The North Anatolian Fault Zone and the Role of Fluids in Seismogenic Deformation

Abstract

A study of the North Anatolian Fault Zone (Turkey) in dicates significant spatial variations of deformation mechanisms and fluid flow along and across a major active strike‐slip fault. Brittle deformation and later dissolution are mostly localized within the fault core, whereas crystal plastic deformation and diffusive mass transfer are more widely distributed. The fault underwent a three‐stage development: (I) Repeated episodes of frictional failure, pressure‐solution, fluid migration, and subsequent healing. Cataclasites and veins were formed during this stage. We propose that the episodic events are associated with open and closed fluid systems during seismogenic cycles. The progressive brittle failure led to stage (II), a more open system with increasing dilation connected with dissolution. The dramatic increase of dissolution processes terminated the episodic character of deformation and marked the beginning of a stage (III), mostly characterized by diagenetic processes. The fluid regime is now an open system. in general, our data do not indicate massive fluid redistribution in response to earthquake cycles of shear stress accumulation and release. Trace element distribution, isotopic data, and fluid inclusions suggest that fluids were derived from the adjacent limestones and that hydrostatic fluid pressure was dominant during fault development. We suggest that meteoric water circulates through the fault zone, causing solution transfer and compaction, which allows frictional failure at lowered shear stress.