Palaeomagnetic investigation in the Pamirs and its tectonic implications

This paper presents a palaeomagnetic investigation in the Pamirs of Tadjiki stan. Remanences are mainly carried by magnetite and are of secondary, synf olding origin. Application of a new method, the small-circle reconstruction ,l, allows to extract palaeomagnetic rotation and tectonic tilting since th e time of remanence acquisition (assumed to be similar to 20 Ma). In some r egions consistent rotations are observed: (i) clockwise in the Muzkol area of the central Pamirs; (ii) following the trend of oroclinal bending in the northern Pamirs, and (iii) counterclockwise in the northern folded sequenc e of the southern Pamirs. However, variations within different regions are obvious and scattering even occurs within smaller areas. Most likely, local block rotations are caused by N-S shortening. Palaeomagnetic and tectonic results reveal that tilt axes are rotated aroun d vertical axes in the course of progressive shortening/folding. Surprising ly, the scatter of the tilt axes is reduced hereby. By comparing the distri butions of the present and former tilt axes the amount of shortening is est imated for the southern Pamirs (shortened to similar to 40%) and the centra l Pamirs (shortened to similar to 60%). (C) 2001 Elsevier Science Ltd. All rights reserved.