Abstract
AbstractTo increase the knowledge about the origin of the difference in fold axis strikes between the Upper and Middle Yangtze fold belt, we conducted a paleomagnetic study of Middle and Late Jurassic sandstones from the Wanzhou and Yunyang area, Chongqing City, a transition zone between the Upper and Middle Yangtze fold belt. Stepwise thermal demagnetization isolated two components. The low temperature components (LTC) were isolated from all the samples and overprinted by the recent geomagnetic field. The high temperature components (HTC) isolated from the Middle and Late Jurassic samples from the Wanzhou area were also overprinted by the recent geomagnetic field. Stepwise unfolding indicates that the maximum precision parameter of HTC isolated from the Late Jurassic samples from the Yunyang area reaches 33.8% unfolding. The best‐clustered HTC mean direction is D=19.1°, I=48.9° (α95=6.3°), corresponding to a paleopole at 73.5°N, 198.2°E (dp=5.5°, dm=8.3°). Compared with the Cretaceous reference paleopole, it reveals that the Yunyang area has experienced a clockwise rotation of 7.7°±6.1° at the late stage of folding. Combined with previous data, our new results support a general orocline in the middle Yangtze fold belt, most probably caused by indentation of the North China block into the South China block. However, the curvature in the transition zone of Upper and Middle Yangtze fold belt could be due to strain partitioning in the course of NW directed subduction of the Pacific plate rather than oroclinal bending.
Published Version
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