocene continental collision, spanning about 90 Myr.

Line-length balancing technique applied to the near top Sarvak Formation in the Simply Folded Belt only determine 21 km of shortening (11%), which mostly accounts for the growth of the superbly developed whale-back anticlines from early Miocene to

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.