The Sistan Suture Zone in eastern Iran preserves remnants of an ocean basin that subducted between the Lut and Helmand blocks in Late Cretaceous-Early Eocene time. Surprisingly, this N-S trending suture is nearly perpendicular to the regional E-W striking Neo-Tethyan suture zone. The suture is defined by folds and thrusts of a westward and structurally downward-younging ocean-derived accretionary prism. We show that in the north,where the suture bends towards NW-SE, the accretionary prism abruptly terminates against the steep, NE-SW striking Madar-Kuh thrust. This thrust strikes perpendicular to the prism, ends where the prism disappears southwestward but continues northeastward, suggesting a genetic relation to the former subduction zone. The Madar-Kuh thrust emplaces continental Lut Block rocks over ocean-derived units. Thrust-parallel folds were later refolded, giving the Madar-Kuh Fault a curvilinear trend. Radial microdioritic dikes, consistently strikeperpendicular to the first-generation folds yield U/Pb ages of 64.6 ± 1.1 Ma and 43.2 ± 0.6 Ma, demonstrating that refolding postdates Sistan Suture closure. We hypothesize that during active subduction, the MadarKuh Fault was a trench- perpendicular, subduction-parallel fault marking the termination of the Sistan subduction zone. We speculate that this fault accommodated westward motion of the Helmand Block towards the Sistan Ocean, facilitating subduction. Our findings clarify how microplates and continental fragments interacted within the upper plate of the Neo-Tethys system and highlight that long-lived E-W to NE-SW tectonic motion along the southern Eurasian margin involved crustal extrusion away from western Tibet and into Iranian back-arc basins, impacting the tectonic evolution of the Iranian and Tibetan plateaus alike.

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