Three-Dimensional Seismic Velocity Structure of the Crust and Upper Mantle beneath Western Tibet from Multiscale, Finite-Frequency Travel-Time Tomography
Abstract
Three-dimensional seismic velocity structure of western Tibet has been resolved down to depths about 400 km from tomographic inversion of relative travel-time residuals of teleseismic P- and S-waves recorded during the Hi-CLIMB Experiment. A broad swath of high wave-speeds extends northward under much of the Lhasa terrane, passing beyond the Bangong-Nujang Suture and abruptly turns to low wave-speeds beneath the Qiangtang terrane in northern Tibet. The strong velocity contrast manifestly marks the leading edge of underthrusting Indian lithosphere. Two disjointed low-velocity anomalies straddling the Indus-Yarlung Suture in the uppermost 100 km or less are collocated with regions of high conductivity revealed from magnetotelluric imaging profiles, interpreted by many researchers as evidence for partial melt or aqueous fluids that weaken the lower crust and induce ductile flow. However, regional coverage of our data clearly shows that the two seismically slow regions throughout the thickened crust are not connected, suggesting that the popular geodynamic model of pervasive, south-directed channel flow in the mid-to-lower crust beneath southern Tibet is either presently inactive or in need of modifications.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T11E..05H
- Keywords:
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- 7203 Body waves;
- 7270 Tomography (6982;
- 8180);
- 8102 Continental contractional orogenic belts and inversion tectonics;
- 8108 Continental tectonics: compressional;
- 8120 Dynamics of lithosphere and mantle: general (1213)