Vertical movements and Neogene propagation of the deformation in the Zagros Fold and Thrust Belt (Iran): insights from sections balancing and detrital low temperature thermochronology (U-Th/He on apatites and AFT)

Abstract

The Zagros Fold and Thrust belt contains about 50% of the yet-to-find hydrocarbon reserves hosted in fold and thrust belts worldwide, making this area of particularly high interest for the petroleum industry. In particular, understanding the structural and kinematic evolution as well as the vertical movements of this deformed part of the Arabian platform is important because it provides insights into the history of structural trap formation and how it relates to the timing of oil generation.

Our work focusses on the Pusht-e Kuh arc and the Dezful embayment areas and is based on a combination of field observations, construction of regional crustal scale balanced cross-sections, detrital low temperature thermochronology [AFT and (U-Th)/He on apatite] and structural forward modelling.

The results of detrital low temperature thermochronology analysis [AFT and (U-Th)/He on apatite] on samples taken mainly in the Late Cretaceous-Paleocene Amiran flysch (Saura et al., 2011) and in the Mid-Upper Agha Jari Molasse (Homke et al., 2004) show 1) a general foreland propagation of the cooling ages (from 13 to 2 Ma) along the Lurestan transect, 2) the tectonic burial of the Kermanshah suture zone (16-13 Ma) under the advancing Sanandaj-Sirjan front, and 3) the deposition of a thick Razak basin in flexural basin (16-13 Ma) over the northern part of the Simply Folded Belt.

Our main contributions to the interpretation of the regional structural style in the Lurestan, include 1) the presence of basement imbrications below the internal zone (Kermanshah suture) without creation of very high topography (underplating), 2) a relatively low to inexistent involvement of a basal décollement level (Hormuz equivalent) thus an important part of the topography of the Lurestan Plateau being explained by the existence of basement thrusting, 3) the integration of inverted Cretaceous grabens at the front of the belt (previously suggested by Kent, 2010). The structural style of the crustal scale cross-section Dezful is solved using a combination of 1) thin-skinned tectonics with multi-detachment folding in the sedimentary pile as already proposed in the literature (Sherkati et al., 2006; Carruba et al., 2006; Verges et al., 2009), and 2) thick-skinned tectonics (i.e. basement thrusting).

Comparison of the structural style along Zagros Fold-Thrust Belt highlights the fundamental difference in tectonic style between the Pusht-e Kuh and the Fars arcs respectively formed by thick-skinned and thin-skinned tectonic style.

These results and integration of the recent literature about the timing of the deformation in the Zagros Fold and Thrust Belt (Fakhari et al., 2008; Gavillot et al., 2010; Khadivi et al., 2010; Ruh et al., 2014), allows proposing a synthetic kinematic forward modelling in cross-section (using Geosec, a 2D geometric modelling tool) and a map view of the advance of the deformation front.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015