Common features of lithosphere structures in various collision zones of Eurasia based on seismic tomography studies

There are a large number of different collision zones on Earth, formed in different geodynamic settings as a result of the collision of continental plates of different shapes and sizes. Researchers often use one or a combination of methods to study one region. In this study, we propose to compare the models of P and S anomalies of several regions. In this study, vertical sections were built under the collision zones of the Caucasus, Eastern Anatolia, NW Himalayas and Tien Shan using the method of local seismic tomography. 3D models of crustal inhomogeneities down to ~ 60-150 km were constructed using the LOTOS algorithm [Koulakov, 2009].

The main characteristic feature of all crustal models of collisional zones is a clear differentiation of the velocity anomalies of the orogen, formed due to shortening, and the continental plates, participating in the collision. Thus, the Arabian, East European, Indian, Tarim plates are associated with high velocity anomalies, and mountain structures, for example, the Greater and Lesser Caucasus, the Himalayas, are characterized by low velocities.

Volcanism is another geological feature that shows up well in seismic tomographic models. Young volcanism (up to ~ 2.5Ma) characterized by low-velocity anomalies in the models, while the older one characterized by high-velocity anomalies. Thus, the volcanic area of Kazbegi province including a group of Quaternary volcanoes (455-30 Ka) in Great Caucasus match to the locations of low-velocities in the P- and S-seismic models. But the Eastern Anatolia younger magmatism (6–4 Ma) occurred in the south around Lake Van, stands out as high velocity anomalies.

It is known that there is the lithospheric window under Tien Shan and Anatolia which is filled with overheated asthenospheric material that reaches the bottom of the crust, thereby weakening and heating the lower crust. It is most likely that the upper crustal high-velocity anomaly corresponds to the strong upper crust which is compacted by solidified material from Neogene-Quaternary volcanism, while the low-velocity anomaly is associated with the weak heated lower crust.

Thus, comparison of seismic tomography models of different collision zones can be the key to better understanding the processes in the crust and lithosphere.

The reported study was funded by Russian Foundation for Basic Research, project number 19-35-60002.