XUE Yi,
HUANG BaoChun,
ZHAO Qian et al
.2021.Reconnaissance on inclination shallowing effect of Lower Triassic red beds from North China Block by the anisotropy of remanence Chinese Journal of Geophysics(in Chinese),64(3): 916-924,doi: 10.6038/cjg2021O0112
基于剩磁各向异性方法对华北下三叠统红层磁倾角浅化效应的研究
薛艺, 黄宝春, 赵千, 韩露, 李能韬
北京大学地球与空间科学学院, 造山带与地壳演化教育部重点实验室, 北京 100871
Reconnaissance on inclination shallowing effect of Lower Triassic red beds from North China Block by the anisotropy of remanence
XUE Yi, HUANG BaoChun, ZHAO Qian, HAN Lu, LI NengTao
The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
Abstract:A magnetic anisotropy study was performed on red beds of Early Triassic Liujiagou Formation from the Qinshui Basin, North China Block (NCB). First, a magnetic field was applied at 45° to the cylinder axis in a plane and then the samples were subjected to successively thermal demagnetization up to about 680 ℃. Measurements of isothermal remanent magnetizations along specimen's axial and radial axes yielded an inclination shallowing (IF) factor of 0.70. Second, high-field isothermal remanent magnetization was used in conjunction with 100 mT alternating field and 120 ℃ thermal demagnetization to isolate the contribution of hematite to the remanence anisotropy, and we finally obtained an IF factor of 0.59 in the light of a direct measurement of remanence anisotropy of single hematite grain (a=1.35). The IF factor isolated from the anisotropy of high-field isothermal remanent magnetization (hf-AIR) is more consistent with that calculated previously from E/I (elongation/inclination) method (f=0.60). This further indicates that the Early Triassic red beds in the NCB suffered from a conspicuous IF with a factor of 0.59. Noting that the hf-AIR measurements is an effective method for identifying and correcting possible IF in red beds, the E/I method is also available to estimate the IF factor of red beds given that enough individual remanence directions are obtained from single sampling section/locality or from multiple sections/localities without significant relative motions within them.
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