No 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.

SUMMARY Palaeomagnetic data on Eocene rocks from within the ‘Almacik Flake’, bounded by two strands of the North Anatolian right‐lateral fault indicate that the flake has undergone an apparent counterclockwise rotation of about 148° on average. We interpret this as a real 212° clockwise rotation, because the Almacik flake is entirely delimited by the right‐lateral North Anatolian Fault strands, the only dominant post‐Eocene structure in the area, and because areas surrounding the flake do not show the same rotation. This rotation must have occurred since the North Anatolian Fault originated in the late medial Miocene (late Serravallian: 11.5 Ma) and, if so, may imply either a larger total slip along it than hitherto estimated or that the Almacik flake is the surface expression of a flower structure rotating above a shear zone narrower than the present width of the flake.

No abstract

This paper reports preliminary results of palaeomagnetic data obtained from the lowerTriassic (Schtian) and mid-Triassic (Anisian) rocks in the western Pontides, NW Turkey. The Triassic rocks have been studied by applying thermal and/or alternating-field demagnetization. The characteristic magnetization has a 50" mean inclination derived from 41 samples taken from three separate sites. Although the inclination values for the three sites are similar, the corresponding declination angles indicate that the GumuSdere site, which lies to the north of Istanbul city, has undergone 68" anticlockwise rotation; while the TavSancil and Denizlikoy sites, which are to the southeast of Istanbul, have rotated 40" clockwise on average. The mean inclination (SO0) places the western Pontides at the southern margin of Laurasia during lowerand mid-Triassic time.