New Paleomagnetic Study on Early Triasic Liujiagou Formation of NorthChina Block

This paper introduces the result of studying on paleomagnetism of 91 specimens from 13 sites from Liujiagou Formation in Dashu Village, Wu ’an city, Hebei Province. The result reveals that North China block (NCB) was not united with Yangtze block (YB) in the Early Triassic. From the Early Triassic to now, NCB has rotated 30.0° counterclockwise, but YB has rotated 45.1° clockwise.

华北地块沁水盆地下三叠统刘家沟组古地磁倾角浅化研究

对华北地块沁水盆地下三叠统刘家沟组红层样品进行系统的岩石磁学、磁组构和古地磁学研究,并用E/I(elongation/inclination)方法对其进行磁倾角浅化的识别与校正,获得刘家沟组红层磁倾角浅化因子f=0.6。岩石磁学结果显示,刘家沟组红层的主要载磁矿物是赤铁矿及磁铁矿,其磁组构具有典型的静水沉积特征。经地层校正后,15个采样点特征剩磁分量的平均方向为Ds=318.8°,Is=30.9°(α95=6.9°),对应的古地磁极为49.3°N,5.5°E(A95=6.7°),磁倾角浅化校正后的古地磁极为53.5°N,18.0°E。对包括本文数据在内的高质量的华北早三叠世古地磁极数据(Q≥4)进行平均,得到校正前的古地磁极为55.3°N,357.1°E(A95=5.5°),校正后的古地磁极为60.8°N,13.4°E(A95=5.8°)。经过古地磁倾角浅化校正,华北地块早三叠世的古纬度有约10°的明显提高,指示其东部早三叠世时与华南地块之间可能存在一定的纬度差,但是该纬度差很可能并不代表华北地块东部早三叠世时与华南地块尚未对接,而是指示华南地块下三叠统灰岩同样存在显著的磁倾角浅化现象。