Paleomagnetic evidence for 50 m.y. of tectonic rotations in the Junggar block driven by far-field effects of the India-Eurasia collision

The tectonic history of the Junggar block, one of the largest tectonic units within the Central Asia orogenic belt, is pivotal for understanding the geodynamic processes associated with the India-Eurasia collision. Despite recurrent compressional deformation along numerous faults during the Mesozoic and Cenozoic, the magnitude of Cenozoic tectonic rotations in the Junggar block relative to Eurasia remains poorly constrained. To assess such rotations quantitively, we present paleomagnetic data from the Cenozoic sedimentary rocks in the Zaysan Irtysh zone in the northern part of the Junggar block. Stepwise thermal demagnetization revealed a high laboratory unblocking temperature component, interpreted as primary magnetization based on a positive reversal test. Seven mean directions were calculated for age intervals of 45−40 Ma, 42.5−37.5 Ma, 40−35 Ma, 37.5−32.5 Ma, 35−30 Ma, 25−20 Ma, and 22.5−17.5 Ma. The observed declination variations indicate a local counterclockwise rotation of 18.8° ± 11.4° between 40 ± 2.5 Ma and 35 ± 2.5 Ma. Comparison of these results with 23−3.1 Ma paleomagnetic data from the southern Junggar block obtained in previous studies suggests successive local counterclockwise rotations in the block’s northern and southern regions. At a larger scale, the Central Asia right-slip fault zone experienced two stages of tectonic rotation (ca. 60−30 Ma and 25−5 Ma) driven by the far-field effects of the India-Eurasia collision and strike-slip faulting that propagated through intracontinental settings. These insights have broad implications for the tectonic evolution of intracontinental systems, extending beyond Central Asia to other orogenic belts and collision zones worldwide.