Ali Seyrek

Kinematics of active left-lateral faulting in SE Turkey from offset Pleistocene river gorges: improved constraint on the rate and history of relative motion between the Turkish and Arabian plates

In the Arabian Platform of SE Turkey abundant evidence exists of fluvial incision by c. 110 ± 10 m since the late Early Pleistocene, starting in or around marine oxygen isotope stage 22 at 870 ka. This incision, which has accompanied regional surface uplift as the isostatic response to regional erosion, has progressively ‘locked’ rivers into their gorges in landscape that formerly had much lower relief. We use this effect to estimate 4.44 ± 0.06 km of left-lateral slip on this time scale on the Gölbaşı–Türkoğlu Fault, a segment of the East Anatolian Fault Zone, from offset river gorges, giving a slip rate of 5.10 ± 0.07 mm a−1. Piercing points indicate that this fault has slipped a total of 19 km, making its age 3.73 ± 0.05 Ma. A total of 33 km of relative motion between the Turkish and Arabian plates is documented on this time scale in the vicinity of Gölbaşı, at an overall time-averaged rate of 8.85 ± 0.12 mm a−1, the estimated Euler vector for relative motion between these plates being 0.89 ± 0.01° Ma−1 about 33.4°N, 42.3°E. This method can be readily applied to determine slip rates, time-averaged since the late Early Pleistocene, on other strike-slip fault zones worldwide.

Kinematics of the Amanos Fault, southern Turkey, from Ar/Ar dating of offset Pleistocene basalt flows: transpression between the African and Arabian plates

Abstract We report four new Ar/Ar dates and 18 new geochemical analyses of Pleistocene basalts from the Karasu Valley of southern Turkey. These rocks have become offset left-laterally by slip on the N20°E-striking Amanos Fault. The geochemical analyses help to correlate some of the less-obvious offset fragments of basalt flows, and thus to measure amounts of slip; the dates enable slip rates to be calculated. On the basis of four individual slip-rate determinations, obtained in this manner, we estimate a weighted mean slip rate for this fault of 2.89±0.05mm/a (±2σ). We have also obtained a slip rate of 2.68±0.54mm/a (±2σ) for the subparallel East Hatay Fault farther east. Summing these values gives 5.57±0.54mm/a (±2σ) as the overall left-lateral slip rate across the Dead Sea fault zone (DSFZ) in the Karasu Valley. These slip-rate estimates and other evidence from farther south on the DSFZ are consistent with a preferred Euler vector for the relative rotation of the Arabian and African plates of 0.434±0.012° Ma−1 about 31.1°N, 26.7°E. The Amanos Fault is misaligned to the tangential direction to this pole by 52° in the transpressive sense. Its geometry thus requires significant fault-normal distributed crustal shortening, taken up by crustal thickening and folding, in the adjacent Amanos Mountains. The vertical component of slip on the Amanos Fault is estimated as c. 0.15mm/a. This minor component contributes to the uplift of the Amanos Mountains, which reaches rates of c. 0.2–0.4mm/a. These slip rate estimates are considered representative of time since. 3.73±0.05Ma, when the modern geometry of strike-slip faulting developed in this region; an estimated 11km of slip on the Amanos Fault and c. 10km of slip on the East Hatay Fault have occurred since then. It is inferred that both these faults came into being, and the associated deformation in the Amanos Mountains began, at that time. Prior to that, the northern part of the Africa–Arabia plate boundary was located further east.