Why are there no clockwise rotations along the North Anatolian Fault Zone?

Abstract

Mechanical analysis of lithospheric deformation associated with an intracontinental transform fault suggests that it should be associated with a pattern of vertical axis rotations governed by the length of the fault, its displacement, and the mechanical properties of the lithosphere. Paleomagnetic results from two transects across the North Anatolian Fault Zone indicate that there have been no measurable clockwise rotations on a regional scale associated with Neogene dextral strike‐slip motion along the fault. The data come from two groups of volcanic rocks that have been dated by K‐Ar whole rock geochronology and have yielded ages ranging from 45.3±3.1 m.y. to 41.8±1.3 m.y. (Eocene) and 21.7±1.5 m.y. to 7.5±0.2 m.y. (Miocene). The absence of clockwise rotations suggests one of the following explanations. (1) In contrast to the assumptions underlying current mechanical analyses, deformation in the upper crust may not directly reflect the flow in the lithosphere and is localized along a single fault trace. (2) Deformation is distributed, but rotations have been prevented by the presence of elongate fault blocks subparallel to the trace of the main fault. (3) Displacement along the North Anatolian Fault may be too small or the rheologic properties of the lithosphere such that rotations about vertical axes cannot be resolved. Instead of the predicted clockwise rotations, measured declinations show that there has been approximately 30° of anticlockwise rotation of both the Eocene and Miocene volcanic rocks. This suggests that no significant rotation occurred between Eocene and Miocene times and that the anticlockwise rotation occurred either immediately before or concurrent with the Plio‐Pleistocene slip on the North Anatolian Fault.

Global Positioning System measurements of present‐day crustal movements in the Arabia‐Africa‐Eurasia plate collision zone

“…The consistency between the GPS and geologic estimates would appear to support the interpretation that the NAF is Pliocene in age and that fault slip rates have not changed substantially since the fault initiated. The close fit between the NAF and the small circle about the Euler pole and the absence of paleomagnetic rotations along the central and eastern NAF [Platzman et al, 1994] are consistent with slip being concentrated along a single fault. The remarkably consistent right-lateral, fault parallel character of focal mechanisms for major earthquakes on the NAF (Figure 2) and the fact that all relative motion can be explained by seismic slip [Jackson and McKenzie, 1988] also argue against significant off-fault deformation.…”

Exhumation with a twist: Paleomagnetic constraints on the evolution of the Menderes metamorphic core complex, western Turkey

“…Clockwise rotations in Anatolia are mainly limited to strike-slip-related rotations within the North Anatolian Fault Zone [Tatar et al, 1995;Piper et al, 1996Piper et al, , 1997, although even that is debated [Platzman et al, 1994], and the Afyon region lies well outside of the strands of this fault zone. It is possible that the shortening that we postulate to accommodated the rotation of the Bey Dağları region is accommodated by distributed right-lateral shear, leading to clockwise rotations in the Afyon area.…”

Middle Eocene paleomagnetic data from the eastern Sakarya Zone and the central Pontides: Implications for the tectonic evolution of north central Anatolia

“…Paleontologic and radiometric data suggest that the volcanic rocks were emplaced during the Lutetian-Bartonian. K/Ar ages in the range of 45.3 ± 3.1 to 41.8 ± 1.3 Myr have been reported by Yılmaz et al [1993a] and Platzman et al [1994]. Ketin [1962] determined a Lutetian age for lavas around Osmancık and Çorum, whereas Yılmaz and Tüysüz [1984] identified Nummulites sp.…”

“…Later studies focused on detecting the deformation that occurred close to the North Anatolian Fault (NAF) [Kissel and Laj, 1988;Morris and Robertson, 1993;Gürsoy et al, 1999;Kaymakcı et al, 2007;Çinku and Orbay, 2010;Piper et al, 2010]. Platzman et al [1994] provided paleomagnetic data from Niksar, along a transect across the NAF, that indicate approximately 30°of counterclockwise (CCW) rotation. In the Pontides, Piper et al [1996Piper et al [ , 2010 detected CCW rotations in Middle Eocene lavas on both sides of the NAF.…”

“…Also shown is the shaded paleomagnetic sampling area in the central Pontides and the eastern Sakarya Zone. tectonic evolution of the Anatolian plate, as well as the block rotations caused by tectonic deformation across the various fault zones [Sarıbudak, 1989;Platzman et al, 1994;Tatar et al, 1995Tatar et al, , 1996Piper et al, 1996Piper et al, , 1997Kaymakcı et al, 2003a;İşseven and Tüysüz, 2006].…”