Mantle Flow and Crustal Deformation Revealed by Seismic Anisotropy in the Subduction Zone Beneath Myanmar

Abstract

The oblique convergence of the Indian and Eurasian plates drives significant deformation in the crust and mantle beneath Myanmar. However, the crustal deformation in the Indo-Burman Ranges (IBR) and mantle flow beneath Myanmar and adjacent areas remain unclear due to limited studies. We utilized data from the newly deployed second phase of the China-Myanmar Geophysical Survey of the Myanmar Orogen array to perform shear wave splitting analysis of PKS, SKKS, and SKS (XKS) phases. Our results, together with previous findings, provide new insights into mantle flow and crustal deformation across central Myanmar. In the IBR, we observed a transition from N-S oriented, structure-induced crustal anisotropy north of 21°N to trench-perpendicular, stress-induced crustal anisotropy in the south. Such a transition contributes to a significant southward decrease in XKS splitting times in the IBR, where the XKS fast orientations predominantly align in a trench-parallel direction. In the West Burma Terrane, the trench-parallel fast orientations gradually transition to nearly trench-perpendicular toward the Sibumasu Terrane (ST), along with the estimated depths of anisotropy, reflecting a change in the primary source of anisotropy from trench-parallel sub-slab flow to mantle wedge flow. The transitional fast orientations in the ST are influenced by three factors: corner flow induced by active subduction, absolute plate motion-driven flow, and the remnant Neo-Tethyan slab, which remains permeable to mantle flow at depths of 50–125 km. Our research advances the understanding of crust-mantle deformation in the subduction zone beneath Myanmar and provides valuable constraints for subduction dynamics studies in the region.