New kinematic and geochronologic evidence for the Quaternary evolution of the Central Anatolian Fault Zone (CAFZ)

Abstract:

First order structures such as the North and East Anatolian faults accomodate extrusion of Anatolia to the west; their activity and kinematics are well constrained. Less well understood is the degree to which the plate has deformed internally along secondary strike-slip faults such as the Central Anatolian fault zone (CAFZ). Original interpretations of the CAFZ characterize it as an active left-lateral ‘tectonic escape’ structure, stretching for 700 km in a NE direction across the Anatolian plate. Here, we provide new structural, geomorphic and geochronologic data for several key faults within the southern and central parts of the CAFZ which suggests Quaternary left-lateral motion has been overstated. We propose a revised model for its evolution during the Quaternary.

Our neotectonic mapping along the Ecemiş fault, the southernmost part of the CAFZ, documents 65.8 ± 3 m of left-lateral displacement of an alluvial fan with a ³⁶Cl exposure age of 133.2 ± 11 ka, and an unfaulted fluvial terrace (47.7 ± 2.8 ka). We estimate a left lateral slip rate of 0.80 ± 0.17 mm a^-1 during the Late- Pleistocene, lower than rates of 3 mm a^-1 originally proposed for the fault zone. To the north, the Erciyes fault is characterized by a linear array of monogenetic vents aligned perpendicular to the maximum horizontal extension. Ar/Ar dating show that the syn-eruptive stress of field on the fault was ESE-WNW extension from 0.58 ± 0.13 to 0.21 ± 0.18 Ma with no record of strike slip displacement. We also find a greater component of extension along the central part of the CAFZ, in the Erciyes basin. We’ve mapped and re-characterized Erkilet and Gesi faults within the northern Erciyes basin as predominantly extensional, contrary to previous kinematic interpretations which required significant strike-slip motion. Our results are consistent with recent GPS studies which show active ESE-WNW extension, which we propose as the driver of faulting since 2.73 ± 0.08 Ma.

Original estimates of left-lateral displacement on the CAFZ have been overstated and slip-rates and kinematics derived in this study are not typical of an ‘escape tectonic’ structure. We characterize the CAFZ as one of an array of several weakly active, highly segmented transtensional fault systems in Central and Eastern Anatolia which have re-activated along older structures.