Tectonic development of the southern Karasu Valley, Turkey: successive structural events during basin formation

New fault data are presented for the Karasu Valley, southern Turkey. Field measurements concentrate on the Eocene–Miocene (c. 48–7 Ma) sediments exposed on the south-western rift margin, in order to investigate the early development of this basin. Fault data show two trends in orientation NW–SE and NE–SW with a subordinate north–south trend. Stress inversions combined with field relationships indicate at least three phases of faulting. Firstly, an extensional event characterized by NE–SW and NW–SE normal faults, which are interpreted to have formed owing to flexural uplift in the forebulge region to the Bitlis–Zagros collisional front prior to the Middle Miocene. Secondly, north–south normal faults invert to give a stress ratio [R=(σ2 – σ3/σ1 – σ3)] indicative of an extensional stress regime, transitional to strike-slip faulting. The final stress phase (Pliocene–Recent) is of strike-slip faulting and east–west-trending normal faulting. This stress regime is interpreted as the result of the propagation of the Dead Sea Fault or East Anatolian Fault. Previous models of rift formation have invoked either transpressional or transtensional origins for the area; the new data presented here indicate that the southernmost Karasu Valley developed through extension followed by transtension.

本文提供了土耳其南部卡拉苏谷的全新断层数据。本次野外测量聚焦于西南裂谷边缘出露的始新世-中新世（约4800万至700万年前）沉积物，以探究该盆地的早期演化过程。断层数据显示其走向存在北西-南东、北东-南西两组优势取向，另有少量南北向次级取向。结合野外构造关系开展的应力反演结果表明，该区域至少经历了三期断层活动：第一期为伸展事件，以发育北东-南西向和北西-南东向正断层为特征，这些断层被认为形成于中中新世之前比特利斯-扎格罗斯碰撞前锋带前隆区域的挠曲隆升作用；第二期为南北向正断层的反转事件，得到的应力比[R=(σ₂ - σ₃)/(σ₁ - σ₃)]指示了向走滑断层作用过渡的伸展应力环境；第三期应力活动（上新世-现今）以走滑断层作用和东西向正断层活动为特征，该应力环境被认为是死海断层或东安纳托利亚断层扩展活动的产物。此前针对该区域裂谷形成的模型均认为其成因属于压扭或张扭构造环境；而本次提供的全新数据表明，最南端的卡拉苏谷是先经历伸展作用，再经历张扭作用演化形成的。