Paleomagnetic Study Of Pliocene Sediments From Yingisar (Northeastern Pamir) And Its Tectonic Implications

The Pamir, western Himalayan syntaxis, lies at the northwestern margin of the Tibetan plateau, is adjacent to Southwestern Tian Shan, and separates the Tarim baisn to the east from the Tajik basin to the west. It is a first-order feature demonstrating partly the northward extent of deformation due to the Cenozoic Indo–Eurasia collision.Thick Cenozoic marine and terrestrial sediments are widely distributed along the piedmont of the Pamir plateau, providing valuable information on the kinematic evolution of the region.To research the deformation history of the northeastern Pamir(NE Pamir) in response to the Indo–Eurasia collision, we conducted paleomagnetic investigations with Pliocene sediments in the Yingisar area. Combined with previous geological data and research results, we study the late Cenozoic tectonic evolution history of NE Pamir.A total of 111 paleomagnetic specimens were collected from 11 sites in the Yingisar area.(1) Anisotropy of magnetic susceptibility(AMS) of representative specimens is incipient deformation magnetic fabric, illustrating that the AMS ellipsoid Kmax parallel to the fold axial trace and perpendicular to the strain direction while Kmin perpendicular to the bedding plane. Pliocene sediments in Yingisar underwent weak compression in direction NE15°.(2) After stepwise thermal demagnetization, a stable magnetic component with characterized reversal test was isolated in the majority of specimens. The direction is: Dg = 342.4°,Ig = 59.2°,κg = 32.3,α95 = 8.6; Ds =352.4°,Is = 49.9°,κs = 59.1,α95 = 6. 3°.(3) Paleomagnetic inclination anomaly took place in Pliocene sediments in Yingisar area. After E/I correction, we calculated the shallowing factor f = 0.8, corrected inclination= 57.7 [50.1, 77.6] and the VGP for the corresponding: 84°N, 343.5°E, dp =6.8°, dm =9.2°, α95 = 7.9°.(4) Take the Eurasian 5Ma VGP as reference, we calculated the Poleward Displacement = 0 ± 6.1°, which suggests the study area did not occur detectable poleward displacement.(5) Take the Eurasian 5 Ma VGP as reference, we calculated the Apparent Rotation=- 12.3 ±7.8°, which demonstrates the significant counterclockwise rotation in NE Pamir. This phenomenon can be reasonably explained by a change in the regional kinematics around the early Pliocene.