TECTONIC HISTORY OF THE EASTERN MARGIN OF THE LUT BLOCK IN THE NEHBANDAN AREA, EASTERN IRAN

The central eastern margin of the microcontinental Lut Block (LB) (Nehbandan area, Eastern Iran) has undergone a complicated tectonic evolution since the late Paleozoic, from rifting from the Gondwanan margin in the Permian-Triassic to counterclockwise rotation and collision with the Afghan plate in the Cenozoic. Our study recognizes seven tectonostratigraphic units that outline this evolution across the margin of the LB. (1) The Dehsalm metamorphic complex that includes a thick pile of platform carbonate and interbeds of continental flood basalt of probable Permian-Triassic ages. This complex may be the remnant of a rifted Neotethyan margin that has later been subject to high temperature metamorphism in a volcanic arc setting during the Late Jurassic. (2) Deep-marine siliciclastic sediments deposited in an Early Jurassic forearc basin overlying deformed sequences of an accretionary prism. Termination of the basin in the Late Jurassic is preceded by transition of the sedimentation from deep- to shallow-water environments and calc-alkaline lavas. This succession was folded in the Late Jurassic and crosscut by the Shah-Kuh granitoids due to Neotethys subduction under the LB. (3) The Jurassic accretionary prism is delimited by a green belt several tens of kilometers long, which includes deformed oceanic basalts and pelagic sediments. (4) A younger, Eocene accretionary prism composed of partly metamorphosed and deformed turbidites locally including lenses of Upper Cretaceous pillow lavas. This prism records continuation of Neotethys subduction under the LB. (5) A syn-collisional granite of Eocene-Oligocene age associated with high-temperature metamorphic occurs along an arc-shaped structure believed to have developed during 90° anticlockwise rotation of the LB at the time of India-Eurasia collision. (6) A Cretaceous ophiolitic mélange and the Eocene Chahar-Farsakh flysch. These units record the closure of the wedge-shaped Sistan ocean in the northern part of Neotethys between the Lut and Afghan blocks. This closure was synchronous with rotation of the LB to its current orientation. (7) A thick, folded Neogene sequence of shallow marine and continental sediments. The sequence is cut by right-lateral strike-slip faults that developed synchronously to the Arabia-Eurasia collision event.