O. Tatar et al., PALEOMAGNETIC STUDY OF BLOCK ROTATIONS IN THE NIKSAR OVERLAP REGION OF THE NORTH ANATOLIAN FAULT ZONE, CENTRAL TURKEY, Tectonophysics, 244(4), 1995, pp. 251-266
This palaeomagnetic study investigates crustal deformation within, and
adjacent to, the Niksar overlap area of the North Anatolian Fault Zon
e (NAFZ) in central-east Turkey. The studied rock formations comprise:
(1) red limestones of Late Cretaceous age (3 sites); (2) mafic lavas
of Eocene age on the north side (13 sites) and south side (9 sites) of
the NAFZ; and (3) volcanic rocks of Pliocene-Quaternary age from the
Niksar pull-apart basin within the NAFZ (8 sites). Comparisons with re
ference palaeofield directions computed from apparent polar wander pat
hs of the Eurasian and Afro-Arabian plates identify two scales of regi
onal and local tectonic rotation: (1) A pre-tilting remanence in the E
ocene volcanic rocks south of the NAFZ (D/I = 144.1/-47.5 degrees, alp
ha(95) = 7.6 degrees) is interpreted to reflect counterclockwise rotat
ion by 30-40 degrees from the reference palaeofields. Contemporaneous
volcanic rocks from the north side of the NAFZ have the same reverse p
olarity recorded in pre-tilting magnetisations. The remanence is also
rotated counterclockwise (D/I = 152.4/-42.5 degrees, alpha(95) = 11 3
degrees), but by about 8 degrees less than the volcanics on the south
side of the NAFZ. Hence similar amounts of rotation are observed on bo
th sides of the NAFZ and are interpreted to reflect motions during the
pre-Middle Miocene collisional history in this sector of the Pontides
. No distributed clockwise rotations anticipated from subsequent dextr
al motion along the NAFZ intracontinental transform are observed. The
slightly larger anticlockwise rotation found on the south side of the
NAFZ probably records relative rotation of en-echelon wedges by contin
ental escape during post-Middle Miocene strike slip along the transfor
m. (2) Within the narrow zone of intense deformation along the NAFZ, C
retaceous limestones appear to be rotated clockwise by dextral strike-
slip motion whilst Plio-Quaternary lavas within a fault-bounded block
in the overlap region associated with the Niksar pull-apart basin, hav
e magnetisations consistently directed 240-270 degrees E. Magnetic inc
linations are not diagnostic of polarity but both polarity solutions i
dentify rapid clockwise rotation at rates in excess of 50 degrees/m.y.
A normal polarity solution is favoured and implies that a block (ca.
5 km across) has undergone a strike-slip displacement of around 12 km
within the NAFZ during the last polarity chron. Cretaceous-Eocene pala
eolatitudes are closer to those predicted from Eurasia than Afro-Arabi
a, but a study of older rocks is required to resolve affinities of thi
s sector of the Anatolian block.