Clockwise rotation of the Baoshan Block due to southeastward tectonic escape of Tibetan crust since the Oligocene
Clockwise rotation of the Baoshan Block due to southeastward tectonic escape of Tibetan crust since the Oligocene
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DOI：
10.1093/gji/ggu009
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发表时间：
2014-04
影响因子：
2.8
通讯作者：
D. Kornfeld;S. Eckert;E. Appel;L. Ratschbacher;J. Pfänder;Deliang Liu;L. Ding
中科院分区：
文献类型：
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作者：
D. Kornfeld;S. Eckert;E. Appel;L. Ratschbacher;J. Pfänder;Deliang Liu;L. Ding
了解东喜马拉雅构造结（EHS）周围的变形模式是青藏高原演化模型的关键。为了限制EHS东部的旋转和平移，我们提出了新的古地磁数据从变质玄武岩层-可能是岩床-在云南西部，西藏高原东南部的保山地块;变质玄武岩要么侵位或变质为绿片岩相在4030 Ma（40 Ar- 39 Ar全岩年龄）。详细的岩石磁性研究-结合反射和透射光显微镜-确定磁铁矿和富钛钛磁铁矿为主要磁性载体。使用交变场退磁，我们分离出良好的集群特征recrystalline磁化。一个折叠测试表明同折叠剩磁收购，支持渐新世磁化由于区域始新世-渐新世缩短的证据。在展开的30%处，倾斜校正的总体站点平均方向产生decliter/倾角= 042.2 <$/47.0 <$，对应于相对于稳定的欧亚大陆顺时针旋转35.1 <$± 12.7 <$。这表示自2030 Ma以来的平均自转速率为1.17 ± 0.42亿年-1，处于现今GPS推导的自转速率的下限。我们解释了沿着哀牢山剪切带的保山地块和兰坪-思茅地块的顺时针旋转是由构造逃逸引起的。随着沿着崇山和高黎贡山剪切带剪切作用的开始，保山地块继续向东南方向逃逸，与这两条剪切带之间的兰坪-思茅地块分离。地壳对流可以解释1.20Ma以后的旋转和向南逃逸。
Understanding the mode of deformation around the Eastern Himalayan Syntaxis (EHS) is crucial for models of Tibetan Plateau evolution. To constrain rotations and translation east of the EHS, we present new palaeomagnetic data from meta-basalt layers—possibly sills— of the Baoshan Block in western Yunnan, southeastern Tibet Plateau; the meta-basalts were either emplaced or metamorphosed to greenschist facies at ∼ 30 Ma ( 40 Ar– 39 Ar whole rock ages). A detailed rock magnetic study—in combination with reflected and transmitted light microscopy—identifies magnetite and Ti-rich titanomagnetite as the main magnetic carriers. Using alternating field demagnetization, we separated well-clustered characteristic remanent magnetizations. A fold test indicates a syn-folding remanence acquisition, supporting an Oligocene magnetization due to evidence for regional Eocene–Oligocene shortening. The tilt corrected overall site mean direction at 30 per cent of unfolding yields declination/inclination = 042.2 ◦ /47.0 ◦ , corresponding to a clockwise rotation of 35.1 ◦ ± 12.7 ◦ with respect to stable Eurasia. This denotes an average rotation rate of 1.17 ± 0.42 ◦ Myr − 1 since ∼ 30 Ma, ranging at the lower limit of the present-day, GPS-derived rotation rates. We explain the clockwise rotation by tectonic escape of the Baoshan and the Lanping-Simao blocks along the Ailao Shan shear zone. With the onset of shearing along the Chong Shan and Gaoligong Shan shear zones, the Baoshan Block continued its southeastward escape, decoupled from the Lanping-Simao Block between these two major shear zones. Crustal flow could explain rotation and southward escape after ∼ 20 Ma.