STRUCTURAL STYLE AND TIMING OF NW-SE TRENDING ZAGROS FOLDS IN SW IRAN: INTERACTION WITH NORTH-SOUTH TRENDING ARABIAN FOLDS AND IMPLICATIONS FOR PETROLEUM GEOLOGY

Jaume Vergés*1, Giulio Casini1,2, Jonas Ruh3, John Cosgrove4, Shahram Sherkati5,6, Mahdi Najafi1,7, Emilio Casciello1, Eduard Saura1,2, Iraj Abdollahie Fard5, Alireza Piryaei5, Dominique Frizon de Lamotte8, Jean Letouzey9, Hasan Goodarzi5, Bahman Soleimany10 and Salman Jahani5

1 Group of Dynamics of the Lithosphere (GDL), Geosciences Barcelona Geo3Bcn-CSIC, 08028 Barcelona, Spain.

2 Lithica SCCL, Av. Farners, 16, 17430 Girona, Spain.

3 Institut de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Spain.

4 Dept of Earth Science & Engineering, Imperial College, London SW7 2AZ.

5 National Iranian Oil Company Exploration Directorate, (NIOC), PO Box 1994814695, Tehran, Iran.

6 Petronas Upstream, 50088 Kuala Lumpur, Malaysia.

7 Department of Geology, Tarbiat Modares University, PO Box 1411713116, Tehran, Iran.

8 CY Cergy Paris Université, Dept. of Earth and Environmental Sciences, F95 000 Cergy-Pontoise, France.

9 Sorbonne Université, ISTEP-UMR7193, 4 place Jussieu, Paris, France.

10 Board Member, Geological Society of Iran, Tehran, Iran.

* Corresponding author: email jverges@geo3bcn.csic.es

The Zagros foldbelt – foreland system in SW Iran is a prolific hydrocarbon province with known reserves of more than 90 billion brl of oil and 800 TCF of natural gas. Establishing the structural style of folding in the Zagros area presents a major challenge due both to the geographical extent of the foldbelt, which is some 1600 km long in total, and the presence of marked lateral variations in fold style related to the complex regional tectonic history. In addition, while numerous high-quality structural studies of the Zagros have been completed over the last 20 years, they support a variety of different interpretations and are therefore diffcult to synthesize. In this paper, we review the general structural style of the Zagros fold-and-thrust belt in SW Iran, and in particular the style of folding in the Lurestan arc, Dezful embayment, Izeh Zone and Fars arc. We summarise relationships between folding in these areas and fracture development, and investigate the timing of folding and the interaction between NW-SE oriented "Zagros" folds and north-south oriented "Arabian" folds. Finally, we briefly assess the implications of fold style for petroleum systems in the Zagros area. Although no new data are presented in this paper, a series of unpublished maps are used to illustrate the main results and include: a map showing the extent of the main detachment levels across the Lurestan, Dezful and Fars structural domains; two palaeotectonic maps (for Late Cretaceous – Paleocene and Miocene – Pliocene times, respectively), showing the position of the deformation fronts of the Zagros and the North Oman thrust systems and their potential spatial and temporal relationship with folding; and a set of four maps showing the distribution of reservoir rocks which are grouped by age into the Permian – Triassic Dehram Group, the Late Jurassic – Early Cretaceous Khami Group, the Late Cretaceous Bangestan Group, and the Oligocene – Miocene Asmari Formation. In addition, for the Lurestan, Dezful and Fars structural domains, a series of regional cross-sections at the same scale are presented and discussed.

Most of the data in this review paper were acquired in order to gain an improved understanding of the petroleum systems in the Zagros area; however the data are used here to investigate a range of interacting processes including tectonics, sediment deposition and subsurface fluid flow in the development of the fold-and-thrust belt and its associated foreland basins. The resulting synthesis is intended to provice a starting point for future tectonostratigraphic and hydrocarbon-related studies which will make use of both existing and new multidisciplinary techniques to constrain the results. The knowledge acquired and the techniques used will be of benefit in future challenges including the identification of subsurface reservoirs suitable for the permanent storage of CO2 to mitigate the effects of climate change.

Key words: Zagros fold-and-thrust belt, Iran, structural style, fold mechanism, detachment levels, fractures, Zagros folds, Arabian folds, modelling, petroleum systems.

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