Mesozoic-Cenozoic history of subduction within the Tethyan region as inferred from seismic tomography and plate tectonic reconstructions

We have studied the large-scale history of subduction within the Tethyan region, the Alpine-Himalayan-Indonesian mountain chain that stretches from the Mediterranean to Southeast Asia. From tomographic images of the present mantle structure, the volumes and locations of the positive seismic velocity anomalies are determined. The large tomographic volumes, and the large depths at which they are found, indicate that they must have resulted from long periods of subduction in Cenozoic and Mesozoic times. We therefore examine the large-scale surface motions within the region since 200 Ma, the time window that is thought to be necessary to explain the inferred tomographic anomalies. From plate tectonic reconstructions, the amount of convergence and velocities, both relative and absolute, are determined using the relevant poles of rotation. In general, we find the tomographic volumes in the upper mantle in the eastern Mediterranean and Middle East to be similar to the tectonic volumes that are expected to have subducted during the Cenozoic. On the contrary, the results indicate that the Cenozoic amount of shortening in the Indian region was probably not accompanied by lithosphere subducting into the mantle. For all regions, the tomographic volumes found in the lower mantle are larger than the tectonic volumes expected to have subducted during mainly Mesozoic times. The volumes in the Indian region and the Middle East approximately differ a factor 1-2. However, the results suggest that much more material must have been subducted in the eastern Mediterranean than is calculated for the African-Eurasian convergence alone. This points to a major role of oceanic spreading during lithospheric subduction in the area.