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首页> 外文期刊>Chinese science bulletin >Cretaceous synfolding remagnetization components revealing tectonic rotation of the middle Yangtze fold belt
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Cretaceous synfolding remagnetization components revealing tectonic rotation of the middle Yangtze fold belt

机译：白垩纪共褶复磁作用揭示了扬子中褶皱带的构造旋转

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To reveal the deformation process of the middle Yangtze fold belt, we conducted a paleomagnetic study on Middle Triassic limestones and Middle to Late Jurassic sandstones from Wanzhou, Chongqing. Stepwise thermal and alternating field demagnetizationwere used to isolate the multi-component re-manent magnetizations. The Jurassic samples were overprinted by recent geomagnetic field, while three magnetization components were isolated from the Middle Triassic samples. A low temperature component (LTC) was isolated at temperatures below 200 deg C, an intermediate temperature component (ITC) at 200—360 deg C and a high temperature component (HTC) at 400—460 deg C. The LTC is distributed around the present-day Earth magnetic field, probably a viscous component. Stepwise unfolding indicates that the maximum precision parameters of ITC and HTC components are achieved at 33+-8% and 50+-27% (with 95% confidence) unfolding, respectively. The best-clustered ITC mean direction, Dec = 11.2 deg , Inc =45.2 deg(alpha_95 = 4.5 deg , N = 34), corresponding to a paleopole at 79.3 deg N, 219.5 deg E (d_p =3.6 deg , d_m =5.7 deg ), is consistent with the Cretaceous reference direction of the South China Block (SCB). The best-clustered HTC mean direction (taking 70% unfolding), Dec = 24.2 deg , Inc =49.0 deg (alpha_95 = 3.6 deg , N = 23), corresponding to a paleopole at 69.2 deg N, 195.5 deg E (d_p =3.1 deg , d_m =4.8 deg ), suggests a clockwise rotation of 12.8 deg +-3.5 deg . These synfolding remagnetization components clearly reveal that a clockwise rotation happened at the middle stage of folding, thus supporting that at least part of the variation in fold axis strikes is due to orocline rotation. Combined with published data, our analysis indicates that theWan-zhou-Xiangxi segment of the middle Yangtze fold belt experienced oroclinal bending. Furthermore, a published post-folding component isolated from the Middle Triassic Puqi Formation suggests a 27.5 deg +-5.8 deg clockwise rotation, confirming that at least 50% of the observed clockwise rotations in the eastern middle Yangtze fold belt can be attributed to oroclinal bending. The remagnetization data and geological evidence observed in the middle Yangtze fold belt suggest that collision between SCB and North China Block (NCB) probably lasted till the early period of Early Cretaceous.
机译：为了揭示长江中部褶皱带的变形过程，我们对重庆万州的中三叠统石灰岩和中侏罗世至晚侏罗世砂岩进行了古磁研究。使用逐步热磁场和交变磁场去磁来隔离多组分剩余磁化强度。侏罗纪样品被最近的地磁场套印，而中三叠纪样品中分离出三个磁化分量。在低于200摄氏度的温度下分离出低温成分（LTC），在200-360摄氏度的温度下分离出中间温度成分（ITC），在400-460摄氏度的温度下分离出高温成分（HTC）。今天的地球磁场，可能是粘性的。逐步展开表明，分别在33 + -8％和50 + -27％（置信度为95％）展开时，可以实现ITC和HTC组件的最大精度参数。最佳集群的ITC平均方向Dec = 11.2 deg，Inc = 45.2 deg（alpha_95 = 4.5 deg，N = 34），对应于古极在N 79.3 deg，E 219.5 deg（d_p = 3.6 deg，d_m = 5.7 deg） ），与华南区块（SCB）的白垩纪参考方向一致。最佳簇HTC平均方向（展开70％），Dec = 24.2度，Inc = 49.0度（alpha_95 = 3.6度，N = 23），对应于古北极在69.2度N，195.5度E（d_p = 3.1） deg，d_m = 4.8 deg，表示顺时针旋转12.8 deg + -3.5 deg。这些同折复磁成分清楚地表明，在折页的中间阶段发生了顺时针旋转，因此支持了折页轴撞击的至少一部分变化是由于斜行旋转引起的。结合已发表的数据，我们的分析表明，长江中褶皱带的万州—湘西段经历了口弯。此外，从中三叠世普奇组中分离出的已公布的褶皱后成分表明顺时针旋转为27.5度+ -5.8度，这证实了在长江中东部褶皱带中观察到的至少50％的顺时针旋转可以归因于眼眶弯曲。在长江中部褶皱带的磁化资料和地质证据表明，SCB和华北地块（NCB）之间的碰撞可能一直持续到白垩纪早期。

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