Paleomagnetism and magnetic anisotropy of Cretaceous red beds from the Tarim basin, northwest China: Evidence for a rock magnetic cause of anomalously shallow paleomagnetic inclinations from central Asia

Abstract

Anomalously shallow paleomagnetic inclinations from Tarim basin red beds have suggested more than 1000 km of northward translation of the Tarim block since the Cretaceous. This is in conflict with geologic observations that indicate only a few hundred kilometers of crustal shortening north of the Tarim basin. To determine whether a rock magnetic effect could be the cause of the shallow inclinations, samples were collected from the Cretaceous Kapusaliang Group red beds. Both thermal and chemical demagnetization were employed to isolate the characteristic remanence (ChRM). The ChRMs pass the reversals test, as well as a local fold test. The anisotropy of magnetic susceptibility of the ChRM‐bearing particles was isolated by chemical demagnetization and had an oblate fabric with minimum axes perpendicular to bedding and foliations of ∼1.035. A 10–20% remanent anisotropy was obtained by comparing the saturation isothermal remanent magnetization for subsamples drilled parallel and perpendicular to bedding planes. The correlation of AMS and remanent anisotropy parameters yielded a value for the individual particle magnetic susceptibility anisotropy between 1.05 and 1.62. A particle anisotropy of 1.0638 allowed the best fit between corrected data and theoretical correction curves. An inclination correction corrected the mean Kapusaliang direction from D = 16.3°, I = 29.0°, α95 = 7.4° to D = 14.1°, I = 61.5°, α95 = 6.4°. The inclination correction reduced the paleomagnetically predicted latitudinal offset from more than 1000 km to less than the mean direction's 95% confidence limits, suggesting that paleomagnetic inclination shallowing is the cause of low inclinations recorded by the red beds from the Tarim basin.