Palaeomagnetic evidence for substantial rotation of the Almacik flake within the North Anatolian Fault zone, NW Turkey

Abstract

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.

Palaeomagnetic study of crustal deformation across an intracontinental transform: the North Anatolian Fault Zone in Northern Turkey

“…The palaeomagnetism of these volcanic rocks has been studied in the vicinity of the town of Niksar by Van der Voo (1968), Saribudak (1989), Platzman et al (1994)and Tatar et al (1995). Platzman et al (1994) also report K-Ar whole rock ages ranging from 45.3 to 41.8 Ma; these dates define a mid-Eocene age and support stratigraphic assessments described by Blumenthal (1950) and in unpublished reports of the Turkish Geological Survey (MTA).…”

Palaeomagnetically defined rotations of fault-bounded continental blocks in the North Anatolian Shear Zone, North Central Anatolia

“…Sarıbudak et al (1990) described a 2128 clockwise rotation of the Almacık flake, a continental block delimited by two branches of the NAF, although Michel et al (1995) refuted this conclusion. Similar clockwise rotation has also been described by Channell et al (1996) around Reşadiye, on the eastern part of the NAF.…”

“…There are no palaeomagnetic results for the Gümüş Block. Nevertheless a clockwise rotation is expected for this region by comparison with similar areas (Sarıbudak et al, 1990;Channell et al, 1996) along the NAF. Palaeomagnetic data from the Osmancık Block do not identify any important rotation in this region.…”

“…Block rotations about a vertical axis have been widely studied in Anatolia and specifically along the NAF ( Van der Voo, 1968;Sarıbudak et al, 1990;Platzman et al, 1994Platzman et al, , 1998Tatar et al, 1995Tatar et al, , 2000Tatar et al, , 1996Piper et al, 1996Piper et al, , 1997aChannell et al, 1996;Gürsoy et al, 1997Gürsoy et al, , 1998. Sarıbudak et al (1990) described a 2128 clockwise rotation of the Almacık flake, a continental block delimited by two branches of the NAF, although Michel et al (1995) refuted this conclusion.…”

A tectonic interpretation of the Marmara Sea, NW Turkey from geophysical data

“…The E-W elongation of the aeromagnetic anomaly of the cen-tral Marmara Sea is consistent with the mobilistic system of Storetvedt (2003). There is a similar barrier to the east of the study area in land known as the "Almacik Flake" (Saribudak et al, 1990). The estimated inclinations of magnetization are low compared to the inclination angle of the present geomagnetic filed in the region.…”