Upper mantle melt caused by a subducted slab in the Indian-Eurasian continental subduction zone

Abstract

A low-velocity layer atop the mantle transition zone has been extensively observed worldwide. In subduction zones, this layer is widely explained as partial melting triggered by slab subduction on a regional or global scale. However, direct observational evidence is still absent, and the response of the layer to slab subduction is not well known. Here, we image the seismic velocity around the mantle transition zone by matching synthetic and observed triplicated seismic P and sP waveforms in the Indian–Eurasian continental subduction zone. Our observations reveal a laterally varied low-velocity layer atop the mantle transition zone beneath the Hindu Kush, where a subducted slab extends to the mantle transition zone. The geometric morphology of the low-velocity layer documents that it is a partially molten layer induced by the subducted slab on a regional scale. Interestingly, our observations also support that the layer has a low viscosity. The decreased viscosity may facilitate slab motion in the deep mantle, contributing to slab stretching, tearing and break-off and its resultant rare recurring large intermediate-depth earthquakes in an intracontinental setting.

The Mantle Transition Zone Structure Beneath the Pamir Plateau and Western Tian Shan and Adjacent Regions

“…, and 7b) (GLi et al, 2023). Combined with the tomographic models, our findings offer significant Journal of Geophysical Research: Solid Earth 10.1029/2023JB028129 support for the deep subduction of continental lithosphere into the bottom of the MTZ without the slab-pull of a colder and denser oceanic lithosphere.…”

“…In addition, the presence of a discontinuity at a depth of ∼520 km (d520) (Figure 7b) is also an indicator that further suggests the MTZ is hydrous beneath the Pamir Plateau (Meijde et al, 2003). Coincidentally, the hydrous MTZ and partially molten LVL atop the d410 beneath Pamir is also determined by triplicated wave modeling using independent data and method (G Li et al, 2023), which is possibly contributed by the ancient oceanic slab subduction.…”