Clay mineralogical and isotopic (K–Ar, δ 18O, δD) constraints on the evolution of the North Anatolian Fault Zone, Turkey

• Published in: Earth and planetary science letters 2006-03, Vol.243 (1), p.181-194
• Main Authors: Uysal, I. Tonguç, Mutlu, Halim, Altunel, Erhan, Karabacak, Volkan, Golding, Suzanne D.
• Format: Article
• Language: English
• Subjects: fluid flow; hydrothermal; illitic clay minerals; K–Ar dating; North Anatolian Fault Zone; δ18O and δD
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2005.12.025

This study presents the first attempt to constrain the evolution of the North Anatolian Fault Zone (NAFZ) by age dating and isotope tracing of clay minerals formed during near-surface faulting. Extensive illitic clay mineralisation occurred along the NAFZ related to hydrothermal alteration of the fault gouges and pseudotachylytes. Samples representing the pre-fault protoliths outside the fault zone do not contain authigenic illitic clay minerals indicating that hydrothermal processes were confined to the areas within the fault zone. K–Ar age data indicate that the hydrothermal system and the associated illite authigenesis initiated at ∼57 Ma. This process is interpreted to reflect the onset of significant strike-slip or transtensional faulting immediately after the continental collision related to the closure of the Neotethys Ocean. Following the initiation of the fault movements in the latest Paleocene–Early Eocene, displacements along the NAFZ have continued, with probably intensified fault activities at ∼26 Ma and later than ∼8 Ma. Oxygen isotope compositions of the illitic clays from different locations along the NAFZ are similar, with narrow ranges in δ 18O values indicating clay precipitation from fluids with similar oxygen isotope compositions and crystallisation temperatures. The δ 18O and δD values of the calculated fluid isotopic composition ( δ 18O = 5.9‰ to 11.2‰, δD = − 59‰ to − 73‰) are consistent with metamorphic and magmatic origin of fluids mobilised during active tectonism. The interpretation of the fluid flow history of the NAFZ is in agreement with that reported previously for some well-known large-scale high-angle fault zones, which similarly developed along collisional-type orogenic belts and are commonly associated with significant mesothermal ore mineralisation.