none 10.1144/SP330.9 Geological Society of London Geological Society of London 1881 42632271 65091 2024072310103700834 10.1144 2024-07-24T01:28:40Z 2010-06-01T18:07:09Z 77 Geological Society, London, Special Publications SP 0305-8719 2041-4927 06 2010 01 2010 330 1 H. Emami Group of Dynamic of Lithosphere (GDL), Institute of Earth Sciences ‘Jaume Almera’, CSIC, Lluís Solé i Sabarís s/n, Barcelona, 08028, Spain Statoil ASA, 15th Floor, 30 Bokharest Blg., 9th St., Bokharest Ave., Tehran 115137 Iran J. Vergés Group of Dynamic of Lithosphere (GDL), Institute of Earth Sciences ‘Jaume Almera’, CSIC, Lluís Solé i Sabarís s/n, Barcelona, 08028, Spain T. Nalpas Géosciences Rennes (UMR 6118), Université de Rennes 1, Campus de Beaulieu, 35042 Rennes cedex, France P. Gillespie Statoil, Tectonics and Structural Geology, Forushagen, Stavanger, Norway I. Sharp Statoil ASA, Technology and New Energy, Research Centre, Sandsliveien 90, Sandsli, NO-5020 Bergen, Norway R. Karpuz OMV Exploration and Production, Vienna, Austria E. P. Blanc Statoil, Vækerø Bygg B311B, Drammensveien 261, N0246 Oslo, Norway M. G. H. Goodarzi National Iranian Oil Company, Exploration Directorate, Surface Geology, 1st Seoul St., Sheaikh Bahaie Ave., Tehran 19948-14695, Iran Abstract The Mountain Frontal Flexure shows a single step along the front of the Pusht-e Kuh Arc with about 3 km of structural relief. This front has been interpreted as being formed by a basement monocline above a blind crustal-scale and low-angle thrust with a ramp–flat geometry (the ramp dips 12–15° towards the inner part of the orogen and cuts the entire crust). The Anaran anticline on top of the Mountain Frontal Flexure shows an irregular geometry in map view and consists of four segments with diverse directions of which the SE Anaran, the Central Anaran and the NW Dome are culminations. The North–South Anaran segment may form a linking zone developed during the rise and amplification of single culminations, the NW Dome and the Central Anaran, above the Mountain Frontal Flexure. The asymmetric Anaran anticline is characterized by the existence of multiple normal faults, some of them with significant dip-slip displacements of up to 1000 m. These faults limit grabens located along the crests of the anticline segments. Cross-cutting relationships show that the normal faults along the Central Anaran are older than along the North–South Anaran, reinforcing the temporal constraints on the later growth of this segment of the anticline. The geometry of the Anaran anticline is asymmetric with the subvertical forelimb very little exposed. This forelimb is cut above and below by a thrust system that seems to develop along the fold hinges. The lower thrust, with a ramp–flat geometry, carries the entire anticline towards the foreland on top of slightly deformed rocks in the footwall. The thrust flattens in the Gachsaran evaporitic level forming a typical triangular zone filled with evaporites, which produce a strong fold disharmony between the overburden (Passive Group) and the underlying rocks (Competent Group). The growth of the Anaran anticline lasted for about 6 Ma and was the consequence of detachment folding that was subsequently thrust, rotated and uplifted above the Mountain Frontal Flexure with coeval reactivation of earlier crestal layer-parallel extension normal faults to accommodate the large increase of structural relief between the foreland and the tectonic arc. Three main results from analogue modelling have been combined with field data to resolve the geometry of the Anaran anticline as well as its evolution: (1) a thickening of intermediate evaporites (Gachsaran Formation) is produced above the flat segment of the thrust carrying the anticline on top of foreland strata; (2) growth strata deposited in the adjacent syncline modify the geometry of the anticline by increasing the dip and the length of its forelimb; (3) coeval erosion to anticline growth, as well as thick growth strata deposition, increases fold amplification rather than foreland propagation of deformation. The proposed fold model may be applied to other anticlines on top of this major basement-related thrust, such as the Siah Kuh and Khaviz anticlines in the Pusht-e Kuh Arc and Dezful Embayment domains. 06 2010 01 2010 155 178 10.1144/SP330.9 https://doi.org/10.15223/policy-002 10.1144/SP330.9 https://www.lyellcollection.org/doi/10.1144/SP330.9 https://www.lyellcollection.org/doi/pdf/10.1144/SP330.9 https://pubs.geoscienceworld.org/books/book/1694/chapter/107531661/structure-of-the-mountain-front-flexure-along-the https://pubs.geoscienceworld.org/UrlRedirectHandler.ashx?routename=books&chapterdoi=10.1144/SP330.9&request=chapter 10.1016/S0037-0738(01)00168-3 10.1016/0040-1951(94)00185-C AAPG Bulletin Berg R. R. 2019 46 1962 Mountain flank thrusting in Rocky Mountain foreland, Wyoming and Colorado Berg R. 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