Paleomagnetic constraints on neotectonic deformation within the SouthernTian Shan piedmont and implications for the latest Miocene enhancedaridification in the Tarim Basin

The India-Eurasia collision reactivated the Tian Shan belt of Central Asia and led to crustal shortening which has
been accommodated by fold-and-thrust belts on both flanks of the orogen. Southward propagation into the Tarim
Basin has been accommodated by the Kuqa fold-and-thrust belts which record a range of well-preserved syntectonic
continental sequences. Using existing magnetostratigraphic age constraints, we have conducted an indepth
paleomagnetic and rock magnetic investigation of this fold-and-thrust belt with the aim of linking the
neotectonic deformation to the uplift of the Tian Shan orogen to the north. Anisotropy of magnetic susceptibility
(AMS) shows “pencil structure” fabrics between levels dated 31.0 and 5.5 Ma. These are succeeded by incipient
deformation fabrics at ~5.3 Ma, which dates an abrupt decrease in shortening by synsedimentary strain. This
change coincides with the timing of initial syntectonic growth strata in the foreland basin of the Southern Tian
Shan and contemporaneous vertical-axis rotations in the Yaha section. Collectively this evidence implies that the
Southern Tian Shan piedmont underwent transpressional deformation with rotation accompanying strain partitioning
during a regional sinistral shear. The extreme aridification which has occurred in the Tarim Basin since
the latest Miocene is interpreted in terms of the deflection of the ambient westerly airstream away from this
region due to the growth of the Tian Shan and its final collision with the Pamir.