Teleseismic P-wave tomography and the upper mantle structure of the central Tien Shan orogenic belt

In this study, an updated version of the teleseismic tomographic method is applied to 7176 high-quality first P-wave arrivals from four combined seismic networks to determine the detailed deep structure under the central Tien Shan. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. A much narrower tilted columnar high-velocity anomaly with a diameter of about 60 km below 150-200 km depth under the Tien Shan extends down to the mantle transition zone, suggesting the breaking- and dropping-off of the collided portions of the southward underthrusting Kazakh Shield and the northward underthrusting Tarim Basin. Prominent low-velocity (low-V) anomalies above 150-200 km depth beneath the Tien Shan may be related to two branches of ascending hot anomalies. One rises upward from the lower mantle beneath the Tarim Basin, while the other rises up from the top of the mantle transition zone beneath the western Kazakh Shield. These results suggest that the underthrusting of the Tarim Basin and Kazakh Shield and the upwelling of hot anomalies indeed play an important role in the mountain building of the central Tien Shan. These dynamic processes might be related to the collision of the Indian plate with Eurasian plate.