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

Authors:
  • EPE. S. Platzman
    E. S. Platzman
  • CTC. Tapirdamaz
    C. Tapirdamaz
  • MSM. Sanver
    M. Sanver
  • CRC. C. Rundle
    C. C. Rundle
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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.

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