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Paleomagnetic Inclination Shallowing in Badong Formation Red Beds, Middle Triassic of South China Block
HAN Lu, HUANG Baochun, ZHAO Qian, XUE Yi, LI Nengtao, Umar Farooq Jadoon
Acta Scientiarum Naturalium Universitatis Pekinensis    2022, 58 (3): 469-480.   DOI: 10.13209/j.0479-8023.2022.031
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Paleomagnetic and rock magnetic studies are conducted on Middle Triassic Badong Formation red beds from the South China Block (SCB). The anisotropy of high-field isothermal remanent magnetization (hf-AIR) method indicates that the characteristic remanent magnetization (ChRM) is significantly affected by inclination shallowing with a flattening factor f = 0.63. Rock magnetic analysis indicates that hematite is the main magnetic carrier with a subordinate contribution from magnetite. Anisotropy of magnetic susceptibility (AMS) and hf-AIR results both show a typical depositional fabrics without significant distortion from tectonic stress. The ChRM, carried by detrital hematite, has a unique negative polarity and passes the fold test at the 95% confidence level. The ChRM yields a common mean direction with that previously reported from the same section. The ChRM yields a tilt-corrected mean direction of Ds = 222.1°, Is = ?27.2° (α95 = 8.7°) and a corresponding paleomagnetic pole at 48.1°N, 215.5°E (A95 = 8.4°). Combined with high quality published data (Q≥5) for the Middle Triassic, the mean paleomagnetic pole for the SCB is corrected to 48.5°N, 207.6°E with A95 = 10.7° by using a flattening factor f = 0.63. Comparing this inclination shallowing-corrected mean paleomagnetic pole with Early Triassic pole for the North China Block, which has also inclination shallowing-corrected by the hf-AIR method, it shows that paleolatitudes of these two blocks at their eastern reference points are exactly compatible. This further confirms that the South and North China blocks experienced a scissors-like rotational collision during the Mesozoic times, as proposed by previous researches. 
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Paleomagnetic Inclination Shallowing in Lower Triassic Liujiagou Formation from Qinshui Basin, North China Block
ZHOU Tinghong, HUANG Baochun, JIA Shufei, LIANG Yalun, ZHANG Donghai, ZHAO Qian, ZHANG Ye, YAN Yonggang
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (3): 521-534.   DOI: 10.13209/j.0479-8023.2017.100
Abstract900)   HTML9)    PDF(pc) (1526KB)(350)       Save

A combined paleomagnetic, rock magnetic and magnetic fabrics study is conducted on the redbeds of Early Triassic Liujiagou Formation from Qinshui Basin, North China Block (NCB). The E/I (elongation/inclination) method indicates that the characteristic remanent magnetizations (ChRM) was significantly affected by inclination shallowing with a flattening factor f=0.6. Rock magnetic analysis indicates that hematite and magnetite are the main magnetic carriers. Anisotropy of magnetic susceptibility (AMS) result shows typical depositional fabrics in water. The chRM has been successfully isolated from 15 sites with tilt-corrected mean direction of Ds=318.8°, Is=30.9° (α95=6.9°) and a corresponding paleomagnetic pole at 49.3°N, 5.5°E (A95=6.7°). The pole after E/I correction is 53.5°N, 18.0°E. Combining with published high quality Early Triassic pole (Q≥4) for NCB, the mean Early Triassic pole for NCB before and after inclination shallowing correction is 55.3°N, 357.1°E (A95=5.5°) and 60.8°N, 13.4°E (A95=5.8°), respectively. The paleolatitude of NCB is obviously higher at Early Triassic after inclination shallowing correction with ~10° increase. Furthermore, the corrected Early Triassic paleolatitude of NCB seems to be different from that of South China Block (SCB) at the east, which may result from the inclination shallowing error in Early Triassic limestone rocks of SCB instead of the real separation between the two blocks.

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