Uppermost mantle structure of the eastern margin of the Tibetan plateau from interstation Pn traveltime difference tomography
Uppermost mantle structure of the eastern margin of the Tibetan plateau from interstation Pn traveltime difference tomography
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DOI：
10.1016/j.epsl.2012.05.005
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发表时间：
2012-06
影响因子：
5.3
通讯作者：
Zhiwei Li;S. Ni;T. Hao;Yi Xu;S. Roecker
中科院分区：
文献类型：
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作者：
Zhiwei Li;S. Ni;T. Hao;Yi Xu;S. Roecker
利用台间Pn差分走时资料进行层析成像反演，获得了横跨龙门山断裂带的上地幔速度图像。龙门山断裂带以西的青藏高原东部地区的Pn速度较低（<7.8km/s），而以东的四川盆地地区的Pn速度较高（>8.1km/s），表明青藏高原东部地区的上地幔相对较弱，而四川盆地地区的上地幔相对较强。Pn速度与四川盆地刚性稳定的岩石圈可能是青藏高原东部韧性地壳向东逃逸流的屏障这一命题是一致的。Pn速度与平滑地形、地壳厚度和布格重力场的一致性表明，青藏高原东部地壳增厚和隆升的减缓是岩石圈地幔动力学过程的结果。然而，从地形梯度、地震活动性、破裂过程和汶川地震余震分布等方面来看，龙马山断裂带似乎被虎牙断裂和雷东断裂一分为二。沿着断裂带走向Pn速度的差异也支持这种分段，表明地壳和岩石圈地幔的不同构造环境。对分割机制的理解需要进一步研究。
Tomographic inversion with interstation Pn differential traveltime data provides a reliable velocity image of the uppermost mantle across the Longmenshan Fault Belt, which borders the eastern Tibetan plateau and Sichuan Basin. Low Pn velocities (<7.8km/s) are revealed beneath the eastern Tibetan plateau to the west of the Longmenshan Fault Belt, while high Pn velocities (>8.1km/s) appear beneath the Sichuan Basin to the east, suggesting a relatively weak upper mantle beneath eastern Tibetan plateau and a strong upper mantle beneath the Sichuan Basin. The Pn velocities are consistent with the proposition that the rigid and stable lithosphere of the Sichuan Basin may act as a barrier to the eastward escape flow of the ductile crust of the eastern Tibetan plateau. Consistency of Pn velocities with the smoothed topography, crustal thickness and Bouguer gravity implies that the dynamic processes of the lithospheric mantle should be responsible for the crustal thickening and relief of uplift in the eastern Tibetan plateau. However, the Longmeshan Fault Belt appears to be separated into two segments by the Huya and Leidong faults as manifested by significant discrepancies in topography gradient, seismic activity, rupture process and aftershock distribution of Wenchuan earthquake. This segmentation is also supported by difference in Pn velocities along the strike of the fault belt, suggesting different tectonic environments in the crust and lithospheric mantle. Understanding of the mechanism for the segmentation requires further investigation.