Vertical axis rotation (or lack thereof) of the eastern Mongolian Altay Mountains: Implications for far-field transpressional mountain building
Vertical axis rotation (or lack thereof) of the eastern Mongolian Altay Mountains: Implications for far-field transpressional mountain building
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DOI：
10.1016/j.tecto.2018.03.020
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发表时间：
2018-06
期刊：
影响因子：
2.9
通讯作者：
L. Gregory;C. Mac Niocaill;R. Walker;G. Bayasgalan;T. Craig
中科院分区：
文献类型：
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作者：
L. Gregory;C. Mac Niocaill;R. Walker;G. Bayasgalan;T. Craig
西蒙古的阿尔泰山在一个逆冲机制中容纳了目前印度-亚洲碰撞缩短的10-20%。阿尔泰的运动学模型要求断层围绕垂直轴逆时针旋转，以适应穿越该地区的主要走滑断层的挤压变形。这样的旋转应该可以通过古地磁数据检测到。根据对阿尔泰山的古地磁研究，对西伯利亚阿尔泰山丘亚盆地渐新世和更年轻的沉积物进行的先前估计表明，阿尔泰山至少有部分地区经历了高达39 ± 8°的逆时针旋转。在这里，我们提出了新的古地磁结果，从白垩纪和年轻的沉积物中收集的样品在Zereg盆地沿着哈尔-乌斯-努尔断裂在阿尔泰山东部，蒙古。我们的新的古地磁结果从Zereg盆地提供可靠的磁偏角，与古地磁方向从10个网站，通过折叠测试，并包括磁反转。相对于白垩纪和更年轻的虚拟地磁极的预期方向，磁偏角没有明显旋转，这表明阿尔泰东部的断层没有经历过大程度的垂直轴旋转，在过去的500万年里旋转不超过7°。沿哈尔-乌斯-努尔断层沿着缺乏旋转，加上北方阿尔泰的大量旋转，这与压扭变形的运动学模型相吻合，在该模型中，阿尔泰的断层旋转到有利于花状构造发育和山地地形建设的方向，而与此同时，随着应变转移到更好的定向构造，边缘的范围扩大。因此，哈尔-乌斯-努尔断层在阿尔泰地区是一个相对年轻的断层，尚未发生显著的旋转。
The Altay Mountains of Western Mongolia accommodate 10–20% of the current shortening of the India-Asia collision in a transpressive regime. Kinematic models of the Altay require faults to rotate anticlockwise about a vertical axis in order to accommodate compressional deformation on the major strike slip faults that cross the region. Such rotations should be detectable by palaeomagnetic data. Previous estimates from the one existing palaeomagnetic study from the Altay, on Oligocene and younger sediments from the Chuya Basin in the Siberian Altay, indicate that at least some parts of the Altay have experienced up to 39 ± 8° of anticlockwise rotation. Here, we present new palaeomagnetic results from samples collected in Cretaceous and younger sediments in the Zereg Basin along the Har-Us-Nuur fault in the eastern Altay Mountains, Mongolia. Our new palaeomagnetic results from the Zereg Basin provide reliable declinations, with palaeomagnetic directions from 10 sites that pass a fold test and include magnetic reversals. The declinations are not significantly rotated with respect to the directions expected from Cretaceous and younger virtual geomagnetic poles, suggesting that faults in the eastern Altay have not experienced a large degree of vertical axis rotation and cannot have rotated >7° in the past 5 m.y. The lack of rotation along the Har-Us-Nuur fault combined with a large amount of rotation in the northern Altay fits with a kinematic model for transpressional deformation in which faults in the Altay have rotated to an orientation that favours the development of flower structures and building of mountainous topography, while at the same time the range widens at the edges as strain is transferred to better oriented structures. Thus the Har-Us-Nuur fault is a relatively young fault in the Altay, and has not yet accommodated significant rotation.