The Mississippian rocks at 5 sections, Kalariz, Peyghambaran, Jaban, Naserabad, and Dozdehban, have been measured and sampled in a SE–NW direction across the Alborz Mountains. Foraminiferal zones recognized in those sections, as well as a revision of other foraminiferal assemblage previously published from the Alborz Mountains, allow to recognize 12 biozones: 5 in the Tournaisian: Unilocular (MFZ1–MFZ2? interval), Septabrunsiina krainica (MFZ3–MFZ5 interval), Eotextularia diversa (MFZ6), Darjella monilis (MFZ7), and primitive Eoparastaffella (MFZ8); 5 Viséan biozones: Eoparastaffella simplex (MFZ9), primitive archaediscids (MFZ10), Uralodiscus rotundus (MFZ11), Pojarkovella–Koskinotextularia (MFZ12), Neoarchaediscus (Upper Mikhailovian), Howchinia gibba–Archaediscus/Paraarchaediscus at angulatus‐tenuis stage–Neoarchaediscus akchimensis (Venevian substage); and 2 Serpukhovian biozones: Biseriella parva–Climacammina (Tarusian–Steshevian substages) and Turrispiroides multivolutus–Brenckleina–Eostaffellina protvae (Protvian substage) for the Mississippian rocks of Alborz. Analysis of foraminiferal assemblages indicates a noticeable age difference of the Mississippian rocks between the northern and southern flanks of Alborz. Accordingly, south‐eastern and east‐central Alborz (Kalariz, Peyghambaran, and Jaban sections) display complete Tournaisian deposits (MFZ1–MFZ8), whereas northern Alborz contains the strata dated from Late Tournaisian to Late Serpukhovian (MFZ8–MFZ16). The sedimentological studies also reveal sharp facies variations following the mentioned age variation. Previously, the age variations of these rocks were attributed to various events, such as the Mississippian glaciation phases. However, the age, facies, and thickness variations of lithostratigraphic units in the Alborz are not specific to the Mississippian and are reported during the entire Palaeozoic and even Mesozoic and Cenozoic. They can rather be attributed to the inherited basement and syn‐sedimentary E–W‐trending faults.

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The Mosha Fault is a multiply inverted fault in the Central Alborz. Field observations and structural data from this fault show that a footwall shortcut is the major mode of response of this fault to contractional deformation. Although the Mosha Fault is a basement-involved fault, there is no evidence of involvement of basement along its footwall shortcuts, at least in the study area. Footwall shortcuts along this fault vary in size from several hundreds of metres to tens of kilometres, suggesting that a footwall shortcut can be scale independent. It is proposed that footwall shortcuts can also occur as blind thrusts under fault-related folds in the terrains near the major inverted faults. Similar cases also exist in other regions such as Japan. Some large footwall shortcuts may be the causative fault of devastating earthquakes in the active inverted terrains such as the south Central Alborz. Incompetent layers acting as detachments may play an important role in the development of footwall shortcuts. Recumbent folding in the form of a cover nappe in the footwall of the Mosha Fault is another case of southward migration of deformation along the Mosha Fault by which the fault has responded to the Oligo-Miocene compression. This case can be considered as a newly recognized style of deforming structure that occurred along an inverted fault.Résumé : La faille de Mosha est une faille à multiples inversions située dans l'Elbourz central. Les observations sur le terrain et les données structurales obtenues pour cette faille montrent qu'un raccourcissement de l'éponte inférieure « footwall shortcut » constitue le principal mode de réponse de cette faille à une déformation de contraction. Bien que la faille de Mosha soit une faille dans le socle, il n'y a pas de preuve d'implication du socle le long des raccourcissements de l'éponte inférieure, du moins dans le secteur à l'étude. Les raccourcissements de l'éponte inférieure le long de cette faille varient de plusieurs centaines de mètres à des dizaines de kilomètres, suggérant que le raccourcissement de l'éponte inférieure puisse être indépendant de l'échelle. Il est proposé que les raccourcissements de l'éponte inférieure puissent aussi se retrouver en tant que chevauchements aveugles sous des plis reliés aux failles dans les terrains à proximité des grandes failles inverses. Des cas semblables peuvent aussi exister dans d'autres régions telles que le Japon. Certains grands raccourcissements de l'éponte inférieure peuvent aussi être les causes des séismes dévastateurs dans des terrains inversés actifs tels que dans l'Elbourz centre-sud. Des couches incompétentes agissant en tant que détachements pourraient jouer un rôle important dans le développement de raccourcissements de l'éponte inférieure. Des plis couchés ayant la forme d'une nappe de couverture dans l'éponte inférieure de la faille de Mosha constituent un autre cas de migration vers le sud de la déformation le long de la faille de Mosha par lesquels la faille a réagi à la compression à l'Oligocène-Miocène. Ce cas ...

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