Abstract
Geological and geomorphologic offsets are used to constrain the total displacement and estimate the slip rate of the right-lateral Deshir Fault. Cumulative morphologic offsets have been found along the southern portion of the fault, on the Iranian Plateau. High-resolution SPOT5 images (pixel size 2.5 m) combined with SRTM DEM document right-lateral offsets of rills, terrace risers and successive alluvial fan systems. Cumulative offsets range from 25 to 900 m and increase with relative elevation, hence relative age, of offset markers. The smallest cumulative offsets are most probably of Holocene age (12 ± 2 ka) and suggest that the fault slips at an average slip rate close to 2 mm yr−1. Coeval normal faulting is associated to strike-slip motion at several places along the southern portion of the fault. Normal and probably active faults are encountered within the High Zagros 70 km ahead the tip of the Deshir Fault and may suggest the fault is propagating southwards. The total displacement of the Deshir fault, estimated from right-lateral offset of the Nain-Baft suture, is 65 ± 15 km. The total displacement would have accumulated over the last 25–40 Ma at an averaged Holocene slip rate of 2 mm yr−1. Placing these observations within the framework of the tectonics of Iran allows a discussion of the timing of the transition between collision and subduction in Eastern Iran.
Highlights
Active tectonics of Zagros and Central Iran involves a combination of strike-slip and thrust faulting that accounts for a fraction of the present-day Arabia–Eurasia convergence (e.g. Jackson & MacKenzie 1984; Fig. 1)
While about 16 mm yr−1 right-lateral shear currently occurs between Central Iran–Zagros and Lut–Makran regions (Vernant et al 2004), the interaction between strike-slip faulting and shortening remains uncertain over the longer term
The recent offsets we document indicate the fault is probably moving at an average slip rate of 2 mm yr−1
Summary
Active tectonics of Zagros and Central Iran involves a combination of strike-slip and thrust faulting that accounts for a fraction of the present-day Arabia–Eurasia convergence (e.g. Jackson & MacKenzie 1984; Fig. 1). Active tectonics of Zagros and Central Iran involves a combination of strike-slip and thrust faulting that accounts for a fraction of the present-day Arabia–Eurasia convergence NNW–SSE strike-slip faults occur at the transition between Zagros and Makran as well as along the border between Central Iran and Lut block, where right-lateral shear is expected to accommodate the differential motion between the already colliding domain and that continuing to subduct. Recent GPS studies show the present-day displacement field for all of Iran and give a shortening rate of 6.5 ± 2 mm yr−1 across the Zagros (Vernant et al 2004, Fig. 1). While about 16 mm yr−1 right-lateral shear currently occurs between Central Iran–Zagros and Lut–Makran regions (Vernant et al 2004), the interaction between strike-slip faulting and shortening remains uncertain over the longer term. Our main objectives are to discuss finite offset, onset of motion and Quaternary slip rate. We discuss our observations in the framework of the Tertiary tectonic evolution of southern Iran
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