The Geological Evolution of Southern Iran: The Report of the Iranian Makran Expedition

Abstract

The geological evolution of southern Iran is considered in the light of observations made in late 1974 and early 1976, when the author led the Royal Geographical Society/Imperial College Expedition to the Iranian Makran. The landforms, rock types and structure of much of the Makran contrast markedly with those of the Zagros Mountains to the west, from which it is separated by the Zendan Fault. The simple folds of the Zagros trend NW-SE and formed chiefly in the Pliocene and Pleistocene; they comprise Palaeozoic, Mesozoic and Tertiary sedimentary rocks deposited in a relatively shallow shelf-sea. The Inner Makran consists of Upper Cretaceous to Miocene sandstones and shales laid down in a marine trench by turbidity currents, and of strongly disturbed ophiolitic melanges representing disrupted oceanic crust. In Coastal Makran, however, gently folded nearshore shallowwater sediments predominate, and appear to be continuous with the southernmost folds of the Zagros. The marine trench postulated for the turbidites of the Inner Makran may be an extension of the Kermanshah-Neyriz trench, which opened during the Mesozoic when the Arabian and central Iranian plates drifted apart, and closed when this movement was reversed in the Late Cretaceous; the Zendan Fault could represent a transform fault associated with the closure. Subduction promoted early Tertiary volcanicity behind the trench. Renewed movement in the Pliocene produced the Zagros folds, and is reflected in the area's high seismicity and in recent volcanic action. Appendix I, by G. P. L. Walker and B. Booth, describes various volcanic landforms near Kuh-e Bazman. In Appendix II the author suggests that the ophiolitic melanges near Faryab are debris flows. Appendix III, by N. L. Falcon, shows a diagrammatic section of the Minab anticline and describes the structure and formation of the coastal area in which it lies.