Kinematics of the Malatya-Ovacik fault zone

We investigate the left-lateral slip on the 240-km-long, NE-SW-trending, Ma latya-Ovacik fault zone in eastern Turkey. This fault zone splays southwest ward from the North Anatolian fault zone near Erzincan, then follows the WS W-trending Ovacik valley between the Munzur and Yilan mountain ranges. It b ends back to a SW orientation near Arapkir, from where we trace its main st rand SSW beneath the Plio-Quaternary sediment of the Malatya basin. We prop ose that this fault zone was active during similar to5-3 Ma, when it took u p 29 lan of relative motion between the Turkish and Arabian plates; it ceas ed to be active when the East Anatolian fault zone formed at similar to3 Ma . The geometry of the former Erzincan triple junction, which differs from t he modern Karliova triple junction, where the North and East Anatolian faul t zones intersect, suggests a possible explanation for why slip on the Mala tya-Ovacik fault zone was unable to continue. We interpret the SW-and SSW-t rending segments of the Malatya-Ovacik fault zone as transform faults, whic h define an Euler pole similar to1 400 km to the southeast. Its central par t along the Ovacik valley, which is similar to 30 degrees oblique to the ad joining transform faults, is interpreted as the internal fault of a stepove r. The adjoining mountain ranges, which now rise up to similar to3 300 m, s imilar to2 000 m above the surrounding land surface, are largely the result of the surface uplift which accompanied the components of shortening and t hickening of the upper crustal brittle layer that occurred around this step over while the left-lateral faulting was active. (C) 2001 Editions scientif iques et medicales Elsevier SAS.