Paleomagnetic constraints on neotectonic deformation within the Southern Tian Shan piedmont and implications for the latest Miocene enhanced aridification 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 in-depth 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.