Characteristic of Anisotropy of Magnetic Susceptibility (AMS) and its tectonic significance in typical Cretaceous section from Xixia basin, Central China

Through preliminary rock magnetic investigation on samples from the Yangcheng-Danshui section of the Xixia basin in Henan Province, Central China, hematite and subordinate magnetite were asserted to be the main magnetic carriers of remanence in this terrestrially depositional section The results showed also a general gradually-Increasing trend of the relative proportion of magnetite to hematite complying with height from the base to the top of the studied section On the other hand, relatively low magnetic susceptibility values of the samples from the whole section indicate that the observed magnetic fabric is mainly dominated by antiferromagnetic hematite and some paramagnetic minerals, such as silicate Though the tightly grouped principal minimum (k3) axes are nearly perpendicular to the bedding plane, indicating a predominant sedimentary fabric for the studied section, the relatively low corrected anisotropy values and the tightly grouped principal maximum (k1) axes suggest that the studied section was subject to an embryonic deformation Variations of principal maximum (k1) axis' preferred orientation for the whole section and each rock unit unravel that preferred stress orientation in the studied strata has experienced a transformation from NEE SWW to NE SW, and then back again to NEE-SWW direction This systematic change of preferred compressive orientation could be interpreted as reflecting one of the compression by persistent NE-directed indentation of the South China Block into the North China Block until the Late Triassic and the other triggered by extruded part of the upper crust from the lower crust colliding with substance to the east of the Tongbaishan-Dabie orogenic belt, these two different kinds of compaction may alternatively dominate the tectonic setting in different evolutionary stages of the basin