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为研究中扬子褶皱带的变形过程,对重庆万州地区中三叠世灰岩和中晚侏罗世砂岩进行了古地磁研究.系统热退磁表明,侏罗纪样品受现代地磁场重磁化严重,三叠纪样品分离出3个重磁化组分:低温(0～200℃)、中温(200～360℃)和高温(400～460℃)组分.低温组分分布于现代地磁场方向附近,可能为黏滞剩磁.逐步展平褶皱检验显示:中温组分在褶皱展平至33%±8%时获得,相应古地磁方向为Dec=11.2°,Inc=45.2°(α95=4.5°,N=34),对应古地磁极位置79.3°N,219.5°E(dp=3.6°,dm=5.7°);高温组分在褶皱展平至50%±27%时获得,在95%置信范围内取褶皱展平至70%,相应古地磁方向为Dec=24.2°,Inc=49.0°(α95=3.6°,N=23),对应古地磁极位置为69.2°N,195.5°E(dp=3.1°,dm=4.8°).与白垩纪参考古地磁方向或极位置比较,上述重磁化组分揭示该地区在褶皱变形的中期经历了12.8°±3.5°的顺时针旋转,而变形后期以来没有发生旋转.结合前人数据,认为中扬子褶皱带万州-香溪段部分弯曲是由弯山构造引起的;湖北蒲圻地区在褶皱变形末期以来经历了27.5°±5.8°的顺时针旋转,因此至少50%的构造旋转是由于弯山构造导致的.中扬子褶皱带发生于侏罗纪末期和早白垩纪的褶皱造山事件也揭示了华南-华北地块碰撞可能一直持续到早白垩纪早期.
In order to study the deformation process of the middle Yangtze fold belt, the paleomagnetic study was carried out on the Middle Triassic limestones and mid-late Jurassic sandstones in Wanzhou area of Chongqing.The thermal demagnetization shows that the Jurassic samples are heavily magnetized by the modern geomagnetic field, Three heavy magnetic components were separated from the Triassic samples: low temperature (0 ~ 200 ℃), medium temperature (200 ~ 360 ℃) and high temperature (400 ~ 460 ℃) .The low temperature components distributed in the direction of the modern geomagnetic field, The results show that the middle temperature component is obtained when the wrinkle is flattened to 33% ± 8%, the corresponding paleomagnetic direction is Dec = 11.2 °, Inc = 45.2 ° (α95 = 4.5 °, (D = 3.6 °, dm = 5.7 °) corresponding to the paleomagnetic pole position, corresponding to the paleomagnetic pole position 79.3 ° N and d = 5.7 °. The high temperature component was obtained when the wrinkle was flattened to 50% ± 27% The folds were flattened to 70% with the corresponding paleomagnetic directions of Dec = 24.2 ° and Inc = 49.0 ° (α95 = 3.6 ° and N = 23), corresponding to 69.2 ° N and 195.5 ° E (dp = 3.1 °, dm = 4.8 °) .Comparing with the Cretaceous reference paleomagnetic direction or pole position, the above re-magnetization components reveal that the region experienced a clockwise rotation of 12.8 ° ± 3.5 ° in the middle of fold deformation, No rotation occurred. Based on previous data, it is believed that part of the bending of the Wanzhou-Xiangxi section of the middle Yangtze fold belt is caused by the bend-mountain structure. Since the late Pleistocene fold in Hubei Province experienced a clockwise rotation of 27.5 ° ± 5.8 °, at least 50% The tectonic rotation was caused by the bend mountain structure.The middle Yangtze fold belt occurred in the fold orogen of the Late Jurassic and Early Cretaceous also revealed that the collision between South China and North China blocks may continue until early Early Cretaceous.