Palaeomagnetic investigation in the Pamirs and its tectonic implications

Abstract

This paper presents a palaeomagnetic investigation in the Pamirs of Tadjikistan. Remanences are mainly carried by magnetite and are of secondary, synfolding origin. Application of a new method, the small-circle reconstruction, allows to extract palaeomagnetic rotation and tectonic tilting since the time of remanence acquisition (assumed to be ∼20 Ma). In some regions 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 sequence 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 around vertical axes in the course of progressive shortening/folding. Surprisingly, the scatter of the tilt axes is reduced hereby. By comparing the distributions of the present and former tilt axes the amount of shortening is estimated for the southern Pamirs (shortened to ∼40%) and the central Pamirs (shortened to ∼60%).