Three-dimensional variations in the Tibetan mantle lid velocity from Pn tomography
Abstract
We have used Pn arrivals from seismic experiments and networks in Tibet and surrounding regions to image the structure of the mantle lid. Previous Pn tomography studies have remarked on the contrast between high velocities beneath southern Tibet and low velocities beneath northern Tibet. We find that this model is oversimplified. Longer raypaths show a vastly different velocity structure than do the shorter raypaths, thus there is significant vertical variation in the velocity structure of the mantle lid. Only longer raypaths show low velocity beneath northern Tibet. The lowest velocities occur beneath the central Qiangtang and Songpan-Ganzi terranes, but are not coincident with the Bangong-Nujiang suture that separates northern and southern Tibet. These deep low velocity zones suggest a thin lithosphere there. There is also low velocity mantle beneath the northeast Songpan-Ganzi Terrane (in Gansu province). Shorter raypaths image the top of the mantle lid and show two distinct high velocity zones beneath the Himalayas. Several similar high velocity regions occur north of the eastern Himalayan syntaxis beneath the Lhasa, Qiangtang, and Songpan-Ganzi terranes. We interpret these as underthusted Indian continental lithosphere segments. The east-west variability of Pn velocity beneath the Himalayas and southern Tibet indicates that the underthrusted Indian continental lithosphere is not a homogeneous body. Qaidam Basin along with the Gonghe and Xining Basins east of it show an east-west high velocity anomaly. We interpret this as a preexisting cratonic core that deformed little while the Tibetan Plateau to the south and the Qilian Shan to the north did.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T43A2293H
- Keywords:
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- 7270 SEISMOLOGY / Tomography;
- 8110 TECTONOPHYSICS / Continental tectonics: general;
- 8180 TECTONOPHYSICS / Tomography;
- 9320 GEOGRAPHIC LOCATION / Asia