Cenozoic clockwise rotation of the Tengchong block, southeastern Tibetan Plateau: A paleomagnetic and geochronologic study
Cenozoic clockwise rotation of the Tengchong block, southeastern Tibetan Plateau: A paleomagnetic and geochronologic study
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DOI：
10.1016/j.tecto.2014.04.032
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发表时间：
2014-07
期刊：
影响因子：
2.9
通讯作者：
D. Kornfeld;S. Eckert;E. Appel;L. Ratschbacher;Benita-Lisette Sonntag;J. Pfänder;L. Ding;Deliang Liu
中科院分区：
文献类型：
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作者：
D. Kornfeld;S. Eckert;E. Appel;L. Ratschbacher;Benita-Lisette Sonntag;J. Pfänder;L. Ding;Deliang Liu
青藏高原东南部云南~ 50-35 Ma（可能~ 40 Ma）镁铁质岩墙切割~ 115 Ma花岗岩的古地磁数据记录了腾冲（拉萨）地块围绕东喜马拉雅构造结（EHS）的旋转。富钛的钛磁铁矿和磁铁矿带有主要磁性成分（第1组）;磁铁矿（第2组）中存在磁性叠加，可能由~ 30和10 Ma之间的低级变质作用引起。组1的倾斜校正总体平均方向为D/I = 89.8°/35.1°，组2的D/I = 33.3°/41.4°。这些数据意味着腾冲地块自~ 40 Ma获得剩磁以来相对于稳定的欧亚大陆顺时针旋转了~ 87°（87.3 ± 12.5°）。平均自转速率为2.18 ± 0.31°/Myr，这是从GPS速度和第四纪应变率获得的EHS周围现今自转速率的上限。第2组重磁化后的α-弱旋度约为31°（31.2 ± 32.9°）。我们的关键结果single bond检测到~ 87°的顺时针旋转，在印度-亚洲碰撞之后的高旋转速率，以及在中新世single bond期间旋转速率的降低表明，首先腾冲块体围绕EHS快速旋转，与岩石圈块体向东的构造逃逸同步。晚些时候，较慢，顺时针旋转-类似于那些记录的大地测量-可能与西藏地壳的粘性流动。
Paleomagnetic data from ~ 50–35 Ma (likely ~ 40 Ma) mafic dykes in Yunnan, southeastern Tibetan Plateau, cutting ~ 115 Ma granitoids record the rotation of the Tengchong (Lhasa) block around the East Himalayan Syntaxis (EHS). Ti-rich titanomagnetite and magnetite carry a primary magnetic component (Group1); a magnetic overprint resides in magnetite (Group2), likely induced by low-grade metamorphism between ~ 30 and 10 Ma. The tilt-corrected overall mean directions are D/I = 89.8°/35.1° for Group1 and D/I = 33.3°/41.4° for Group2. These data imply a clockwise rotation of ~ 87° (87.3 ± 12.5°) of the Tengchong block since remanence acquisition at ~ 40 Ma with respect to stable Eurasia. The average rotation rate of 2.18 ± 0.31°/Myr is at the upper limit of the present-day rotation rates around the EHS obtained from GPS velocities and Quaternary strain rates. The remagnetized Group2 indicates a—poorly defined—rotation of ~ 31° (31.2 ± 32.9°). Our key resultssingle bondthe detection of ~ 87° clockwise rotation, with high rotation rates following the India–Asia collision, and a decrease in rotation rates during the Miocenesingle bondsuggest that first the Tengchong block rotated rapidly around the EHS, synchronous with eastward tectonic escape of lithospheric blocks. The later, slower, clockwise rotation—similar to those recorded geodetically—may be related to viscous flow of Tibetan crust.