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

[1] 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°, a 95 = 7.4°to D = 14.1°, I = 61.5°, a 95 = 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.

Climatic and tectonic controls on sedimentation and erosion during the Pliocene-Quaternary in the Qaidam Basin (China)

“…Inclination values from all these studies are lower than that expected (58.1°) for the Pliocene magnetic fi eld interpreted for Eurasia at that time (Besse and Courtillot, 2002). This inclination shallowing, also common in other sedimentary rocks from the Qaidam and Tarim Basins, has been attributed to depositional processes, sediment compaction, or rock-magnetic effects during deposition (Dupont-Nivet et al, 2002;Tan et al, 2003). Regardless of the cause, the shallow inclination has no effect on our polarity interpretations.…”

Cenozoic Evolution of Hinterland Basins in the Andes and Tibet

“…Although paleomagnetic data suggest much greater north-south convergence (up to 2500 km) between Tibet and the stable Asian interior (Achache et al, 1984), structural restorations cannot account for such large values. Shallowing of magnetic inclination in CretaceousCenozoic strata, rather than extreme shortening, may explain the paleomagnetic data (Tan et al, 2003).…”

Lower Cretaceous Xigaze ophiolites formed in the Gangdese forearc: Evidence from paleomagnetism, sediment provenance, and stratigraphy

“…The two most common methods used to perform this correction are based on the elongation/inclination (E/I) correction of the ChRM distribution (Tauxe and Kent, 2004), and the anisotropy of susceptibility or remanence ( Comparative studies show that these two methods provide correction values that are comparable within error (e.g., Huang et al, 2013). We applied both methods for the correction of the inclination shallowing affecting the sandstones in Sangsang section, which is indicated by the strong ellipsoid distribution of the VPGs (Fig.…”

“…The E/I correction is based on the statistical paleosecular variation models of the geocentric axial dipole magnetic field (Tauxe and Kent, 2004). After application of the E/I method on the dataset of the Sangsang sandstones, the mean inclination is corrected from 16.9 ± 6.6 • to 30.2 • with 95% confidence limits between 24.8 • and 37.3 • (Fig.…”