Complex deformation mechanisms of the crust in eastern and northeastern Tibetan Plateau: Insights from ambient noise tomography that captures azimuthal anisotropy

Comprehensive analysis of geodetic and seismological study findings in eastern and northeastern Tibetan Plateau (TP) can offer new insights into regional tectonic movements, crustal material properties, and crustal deformation. In this study, to uncover the crustal deformation mechanisms in eastern and northeastern TP, we constructed an azimuthal anisotropy model through ambient noise tomography that captures azimuthal anisotropy. Based on our inverted model and insights from previous geodetic and seismological studies, we reveal the deformation patterns across various blocks within the regional crust. In eastern TP, the deformation of the Lhasa and Qiangtang blocks is predominantly controlled by the subduction of the Indian lithosphere and the strike of regional large-scale fault systems. The Songpan-Ganzi terrane is primarily driven by W-E-oriented tectonic movements of the plateau crustal materials, further impacted by the obstruction of the rigid Sichuan Basin (SCB), leading to clockwise rotational deformation features. The continuous uplift and expansion of the TP have subjected the Qaidam Basin (QDB) to intense crustal shortening and horizontal compression. Moreover, multi-stage tectonic activities have resulted in the redistribution of tectonic stress within the crust of QDB over time, thus developing an NW-SE-oriented deformation pattern. In northeastern TP, the deformation of the Qilian and West Qinling orogens is primarily driven by the southward subduction of the Alxa block (ALB) and associated orogenic activities. The complex deformation of the ALB is mainly related to the closure of the Paleo-Tethys Ocean and subsequent plate collision and suturing within the Asian continent, while it is also affected by the edge effects of the North China Craton (NCC). The crust deformation of the SCB is primarily governed by the intense compression stress caused by the collision between the Indian and Eurasian plates. In contrast, the deformation observed in the Ordos Basin (OB) is comparatively mild, influenced by local uplifts at the edges, differential tectonic stress transmitted by orogenic activities, and the overall stability of the NCC lithosphere. In addition, the deformation in the uppermost mantle of the SCB and OB is mainly driven by regional plate motion and mantle flow.