Indian continental lithosphere and related volcanism beneath Myanmar: Constraints from local earthquake tomography

Abstract

The Indian plate descends obliquely eastward beneath the Eurasian plate along the Burmese arc. Previous tomographic results revealed a high-velocity structure that plunges eastward into the deep mantle beneath Myanmar. However, the shallow structure beneath Myanmar remains unclear due to the lack of local seismic observations. Based on the local seismic data recorded by a newly deployed dense array in Myanmar, we obtain a three-dimensional velocity structure of the crust and lithospheric mantle above 100 km by employing the double-difference tomography method. Our imaging results support the existence of the Indian continental lithosphere to a depth of at least 100 km with a dip angle of ∼25° beneath the Indo-Burma Ranges and the Central Myanmar Basin. At the deep end of the continental slab, the high VP, high Vs and rather low average VP/VS ratio indicate that the lowermost portion of the crust from 80 to 120 km may have experienced partially metamorphic eclogitization. The imaging results also provide direct seismic evidence for the origin of the last Monywa volcanic activity in the Holocene. This subduction-related volcanism is characterized by a prominent low Vs anomaly in the lithospheric mantle, which indicates continental lithosphere dehydration and partial melting in mantle wedge. These findings provide new seismic constraints to understand the continental collision system between India and Eurasia under Myanmar and the related magmatic activities of the Monywa volcano.