Kinematic evolution of a continental collision: Constraining the Himalayan-Tibetan orogen via bulk strain rates
Kinematic evolution of a continental collision: Constraining the Himalayan-Tibetan orogen via bulk strain rates
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DOI：
10.1016/j.tecto.2020.228642
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发表时间：
2020-12
期刊：
影响因子：
2.9
通讯作者：
A. Zuza;Y. Gavillot;P. Haproff;Chen Wu
中科院分区：
文献类型：
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作者：
A. Zuza;Y. Gavillot;P. Haproff;Chen Wu
从大地测量中估计的现今应变速率为~5-6×10-16s-1and过去应变速率的估计取决于造山带缩短速率和有效造山带宽度。板块电路重建提供了时变印度-亚洲辐合速率的约束条件，显示出在日喀则后弧闭合后大约58 Ma至45 Ma的初始碰撞后明显减速。模型1、3和4得出的早期新生代体应变率与现在的速率相匹配（5-6×10-16s-1），而模型2得出的更快的速率（1.2×10-15s-1）必须随着时间的推移而减小，以避免缩短超过板块的总收敛。利用这些边界，我们约束了整个造山带及其南缘和北缘的地壳缩短，它们分别由喜马拉雅山脉和祁连山界定。15 Ma，对应于侧向变形（例如走滑和正断层）的开始。在逆冲带的尺度上，我们的模型得出了与地质观测相符的缩短速度和幅度。这种方法提供了可测试的外部运动学约束，以指导未来的地质和地球物理调查。
We investigated temporal variations of the bulk strain rate across the Himalayan-Tibetan orogen, which impact the magnitudes, rates, and distribution of deformation across the orogen. The present-day strain rate estimated from geodesy is ~5-6×10-16s-1and estimation of past rates depends on the orogenic shortening rate and effective orogen width. Plate-circuit reconstructions provide constraints on time-varying India-Asia convergence rates, showing a marked deceleration since initial collision at ca. 58 Ma. Geologic evidence suggests that most of the Tibetan crust started deforming shortly after initial collision, which simplifies estimation of the initial orogen width. We examined several kinematic models: (1) Greater Indian and Tibetan crust started deforming immediately after collision, (2) only Tibetan crust deformed initially, (3) plate convergence was decoupled from crustal shortening, with Tibetan crust deforming slower than plate rates, or (4) a hard India-Asia collision at ca. 45 Ma following closure of the Xigaze backarc. Models 1, 3, and 4 yield early Cenozoic bulk strain rates that match present-day rates (5-6×10-16s-1), whereas Model 2 yields faster rates (1.2×10-15s-1) that must have decreased through time to avoid shortening exceeding total plate convergence. Using these bounds, we constrain crustal shortening across the entire orogen and along its southern and northern margins, defined by the Himalaya and Qilian Shan, respectively. Application of these models to Tibetan crustal thickening suggests that the plateau reached its present-day value (~70 km) by ca. 15 Ma, which corresponds to the onset of lateral deformation (e.g., strike-slip and normal faulting). Lateral deformation in the Himalayan-Tibetan orogen may have resulted from progressive crustal thickening and reorientation of the intermediate principal stress axis. At the thrust-belt scale, our modeling yields shortening rates and magnitudes that match geologic observations. This approach provides testable external kinematic constraints to guide future geological and geophysical investigations.