GJI Geomagnetism, rock magnetism and palaeomagnetism Palaeomagnetic evidence and tectonic origin of clockwise rotations in the Yangtze fold belt, South China Block
GJI Geomagnetism, rock magnetism and palaeomagnetism Palaeomagnetic evidence and tectonic origin of clockwise rotations in the Yangtze fold belt, South China Block
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发表时间：
2007
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通讯作者：
X. Tan;K. Kodama;S. Gilder;V. Courtillot
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作者：
X. Tan;K. Kodama;S. Gilder;V. Courtillot
华南地块扬子褶皱带的褶皱轴走向在1000 km以上的距离上发生了显著的变化。这种大规模的变化提供了一个理想的机会，以测试使用古地磁方法，我们已经尝试了钻探下三叠统大冶组灰岩在鄂西的造山弯曲假说。热退磁隔离两个组件在大多数样品。一个低的解封温度组件（400摄氏度），解封univectorally向原点。HTC通过McFadden倍检验，总体平均倾斜校正方向为Dec = 255 <$，Inc =− 24 <$（N = 7，α 95 = 9 <$）。扫描电子显微镜（SEM）观察表明，早期成岩，可能的（生物）化学来源的磁性提取物为主的钛贫磁铁矿。岩石磁性数据显示，没有证据表明HTC已受到构造或压实应变。结合前人的研究结果，我们认为中扬子褶皱带总体上呈顺时针旋转，这可能与华北板块与华南板块的碰撞有关。褶皱带古地磁自转与褶皱轴走向的对比表明，长江中游地区发生了约30度的顺时针自转，而褶皱轴走向的15度差异可能是由于褶皱带内部的初始变化。然而，由于对顺时针旋转的时间知之甚少，中扬子褶皱带是否是一个造山带有待进一步研究。
SUMMARY Fold axis strikes in the Yangtze fold belt of the South China Block (SCB) undergo significant changes over distances of >1000 km. This large-scale variation provides an ideal opportunity to test the oroclinal-bending hypothesis using palaeomagnetic methods, which we have attempted by drilling the Lower Triassic Daye Formation limestones in western Hubei Province. Thermal demagnetization isolated two components in most samples. A low unblocking temperature component ( 400 ◦ C, unblocks univectorially towards the origin. The HTC passes the McFadden-fold test with an overall mean tilt-corrected direction of Dec = 255 ◦ , Inc =− 24 ◦ (N = 7, α 95 = 9 ◦ ). Scanning electron microscopy (SEM) observations suggest an early diagenetic, possible (bio)chemical origin for the magnetic extracts dominated by Ti-poor magnetite. Rock magnetic data show no evidence that the HTC has been affected by tectonic or compaction strain. Our data together with previously published results suggest a general clockwise rotation pattern in the Middle Yangtze fold belt, which is probably related to the collision between the North and SCBs. Comparison of palaeomagnetic rotations with fold axis trends in the fold belt suggests that about 30 ◦ clockwise rotation occurred in the Middle reaches of the Yangtze River, while a 15 ◦ difference in fold axis trends would be due to initial variation within the fold belt. However, since little is known about the timing of the clockwise rotation, whether the Middle Yangtze fold belt is an orocline awaits further studies.